Attribute duplicate-code messages to involved modules, not the last-checked one

R0801 messages emitted in SimilaritiesChecker.close() were attributed
to whichever module happened to be checked last, because add_message()
without a node falls back to linter.current_name. Now the checker
saves a module→filepath mapping during process_module() and sets the
correct module context before each add_message() call.

Closes #2368

Co-Authored-By: Claude Opus 4.6 <[email protected]>

Author: Pierre-Sassoulas

doc/whatsnew/fragments/2368.bugfix

@@ -0,0 +1,3 @@
+``duplicate-code`` messages are now attributed to a module that actually contains the duplicated lines, instead of whichever module happened to be checked last.
+
+Closes #2368

pylint/checkers/symilar.py

@@ -812,10 +812,12 @@ def __init__(self, linter: PyLinter) -> None:
             ignore_imports=self.linter.config.ignore_imports,
             ignore_signatures=self.linter.config.ignore_signatures,
         )
+        self._module_filepaths: dict[str, str | None] = {}
 
     def open(self) -> None:
         """Init the checkers: reset linesets and statistics information."""
         self.linesets = []
+        self._module_filepaths.clear()
         self.linter.stats.reset_duplicated_lines()
 
     def process_module(self, node: nodes.Module) -> None:
@@ -835,6 +837,7 @@ def process_module(self, node: nodes.Module) -> None:
                 DeprecationWarning,
                 stacklevel=2,
             )
+        self._module_filepaths[self.linter.current_name] = self.linter.current_file
         with node.stream() as stream:
             self.append_stream(self.linter.current_name, stream, node.file_encoding)
 
@@ -843,6 +846,8 @@ def close(self) -> None:
         total = sum(len(lineset) for lineset in self.linesets)
         duplicated = 0
         stats = self.linter.stats
+        original_name = self.linter.current_name
+        original_file = self.linter.current_file
         for num, couples in self._compute_sims():
             msg = []
             lineset = start_line = end_line = None
@@ -854,8 +859,15 @@ def close(self) -> None:
                 for line in lineset.real_lines[start_line:end_line]:
                     msg.append(line.rstrip())
 
+            # Attribute the message to the first involved module rather than
+            # the last-checked module which may be unrelated (see #2368).
+            first_module = min(c[0].name for c in couples)
+            self.linter.current_name = first_module
+            self.linter.current_file = self._module_filepaths.get(first_module)
             self.add_message("R0801", args=(len(couples), "\n".join(msg)))
             duplicated += num * (len(couples) - 1)
+        self.linter.current_name = original_name
+        self.linter.current_file = original_file
         stats.nb_duplicated_lines += int(duplicated)
         stats.percent_duplicated_lines += float(total and duplicated * 100.0 / total)
 

tests/test_similar.py

@@ -15,6 +15,7 @@
 
 from pylint.reporters.text import TextReporter
 from pylint.testutils._run import _Run as Run
+from pylint.testutils.reporter_for_tests import GenericTestReporter
 from pylint.testutils.utils import _patch_streams
 
 HERE = abspath(dirname(__file__))
@@ -266,6 +267,41 @@ def test_useless_suppression() -> None:
         )
         assert not runner.linter.stats.by_msg
 
+    @staticmethod
+    def test_duplicate_code_module_attribution() -> None:
+        """R0801 should be attributed to a module with duplicates, not the last-checked one.
+
+        Regression test for https://github.com/pylint-dev/pylint/issues/2368
+        """
+        path = join(DATA, "2368")
+        reporter = GenericTestReporter()
+        # Pass files explicitly with the unrelated module last, so that current_name
+        # points to a file without duplication when close() fires.
+        Run(
+            [
+                join(path, "databaselib.py"),
+                join(path, "projectlib.py"),
+                join(path, "xmlgen.py"),
+                "--disable=all",
+                "--enable=duplicate-code",
+                "--min-similarity-lines=4",
+            ],
+            reporter=reporter,
+            exit=False,
+        )
+        messages = reporter.messages
+        assert messages, "Expected at least one R0801 message"
+        for msg in messages:
+            assert msg.symbol == "duplicate-code"
+            # The message text contains "=={module_name}:[start:end]" for each
+            # involved module. The message's own .module must be one of them,
+            # but not the unrelated module.
+            involved = re.findall(r"==(\S+?):\[", msg.msg)
+            assert msg.module in involved, (
+                f"R0801 attributed to {msg.module!r} which is not in "
+                f"the involved modules {involved}"
+            )
+
     def test_conditional_imports(self) -> None:
         """Tests enabling ignore-imports with conditional imports works correctly."""
         path = join(DATA, "ignore_conditional_imports")