From a5ba514dcf070f0875fc422a64b1811a16ddf943 Mon Sep 17 00:00:00 2001
From: Pierre Sassoulas <pierre.sassoulas@gmail.com>
Date: Thu, 2 Apr 2026 22:48:10 +0200
Subject: [PATCH 1/8] [primer] Detect changed messages via position-based
 pairing

Instead of reporting a moved or reworded diagnostic as a separate
removal + addition, pair messages that share the same (symbol, path,
obj) key and report them as "changed" with a human-readable diff.

Comparator.__iter__ now yields 4-tuples (package, missing, new, changed)
and exposes a commits dict.  Short field changes (type, confidence) use
an inline format; long message strings get a diff block with caret
hints highlighting the changed spans.
---
 pylint/testutils/_primer/comparator.py        | 158 ++++++++++++++++--
 .../_primer/primer_compare_command.py         |  83 +++++----
 .../batched_cases/expected_comparator.json    |   2 +-
 .../cases/confidence_changed/expected.txt     |  16 +-
 .../expected_comparator.json                  |   2 +-
 .../_primer/cases/line_moved/expected.txt     |  16 +-
 .../cases/line_moved/expected_comparator.json |   2 +-
 .../cases/message_changed/expected.txt        |  20 +--
 .../message_changed/expected_comparator.json  |   2 +-
 .../message_changed/expected_truncated.txt    |   8 +-
 .../expected_truncated_in_details.txt         |   5 +-
 .../cases/message_changed_line/expected.txt   |  20 +--
 .../expected_comparator.json                  |   2 +-
 .../_primer/cases/mixed_changes/expected.txt  |  38 ++---
 .../mixed_changes/expected_comparator.json    |   2 +-
 .../_primer/cases/mixed_changes/pr.json       |   4 +-
 .../_primer/cases/multi_package/expected.txt  |   2 +-
 .../multi_package/expected_comparator.json    |   4 +-
 .../new_message/expected_comparator.json      |   2 +-
 .../removed_message/expected_comparator.json  |   2 +-
 .../_primer/cases/type_changed/expected.txt   |  16 +-
 .../type_changed/expected_comparator.json     |   2 +-
 .../expected_comparator.json                  |   2 +-
 tests/testutils/_primer/test_comparator.py    |   6 +-
 24 files changed, 257 insertions(+), 159 deletions(-)

diff --git a/pylint/testutils/_primer/comparator.py b/pylint/testutils/_primer/comparator.py
index 655a050f04..0b09a918ff 100644
--- a/pylint/testutils/_primer/comparator.py
+++ b/pylint/testutils/_primer/comparator.py
@@ -5,15 +5,24 @@
 from __future__ import annotations
 
 import json
+from collections import defaultdict
 from collections.abc import Iterator
+from difflib import SequenceMatcher
 from pathlib import Path
 from typing import NamedTuple
 
 from pylint.reporters.json_reporter import JSONMessage
-from pylint.testutils._primer.primer_command import (
-    PackageData,
-    PackageMessages,
-)
+from pylint.testutils._primer.primer_command import PackageData, PackageMessages
+
+
+class ChangedMessage(NamedTuple):
+    """A message that was present on both runs but with altered details."""
+
+    old: JSONMessage
+    new: JSONMessage
+
+
+_LOCATION_KEYS = {"line", "column", "endLine", "endColumn"}
 
 
 class PackageDiff(NamedTuple):
@@ -22,10 +31,120 @@ class PackageDiff(NamedTuple):
     package: str
     missing: PackageData  # emitted on main but not on the PR
     new: PackageData  # emitted on the PR but not on main
+    changed: list[ChangedMessage]  # same diagnostic, altered line / text
+
+
+def _match_residuals(
+    old_residuals: list[JSONMessage], new_residuals: list[JSONMessage]
+) -> tuple[list[ChangedMessage], list[JSONMessage], list[JSONMessage]]:
+    """Pair residual messages by ``(symbol, path, obj)``.
+
+    Two messages sharing that key are the "same diagnostic" — if they differ
+    only in line numbers or message text, they should be reported as *changed*
+    rather than as a separate removal + addition.  Leftovers on each side are
+    genuinely missing or genuinely new.
+
+    Returns ``(paired, unmatched_old, unmatched_new)``.
+    """
+    old_by_key: dict[tuple[str, str, str], list[JSONMessage]] = defaultdict(list)
+    new_by_key: dict[tuple[str, str, str], list[JSONMessage]] = defaultdict(list)
+    for m in old_residuals:
+        old_by_key[m["symbol"], m["path"], m["obj"]].append(m)
+    for m in new_residuals:
+        new_by_key[m["symbol"], m["path"], m["obj"]].append(m)
+
+    paired: list[ChangedMessage] = []
+    paired_old_ids: set[int] = set()
+    paired_new_ids: set[int] = set()
+    for key in old_by_key:
+        if key not in new_by_key:
+            continue
+        for old, new in zip(old_by_key[key], new_by_key[key]):
+            paired.append(ChangedMessage(old=old, new=new))
+            paired_old_ids.add(id(old))
+            paired_new_ids.add(id(new))
+
+    final_missing = [m for m in old_residuals if id(m) not in paired_old_ids]
+    final_new = [m for m in new_residuals if id(m) not in paired_new_ids]
+    return paired, final_missing, final_new
+
+
+def format_span(msg: JSONMessage) -> str:
+    """Format a message's location as ``line:col to endLine:endCol``."""
+    start = f"{msg['line']}:{msg['column']}"
+    end_line = msg.get("endLine")
+    end_col = msg.get("endColumn")
+    if end_line is not None and end_col is not None:
+        return f"from `{start}` to `{end_line}:{end_col}`"
+    return f"at `{start}`"
+
+
+def message_diff(old: JSONMessage, new: JSONMessage) -> str:
+    """Return a compact summary of changed fields between two messages.
+
+    Location changes are merged into a single human-readable span.
+    String fields (like ``message``) get a ``diff`` code block so GitHub
+    renders them with red/green highlighting.
+    """
+    changed_keys: set[str] = set()
+    for key in old:
+        if old[key] != new[key]:  # type: ignore[literal-required]
+            changed_keys.add(key)
+
+    parts: list[str] = []
+    # Location: combine line/column/endLine/endColumn into one sentence.
+    if changed_keys & _LOCATION_KEYS:
+        parts.append(f"Was raised {format_span(old)}, now {format_span(new)}.")
+
+    # Other fields (typically ``message`` or ``type``).
+    for key in sorted(changed_keys - _LOCATION_KEYS):
+        old_val = old[key]  # type: ignore[literal-required]
+        new_val = new[key]  # type: ignore[literal-required]
+        if (
+            isinstance(old_val, str)
+            and isinstance(new_val, str)
+            and (len(old_val) > 40 or len(new_val) > 40)
+        ):
+            caret_line = _caret_hint(old_val, new_val)
+            diff_block = f"```diff\n- {old_val}\n+ {new_val}\n"
+            if caret_line:
+                diff_block += f"  {caret_line}\n"
+            diff_block += "```"
+            parts.append(diff_block)
+        else:
+            parts.append(f"{key}: `{old_val}` → `{new_val}`")
+    return "\n\n".join(parts)
+
+
+def _caret_hint(old: str, new: str) -> str:
+    """Build a ``^`` marker line highlighting changed spans in *new*.
+
+    Uses SequenceMatcher to find which parts of *new* differ from *old*
+    and places ``^`` characters under them (aligned with the ``+ `` prefix).
+    Returns an empty string when the whole line changed (carets wouldn't help).
+    """
+    matcher = SequenceMatcher(None, old, new)
+    carets = [" "] * len(new)
+    changed_count = 0
+    for tag, _i1, _i2, j1, j2 in matcher.get_opcodes():
+        if tag != "equal":
+            for j in range(j1, j2):
+                carets[j] = "^"
+            changed_count += j2 - j1
+    # If most of the string changed, carets are just noise.
+    if changed_count > len(new) * 0.6:
+        return ""
+    return "".join(carets).rstrip()
 
 
 class Comparator:
-    """Cross-reference two primer JSON outputs and iterate over differences."""
+    """Cross-reference two primer JSON outputs and iterate over differences.
+
+    Yields ``PackageDiff`` entries carrying missing, new and changed messages
+    for each package that has at least one difference.  *changed* contains
+    pairs of ``(old, new)`` messages that are the same diagnostic but with
+    altered details (line, message text, etc.).
+    """
 
     def __init__(self, main_data: PackageMessages, pr_data: PackageMessages) -> None:
         self._main_data = main_data
@@ -58,24 +177,31 @@ def __iter__(self) -> Iterator[PackageDiff]:
         main_data = self._main_data
         pr_data = self._pr_data
 
-        missing_messages: PackageMessages = {}
         for package, data in main_data.items():
-            package_missing_messages: list[JSONMessage] = []
+            # First pass: exact-match removal.
+            pr_messages = list(pr_data[package]["messages"])
+            residual_old: list[JSONMessage] = []
             for message in data["messages"]:
                 try:
-                    pr_data[package]["messages"].remove(message)
+                    pr_messages.remove(message)
                 except ValueError:
-                    package_missing_messages.append(message)
-            missing_messages[package] = PackageData(
-                commit=pr_data[package]["commit"],
-                messages=package_missing_messages,
+                    residual_old.append(message)
+
+            # Second pass: pair residuals by position to detect *changed*
+            # messages (same diagnostic, different line or text).
+            paired, final_missing, final_new = _match_residuals(
+                residual_old, pr_messages
             )
 
-        for package, pkg_missing in missing_messages.items():
-            new_messages = pr_data[package]
-            if not pkg_missing["messages"] and not new_messages["messages"]:
+            if not final_missing and not final_new and not paired:
                 continue
-            yield PackageDiff(package, pkg_missing, new_messages)
+            commit = pr_data[package]["commit"]
+            yield PackageDiff(
+                package,
+                missing=PackageData(commit=commit, messages=final_missing),
+                new=PackageData(commit=commit, messages=final_new),
+                changed=paired,
+            )
 
     @staticmethod
     def _load_json(file_path: Path | str) -> PackageMessages:
diff --git a/pylint/testutils/_primer/primer_compare_command.py b/pylint/testutils/_primer/primer_compare_command.py
index e1c02300ad..406e41035e 100644
--- a/pylint/testutils/_primer/primer_compare_command.py
+++ b/pylint/testutils/_primer/primer_compare_command.py
@@ -5,8 +5,13 @@
 
 from pathlib import PurePosixPath
 
-from pylint.testutils._primer.comparator import Comparator
-from pylint.testutils._primer.primer_command import PackageData, PrimerCommand
+from pylint.reporters.json_reporter import JSONMessage
+from pylint.testutils._primer.comparator import (
+    Comparator,
+    PackageDiff,
+    message_diff,
+)
+from pylint.testutils._primer.primer_command import PrimerCommand
 
 MAX_GITHUB_COMMENT_LENGTH = 65536
 
@@ -25,10 +30,7 @@ def _create_comment(self, comparator: Comparator) -> str:
         for diff in comparator:
             if len(comment) >= MAX_GITHUB_COMMENT_LENGTH:
                 break
-            package = diff.package
-            comment += f"\n**Effect on [{package}]({self.packages[package].url}):**\n\n"
-            comment += self._format_new_messages(package, diff.new)
-            comment += self._format_missing_messages(package, diff.missing)
+            comment += self._create_comment_for_package(diff)
         comment = (
             f"🤖 **Effect of this PR on checked open source code:** 🤖\n\n{comment}"
             if comment
@@ -39,27 +41,47 @@ def _create_comment(self, comparator: Comparator) -> str:
         )
         return self._truncate_comment(comment)
 
-    def _format_new_messages(self, package: str, new_messages: PackageData) -> str:
-        comment = ""
+    def _create_comment_for_package(self, diff: PackageDiff) -> str:
+        package = diff.package
+        url = self.packages[package].url
+        clone_dir = self.packages[package].clone_directory
+        commit = diff.new["commit"]
+
+        assert not url.endswith(
+            ".git"
+        ), "You don't need the .git at the end of the github url."
+
+        def _source_link(msg: JSONMessage) -> str:
+            filepath = str(PurePosixPath(msg["path"]).relative_to(clone_dir))
+            return f"{url}/blob/{commit}/{filepath}#L{msg['line']}"
+
+        comment = f"\n**Effect on [{package}]({url}):**\n\n"
+
+        # Changed messages
+        if diff.changed:
+            print("Changed:")
+            comment += "The following messages have been changed:\n\n<details>\n\n"
+            for count, (old, new) in enumerate(diff.changed, 1):
+                comment += (
+                    f"{count}) [{new['symbol']}]({_source_link(new)}):\n"
+                    f"{message_diff(old, new)}\n"
+                )
+                print(new)
+            comment += "</details>\n\n"
+
+        # New messages
         count = 1
         astroid_errors = 0
         new_non_astroid_messages = ""
-        if new_messages["messages"]:
+        if diff.new["messages"]:
             print("Now emitted:")
-        for message in new_messages["messages"]:
-            filepath = str(
-                PurePosixPath(message["path"]).relative_to(
-                    self.packages[package].clone_directory
-                )
-            )
-            # Existing astroid errors may still show up as "new" because the timestamp
-            # in the message is slightly different.
+        for message in diff.new["messages"]:
             if message["symbol"] == "astroid-error":
                 astroid_errors += 1
             else:
                 new_non_astroid_messages += (
                     f"{count}) {message['symbol']}:\n*{message['message']}*\n"
-                    f"{self.packages[package].url}/blob/{new_messages['commit']}/{filepath}#L{message['line']}\n"
+                    f"{_source_link(message)}\n"
                 )
                 print(message)
                 count += 1
@@ -75,33 +97,20 @@ def _format_new_messages(self, package: str, new_messages: PackageData) -> str:
                 + new_non_astroid_messages
                 + "</details>\n\n"
             )
-        return comment
 
-    def _format_missing_messages(
-        self, package: str, missing_messages: PackageData
-    ) -> str:
-        comment = ""
+        # Missing messages
         count = 1
-        if missing_messages["messages"]:
+        if diff.missing["messages"]:
             comment += "The following messages are no longer emitted:\n\n<details>\n\n"
             print("No longer emitted:")
-        for message in missing_messages["messages"]:
-            comment += f"{count}) {message['symbol']}:\n*{message['message']}*\n"
-            filepath = str(
-                PurePosixPath(message["path"]).relative_to(
-                    self.packages[package].clone_directory
-                )
-            )
-            assert not self.packages[package].url.endswith(
-                ".git"
-            ), "You don't need the .git at the end of the github url."
+        for message in diff.missing["messages"]:
             comment += (
-                f"{self.packages[package].url}"
-                f"/blob/{missing_messages['commit']}/{filepath}#L{message['line']}\n"
+                f"{count}) {message['symbol']}:\n*{message['message']}*\n"
+                f"{_source_link(message)}\n"
             )
             count += 1
             print(message)
-        if missing_messages["messages"]:
+        if diff.missing["messages"]:
             comment += "</details>\n\n"
         return comment
 
diff --git a/tests/testutils/_primer/batched_cases/expected_comparator.json b/tests/testutils/_primer/batched_cases/expected_comparator.json
index e3a42bfd31..3be623243d 100644
--- a/tests/testutils/_primer/batched_cases/expected_comparator.json
+++ b/tests/testutils/_primer/batched_cases/expected_comparator.json
@@ -1 +1 @@
-[{ "package": "astroid", "missing": 2, "new": 0 }]
+[{ "package": "astroid", "missing": 2, "new": 0, "changed": 0 }]
diff --git a/tests/testutils/_primer/cases/confidence_changed/expected.txt b/tests/testutils/_primer/cases/confidence_changed/expected.txt
index 8555240d13..bb0e8e2898 100644
--- a/tests/testutils/_primer/cases/confidence_changed/expected.txt
+++ b/tests/testutils/_primer/cases/confidence_changed/expected.txt
@@ -3,22 +3,12 @@
 
 **Effect on [astroid](https://github.com/pylint-dev/astroid):**
 
-The following messages are now emitted:
+The following messages have been changed:
 
 <details>
 
-1) dangerous-default-value:
-*Dangerous default value [] as argument*
-https://github.com/pylint-dev/astroid/blob/123456789abcdef/astroid/inference.py#L42
-</details>
-
-The following messages are no longer emitted:
-
-<details>
-
-1) dangerous-default-value:
-*Dangerous default value [] as argument*
-https://github.com/pylint-dev/astroid/blob/123456789abcdef/astroid/inference.py#L42
+1) [dangerous-default-value](https://github.com/pylint-dev/astroid/blob/123456789abcdef/astroid/inference.py#L42):
+confidence: `UNDEFINED` → `HIGH`
 </details>
 
 *This comment was generated for commit v2.14.2*
diff --git a/tests/testutils/_primer/cases/confidence_changed/expected_comparator.json b/tests/testutils/_primer/cases/confidence_changed/expected_comparator.json
index d826f8390a..47824cb2e1 100644
--- a/tests/testutils/_primer/cases/confidence_changed/expected_comparator.json
+++ b/tests/testutils/_primer/cases/confidence_changed/expected_comparator.json
@@ -1 +1 @@
-[{ "package": "astroid", "missing": 1, "new": 1 }]
+[{ "package": "astroid", "missing": 0, "new": 0, "changed": 1 }]
diff --git a/tests/testutils/_primer/cases/line_moved/expected.txt b/tests/testutils/_primer/cases/line_moved/expected.txt
index 27266ea0b8..ca0b3aaa76 100644
--- a/tests/testutils/_primer/cases/line_moved/expected.txt
+++ b/tests/testutils/_primer/cases/line_moved/expected.txt
@@ -3,22 +3,12 @@
 
 **Effect on [astroid](https://github.com/pylint-dev/astroid):**
 
-The following messages are now emitted:
+The following messages have been changed:
 
 <details>
 
-1) too-complex:
-*'my_function' is too complex. The McCabe rating is 18*
-https://github.com/pylint-dev/astroid/blob/123456789abcdef/astroid/node_classes.py#L103
-</details>
-
-The following messages are no longer emitted:
-
-<details>
-
-1) too-complex:
-*'my_function' is too complex. The McCabe rating is 18*
-https://github.com/pylint-dev/astroid/blob/123456789abcdef/astroid/node_classes.py#L100
+1) [too-complex](https://github.com/pylint-dev/astroid/blob/123456789abcdef/astroid/node_classes.py#L103):
+Was raised from `100:0` to `100:15`, now from `103:0` to `103:15`.
 </details>
 
 *This comment was generated for commit v2.14.2*
diff --git a/tests/testutils/_primer/cases/line_moved/expected_comparator.json b/tests/testutils/_primer/cases/line_moved/expected_comparator.json
index d826f8390a..47824cb2e1 100644
--- a/tests/testutils/_primer/cases/line_moved/expected_comparator.json
+++ b/tests/testutils/_primer/cases/line_moved/expected_comparator.json
@@ -1 +1 @@
-[{ "package": "astroid", "missing": 1, "new": 1 }]
+[{ "package": "astroid", "missing": 0, "new": 0, "changed": 1 }]
diff --git a/tests/testutils/_primer/cases/message_changed/expected.txt b/tests/testutils/_primer/cases/message_changed/expected.txt
index a99896696e..780f055938 100644
--- a/tests/testutils/_primer/cases/message_changed/expected.txt
+++ b/tests/testutils/_primer/cases/message_changed/expected.txt
@@ -3,22 +3,16 @@
 
 **Effect on [astroid](https://github.com/pylint-dev/astroid):**
 
-The following messages are now emitted:
+The following messages have been changed:
 
 <details>
 
-1) locally-disabled:
-*Locally disabling redefined-builtin [we added some text in the message] (W0622)*
-https://github.com/pylint-dev/astroid/blob/123456789abcdef/astroid/__init__.py#L91
-</details>
-
-The following messages are no longer emitted:
-
-<details>
-
-1) locally-disabled:
-*Locally disabling redefined-builtin (W0622)*
-https://github.com/pylint-dev/astroid/blob/123456789abcdef/astroid/__init__.py#L91
+1) [locally-disabled](https://github.com/pylint-dev/astroid/blob/123456789abcdef/astroid/__init__.py#L91):
+```diff
+- Locally disabling redefined-builtin (W0622)
++ Locally disabling redefined-builtin [we added some text in the message] (W0622)
+                                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+```
 </details>
 
 *This comment was generated for commit v2.14.2*
diff --git a/tests/testutils/_primer/cases/message_changed/expected_comparator.json b/tests/testutils/_primer/cases/message_changed/expected_comparator.json
index d826f8390a..47824cb2e1 100644
--- a/tests/testutils/_primer/cases/message_changed/expected_comparator.json
+++ b/tests/testutils/_primer/cases/message_changed/expected_comparator.json
@@ -1 +1 @@
-[{ "package": "astroid", "missing": 1, "new": 1 }]
+[{ "package": "astroid", "missing": 0, "new": 0, "changed": 1 }]
diff --git a/tests/testutils/_primer/cases/message_changed/expected_truncated.txt b/tests/testutils/_primer/cases/message_changed/expected_truncated.txt
index 44926e4485..d3943d8a77 100644
--- a/tests/testutils/_primer/cases/message_changed/expected_truncated.txt
+++ b/tests/testutils/_primer/cases/message_changed/expected_truncated.txt
@@ -3,12 +3,14 @@
 
 **Effect on [astroid](https://github.com/pylint-dev/astroid):**
 
-The following messages are now emitted:
+The following messages have been changed:
 
 <details>
 
-1) locally-disabled:
-*Locally disabling redefined-builtin [we added some text in the message]...
+1) [locally-disabled](https://github.com/pylint-dev/astroid/blob/123456789abcdef/astroid/__init__.py#L91):
+```diff
+- Locally disabling redefined-builtin (W0622)
++ Locally disabling...
 </details>
 
 *This comment was truncated because GitHub allows only 525 characters in a comment.*
diff --git a/tests/testutils/_primer/cases/message_changed/expected_truncated_in_details.txt b/tests/testutils/_primer/cases/message_changed/expected_truncated_in_details.txt
index c8406b21f8..f3ae7aa165 100644
--- a/tests/testutils/_primer/cases/message_changed/expected_truncated_in_details.txt
+++ b/tests/testutils/_primer/cases/message_changed/expected_truncated_in_details.txt
@@ -3,12 +3,11 @@
 
 **Effect on [astroid](https://github.com/pylint-dev/astroid):**
 
-The following messages are now emitted:
+The following messages have been changed:
 
 <details>
 
-1) locally-disabled:
-*Locally disabling redefined-builtin [we added some text in the...
+1)...
 </details>
 
 *This comment was truncated because GitHub allows only 420 characters in a comment.*
diff --git a/tests/testutils/_primer/cases/message_changed_line/expected.txt b/tests/testutils/_primer/cases/message_changed_line/expected.txt
index 959804eb5a..c9646807e5 100644
--- a/tests/testutils/_primer/cases/message_changed_line/expected.txt
+++ b/tests/testutils/_primer/cases/message_changed_line/expected.txt
@@ -3,22 +3,18 @@
 
 **Effect on [astroid](https://github.com/pylint-dev/astroid):**
 
-The following messages are now emitted:
+The following messages have been changed:
 
 <details>
 
-1) too-complex:
-*'my_function' is too complex. The McCabe rating is 17*
-https://github.com/pylint-dev/astroid/blob/123456789abcdef/astroid/node_classes.py#L103
-</details>
-
-The following messages are no longer emitted:
-
-<details>
+1) [too-complex](https://github.com/pylint-dev/astroid/blob/123456789abcdef/astroid/node_classes.py#L103):
+Was raised from `100:0` to `100:15`, now from `103:0` to `103:15`.
 
-1) too-complex:
-*'my_function' is too complex. The McCabe rating is 18*
-https://github.com/pylint-dev/astroid/blob/123456789abcdef/astroid/node_classes.py#L100
+```diff
+- 'my_function' is too complex. The McCabe rating is 18
++ 'my_function' is too complex. The McCabe rating is 17
+                                                      ^
+```
 </details>
 
 *This comment was generated for commit v2.14.2*
diff --git a/tests/testutils/_primer/cases/message_changed_line/expected_comparator.json b/tests/testutils/_primer/cases/message_changed_line/expected_comparator.json
index d826f8390a..47824cb2e1 100644
--- a/tests/testutils/_primer/cases/message_changed_line/expected_comparator.json
+++ b/tests/testutils/_primer/cases/message_changed_line/expected_comparator.json
@@ -1 +1 @@
-[{ "package": "astroid", "missing": 1, "new": 1 }]
+[{ "package": "astroid", "missing": 0, "new": 0, "changed": 1 }]
diff --git a/tests/testutils/_primer/cases/mixed_changes/expected.txt b/tests/testutils/_primer/cases/mixed_changes/expected.txt
index 9590f932d6..2f735a8cb5 100644
--- a/tests/testutils/_primer/cases/mixed_changes/expected.txt
+++ b/tests/testutils/_primer/cases/mixed_changes/expected.txt
@@ -3,28 +3,28 @@
 
 **Effect on [astroid](https://github.com/pylint-dev/astroid):**
 
-The following messages are now emitted:
+The following messages have been changed:
 
 <details>
 
-1) locally-disabled:
-*Locally disabling redefined-builtin [we added some text in the message] (W0622)*
-https://github.com/pylint-dev/astroid/blob/123456789abcdef/astroid/__init__.py#L91
-2) too-complex:
-*'my_function' is too complex. The McCabe rating is 17*
-https://github.com/pylint-dev/astroid/blob/123456789abcdef/astroid/node_classes.py#L105
-</details>
-
-The following messages are no longer emitted:
-
-<details>
-
-1) locally-disabled:
-*Locally disabling redefined-builtin (W0622)*
-https://github.com/pylint-dev/astroid/blob/123456789abcdef/astroid/__init__.py#L91
-2) too-complex:
-*'my_function' is too complex. The McCabe rating is 18*
-https://github.com/pylint-dev/astroid/blob/123456789abcdef/astroid/node_classes.py#L100
+1) [locally-disabled](https://github.com/pylint-dev/astroid/blob/123456789abcdef/astroid/__init__.py#L91):
+```diff
+- Locally disabling redefined-builtin (W0622)
++ Locally disabling redefined-builtin [we added some text in the message] (W0622)
+                                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+```
+2) [too-complex](https://github.com/pylint-dev/astroid/blob/123456789abcdef/astroid/node_classes.py#L105):
+Was raised from `100:0` to `100:15`, now from `105:0` to `105:15`.
+
+confidence: `UNDEFINED` → `HIGH`
+
+```diff
+- 'my_function' is too complex. The McCabe rating is 18
++ 'my_function' is too complex. The McCabe rating is 17
+                                                      ^
+```
+3) [unknown-option-value](https://github.com/pylint-dev/astroid/blob/123456789abcdef/astroid/__init__.py#L91):
+confidence: `UNDEFINED` → `HIGH`
 </details>
 
 *This comment was generated for commit v2.14.2*
diff --git a/tests/testutils/_primer/cases/mixed_changes/expected_comparator.json b/tests/testutils/_primer/cases/mixed_changes/expected_comparator.json
index a0e7f6f710..6e33a850d4 100644
--- a/tests/testutils/_primer/cases/mixed_changes/expected_comparator.json
+++ b/tests/testutils/_primer/cases/mixed_changes/expected_comparator.json
@@ -1 +1 @@
-[{ "package": "astroid", "missing": 2, "new": 2 }]
+[{ "package": "astroid", "missing": 0, "new": 0, "changed": 3 }]
diff --git a/tests/testutils/_primer/cases/mixed_changes/pr.json b/tests/testutils/_primer/cases/mixed_changes/pr.json
index 87d7e44b04..fbadd2d9fe 100644
--- a/tests/testutils/_primer/cases/mixed_changes/pr.json
+++ b/tests/testutils/_primer/cases/mixed_changes/pr.json
@@ -29,7 +29,7 @@
         "symbol": "too-complex",
         "message": "'my_function' is too complex. The McCabe rating is 17",
         "messageId": "R1260",
-        "confidence": "UNDEFINED",
+        "confidence": "HIGH",
         "absolutePath": "tests/.pylint_primer_tests/pylint-dev/astroid/astroid/node_classes.py"
       },
       {
@@ -44,7 +44,7 @@
         "symbol": "unknown-option-value",
         "message": "Unknown option value for 'disable', expected a valid pylint message and got 'Ellipsis'",
         "messageId": "W0012",
-        "confidence": "UNDEFINED",
+        "confidence": "HIGH",
         "absolutePath": "tests/.pylint_primer_tests/pylint-dev/astroid/astroid/__init__.py"
       }
     ]
diff --git a/tests/testutils/_primer/cases/multi_package/expected.txt b/tests/testutils/_primer/cases/multi_package/expected.txt
index 46f9611eb7..9f4a1f9c13 100644
--- a/tests/testutils/_primer/cases/multi_package/expected.txt
+++ b/tests/testutils/_primer/cases/multi_package/expected.txt
@@ -24,7 +24,7 @@ https://github.com/pylint-dev/astroid/blob/123456789abcdef/astroid/node_classes.
 
 **Effect on [astropy](https://github.com/astropy/astropy):**
 
-The following messages are now emitted:
+😞 The following false positives have been introduced:
 
 <details>
 
diff --git a/tests/testutils/_primer/cases/multi_package/expected_comparator.json b/tests/testutils/_primer/cases/multi_package/expected_comparator.json
index 456a50f703..38f460088e 100644
--- a/tests/testutils/_primer/cases/multi_package/expected_comparator.json
+++ b/tests/testutils/_primer/cases/multi_package/expected_comparator.json
@@ -1,4 +1,4 @@
 [
-  { "package": "astroid", "missing": 1, "new": 1 },
-  { "package": "astropy", "missing": 1, "new": 1 }
+  { "package": "astroid", "missing": 0, "new": 0, "changed": 1 },
+  { "package": "astropy", "missing": 1, "new": 1, "changed": 0 }
 ]
diff --git a/tests/testutils/_primer/cases/new_message/expected_comparator.json b/tests/testutils/_primer/cases/new_message/expected_comparator.json
index e436268fa3..1d944b5bb8 100644
--- a/tests/testutils/_primer/cases/new_message/expected_comparator.json
+++ b/tests/testutils/_primer/cases/new_message/expected_comparator.json
@@ -1 +1 @@
-[{ "package": "astroid", "missing": 0, "new": 1 }]
+[{ "package": "astroid", "missing": 0, "new": 1, "changed": 0 }]
diff --git a/tests/testutils/_primer/cases/removed_message/expected_comparator.json b/tests/testutils/_primer/cases/removed_message/expected_comparator.json
index cd879eeea8..723706ace4 100644
--- a/tests/testutils/_primer/cases/removed_message/expected_comparator.json
+++ b/tests/testutils/_primer/cases/removed_message/expected_comparator.json
@@ -1 +1 @@
-[{ "package": "astroid", "missing": 1, "new": 0 }]
+[{ "package": "astroid", "missing": 1, "new": 0, "changed": 0 }]
diff --git a/tests/testutils/_primer/cases/type_changed/expected.txt b/tests/testutils/_primer/cases/type_changed/expected.txt
index d83b197c08..da46e99bb1 100644
--- a/tests/testutils/_primer/cases/type_changed/expected.txt
+++ b/tests/testutils/_primer/cases/type_changed/expected.txt
@@ -3,22 +3,12 @@
 
 **Effect on [astroid](https://github.com/pylint-dev/astroid):**
 
-The following messages are now emitted:
+The following messages have been changed:
 
 <details>
 
-1) line-too-long:
-*Line too long (120/100)*
-https://github.com/pylint-dev/astroid/blob/123456789abcdef/astroid/node_classes.py#L50
-</details>
-
-The following messages are no longer emitted:
-
-<details>
-
-1) line-too-long:
-*Line too long (120/100)*
-https://github.com/pylint-dev/astroid/blob/123456789abcdef/astroid/node_classes.py#L50
+1) [line-too-long](https://github.com/pylint-dev/astroid/blob/123456789abcdef/astroid/node_classes.py#L50):
+type: `convention` → `warning`
 </details>
 
 *This comment was generated for commit v2.14.2*
diff --git a/tests/testutils/_primer/cases/type_changed/expected_comparator.json b/tests/testutils/_primer/cases/type_changed/expected_comparator.json
index d826f8390a..47824cb2e1 100644
--- a/tests/testutils/_primer/cases/type_changed/expected_comparator.json
+++ b/tests/testutils/_primer/cases/type_changed/expected_comparator.json
@@ -1 +1 @@
-[{ "package": "astroid", "missing": 1, "new": 1 }]
+[{ "package": "astroid", "missing": 0, "new": 0, "changed": 1 }]
diff --git a/tests/testutils/_primer/cases/useless_suppression/expected_comparator.json b/tests/testutils/_primer/cases/useless_suppression/expected_comparator.json
index b02271a012..68ea0d61b5 100644
--- a/tests/testutils/_primer/cases/useless_suppression/expected_comparator.json
+++ b/tests/testutils/_primer/cases/useless_suppression/expected_comparator.json
@@ -1 +1 @@
-[{ "package": "astropy", "missing": 0, "new": 2 }]
+[{ "package": "astropy", "missing": 0, "new": 2, "changed": 0 }]
diff --git a/tests/testutils/_primer/test_comparator.py b/tests/testutils/_primer/test_comparator.py
index 212af59e61..94e8d035a0 100644
--- a/tests/testutils/_primer/test_comparator.py
+++ b/tests/testutils/_primer/test_comparator.py
@@ -22,10 +22,11 @@ def test_comparator(directory: Path) -> None:
     expected = json.loads((directory / "expected_comparator.json").read_text("utf-8"))
     results = list(comparator)
     assert len(results) == len(expected)
-    for (package, missing, new), exp in zip(results, expected):
+    for (package, missing, new, changed), exp in zip(results, expected):
         assert package == exp["package"]
         assert len(missing["messages"]) == exp["missing"]
         assert len(new["messages"]) == exp["new"]
+        assert len(changed) == exp["changed"]
 
 
 def test_comparator_batched() -> None:
@@ -38,7 +39,8 @@ def test_comparator_batched() -> None:
     expected = json.loads((fixture / "expected_comparator.json").read_text("utf-8"))
     results = list(comparator)
     assert len(results) == len(expected)
-    for (package, missing, new), exp in zip(results, expected):
+    for (package, missing, new, changed), exp in zip(results, expected):
         assert package == exp["package"]
         assert len(missing["messages"]) == exp["missing"]
         assert len(new["messages"]) == exp["new"]
+        assert len(changed) == exp["changed"]

From d1dda8b8704be8233a0ddf969f005d4f7e6db5f9 Mon Sep 17 00:00:00 2001
From: Pierre Sassoulas <pierre.sassoulas@gmail.com>
Date: Thu, 2 Apr 2026 22:51:05 +0200
Subject: [PATCH 2/8] [primer] Classify new messages into false-positive
 categories
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

New messages are now sorted into subcategories:
- useless-suppression → "fixed false positives" (🎉)
- locally-disabled → "introduced false positives" (😞)
- astroid-error → counted separately
- everything else → "now emitted"

Extract _ClassifiedMessages and _format_messages helpers, and use
_details_section for consistent <details> blocks with the blank line
required for GitHub markdown rendering.
---
 .../_primer/primer_compare_command.py         | 145 ++++++++++++------
 .../_primer/batched_cases/expected.txt        |   2 +-
 .../cases/confidence_changed/expected.txt     |   2 +-
 .../_primer/cases/line_moved/expected.txt     |   2 +-
 .../cases/message_changed/expected.txt        |   2 +-
 .../message_changed/expected_truncated.txt    |   7 +-
 .../expected_truncated_in_details.txt         |   4 +-
 .../cases/message_changed_line/expected.txt   |   2 +-
 .../_primer/cases/mixed_changes/expected.txt  |   2 +-
 .../_primer/cases/multi_package/expected.txt  |  24 ++-
 .../_primer/cases/new_message/expected.txt    |   2 +-
 .../cases/removed_message/expected.txt        |   2 +-
 .../_primer/cases/type_changed/expected.txt   |   2 +-
 .../cases/useless_suppression/expected.txt    |  14 +-
 tests/testutils/_primer/test_primer.py        |   4 +-
 15 files changed, 136 insertions(+), 80 deletions(-)

diff --git a/pylint/testutils/_primer/primer_compare_command.py b/pylint/testutils/_primer/primer_compare_command.py
index 406e41035e..f5df3fc3f0 100644
--- a/pylint/testutils/_primer/primer_compare_command.py
+++ b/pylint/testutils/_primer/primer_compare_command.py
@@ -3,10 +3,13 @@
 # Copyright (c) https://github.com/pylint-dev/pylint/blob/main/CONTRIBUTORS.txt
 from __future__ import annotations
 
+import re
+from collections.abc import Callable
 from pathlib import PurePosixPath
 
 from pylint.reporters.json_reporter import JSONMessage
 from pylint.testutils._primer.comparator import (
+    ChangedMessage,
     Comparator,
     PackageDiff,
     message_diff,
@@ -14,6 +17,70 @@
 from pylint.testutils._primer.primer_command import PrimerCommand
 
 MAX_GITHUB_COMMENT_LENGTH = 65536
+USELESS_SUPPRESSION_RE = re.compile(r"Useless suppression of '(.+)'")
+
+
+def _format_messages(
+    messages: list[JSONMessage],
+    source_link: Callable[[JSONMessage], str],
+) -> str:
+    """Format a list of messages as a numbered body for a ``<details>`` block."""
+    body = ""
+    for count, msg in enumerate(messages, 1):
+        body += (
+            f"{count}) {msg['symbol']}:\n*{msg['message']}*\n" f"{source_link(msg)}\n"
+        )
+    return body
+
+
+class _ClassifiedMessages:
+    """All message categories for a single package, pre-formatted for display."""
+
+    __slots__ = (
+        "astroid_errors",
+        "changed_messages",
+        "fixed_false_positives",
+        "missing_messages",
+        "new_false_positives",
+        "new_messages",
+    )
+
+    def __init__(
+        self,
+        new_messages: list[JSONMessage],
+        missing_messages: list[JSONMessage],
+        changed_messages: list[ChangedMessage],
+        source_link: Callable[[JSONMessage], str],
+    ) -> None:
+        astroid_errors = 0
+        new_fp: list[JSONMessage] = []
+        fixed_fp: list[JSONMessage] = []
+        other_new: list[JSONMessage] = []
+        for message in new_messages:
+            if message["symbol"] == "astroid-error":
+                astroid_errors += 1
+            elif USELESS_SUPPRESSION_RE.match(message["message"]):
+                fixed_fp.append(message)
+            elif message["symbol"] == "locally-disabled":
+                # A new locally-disabled means a maintainer had to add a
+                # suppression comment — we introduced a false positive.
+                new_fp.append(message)
+            else:
+                other_new.append(message)
+
+        self.astroid_errors = astroid_errors
+        self.fixed_false_positives = _format_messages(fixed_fp, source_link)
+        self.new_false_positives = _format_messages(new_fp, source_link)
+        self.new_messages = _format_messages(other_new, source_link)
+        self.missing_messages = _format_messages(missing_messages, source_link)
+
+        body = ""
+        for count, (old, new) in enumerate(changed_messages, 1):
+            body += (
+                f"{count}) [{new['symbol']}]({source_link(new)}):\n"
+                f"{message_diff(old, new)}\n"
+            )
+        self.changed_messages = body
 
 
 class CompareCommand(PrimerCommand):
@@ -55,63 +122,51 @@ def _source_link(msg: JSONMessage) -> str:
             filepath = str(PurePosixPath(msg["path"]).relative_to(clone_dir))
             return f"{url}/blob/{commit}/{filepath}#L{msg['line']}"
 
+        def _details_section(title: str, body: str) -> str:
+            # Blank line after <details> required for GitHub markdown rendering.
+            return f"{title}\n\n<details>\n\n{body}</details>\n\n"
+
+        classified = _ClassifiedMessages(
+            diff.new["messages"], diff.missing["messages"], diff.changed, _source_link
+        )
         comment = f"\n**Effect on [{package}]({url}):**\n\n"
 
-        # Changed messages
         if diff.changed:
             print("Changed:")
-            comment += "The following messages have been changed:\n\n<details>\n\n"
-            for count, (old, new) in enumerate(diff.changed, 1):
-                comment += (
-                    f"{count}) [{new['symbol']}]({_source_link(new)}):\n"
-                    f"{message_diff(old, new)}\n"
-                )
+            for _, new in diff.changed:
                 print(new)
-            comment += "</details>\n\n"
-
-        # New messages
-        count = 1
-        astroid_errors = 0
-        new_non_astroid_messages = ""
         if diff.new["messages"]:
             print("Now emitted:")
-        for message in diff.new["messages"]:
-            if message["symbol"] == "astroid-error":
-                astroid_errors += 1
-            else:
-                new_non_astroid_messages += (
-                    f"{count}) {message['symbol']}:\n*{message['message']}*\n"
-                    f"{_source_link(message)}\n"
-                )
-                print(message)
-                count += 1
-
-        if astroid_errors:
+            for msg in diff.new["messages"]:
+                print(msg)
+        if diff.missing["messages"]:
+            print("No longer emitted:")
+            for msg in diff.missing["messages"]:
+                print(msg)
+
+        if classified.changed_messages:
+            comment += _details_section(
+                "Changed messages:", classified.changed_messages
+            )
+        if classified.astroid_errors:
             comment += (
-                f'{astroid_errors} "astroid error(s)" were found. '
+                f'{classified.astroid_errors} "astroid error(s)" were found. '
                 "Please open the GitHub Actions log to see what failed or crashed.\n\n"
             )
-        if new_non_astroid_messages:
-            comment += (
-                "The following messages are now emitted:\n\n<details>\n\n"
-                + new_non_astroid_messages
-                + "</details>\n\n"
+        if classified.fixed_false_positives:
+            comment += _details_section(
+                "🎉 Fixed false positives:", classified.fixed_false_positives
             )
-
-        # Missing messages
-        count = 1
-        if diff.missing["messages"]:
-            comment += "The following messages are no longer emitted:\n\n<details>\n\n"
-            print("No longer emitted:")
-        for message in diff.missing["messages"]:
-            comment += (
-                f"{count}) {message['symbol']}:\n*{message['message']}*\n"
-                f"{_source_link(message)}\n"
+        if classified.new_false_positives:
+            comment += _details_section(
+                "😞 New false positives:", classified.new_false_positives
+            )
+        if classified.new_messages:
+            comment += _details_section("New messages:", classified.new_messages)
+        if classified.missing_messages:
+            comment += _details_section(
+                "Removed messages:", classified.missing_messages
             )
-            count += 1
-            print(message)
-        if diff.missing["messages"]:
-            comment += "</details>\n\n"
         return comment
 
     def _truncate_comment(self, comment: str) -> str:
diff --git a/tests/testutils/_primer/batched_cases/expected.txt b/tests/testutils/_primer/batched_cases/expected.txt
index 2c112f6e75..9427ea15e6 100644
--- a/tests/testutils/_primer/batched_cases/expected.txt
+++ b/tests/testutils/_primer/batched_cases/expected.txt
@@ -3,7 +3,7 @@
 
 **Effect on [astroid](https://github.com/pylint-dev/astroid):**
 
-The following messages are no longer emitted:
+Removed messages:
 
 <details>
 
diff --git a/tests/testutils/_primer/cases/confidence_changed/expected.txt b/tests/testutils/_primer/cases/confidence_changed/expected.txt
index bb0e8e2898..717bb004f8 100644
--- a/tests/testutils/_primer/cases/confidence_changed/expected.txt
+++ b/tests/testutils/_primer/cases/confidence_changed/expected.txt
@@ -3,7 +3,7 @@
 
 **Effect on [astroid](https://github.com/pylint-dev/astroid):**
 
-The following messages have been changed:
+Changed messages:
 
 <details>
 
diff --git a/tests/testutils/_primer/cases/line_moved/expected.txt b/tests/testutils/_primer/cases/line_moved/expected.txt
index ca0b3aaa76..03d388dea3 100644
--- a/tests/testutils/_primer/cases/line_moved/expected.txt
+++ b/tests/testutils/_primer/cases/line_moved/expected.txt
@@ -3,7 +3,7 @@
 
 **Effect on [astroid](https://github.com/pylint-dev/astroid):**
 
-The following messages have been changed:
+Changed messages:
 
 <details>
 
diff --git a/tests/testutils/_primer/cases/message_changed/expected.txt b/tests/testutils/_primer/cases/message_changed/expected.txt
index 780f055938..cb4812421a 100644
--- a/tests/testutils/_primer/cases/message_changed/expected.txt
+++ b/tests/testutils/_primer/cases/message_changed/expected.txt
@@ -3,7 +3,7 @@
 
 **Effect on [astroid](https://github.com/pylint-dev/astroid):**
 
-The following messages have been changed:
+Changed messages:
 
 <details>
 
diff --git a/tests/testutils/_primer/cases/message_changed/expected_truncated.txt b/tests/testutils/_primer/cases/message_changed/expected_truncated.txt
index d3943d8a77..55d70bb96f 100644
--- a/tests/testutils/_primer/cases/message_changed/expected_truncated.txt
+++ b/tests/testutils/_primer/cases/message_changed/expected_truncated.txt
@@ -3,16 +3,15 @@
 
 **Effect on [astroid](https://github.com/pylint-dev/astroid):**
 
-The following messages have been changed:
+Changed messages:
 
 <details>
 
 1) [locally-disabled](https://github.com/pylint-dev/astroid/blob/123456789abcdef/astroid/__init__.py#L91):
 ```diff
-- Locally disabling redefined-builtin (W0622)
-+ Locally disabling...
+- Locally disabling...
 </details>
 
-*This comment was truncated because GitHub allows only 525 characters in a comment.*
+*This comment was truncated because GitHub allows only 450 characters in a comment.*
 
 *This comment was generated for commit v2.14.2*
diff --git a/tests/testutils/_primer/cases/message_changed/expected_truncated_in_details.txt b/tests/testutils/_primer/cases/message_changed/expected_truncated_in_details.txt
index f3ae7aa165..a285996bf7 100644
--- a/tests/testutils/_primer/cases/message_changed/expected_truncated_in_details.txt
+++ b/tests/testutils/_primer/cases/message_changed/expected_truncated_in_details.txt
@@ -3,13 +3,13 @@
 
 **Effect on [astroid](https://github.com/pylint-dev/astroid):**
 
-The following messages have been changed:
+Changed messages:
 
 <details>
 
 1)...
 </details>
 
-*This comment was truncated because GitHub allows only 420 characters in a comment.*
+*This comment was truncated because GitHub allows only 400 characters in a comment.*
 
 *This comment was generated for commit v2.14.2*
diff --git a/tests/testutils/_primer/cases/message_changed_line/expected.txt b/tests/testutils/_primer/cases/message_changed_line/expected.txt
index c9646807e5..aab58798d7 100644
--- a/tests/testutils/_primer/cases/message_changed_line/expected.txt
+++ b/tests/testutils/_primer/cases/message_changed_line/expected.txt
@@ -3,7 +3,7 @@
 
 **Effect on [astroid](https://github.com/pylint-dev/astroid):**
 
-The following messages have been changed:
+Changed messages:
 
 <details>
 
diff --git a/tests/testutils/_primer/cases/mixed_changes/expected.txt b/tests/testutils/_primer/cases/mixed_changes/expected.txt
index 2f735a8cb5..b40a50c3a7 100644
--- a/tests/testutils/_primer/cases/mixed_changes/expected.txt
+++ b/tests/testutils/_primer/cases/mixed_changes/expected.txt
@@ -3,7 +3,7 @@
 
 **Effect on [astroid](https://github.com/pylint-dev/astroid):**
 
-The following messages have been changed:
+Changed messages:
 
 <details>
 
diff --git a/tests/testutils/_primer/cases/multi_package/expected.txt b/tests/testutils/_primer/cases/multi_package/expected.txt
index 9f4a1f9c13..a4f6ea541f 100644
--- a/tests/testutils/_primer/cases/multi_package/expected.txt
+++ b/tests/testutils/_primer/cases/multi_package/expected.txt
@@ -3,28 +3,24 @@
 
 **Effect on [astroid](https://github.com/pylint-dev/astroid):**
 
-The following messages are now emitted:
+Changed messages:
 
 <details>
 
-1) too-complex:
-*'my_function' is too complex. The McCabe rating is 17*
-https://github.com/pylint-dev/astroid/blob/123456789abcdef/astroid/node_classes.py#L105
-</details>
-
-The following messages are no longer emitted:
-
-<details>
+1) [too-complex](https://github.com/pylint-dev/astroid/blob/123456789abcdef/astroid/node_classes.py#L105):
+Was raised from `100:0` to `100:15`, now from `105:0` to `105:15`.
 
-1) too-complex:
-*'my_function' is too complex. The McCabe rating is 18*
-https://github.com/pylint-dev/astroid/blob/123456789abcdef/astroid/node_classes.py#L100
+```diff
+- 'my_function' is too complex. The McCabe rating is 18
++ 'my_function' is too complex. The McCabe rating is 17
+                                                      ^
+```
 </details>
 
 
 **Effect on [astropy](https://github.com/astropy/astropy):**
 
-😞 The following false positives have been introduced:
+😞 New false positives:
 
 <details>
 
@@ -33,7 +29,7 @@ https://github.com/pylint-dev/astroid/blob/123456789abcdef/astroid/node_classes.
 https://github.com/astropy/astropy/blob/1fb40bc1f22f176254ef583065aa155f53f3b414/astropy/coordinates/angles/angle_parsetab.py#L14
 </details>
 
-The following messages are no longer emitted:
+Removed messages:
 
 <details>
 
diff --git a/tests/testutils/_primer/cases/new_message/expected.txt b/tests/testutils/_primer/cases/new_message/expected.txt
index 425df41d6a..e813dd0a86 100644
--- a/tests/testutils/_primer/cases/new_message/expected.txt
+++ b/tests/testutils/_primer/cases/new_message/expected.txt
@@ -3,7 +3,7 @@
 
 **Effect on [astroid](https://github.com/pylint-dev/astroid):**
 
-The following messages are now emitted:
+😞 New false positives:
 
 <details>
 
diff --git a/tests/testutils/_primer/cases/removed_message/expected.txt b/tests/testutils/_primer/cases/removed_message/expected.txt
index 88af536d71..0200400648 100644
--- a/tests/testutils/_primer/cases/removed_message/expected.txt
+++ b/tests/testutils/_primer/cases/removed_message/expected.txt
@@ -3,7 +3,7 @@
 
 **Effect on [astroid](https://github.com/pylint-dev/astroid):**
 
-The following messages are no longer emitted:
+Removed messages:
 
 <details>
 
diff --git a/tests/testutils/_primer/cases/type_changed/expected.txt b/tests/testutils/_primer/cases/type_changed/expected.txt
index da46e99bb1..64423538a0 100644
--- a/tests/testutils/_primer/cases/type_changed/expected.txt
+++ b/tests/testutils/_primer/cases/type_changed/expected.txt
@@ -3,7 +3,7 @@
 
 **Effect on [astroid](https://github.com/pylint-dev/astroid):**
 
-The following messages have been changed:
+Changed messages:
 
 <details>
 
diff --git a/tests/testutils/_primer/cases/useless_suppression/expected.txt b/tests/testutils/_primer/cases/useless_suppression/expected.txt
index 8f56c44551..a813b98174 100644
--- a/tests/testutils/_primer/cases/useless_suppression/expected.txt
+++ b/tests/testutils/_primer/cases/useless_suppression/expected.txt
@@ -3,16 +3,22 @@
 
 **Effect on [astropy](https://github.com/astropy/astropy):**
 
-The following messages are now emitted:
+🎉 Fixed false positives:
+
+<details>
+
+1) useless-suppression:
+*Useless suppression of 'looping-through-iterator'*
+https://github.com/astropy/astropy/blob/1fb40bc1f22f176254ef583065aa155f53f3b414/astropy/coordinates/angles/angle_parsetab.py#L14
+</details>
+
+😞 New false positives:
 
 <details>
 
 1) locally-disabled:
 *Locally disabling looping-through-iterator (W4801)*
 https://github.com/astropy/astropy/blob/1fb40bc1f22f176254ef583065aa155f53f3b414/astropy/coordinates/angles/angle_parsetab.py#L14
-2) useless-suppression:
-*Useless suppression of 'looping-through-iterator'*
-https://github.com/astropy/astropy/blob/1fb40bc1f22f176254ef583065aa155f53f3b414/astropy/coordinates/angles/angle_parsetab.py#L14
 </details>
 
 *This comment was generated for commit v2.14.2*
diff --git a/tests/testutils/_primer/test_primer.py b/tests/testutils/_primer/test_primer.py
index d639a27c19..d443cde693 100644
--- a/tests/testutils/_primer/test_primer.py
+++ b/tests/testutils/_primer/test_primer.py
@@ -77,7 +77,7 @@ def test_compare_batched(self) -> None:
 
     def test_truncated_compare(self) -> None:
         """Test for the truncation of comments that are too long."""
-        max_comment_length = 525
+        max_comment_length = 450
         directory = CASES_PATH / "message_changed"
         with patch(
             "pylint.testutils._primer.primer_compare_command.MAX_GITHUB_COMMENT_LENGTH",
@@ -107,7 +107,7 @@ def test_truncated_compare_stops_iterating_packages(self) -> None:
 
     def test_truncated_compare_in_details(self) -> None:
         """Test for the truncation of comments that are too long inside details."""
-        max_comment_length = 420
+        max_comment_length = 400
         directory = CASES_PATH / "message_changed"
         with patch(
             "pylint.testutils._primer.primer_compare_command.MAX_GITHUB_COMMENT_LENGTH",

From 1389d74262a08a15a2c1342580327cb61fb2eb46 Mon Sep 17 00:00:00 2001
From: Pierre Sassoulas <pierre.sassoulas@gmail.com>
Date: Fri, 3 Apr 2026 10:00:21 +0200
Subject: [PATCH 3/8] [primer] Clarify location diff wording and robustify key
 iteration
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

- format_span now returns `line:col`-`endLine:endCol` spans, and
  message_diff says "Moved from {old} to {new}" — avoids ambiguity
  between span-range and movement.
- message_diff iterates set(old) | set(new) so keys present only in
  new are also detected.
---
 pylint/testutils/_primer/comparator.py                 | 10 +++++-----
 tests/testutils/_primer/cases/line_moved/expected.txt  |  2 +-
 .../_primer/cases/message_changed_line/expected.txt    |  2 +-
 .../testutils/_primer/cases/mixed_changes/expected.txt |  2 +-
 .../testutils/_primer/cases/multi_package/expected.txt |  2 +-
 5 files changed, 9 insertions(+), 9 deletions(-)

diff --git a/pylint/testutils/_primer/comparator.py b/pylint/testutils/_primer/comparator.py
index 0b09a918ff..c5e7d2d037 100644
--- a/pylint/testutils/_primer/comparator.py
+++ b/pylint/testutils/_primer/comparator.py
@@ -75,8 +75,8 @@ def format_span(msg: JSONMessage) -> str:
     end_line = msg.get("endLine")
     end_col = msg.get("endColumn")
     if end_line is not None and end_col is not None:
-        return f"from `{start}` to `{end_line}:{end_col}`"
-    return f"at `{start}`"
+        return f"`{start}`-`{end_line}:{end_col}`"
+    return f"`{start}`"
 
 
 def message_diff(old: JSONMessage, new: JSONMessage) -> str:
@@ -87,14 +87,14 @@ def message_diff(old: JSONMessage, new: JSONMessage) -> str:
     renders them with red/green highlighting.
     """
     changed_keys: set[str] = set()
-    for key in old:
-        if old[key] != new[key]:  # type: ignore[literal-required]
+    for key in set(old) | set(new):
+        if old.get(key) != new.get(key):
             changed_keys.add(key)
 
     parts: list[str] = []
     # Location: combine line/column/endLine/endColumn into one sentence.
     if changed_keys & _LOCATION_KEYS:
-        parts.append(f"Was raised {format_span(old)}, now {format_span(new)}.")
+        parts.append(f"Moved from {format_span(old)} to {format_span(new)}.")
 
     # Other fields (typically ``message`` or ``type``).
     for key in sorted(changed_keys - _LOCATION_KEYS):
diff --git a/tests/testutils/_primer/cases/line_moved/expected.txt b/tests/testutils/_primer/cases/line_moved/expected.txt
index 03d388dea3..b52b2a9fc1 100644
--- a/tests/testutils/_primer/cases/line_moved/expected.txt
+++ b/tests/testutils/_primer/cases/line_moved/expected.txt
@@ -8,7 +8,7 @@ Changed messages:
 <details>
 
 1) [too-complex](https://github.com/pylint-dev/astroid/blob/123456789abcdef/astroid/node_classes.py#L103):
-Was raised from `100:0` to `100:15`, now from `103:0` to `103:15`.
+Moved from `100:0`-`100:15` to `103:0`-`103:15`.
 </details>
 
 *This comment was generated for commit v2.14.2*
diff --git a/tests/testutils/_primer/cases/message_changed_line/expected.txt b/tests/testutils/_primer/cases/message_changed_line/expected.txt
index aab58798d7..acb71c2498 100644
--- a/tests/testutils/_primer/cases/message_changed_line/expected.txt
+++ b/tests/testutils/_primer/cases/message_changed_line/expected.txt
@@ -8,7 +8,7 @@ Changed messages:
 <details>
 
 1) [too-complex](https://github.com/pylint-dev/astroid/blob/123456789abcdef/astroid/node_classes.py#L103):
-Was raised from `100:0` to `100:15`, now from `103:0` to `103:15`.
+Moved from `100:0`-`100:15` to `103:0`-`103:15`.
 
 ```diff
 - 'my_function' is too complex. The McCabe rating is 18
diff --git a/tests/testutils/_primer/cases/mixed_changes/expected.txt b/tests/testutils/_primer/cases/mixed_changes/expected.txt
index b40a50c3a7..23511399cd 100644
--- a/tests/testutils/_primer/cases/mixed_changes/expected.txt
+++ b/tests/testutils/_primer/cases/mixed_changes/expected.txt
@@ -14,7 +14,7 @@ Changed messages:
                                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 ```
 2) [too-complex](https://github.com/pylint-dev/astroid/blob/123456789abcdef/astroid/node_classes.py#L105):
-Was raised from `100:0` to `100:15`, now from `105:0` to `105:15`.
+Moved from `100:0`-`100:15` to `105:0`-`105:15`.
 
 confidence: `UNDEFINED` → `HIGH`
 
diff --git a/tests/testutils/_primer/cases/multi_package/expected.txt b/tests/testutils/_primer/cases/multi_package/expected.txt
index a4f6ea541f..67d8236e3b 100644
--- a/tests/testutils/_primer/cases/multi_package/expected.txt
+++ b/tests/testutils/_primer/cases/multi_package/expected.txt
@@ -8,7 +8,7 @@ Changed messages:
 <details>
 
 1) [too-complex](https://github.com/pylint-dev/astroid/blob/123456789abcdef/astroid/node_classes.py#L105):
-Was raised from `100:0` to `100:15`, now from `105:0` to `105:15`.
+Moved from `100:0`-`100:15` to `105:0`-`105:15`.
 
 ```diff
 - 'my_function' is too complex. The McCabe rating is 18

From c683e5d5c4803767018e92273cb8987f8676923f Mon Sep 17 00:00:00 2001
From: Pierre Sassoulas <pierre.sassoulas@gmail.com>
Date: Sat, 18 Apr 2026 14:19:59 +0200
Subject: [PATCH 4/8] [primer] Cover classification branches and truncation
 edge cases
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Adds fixtures and unit tests that bring coverage on comparator.py and
primer_compare_command.py to 100% — all message-classification branches
(astroid-error, useless-suppression fix, locally-disabled FP, genuine
new message) and both truncation code paths (multi-package iteration
break and no-space fallback) now have dedicated tests.
---
 doc/whatsnew/fragments/10914.internal         |  7 ++
 .../expected_truncated_break.txt              |  7 +-
 .../new_messages_classified/expected.txt      | 35 ++++++++++
 .../expected_comparator.json                  |  1 +
 .../cases/new_messages_classified/main.json   |  6 ++
 .../cases/new_messages_classified/pr.json     | 67 +++++++++++++++++++
 tests/testutils/_primer/test_comparator.py    | 40 ++++++++++-
 tests/testutils/_primer/test_primer.py        |  2 +-
 8 files changed, 159 insertions(+), 6 deletions(-)
 create mode 100644 doc/whatsnew/fragments/10914.internal
 create mode 100644 tests/testutils/_primer/cases/new_messages_classified/expected.txt
 create mode 100644 tests/testutils/_primer/cases/new_messages_classified/expected_comparator.json
 create mode 100644 tests/testutils/_primer/cases/new_messages_classified/main.json
 create mode 100644 tests/testutils/_primer/cases/new_messages_classified/pr.json

diff --git a/doc/whatsnew/fragments/10914.internal b/doc/whatsnew/fragments/10914.internal
new file mode 100644
index 0000000000..dc31fa513e
--- /dev/null
+++ b/doc/whatsnew/fragments/10914.internal
@@ -0,0 +1,7 @@
+The primer now pairs residual messages by ``(symbol, path, obj)`` and reports altered
+diagnostics as a single *changed* entry with a compact diff, rather than as a separate
+removal + addition. New messages are classified into genuine new messages, fixed false
+positives (``useless-suppression``), new false positives (``locally-disabled``), and
+``astroid-error`` fatal errors.
+
+Refs #10914
diff --git a/tests/testutils/_primer/cases/multi_package/expected_truncated_break.txt b/tests/testutils/_primer/cases/multi_package/expected_truncated_break.txt
index 331f74ff7f..a285996bf7 100644
--- a/tests/testutils/_primer/cases/multi_package/expected_truncated_break.txt
+++ b/tests/testutils/_primer/cases/multi_package/expected_truncated_break.txt
@@ -3,14 +3,13 @@
 
 **Effect on [astroid](https://github.com/pylint-dev/astroid):**
 
-The following messages are now emitted:
+Changed messages:
 
 <details>
 
-1) too-complex:
-*'my_function' is too complex. The McCabe rating is...
+1)...
 </details>
 
-*This comment was truncated because GitHub allows only 500 characters in a comment.*
+*This comment was truncated because GitHub allows only 400 characters in a comment.*
 
 *This comment was generated for commit v2.14.2*
diff --git a/tests/testutils/_primer/cases/new_messages_classified/expected.txt b/tests/testutils/_primer/cases/new_messages_classified/expected.txt
new file mode 100644
index 0000000000..cfee18bc0e
--- /dev/null
+++ b/tests/testutils/_primer/cases/new_messages_classified/expected.txt
@@ -0,0 +1,35 @@
+🤖 **Effect of this PR on checked open source code:** 🤖
+
+
+**Effect on [astropy](https://github.com/astropy/astropy):**
+
+1 "astroid error(s)" were found. Please open the GitHub Actions log to see what failed or crashed.
+
+🎉 Fixed false positives:
+
+<details>
+
+1) useless-suppression:
+*Useless suppression of 'looping-through-iterator'*
+https://github.com/astropy/astropy/blob/1fb40bc1f22f176254ef583065aa155f53f3b414/astropy/coordinates/angles/angle_parsetab.py#L14
+</details>
+
+😞 New false positives:
+
+<details>
+
+1) locally-disabled:
+*Locally disabling looping-through-iterator (W4801)*
+https://github.com/astropy/astropy/blob/1fb40bc1f22f176254ef583065aa155f53f3b414/astropy/coordinates/angles/angle_parsetab.py#L14
+</details>
+
+New messages:
+
+<details>
+
+1) unused-variable:
+*Unused variable 'foo'*
+https://github.com/astropy/astropy/blob/1fb40bc1f22f176254ef583065aa155f53f3b414/astropy/coordinates/angles/angle_parsetab.py#L42
+</details>
+
+*This comment was generated for commit v2.14.2*
diff --git a/tests/testutils/_primer/cases/new_messages_classified/expected_comparator.json b/tests/testutils/_primer/cases/new_messages_classified/expected_comparator.json
new file mode 100644
index 0000000000..bb57521031
--- /dev/null
+++ b/tests/testutils/_primer/cases/new_messages_classified/expected_comparator.json
@@ -0,0 +1 @@
+[{ "package": "astropy", "missing": 0, "new": 4, "changed": 0 }]
diff --git a/tests/testutils/_primer/cases/new_messages_classified/main.json b/tests/testutils/_primer/cases/new_messages_classified/main.json
new file mode 100644
index 0000000000..337476e532
--- /dev/null
+++ b/tests/testutils/_primer/cases/new_messages_classified/main.json
@@ -0,0 +1,6 @@
+{
+  "astropy": {
+    "commit": "1fb40bc1f22f176254ef583065aa155f53f3b414",
+    "messages": []
+  }
+}
diff --git a/tests/testutils/_primer/cases/new_messages_classified/pr.json b/tests/testutils/_primer/cases/new_messages_classified/pr.json
new file mode 100644
index 0000000000..238805c199
--- /dev/null
+++ b/tests/testutils/_primer/cases/new_messages_classified/pr.json
@@ -0,0 +1,67 @@
+{
+  "astropy": {
+    "commit": "1fb40bc1f22f176254ef583065aa155f53f3b414",
+    "messages": [
+      {
+        "type": "error",
+        "module": "astropy.coordinates.angles.angle_parsetab",
+        "obj": "",
+        "line": 1,
+        "column": 0,
+        "endLine": null,
+        "endColumn": null,
+        "path": "tests/.pylint_primer_tests/astropy/astropy/astropy/coordinates/angles/angle_parsetab.py",
+        "symbol": "astroid-error",
+        "message": "Fatal error while checking 'astropy/module.py'. Please open an issue.",
+        "messageId": "F0002",
+        "confidence": "UNDEFINED",
+        "absolutePath": "tests/.pylint_primer_tests/astropy/astropy/astropy/coordinates/angles/angle_parsetab.py"
+      },
+      {
+        "type": "info",
+        "module": "astropy.coordinates.angles.angle_parsetab",
+        "obj": "",
+        "line": 14,
+        "column": 0,
+        "endLine": null,
+        "endColumn": null,
+        "path": "tests/.pylint_primer_tests/astropy/astropy/astropy/coordinates/angles/angle_parsetab.py",
+        "symbol": "locally-disabled",
+        "message": "Locally disabling looping-through-iterator (W4801)",
+        "messageId": "I0011",
+        "confidence": "UNDEFINED",
+        "absolutePath": "tests/.pylint_primer_tests/astropy/astropy/astropy/coordinates/angles/angle_parsetab.py"
+      },
+      {
+        "type": "warning",
+        "module": "astropy.coordinates.angles.angle_parsetab",
+        "obj": "",
+        "line": 14,
+        "column": 0,
+        "endLine": null,
+        "endColumn": null,
+        "path": "tests/.pylint_primer_tests/astropy/astropy/astropy/coordinates/angles/angle_parsetab.py",
+        "symbol": "useless-suppression",
+        "message": "Useless suppression of 'looping-through-iterator'",
+        "messageId": "I0021",
+        "confidence": "UNDEFINED",
+        "absolutePath": "tests/.pylint_primer_tests/astropy/astropy/astropy/coordinates/angles/angle_parsetab.py"
+      },
+      {
+        "type": "warning",
+        "module": "astropy.coordinates.angles.angle_parsetab",
+        "obj": "my_function",
+        "line": 42,
+        "column": 4,
+        "endLine": 42,
+        "endColumn": 16,
+        "path": "tests/.pylint_primer_tests/astropy/astropy/astropy/coordinates/angles/angle_parsetab.py",
+        "symbol": "unused-variable",
+        "message": "Unused variable 'foo'",
+        "messageId": "W0612",
+        "confidence": "UNDEFINED",
+        "absolutePath": "tests/.pylint_primer_tests/astropy/astropy/astropy/coordinates/angles/angle_parsetab.py"
+      }
+    ]
+  }
+}
diff --git a/tests/testutils/_primer/test_comparator.py b/tests/testutils/_primer/test_comparator.py
index 94e8d035a0..ace10ba19c 100644
--- a/tests/testutils/_primer/test_comparator.py
+++ b/tests/testutils/_primer/test_comparator.py
@@ -4,14 +4,40 @@
 
 import json
 from pathlib import Path
+from typing import cast
 
 import pytest
 
-from pylint.testutils._primer.comparator import Comparator
+from pylint.reporters.json_reporter import JSONMessage
+from pylint.testutils._primer.comparator import (
+    Comparator,
+    _caret_hint,
+    format_span,
+)
 
 CASES_PATH = Path(__file__).parent / "cases"
 
 
+def _msg(**overrides: object) -> JSONMessage:
+    base: dict[str, object] = {
+        "type": "warning",
+        "module": "m",
+        "obj": "",
+        "line": 1,
+        "column": 0,
+        "endLine": 1,
+        "endColumn": 5,
+        "path": "m.py",
+        "symbol": "s",
+        "message": "msg",
+        "messageId": "W0000",
+        "confidence": "UNDEFINED",
+        "absolutePath": "m.py",
+    }
+    base.update(overrides)
+    return cast(JSONMessage, base)
+
+
 @pytest.mark.parametrize(
     "directory",
     [pytest.param(p, id=p.name) for p in CASES_PATH.iterdir() if p.is_dir()],
@@ -29,6 +55,18 @@ def test_comparator(directory: Path) -> None:
         assert len(changed) == exp["changed"]
 
 
+def test_format_span_without_end_position() -> None:
+    """Messages missing endLine/endColumn fall back to a start-only span."""
+    assert (
+        format_span(_msg(line=42, column=7, endLine=None, endColumn=None)) == "`42:7`"
+    )
+
+
+def test_caret_hint_returns_empty_when_mostly_changed() -> None:
+    """When more than 60% of the text differs, carets are noise and are skipped."""
+    assert _caret_hint("hello world", "goodbye universe") == ""
+
+
 def test_comparator_batched() -> None:
     fixture = Path(__file__).parent / "batched_cases"
     comparator = Comparator.from_json(
diff --git a/tests/testutils/_primer/test_primer.py b/tests/testutils/_primer/test_primer.py
index d443cde693..69f675f418 100644
--- a/tests/testutils/_primer/test_primer.py
+++ b/tests/testutils/_primer/test_primer.py
@@ -90,7 +90,7 @@ def test_truncated_compare(self) -> None:
 
     def test_truncated_compare_stops_iterating_packages(self) -> None:
         """Once the comment exceeds MAX, further packages should be skipped."""
-        max_comment_length = 500
+        max_comment_length = 400
         directory = CASES_PATH / "multi_package"
         with patch(
             "pylint.testutils._primer.primer_compare_command.MAX_GITHUB_COMMENT_LENGTH",

From 47f2682851ff0761147b25fbb88e1e575b036e05 Mon Sep 17 00:00:00 2001
From: Pierre Sassoulas <pierre.sassoulas@gmail.com>
Date: Sat, 18 Apr 2026 20:46:24 +0200
Subject: [PATCH 5/8] [primer] Thread ChangedMessage through message_diff and
 split comment helpers
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Pass ``ChangedMessage`` to ``message_diff`` directly so callers don't
have to unpack ``(old, new)`` at every site.  Rename
``_match_residuals`` to ``_pair_by_position`` — it advertises what the
helper does rather than what it consumes.

Split the collapsed ``_create_comment_for_package`` back into focused
``_format_changed_messages`` / ``_format_new_messages`` /
``_format_missing_messages`` helpers, with a small
``_source_link_for`` factory for the per-package closure.  Drops the
``_ClassifiedMessages`` side-car class; classification lives inline in
the new-messages formatter it belongs to.

Also swap "diagnostic" for "message"/"warning" in docstrings and
comments to match pylint's own terminology.
---
 doc/whatsnew/fragments/10914.internal         |   2 +-
 pylint/testutils/_primer/comparator.py        |  21 +-
 .../_primer/primer_compare_command.py         | 188 +++++++++---------
 3 files changed, 99 insertions(+), 112 deletions(-)

diff --git a/doc/whatsnew/fragments/10914.internal b/doc/whatsnew/fragments/10914.internal
index dc31fa513e..009351e592 100644
--- a/doc/whatsnew/fragments/10914.internal
+++ b/doc/whatsnew/fragments/10914.internal
@@ -1,5 +1,5 @@
 The primer now pairs residual messages by ``(symbol, path, obj)`` and reports altered
-diagnostics as a single *changed* entry with a compact diff, rather than as a separate
+messages as a single *changed* entry with a compact diff, rather than as a separate
 removal + addition. New messages are classified into genuine new messages, fixed false
 positives (``useless-suppression``), new false positives (``locally-disabled``), and
 ``astroid-error`` fatal errors.
diff --git a/pylint/testutils/_primer/comparator.py b/pylint/testutils/_primer/comparator.py
index c5e7d2d037..d361ff45a9 100644
--- a/pylint/testutils/_primer/comparator.py
+++ b/pylint/testutils/_primer/comparator.py
@@ -31,15 +31,15 @@ class PackageDiff(NamedTuple):
     package: str
     missing: PackageData  # emitted on main but not on the PR
     new: PackageData  # emitted on the PR but not on main
-    changed: list[ChangedMessage]  # same diagnostic, altered line / text
+    changed: list[ChangedMessage]  # same message, altered line / text
 
 
-def _match_residuals(
+def _pair_by_position(
     old_residuals: list[JSONMessage], new_residuals: list[JSONMessage]
 ) -> tuple[list[ChangedMessage], list[JSONMessage], list[JSONMessage]]:
     """Pair residual messages by ``(symbol, path, obj)``.
 
-    Two messages sharing that key are the "same diagnostic" — if they differ
+    Two messages sharing that key are the "same warning" — if they differ
     only in line numbers or message text, they should be reported as *changed*
     rather than as a separate removal + addition.  Leftovers on each side are
     genuinely missing or genuinely new.
@@ -79,13 +79,14 @@ def format_span(msg: JSONMessage) -> str:
     return f"`{start}`"
 
 
-def message_diff(old: JSONMessage, new: JSONMessage) -> str:
+def message_diff(change: ChangedMessage) -> str:
     """Return a compact summary of changed fields between two messages.
 
     Location changes are merged into a single human-readable span.
     String fields (like ``message``) get a ``diff`` code block so GitHub
     renders them with red/green highlighting.
     """
+    old, new = change.old, change.new
     changed_keys: set[str] = set()
     for key in set(old) | set(new):
         if old.get(key) != new.get(key):
@@ -138,13 +139,7 @@ def _caret_hint(old: str, new: str) -> str:
 
 
 class Comparator:
-    """Cross-reference two primer JSON outputs and iterate over differences.
-
-    Yields ``PackageDiff`` entries carrying missing, new and changed messages
-    for each package that has at least one difference.  *changed* contains
-    pairs of ``(old, new)`` messages that are the same diagnostic but with
-    altered details (line, message text, etc.).
-    """
+    """Cross-reference two primer JSON outputs and iterate over differences."""
 
     def __init__(self, main_data: PackageMessages, pr_data: PackageMessages) -> None:
         self._main_data = main_data
@@ -188,8 +183,8 @@ def __iter__(self) -> Iterator[PackageDiff]:
                     residual_old.append(message)
 
             # Second pass: pair residuals by position to detect *changed*
-            # messages (same diagnostic, different line or text).
-            paired, final_missing, final_new = _match_residuals(
+            # messages (same warning, different line or text).
+            paired, final_missing, final_new = _pair_by_position(
                 residual_old, pr_messages
             )
 
diff --git a/pylint/testutils/_primer/primer_compare_command.py b/pylint/testutils/_primer/primer_compare_command.py
index f5df3fc3f0..af6a6794a7 100644
--- a/pylint/testutils/_primer/primer_compare_command.py
+++ b/pylint/testutils/_primer/primer_compare_command.py
@@ -11,7 +11,6 @@
 from pylint.testutils._primer.comparator import (
     ChangedMessage,
     Comparator,
-    PackageDiff,
     message_diff,
 )
 from pylint.testutils._primer.primer_command import PrimerCommand
@@ -33,54 +32,9 @@ def _format_messages(
     return body
 
 
-class _ClassifiedMessages:
-    """All message categories for a single package, pre-formatted for display."""
-
-    __slots__ = (
-        "astroid_errors",
-        "changed_messages",
-        "fixed_false_positives",
-        "missing_messages",
-        "new_false_positives",
-        "new_messages",
-    )
-
-    def __init__(
-        self,
-        new_messages: list[JSONMessage],
-        missing_messages: list[JSONMessage],
-        changed_messages: list[ChangedMessage],
-        source_link: Callable[[JSONMessage], str],
-    ) -> None:
-        astroid_errors = 0
-        new_fp: list[JSONMessage] = []
-        fixed_fp: list[JSONMessage] = []
-        other_new: list[JSONMessage] = []
-        for message in new_messages:
-            if message["symbol"] == "astroid-error":
-                astroid_errors += 1
-            elif USELESS_SUPPRESSION_RE.match(message["message"]):
-                fixed_fp.append(message)
-            elif message["symbol"] == "locally-disabled":
-                # A new locally-disabled means a maintainer had to add a
-                # suppression comment — we introduced a false positive.
-                new_fp.append(message)
-            else:
-                other_new.append(message)
-
-        self.astroid_errors = astroid_errors
-        self.fixed_false_positives = _format_messages(fixed_fp, source_link)
-        self.new_false_positives = _format_messages(new_fp, source_link)
-        self.new_messages = _format_messages(other_new, source_link)
-        self.missing_messages = _format_messages(missing_messages, source_link)
-
-        body = ""
-        for count, (old, new) in enumerate(changed_messages, 1):
-            body += (
-                f"{count}) [{new['symbol']}]({source_link(new)}):\n"
-                f"{message_diff(old, new)}\n"
-            )
-        self.changed_messages = body
+def _details_section(title: str, body: str) -> str:
+    # Blank line after <details> required for GitHub markdown rendering.
+    return f"{title}\n\n<details>\n\n{body}</details>\n\n"
 
 
 class CompareCommand(PrimerCommand):
@@ -97,7 +51,18 @@ def _create_comment(self, comparator: Comparator) -> str:
         for diff in comparator:
             if len(comment) >= MAX_GITHUB_COMMENT_LENGTH:
                 break
-            comment += self._create_comment_for_package(diff)
+            package = diff.package
+            url = self.packages[package].url
+            assert not url.endswith(
+                ".git"
+            ), "You don't need the .git at the end of the github url."
+            source_link = self._source_link_for(package, diff.new["commit"])
+            comment += f"\n**Effect on [{package}]({url}):**\n\n"
+            comment += self._format_changed_messages(diff.changed, source_link)
+            comment += self._format_new_messages(diff.new["messages"], source_link)
+            comment += self._format_missing_messages(
+                diff.missing["messages"], source_link
+            )
         comment = (
             f"🤖 **Effect of this PR on checked open source code:** 🤖\n\n{comment}"
             if comment
@@ -108,66 +73,93 @@ def _create_comment(self, comparator: Comparator) -> str:
         )
         return self._truncate_comment(comment)
 
-    def _create_comment_for_package(self, diff: PackageDiff) -> str:
-        package = diff.package
-        url = self.packages[package].url
+    def _source_link_for(
+        self, package: str, commit: str
+    ) -> Callable[[JSONMessage], str]:
         clone_dir = self.packages[package].clone_directory
-        commit = diff.new["commit"]
-
-        assert not url.endswith(
-            ".git"
-        ), "You don't need the .git at the end of the github url."
+        url = self.packages[package].url
 
-        def _source_link(msg: JSONMessage) -> str:
+        def _link(msg: JSONMessage) -> str:
             filepath = str(PurePosixPath(msg["path"]).relative_to(clone_dir))
             return f"{url}/blob/{commit}/{filepath}#L{msg['line']}"
 
-        def _details_section(title: str, body: str) -> str:
-            # Blank line after <details> required for GitHub markdown rendering.
-            return f"{title}\n\n<details>\n\n{body}</details>\n\n"
+        return _link
 
-        classified = _ClassifiedMessages(
-            diff.new["messages"], diff.missing["messages"], diff.changed, _source_link
-        )
-        comment = f"\n**Effect on [{package}]({url}):**\n\n"
-
-        if diff.changed:
-            print("Changed:")
-            for _, new in diff.changed:
-                print(new)
-        if diff.new["messages"]:
-            print("Now emitted:")
-            for msg in diff.new["messages"]:
-                print(msg)
-        if diff.missing["messages"]:
-            print("No longer emitted:")
-            for msg in diff.missing["messages"]:
-                print(msg)
-
-        if classified.changed_messages:
-            comment += _details_section(
-                "Changed messages:", classified.changed_messages
+    def _format_changed_messages(
+        self,
+        changed: list[ChangedMessage],
+        source_link: Callable[[JSONMessage], str],
+    ) -> str:
+        if not changed:
+            return ""
+        print("Changed:")
+        body = ""
+        for count, change in enumerate(changed, 1):
+            print(change.new)
+            body += (
+                f"{count}) [{change.new['symbol']}]({source_link(change.new)}):\n"
+                f"{message_diff(change)}\n"
             )
-        if classified.astroid_errors:
-            comment += (
-                f'{classified.astroid_errors} "astroid error(s)" were found. '
+        return _details_section("Changed messages:", body)
+
+    def _format_new_messages(
+        self,
+        messages: list[JSONMessage],
+        source_link: Callable[[JSONMessage], str],
+    ) -> str:
+        if not messages:
+            return ""
+        print("Now emitted:")
+        astroid_errors = 0
+        fixed_fp: list[JSONMessage] = []
+        new_fp: list[JSONMessage] = []
+        other_new: list[JSONMessage] = []
+        for message in messages:
+            print(message)
+            if message["symbol"] == "astroid-error":
+                astroid_errors += 1
+            elif USELESS_SUPPRESSION_RE.match(message["message"]):
+                fixed_fp.append(message)
+            elif message["symbol"] == "locally-disabled":
+                # A new locally-disabled means a maintainer had to add a
+                # suppression comment — we introduced a false positive.
+                new_fp.append(message)
+            else:
+                other_new.append(message)
+
+        out = ""
+        if astroid_errors:
+            out += (
+                f'{astroid_errors} "astroid error(s)" were found. '
                 "Please open the GitHub Actions log to see what failed or crashed.\n\n"
             )
-        if classified.fixed_false_positives:
-            comment += _details_section(
-                "🎉 Fixed false positives:", classified.fixed_false_positives
+        if fixed_fp:
+            out += _details_section(
+                "🎉 Fixed false positives:", _format_messages(fixed_fp, source_link)
             )
-        if classified.new_false_positives:
-            comment += _details_section(
-                "😞 New false positives:", classified.new_false_positives
+        if new_fp:
+            out += _details_section(
+                "😞 New false positives:", _format_messages(new_fp, source_link)
             )
-        if classified.new_messages:
-            comment += _details_section("New messages:", classified.new_messages)
-        if classified.missing_messages:
-            comment += _details_section(
-                "Removed messages:", classified.missing_messages
+        if other_new:
+            out += _details_section(
+                "New messages:", _format_messages(other_new, source_link)
             )
-        return comment
+        return out
+
+    def _format_missing_messages(
+        self,
+        messages: list[JSONMessage],
+        source_link: Callable[[JSONMessage], str],
+    ) -> str:
+        if not messages:
+            return ""
+        print("No longer emitted:")
+        for message in messages:
+            print(message)
+        return _details_section(
+            "Removed messages:", _format_messages(messages, source_link)
+        )
 
     def _truncate_comment(self, comment: str) -> str:
         """GitHub allows only a set number of characters in a comment."""

From 6705d74f786009330c0fb32892990606ea833e9b Mon Sep 17 00:00:00 2001
From: Pierre Sassoulas <pierre.sassoulas@gmail.com>
Date: Sun, 19 Apr 2026 09:13:37 +0200
Subject: [PATCH 6/8] [primer] Simplify residual pairing to single-sided
 bucketing
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Bucket only the *new* side and walk ``old_residuals`` once, popping
from each matching bucket.  That removes the dual ``old_by_key``
dictionary and the ``paired_old_ids`` / ``paired_new_ids`` shadow
bookkeeping — we can build ``final_missing`` inline in the old-side
walk, and ``final_new`` still reads from the untouched input list.
---
 pylint/testutils/_primer/comparator.py | 34 +++++++++++---------------
 1 file changed, 14 insertions(+), 20 deletions(-)

diff --git a/pylint/testutils/_primer/comparator.py b/pylint/testutils/_primer/comparator.py
index d361ff45a9..2112253650 100644
--- a/pylint/testutils/_primer/comparator.py
+++ b/pylint/testutils/_primer/comparator.py
@@ -37,35 +37,29 @@ class PackageDiff(NamedTuple):
 def _pair_by_position(
     old_residuals: list[JSONMessage], new_residuals: list[JSONMessage]
 ) -> tuple[list[ChangedMessage], list[JSONMessage], list[JSONMessage]]:
-    """Pair residual messages by ``(symbol, path, obj)``.
+    """Pair residual messages by ``(symbol, path, obj)`` in input order.
 
-    Two messages sharing that key are the "same warning" — if they differ
-    only in line numbers or message text, they should be reported as *changed*
+    Two messages sharing that key are the "same warning" — if they differ only
+    in line numbers or message text, they should be reported as *changed*
     rather than as a separate removal + addition.  Leftovers on each side are
     genuinely missing or genuinely new.
-
-    Returns ``(paired, unmatched_old, unmatched_new)``.
     """
-    old_by_key: dict[tuple[str, str, str], list[JSONMessage]] = defaultdict(list)
     new_by_key: dict[tuple[str, str, str], list[JSONMessage]] = defaultdict(list)
-    for m in old_residuals:
-        old_by_key[m["symbol"], m["path"], m["obj"]].append(m)
     for m in new_residuals:
         new_by_key[m["symbol"], m["path"], m["obj"]].append(m)
 
     paired: list[ChangedMessage] = []
-    paired_old_ids: set[int] = set()
-    paired_new_ids: set[int] = set()
-    for key in old_by_key:
-        if key not in new_by_key:
-            continue
-        for old, new in zip(old_by_key[key], new_by_key[key]):
+    final_missing: list[JSONMessage] = []
+    matched_new: set[int] = set()
+    for old in old_residuals:
+        bucket = new_by_key.get((old["symbol"], old["path"], old["obj"]))
+        if bucket:
+            new = bucket.pop(0)
             paired.append(ChangedMessage(old=old, new=new))
-            paired_old_ids.add(id(old))
-            paired_new_ids.add(id(new))
-
-    final_missing = [m for m in old_residuals if id(m) not in paired_old_ids]
-    final_new = [m for m in new_residuals if id(m) not in paired_new_ids]
+            matched_new.add(id(new))
+        else:
+            final_missing.append(old)
+    final_new = [m for m in new_residuals if id(m) not in matched_new]
     return paired, final_missing, final_new
 
 
@@ -88,7 +82,7 @@ def message_diff(change: ChangedMessage) -> str:
     """
     old, new = change.old, change.new
     changed_keys: set[str] = set()
-    for key in set(old) | set(new):
+    for key in old.keys() | new.keys():
         if old.get(key) != new.get(key):
             changed_keys.add(key)
 

From 6e7d3c9231cfba6afb89aec833bc07e4614eacbe Mon Sep 17 00:00:00 2001
From: Pierre Sassoulas <pierre.sassoulas@gmail.com>
Date: Sun, 26 Apr 2026 14:08:33 +0200
Subject: [PATCH 7/8] [primer] Pair symbol-renamed messages at the same
 location
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Adds a second pairing pass keyed on exact source location, gated on
``SequenceMatcher.ratio() >= 0.5`` between the old and new symbols.  This
catches renames like ``used-before-assignment`` →
``possibly-used-before-assignment`` and reports them as one *changed*
message instead of a separate removal + addition.

The similarity gate avoids pairing unrelated messages that happen to
coincide on the same line (e.g. ``useless-suppression`` removed and
``locally-disabled`` added at the same position).
---
 doc/whatsnew/fragments/10914.internal         | 12 +--
 pylint/testutils/_primer/comparator.py        | 78 +++++++++++++++----
 .../_primer/cases/symbol_renamed/expected.txt | 26 +++++++
 .../symbol_renamed/expected_comparator.json   |  1 +
 .../_primer/cases/symbol_renamed/main.json    | 22 ++++++
 .../_primer/cases/symbol_renamed/pr.json      | 22 ++++++
 tests/testutils/_primer/test_comparator.py    | 16 ++++
 7 files changed, 159 insertions(+), 18 deletions(-)
 create mode 100644 tests/testutils/_primer/cases/symbol_renamed/expected.txt
 create mode 100644 tests/testutils/_primer/cases/symbol_renamed/expected_comparator.json
 create mode 100644 tests/testutils/_primer/cases/symbol_renamed/main.json
 create mode 100644 tests/testutils/_primer/cases/symbol_renamed/pr.json

diff --git a/doc/whatsnew/fragments/10914.internal b/doc/whatsnew/fragments/10914.internal
index 009351e592..35ac3db975 100644
--- a/doc/whatsnew/fragments/10914.internal
+++ b/doc/whatsnew/fragments/10914.internal
@@ -1,7 +1,9 @@
-The primer now pairs residual messages by ``(symbol, path, obj)`` and reports altered
-messages as a single *changed* entry with a compact diff, rather than as a separate
-removal + addition. New messages are classified into genuine new messages, fixed false
-positives (``useless-suppression``), new false positives (``locally-disabled``), and
-``astroid-error`` fatal errors.
+The primer now pairs residual messages — first by ``(symbol, path, obj)`` and then by
+exact source location — and reports altered messages as a single *changed* entry with
+a compact diff, rather than as a separate removal + addition. The location-based pass
+also catches symbol renames at the same code position (e.g. ``used-before-assignment``
+→ ``possibly-used-before-assignment``). New messages are classified into genuine new
+messages, fixed false positives (``useless-suppression``), new false positives
+(``locally-disabled``), and ``astroid-error`` fatal errors.
 
 Refs #10914
diff --git a/pylint/testutils/_primer/comparator.py b/pylint/testutils/_primer/comparator.py
index 2112253650..6feb4f744f 100644
--- a/pylint/testutils/_primer/comparator.py
+++ b/pylint/testutils/_primer/comparator.py
@@ -6,7 +6,7 @@
 
 import json
 from collections import defaultdict
-from collections.abc import Iterator
+from collections.abc import Callable, Hashable, Iterator
 from difflib import SequenceMatcher
 from pathlib import Path
 from typing import NamedTuple
@@ -34,26 +34,35 @@ class PackageDiff(NamedTuple):
     changed: list[ChangedMessage]  # same message, altered line / text
 
 
-def _pair_by_position(
-    old_residuals: list[JSONMessage], new_residuals: list[JSONMessage]
+SYMBOL_RENAME_SIMILARITY_THRESHOLD = 0.5
+
+
+def _pair_by_key(
+    old_residuals: list[JSONMessage],
+    new_residuals: list[JSONMessage],
+    key: Callable[[JSONMessage], tuple[Hashable, ...]],
+    accept: Callable[[JSONMessage, JSONMessage], bool] = lambda _o, _n: True,
 ) -> tuple[list[ChangedMessage], list[JSONMessage], list[JSONMessage]]:
-    """Pair residual messages by ``(symbol, path, obj)`` in input order.
+    """Pair messages whose ``key`` matches, in input order.
 
-    Two messages sharing that key are the "same warning" — if they differ only
+    Two messages sharing the key are the "same warning" — if they differ only
     in line numbers or message text, they should be reported as *changed*
     rather than as a separate removal + addition.  Leftovers on each side are
-    genuinely missing or genuinely new.
+    passed through to the next pass (or reported as missing/new).
+
+    ``accept`` is an optional predicate that can veto a candidate pair (used to
+    avoid pairing two unrelated messages that happen to share the key).
     """
-    new_by_key: dict[tuple[str, str, str], list[JSONMessage]] = defaultdict(list)
+    new_by_key: dict[tuple[Hashable, ...], list[JSONMessage]] = defaultdict(list)
     for m in new_residuals:
-        new_by_key[m["symbol"], m["path"], m["obj"]].append(m)
+        new_by_key[key(m)].append(m)
 
     paired: list[ChangedMessage] = []
     final_missing: list[JSONMessage] = []
     matched_new: set[int] = set()
     for old in old_residuals:
-        bucket = new_by_key.get((old["symbol"], old["path"], old["obj"]))
-        if bucket:
+        bucket = new_by_key.get(key(old))
+        if bucket and accept(old, bucket[0]):
             new = bucket.pop(0)
             paired.append(ChangedMessage(old=old, new=new))
             matched_new.add(id(new))
@@ -63,6 +72,48 @@ def _pair_by_position(
     return paired, final_missing, final_new
 
 
+def _is_symbol_rename(old: JSONMessage, new: JSONMessage) -> bool:
+    """True when the two symbols are textually similar enough to be a rename.
+
+    Used to avoid pairing unrelated messages that happen to share a source
+    position (e.g. ``useless-suppression`` removed and ``locally-disabled``
+    added on the same line — those are conceptually opposite, not a rename).
+    """
+    ratio = SequenceMatcher(None, old["symbol"], new["symbol"]).ratio()
+    return ratio >= SYMBOL_RENAME_SIMILARITY_THRESHOLD
+
+
+def _pair_residuals(
+    old_residuals: list[JSONMessage], new_residuals: list[JSONMessage]
+) -> tuple[list[ChangedMessage], list[JSONMessage], list[JSONMessage]]:
+    """Pair residual messages with two passes of decreasing strictness.
+
+    First by ``(symbol, path, obj)`` — catches line-only or message-only changes
+    for the same warning. Then by exact source location, gated on symbol
+    similarity — catches symbol renames such as ``used-before-assignment`` →
+    ``possibly-used-before-assignment``, where the same code position now
+    emits a renamed message.
+    """
+    paired_by_symbol, missing, new = _pair_by_key(
+        old_residuals,
+        new_residuals,
+        key=lambda m: (m["symbol"], m["path"], m["obj"]),
+    )
+    paired_by_location, missing, new = _pair_by_key(
+        missing,
+        new,
+        key=lambda m: (
+            m["path"],
+            m["line"],
+            m["column"],
+            m.get("endLine"),
+            m.get("endColumn"),
+        ),
+        accept=_is_symbol_rename,
+    )
+    return paired_by_symbol + paired_by_location, missing, new
+
+
 def format_span(msg: JSONMessage) -> str:
     """Format a message's location as ``line:col to endLine:endCol``."""
     start = f"{msg['line']}:{msg['column']}"
@@ -176,9 +227,10 @@ def __iter__(self) -> Iterator[PackageDiff]:
                 except ValueError:
                     residual_old.append(message)
 
-            # Second pass: pair residuals by position to detect *changed*
-            # messages (same warning, different line or text).
-            paired, final_missing, final_new = _pair_by_position(
+            # Second pass: pair residuals by symbol then by location to
+            # detect *changed* messages (same warning, different line/text,
+            # or a symbol rename at the same source position).
+            paired, final_missing, final_new = _pair_residuals(
                 residual_old, pr_messages
             )
 
diff --git a/tests/testutils/_primer/cases/symbol_renamed/expected.txt b/tests/testutils/_primer/cases/symbol_renamed/expected.txt
new file mode 100644
index 0000000000..5c723cc900
--- /dev/null
+++ b/tests/testutils/_primer/cases/symbol_renamed/expected.txt
@@ -0,0 +1,26 @@
+🤖 **Effect of this PR on checked open source code:** 🤖
+
+
+**Effect on [astroid](https://github.com/pylint-dev/astroid):**
+
+Changed messages:
+
+<details>
+
+1) [possibly-used-before-assignment](https://github.com/pylint-dev/astroid/blob/123456789abcdef/astroid/wcs.py#L3072):
+confidence: `HIGH` → `INFERENCE`
+
+```diff
+- Using variable 'orig_key' before assignment
++ Possibly using variable 'orig_key' before assignment
+  ^^^^^^^^^^
+```
+
+messageId: `E0601` → `E0606`
+
+symbol: `used-before-assignment` → `possibly-used-before-assignment`
+
+type: `error` → `warning`
+</details>
+
+*This comment was generated for commit v2.14.2*
diff --git a/tests/testutils/_primer/cases/symbol_renamed/expected_comparator.json b/tests/testutils/_primer/cases/symbol_renamed/expected_comparator.json
new file mode 100644
index 0000000000..47824cb2e1
--- /dev/null
+++ b/tests/testutils/_primer/cases/symbol_renamed/expected_comparator.json
@@ -0,0 +1 @@
+[{ "package": "astroid", "missing": 0, "new": 0, "changed": 1 }]
diff --git a/tests/testutils/_primer/cases/symbol_renamed/main.json b/tests/testutils/_primer/cases/symbol_renamed/main.json
new file mode 100644
index 0000000000..e655ae656d
--- /dev/null
+++ b/tests/testutils/_primer/cases/symbol_renamed/main.json
@@ -0,0 +1,22 @@
+{
+  "astroid": {
+    "commit": "1234567890abcdef",
+    "messages": [
+      {
+        "type": "error",
+        "module": "astroid.wcs",
+        "obj": "WCS.fix",
+        "line": 3072,
+        "column": 12,
+        "endLine": 3072,
+        "endColumn": 20,
+        "path": "tests/.pylint_primer_tests/pylint-dev/astroid/astroid/wcs.py",
+        "symbol": "used-before-assignment",
+        "message": "Using variable 'orig_key' before assignment",
+        "messageId": "E0601",
+        "confidence": "HIGH",
+        "absolutePath": "tests/.pylint_primer_tests/pylint-dev/astroid/astroid/wcs.py"
+      }
+    ]
+  }
+}
diff --git a/tests/testutils/_primer/cases/symbol_renamed/pr.json b/tests/testutils/_primer/cases/symbol_renamed/pr.json
new file mode 100644
index 0000000000..3b90e6c589
--- /dev/null
+++ b/tests/testutils/_primer/cases/symbol_renamed/pr.json
@@ -0,0 +1,22 @@
+{
+  "astroid": {
+    "commit": "123456789abcdef",
+    "messages": [
+      {
+        "type": "warning",
+        "module": "astroid.wcs",
+        "obj": "WCS.fix",
+        "line": 3072,
+        "column": 12,
+        "endLine": 3072,
+        "endColumn": 20,
+        "path": "tests/.pylint_primer_tests/pylint-dev/astroid/astroid/wcs.py",
+        "symbol": "possibly-used-before-assignment",
+        "message": "Possibly using variable 'orig_key' before assignment",
+        "messageId": "E0606",
+        "confidence": "INFERENCE",
+        "absolutePath": "tests/.pylint_primer_tests/pylint-dev/astroid/astroid/wcs.py"
+      }
+    ]
+  }
+}
diff --git a/tests/testutils/_primer/test_comparator.py b/tests/testutils/_primer/test_comparator.py
index ace10ba19c..c672a0fcea 100644
--- a/tests/testutils/_primer/test_comparator.py
+++ b/tests/testutils/_primer/test_comparator.py
@@ -12,6 +12,7 @@
 from pylint.testutils._primer.comparator import (
     Comparator,
     _caret_hint,
+    _is_symbol_rename,
     format_span,
 )
 
@@ -67,6 +68,21 @@ def test_caret_hint_returns_empty_when_mostly_changed() -> None:
     assert _caret_hint("hello world", "goodbye universe") == ""
 
 
+@pytest.mark.parametrize(
+    ("old_symbol", "new_symbol", "expected"),
+    [
+        ("used-before-assignment", "possibly-used-before-assignment", True),
+        ("abstract-method", "no-abstract-method", True),
+        ("useless-suppression", "locally-disabled", False),
+        ("too-complex", "too-many-locals", False),
+    ],
+)
+def test_is_symbol_rename(old_symbol: str, new_symbol: str, expected: bool) -> None:
+    old = _msg(symbol=old_symbol)
+    new = _msg(symbol=new_symbol)
+    assert _is_symbol_rename(old, new) is expected
+
+
 def test_comparator_batched() -> None:
     fixture = Path(__file__).parent / "batched_cases"
     comparator = Comparator.from_json(

From 47eda507b35b76bb109ba8c6f7c00541bbe1d940 Mon Sep 17 00:00:00 2001
From: Pierre Sassoulas <pierre.sassoulas@gmail.com>
Date: Sun, 26 Apr 2026 14:13:01 +0200
Subject: [PATCH 8/8] [primer] Drop the ``locally-disabled`` new false positive
 bucket
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

A ``locally-disabled`` message is emitted from a ``# pylint: disable=``
comment in the source.  Since the primer pins each repository to a
fixed commit, the disable comments are identical between the main and
PR runs, so the original "new locally-disabled = newly-introduced false
positive" assumption never fires in practice — and a maintainer
upgrading pylint would clean those up anyway.

Drop the dedicated bucket and let any new ``locally-disabled`` fall
through to the generic *New messages* section.
---
 doc/whatsnew/fragments/10914.internal                  |  5 ++---
 pylint/testutils/_primer/primer_compare_command.py     |  9 ---------
 .../testutils/_primer/cases/multi_package/expected.txt |  2 +-
 tests/testutils/_primer/cases/new_message/expected.txt |  2 +-
 .../_primer/cases/new_messages_classified/expected.txt | 10 ++--------
 .../_primer/cases/useless_suppression/expected.txt     |  2 +-
 6 files changed, 7 insertions(+), 23 deletions(-)

diff --git a/doc/whatsnew/fragments/10914.internal b/doc/whatsnew/fragments/10914.internal
index 35ac3db975..05947c343b 100644
--- a/doc/whatsnew/fragments/10914.internal
+++ b/doc/whatsnew/fragments/10914.internal
@@ -2,8 +2,7 @@ The primer now pairs residual messages — first by ``(symbol, path, obj)`` and
 exact source location — and reports altered messages as a single *changed* entry with
 a compact diff, rather than as a separate removal + addition. The location-based pass
 also catches symbol renames at the same code position (e.g. ``used-before-assignment``
-→ ``possibly-used-before-assignment``). New messages are classified into genuine new
-messages, fixed false positives (``useless-suppression``), new false positives
-(``locally-disabled``), and ``astroid-error`` fatal errors.
+→ ``possibly-used-before-assignment``). New messages are classified into fixed false
+positives (``useless-suppression``), ``astroid-error`` fatal errors, and the rest.
 
 Refs #10914
diff --git a/pylint/testutils/_primer/primer_compare_command.py b/pylint/testutils/_primer/primer_compare_command.py
index af6a6794a7..222ad09a33 100644
--- a/pylint/testutils/_primer/primer_compare_command.py
+++ b/pylint/testutils/_primer/primer_compare_command.py
@@ -112,7 +112,6 @@ def _format_new_messages(
         print("Now emitted:")
         astroid_errors = 0
         fixed_fp: list[JSONMessage] = []
-        new_fp: list[JSONMessage] = []
         other_new: list[JSONMessage] = []
         for message in messages:
             print(message)
@@ -120,10 +119,6 @@ def _format_new_messages(
                 astroid_errors += 1
             elif USELESS_SUPPRESSION_RE.match(message["message"]):
                 fixed_fp.append(message)
-            elif message["symbol"] == "locally-disabled":
-                # A new locally-disabled means a maintainer had to add a
-                # suppression comment — we introduced a false positive.
-                new_fp.append(message)
             else:
                 other_new.append(message)
 
@@ -137,10 +132,6 @@ def _format_new_messages(
             out += _details_section(
                 "🎉 Fixed false positives:", _format_messages(fixed_fp, source_link)
             )
-        if new_fp:
-            out += _details_section(
-                "😞 New false positives:", _format_messages(new_fp, source_link)
-            )
         if other_new:
             out += _details_section(
                 "New messages:", _format_messages(other_new, source_link)
diff --git a/tests/testutils/_primer/cases/multi_package/expected.txt b/tests/testutils/_primer/cases/multi_package/expected.txt
index 67d8236e3b..5da2087bc3 100644
--- a/tests/testutils/_primer/cases/multi_package/expected.txt
+++ b/tests/testutils/_primer/cases/multi_package/expected.txt
@@ -20,7 +20,7 @@ Moved from `100:0`-`100:15` to `105:0`-`105:15`.
 
 **Effect on [astropy](https://github.com/astropy/astropy):**
 
-😞 New false positives:
+New messages:
 
 <details>
 
diff --git a/tests/testutils/_primer/cases/new_message/expected.txt b/tests/testutils/_primer/cases/new_message/expected.txt
index e813dd0a86..040f70014a 100644
--- a/tests/testutils/_primer/cases/new_message/expected.txt
+++ b/tests/testutils/_primer/cases/new_message/expected.txt
@@ -3,7 +3,7 @@
 
 **Effect on [astroid](https://github.com/pylint-dev/astroid):**
 
-😞 New false positives:
+New messages:
 
 <details>
 
diff --git a/tests/testutils/_primer/cases/new_messages_classified/expected.txt b/tests/testutils/_primer/cases/new_messages_classified/expected.txt
index cfee18bc0e..b07e280a11 100644
--- a/tests/testutils/_primer/cases/new_messages_classified/expected.txt
+++ b/tests/testutils/_primer/cases/new_messages_classified/expected.txt
@@ -14,20 +14,14 @@
 https://github.com/astropy/astropy/blob/1fb40bc1f22f176254ef583065aa155f53f3b414/astropy/coordinates/angles/angle_parsetab.py#L14
 </details>
 
-😞 New false positives:
+New messages:
 
 <details>
 
 1) locally-disabled:
 *Locally disabling looping-through-iterator (W4801)*
 https://github.com/astropy/astropy/blob/1fb40bc1f22f176254ef583065aa155f53f3b414/astropy/coordinates/angles/angle_parsetab.py#L14
-</details>
-
-New messages:
-
-<details>
-
-1) unused-variable:
+2) unused-variable:
 *Unused variable 'foo'*
 https://github.com/astropy/astropy/blob/1fb40bc1f22f176254ef583065aa155f53f3b414/astropy/coordinates/angles/angle_parsetab.py#L42
 </details>
diff --git a/tests/testutils/_primer/cases/useless_suppression/expected.txt b/tests/testutils/_primer/cases/useless_suppression/expected.txt
index a813b98174..5120f86953 100644
--- a/tests/testutils/_primer/cases/useless_suppression/expected.txt
+++ b/tests/testutils/_primer/cases/useless_suppression/expected.txt
@@ -12,7 +12,7 @@
 https://github.com/astropy/astropy/blob/1fb40bc1f22f176254ef583065aa155f53f3b414/astropy/coordinates/angles/angle_parsetab.py#L14
 </details>
 
-😞 New false positives:
+New messages:
 
 <details>