fix: relative_files should keep relative path maps. #1519

3 files changed, 26 insertions, 6 deletions

diff --git a/CHANGES.rst b/CHANGES.rst
index 352ddb65..fa83063d 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -20,6 +20,10 @@ development at the same time, such as 4.5.x and 5.0.
 Unreleased
 ----------
 
+- Fix: when using the ``[run] relative_files = True`` setting, a relative
+  ``[paths]`` pattern was still being made absolute.  This is now fixed,
+  closing `issue 1519`_.
+
 - Fix: if Python doesn't provide tomllib, then TOML configuration files can
   only be read if coverage.py is installed with the ``[toml]`` extra.
   Coverage.py will raise an error if toml support is not installed when it sees
@@ -41,6 +45,7 @@ Unreleased
 
 .. _issue 1515: https://github.com/nedbat/coveragepy/issues/1515
 .. _issue 1516: https://github.com/nedbat/coveragepy/issues/1516
+.. _issue 1519: https://github.com/nedbat/coveragepy/issues/1519
 
 
 .. _changes_7-0-1:
diff --git a/coverage/files.py b/coverage/files.py
index ed37067f..11dbdaa3 100644
--- a/coverage/files.py
+++ b/coverage/files.py
@@ -395,7 +395,11 @@ class PathAliases:
     map a path through those aliases to produce a unified path.
 
     """
-    def __init__(self, debugfn:Optional[Callable[[str], None]]=None, relative:bool=False) -> None:
+    def __init__(
+        self,
+        debugfn: Optional[Callable[[str], None]]=None,
+        relative: bool=False,
+    ) -> None:
         # A list of (original_pattern, regex, result)
         self.aliases: List[Tuple[str, Regex, str]] = []
         self.debugfn = debugfn or (lambda msg: 0)
@@ -431,10 +435,11 @@ class PathAliases:
         if pattern.endswith("*"):
             raise ConfigError("Pattern must not end with wildcards.")
 
-        # The pattern is meant to match a filepath.  Let's make it absolute
+        # The pattern is meant to match a file path.  Let's make it absolute
         # unless it already is, or is meant to match any prefix.
-        if not pattern.startswith('*') and not isabs_anywhere(pattern + pattern_sep):
-            pattern = abs_file(pattern)
+        if not self.relative:
+            if not pattern.startswith('*') and not isabs_anywhere(pattern + pattern_sep):
+                pattern = abs_file(pattern)
         if not pattern.endswith(pattern_sep):
             pattern += pattern_sep
 
diff --git a/tests/test_files.py b/tests/test_files.py
index 54c91628..2d029a04 100644
--- a/tests/test_files.py
+++ b/tests/test_files.py
@@ -17,7 +17,9 @@ from coverage.files import (
     GlobMatcher, ModuleMatcher, PathAliases, TreeMatcher, abs_file,
     actual_path, find_python_files, flat_rootname, globs_to_regex,
 )
+
 from tests.coveragetest import CoverageTest
+from tests.helpers import os_sep
 
 
 class FilesTest(CoverageTest):
@@ -415,8 +417,16 @@ class PathAliasesTest(CoverageTest):
         # The result shouldn't start with "./" if the map result didn't.
         aliases = PathAliases(relative=rel_yn)
         aliases.add('*/project', '.')
-        # Because the map result has no slash, the actual result is os-dependent.
-        self.assert_mapped(aliases, '/ned/home/project/src/a.py', f'src{os.sep}a.py')
+        self.assert_mapped(aliases, '/ned/home/project/src/a.py', os_sep('src/a.py'))
+
+    def test_relative_pattern(self):
+        aliases = PathAliases(relative=True)
+        aliases.add(".tox/*/site-packages", "src")
+        self.assert_mapped(
+            aliases,
+            ".tox/py314/site-packages/proj/a.py",
+            os_sep("src/proj/a.py"),
+        )
 
     def test_multiple_patterns(self, rel_yn):
         # also test the debugfn...