fix: stdlib might be through a symlink. #2115

nedbat · nedbat · commit a2f248cf095f · 2026-01-22T20:47:19.000-05:00
diff --git a/CHANGES.rst b/CHANGES.rst
@@ -23,10 +23,15 @@ upgrading your version of coverage.py.
 Unreleased
 ----------
 
+- Fix: when Python is installed via symlinks, for example with Homebrew, the
+  standard library files could be incorrectly included in coverage reports.
+  This is now fixed, closing `issue 2115`_.
+
 - Fix: if a data file is created with no read permissions, the combine step
   would fail completely. Now a warning is issued and the file is skipped.
   Closes `issue 2117`_.
 
+.. _issue 2115: https://github.com/coveragepy/coveragepy/issues/2115
 .. _issue 2117: https://github.com/coveragepy/coveragepy/issues/2117
 
 
diff --git a/coverage/files.py b/coverage/files.py
@@ -264,14 +264,14 @@ def __init__(
         super().__init__(self.original_paths, name=name, caption=caption, debug=debug)
         self.paths = []
         for p in paths:
-            ap = os.path.normcase(p)
+            ap = abs_file(p)
             if ap != p and debug:
                 debug(f"        Normalized {p!r} to {ap!r}")
             self.paths.append(ap)
 
     def match(self, fpath: str) -> bool:  # pylint: disable=arguments-renamed
         """Does `fpath` indicate a file in one of our trees?"""
-        fpath = os.path.normcase(fpath)
+        fpath = abs_file(fpath)
         for p in self.paths:
             if fpath.startswith(p):
                 if fpath == p:
diff --git a/coverage/inorout.py b/coverage/inorout.py
@@ -129,7 +129,8 @@ def add_sysconfig_paths(paths: set[str], path_names: list[str]) -> None:
     for scheme in scheme_names:
         config_paths = sysconfig.get_paths(scheme)
         for path_name in path_names:
-            paths.add(config_paths[path_name])
+            if path_name in config_paths:
+                paths.add(config_paths[path_name])
 
 
 def add_stdlib_paths(paths: set[str]) -> None:
diff --git a/tests/test_api.py b/tests/test_api.py
@@ -17,6 +17,7 @@
 
 from collections.abc import Callable, Iterable
 from typing import cast
+from unittest import mock
 
 import pytest
 
@@ -184,6 +185,41 @@ def test_include_can_measure_stdlib(self) -> None:
         _, statements, missing, _ = cov1.analysis("random.py")
         assert statements == missing
 
+    def test_stdlib_symlink(self) -> None:
+        # Find the stdlib and make a symlink to it.
+        import colorsys
+
+        stdlib_dir = os.path.dirname(colorsys.__file__)
+        os.symlink(stdlib_dir, "myliblink")
+
+        sys.path.insert(0, os.path.abspath("myliblink"))
+        del sys.modules["colorsys"]
+
+        class FakeSysconfig:
+            """A fake for the sysconfig module."""
+
+            def get_scheme_names(self) -> list[str]:  # pylint: disable=missing-function-docstring
+                return ["xyzzy"]
+
+            def get_paths(self, _: str) -> dict[str, str]:  # pylint: disable=missing-function-docstring
+                return {
+                    "stdlib": os.path.abspath("myliblink"),
+                }
+
+        self.make_file(
+            "mymain.py",
+            """\
+            import colorsys
+            hls = colorsys.rgb_to_hls(1, 0, 0)
+            """,
+        )
+
+        with mock.patch.object(coverage.inorout, "sysconfig", FakeSysconfig()):
+            cov = coverage.Coverage()
+            self.start_import_stop(cov, "mymain")
+        files = cov.get_data().measured_files()
+        assert not any(os.path.basename(f) == "colorsys.py" for f in files)
+
     def test_exclude_list(self) -> None:
         cov = coverage.Coverage()
         cov.clear_exclude()
