[primer] Show changed messages as diffs instead of removed+added by Pierre-Sassoulas · Pull Request #10914 · pylint-dev/pylint

Pierre-Sassoulas · 2026-03-10T19:15:07Z

Type of Changes

	Type
✓	✨ New feature

Description

Instead of reporting moved or reworded diagnostics as separate removal + addition, the primer comparator now pairs residual messages by (symbol, path, obj) and shows a compact diff of what changed.

Rendering improvements:

Symbol name is a clickable link to the source location
Location changes shown with backtick-formatted spans (100:0 to 100:15)
^^ caret hints highlight exactly which characters changed in the message text
Blank line before ```diff blocks so GitHub renders them correctly
Extract _details_section helper to deduplicate
Details
wrapping

Test infrastructure:

Move test data from cases/ and batched_cases/ to fixtures/
Add fixtures: line_moved, message_changed_line, mixed_changes, type_changed
Add test_truncated_compare_in_details for truncation inside a
Details
block

codecov · 2026-03-10T20:51:56Z

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.22%. Comparing base (b080a21) to head (47eda50).

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #10914      +/-   ##
==========================================
+ Coverage   96.19%   96.22%   +0.02%     
==========================================
  Files         178      178              
  Lines       19683    19778      +95     
==========================================
+ Hits        18934    19031      +97     
+ Misses        749      747       -2

Files with missing lines	Coverage Δ
pylint/testutils/_primer/comparator.py	`100.00% <100.00%> (ø)`
pylint/testutils/_primer/primer_compare_command.py	`100.00% <100.00%> (+2.73%)`	⬆️

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DanielNoord

Is this really better? It seems like a lot of code for very minimal gain?

Perhaps better suggestion would be to show the changes based on position instead of message name? That should catch most "message was slightly changed" cases in a simple overview without the fuzzy matching being necessary

Pierre-Sassoulas · 2026-03-11T05:02:57Z

Right, I'm going to reuse the comparator PR from earlier too.

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.

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.

- 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.

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.

… helpers 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.

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.

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).

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.

github-actions · 2026-04-26T12:44:18Z

🤖 According to the primer, this change has no effect on the checked open source code. 🤖🎉

This comment was generated for commit 47eda50

Pierre-Sassoulas added Maintenance Discussion or action around maintaining pylint or the dev workflow Skip news 🔇 This change does not require a changelog entry primer labels Mar 10, 2026