feat: implicitly combine relative paths

Author: nedbat

coverage/control.py

@@ -741,16 +741,14 @@ def combine(self, data_paths=None, strict=False, keep=False):
         self._post_init()
         self.get_data()
 
-        aliases = None
-        if self.config.paths:
-            aliases = PathAliases(
-                debugfn=(self._debug.write if self._debug.should("pathmap") else None),
-                relative=self.config.relative_files,
-            )
-            for paths in self.config.paths.values():
-                result = paths[0]
-                for pattern in paths[1:]:
-                    aliases.add(pattern, result)
+        aliases = PathAliases(
+            debugfn=(self._debug.write if self._debug.should("pathmap") else None),
+            relative=self.config.relative_files,
+        )
+        for paths in self.config.paths.values():
+            result = paths[0]
+            for pattern in paths[1:]:
+                aliases.add(pattern, result)
 
         combine_parallel_data(
             self._data,

coverage/files.py

@@ -409,6 +409,20 @@ def map(self, path):
                     f"producing {new!r}"
                 )
                 return new
+
+        # If we get here, no pattern matched.
+
+        if self.relative and not isabs_anywhere(path):
+            parts = re.split(r"[/\\]", path)
+            if len(parts) > 1:
+                dir1 = parts[0]
+                pattern = f"*/{dir1}"
+                regex = rf"^(.*[\\/])?{re.escape(dir1)}[\\/]"
+                result = f"{dir1}{os.sep}"
+                self.debugfn(f"Generating rule: {pattern!r} -> {result!r} using regex {regex!r}")
+                self.aliases.append((pattern, re.compile(regex), result))
+                return self.map(path)
+
         self.debugfn(f"No rules match, path {path!r} is unchanged")
         return path
 

coverage/sqldata.py

@@ -596,7 +596,9 @@ def update(self, other_data, aliases=None):
         """Update this data with data from several other :class:`CoverageData` instances.
 
         If `aliases` is provided, it's a `PathAliases` object that is used to
-        re-map paths to match the local machine's.
+        re-map paths to match the local machine's.  Note: `aliases` is None
+        only when called directly from the test suite.
+
         """
         if self._debug.should("dataop"):
             self._debug.write("Updating with data from {!r}".format(

tests/test_files.py

@@ -416,6 +416,26 @@ def test_relative_linux_on_windows(self, paths):
             r"project\module\tests\file.py",
         )
 
+    @pytest.mark.skipif(env.WINDOWS, reason="This test assumes Unix file system")
+    def test_implicit_relative_windows_on_linux(self):
+        # https://github.com/nedbat/coveragepy/issues/991
+        aliases = PathAliases(relative=True)
+        self.assert_mapped(
+            aliases,
+            r"project\module\tests\file.py",
+            r"project/module/tests/file.py",
+        )
+
+    @pytest.mark.skipif(not env.WINDOWS, reason="This test assumes Windows file system")
+    def test_implicit_relative_linux_on_windows(self):
+        # https://github.com/nedbat/coveragepy/issues/991
+        aliases = PathAliases(relative=True)
+        self.assert_mapped(
+            aliases,
+            r"project/module/tests/file.py",
+            r"project\module\tests\file.py",
+        )
+
     def test_multiple_wildcard(self, rel_yn):
         aliases = PathAliases(relative=rel_yn)
         aliases.add('/home/jenkins/*/a/*/b/*/django', './django')