fix: path-mapped results shouldn't start with ./

Unless the actual result in the config starts with ./

Author: nedbat

coverage/files.py

@@ -435,6 +435,9 @@ def map(self, path):
                 new = new.replace(sep(path), sep(result))
                 if not self.relative:
                     new = canonical_filename(new)
+                dot_start = result.startswith(("./", ".\\")) and len(result) > 2
+                if new.startswith(("./", ".\\")) and not dot_start:
+                    new = new[2:]
                 self.debugfn(
                     f"Matched path {path!r} to rule {original_pattern!r} -> {result!r}, " +
                     f"producing {new!r}"

tests/test_files.py

@@ -380,6 +380,13 @@ def test_no_accidental_match(self, rel_yn):
         aliases.add('/home/*/src', './mysrc')
         self.assert_unchanged(aliases, '/home/foo/srcetc')
 
+    def test_no_dotslash(self, rel_yn):
+        # 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')
+
     def test_multiple_patterns(self, rel_yn):
         # also test the debugfn...
         msgs = []