Use git rename from/to information

tests/samples/git_rename.diff

@@ -28,5 +28,5 @@ index a071991..4dbab21 100644
 
 diff --git a/sub/onefile b/sub/otherfile
 similarity index 100%
-rename from onefile
-rename to otherfile
+rename from sub/onefile
+rename to sub/otherfile

tests/test_parser.py

@@ -720,6 +720,76 @@ def test_mode_change_file(self):
         self.assertFalse(res[0].is_symlink)
         self.assertTrue(res[0].is_rename)
 
+    def test_rename_no_prefix(self):
+        # `git diff --no-prefix`: the header names carry no a/ b/ prefix,
+        # so the `rename from` / `rename to` lines are the reliable source
+        diff = (
+            'diff --git a.py b.py\n'
+            'similarity index 100%\n'
+            'rename from a.py\n'
+            'rename to b.py\n'
+        )
+        res = PatchSet(diff)
+
+        self.assertTrue(res[0].is_rename)
+        self.assertEqual(res[0].path, 'b.py')
+        self.assertEqual(res[0].source_file, 'a.py')
+        self.assertEqual(res[0].target_file, 'b.py')
+        self.assertEqual(res[0].rename_from, 'a.py')
+        self.assertEqual(res[0].rename_to, 'b.py')
+        self.assertEqual(str(res), diff)
+
+    def test_rename_no_prefix_single_char_dirs(self):
+        # directory names that look like git prefixes are not stripped
+        diff = (
+            'diff --git x/util.py y/util.py\n'
+            'similarity index 100%\n'
+            'rename from x/util.py\n'
+            'rename to y/util.py\n'
+        )
+        res = PatchSet(diff)
+
+        self.assertTrue(res[0].is_rename)
+        self.assertEqual(res[0].path, 'y/util.py')
+
+        diff = (
+            'diff --git a/x.py b/x.py\n'
+            'similarity index 100%\n'
+            'rename from a/x.py\n'
+            'rename to b/x.py\n'
+        )
+        res = PatchSet(diff)
+
+        self.assertTrue(res[0].is_rename)
+        self.assertEqual(res[0].path, 'b/x.py')
+
+    def test_rename_quoted_filename(self):
+        diff = (
+            'diff --git "a/caf\\303\\251.py" "b/th\\303\\251.py"\n'
+            'similarity index 100%\n'
+            'rename from "caf\\303\\251.py"\n'
+            'rename to "th\\303\\251.py"\n'
+        )
+        res = PatchSet(diff)
+
+        self.assertTrue(res[0].is_rename)
+        self.assertEqual(res[0].path, '"th\\303\\251.py"')
+
+    def test_non_git_tree_diff_not_rename(self):
+        # `diff -ruN v1 v2` names both trees; this is not a rename
+        diff = (
+            'diff -ruN v1/src/foo.c v2/src/foo.c\n'
+            '--- v1/src/foo.c\t2026-10-30 10:00:00.000000000 +0000\n'
+            '+++ v2/src/foo.c\t2026-10-30 10:01:00.000000000 +0000\n'
+            '@@ -1 +1 @@\n'
+            '-a\n'
+            '+b\n'
+        )
+        res = PatchSet(diff)
+
+        self.assertFalse(res[0].is_rename)
+        self.assertEqual(res[0].path, 'v1/src/foo.c')
+
     def test_index_line_mode(self):
         # issue #125: an unchanged mode on the index line applies to both sides
         diff = (

unidiff/constants.py

@@ -53,6 +53,11 @@
 RE_DIFF_GIT_OLD_MODE = re.compile(r'^old mode (?P<mode>\d+)$')
 RE_DIFF_GIT_NEW_MODE = re.compile(r'^new mode (?P<mode>\d+)$')
 
+# check diff git rename markers `rename from old.py` / `rename to new.py`
+# (the paths carry no a/ b/ prefix, whatever prefix the header uses)
+RE_DIFF_GIT_RENAME_FROM = re.compile(r'^rename from (?P<filename>[^\r\n]+)$')
+RE_DIFF_GIT_RENAME_TO = re.compile(r'^rename to (?P<filename>[^\r\n]+)$')
+
 # check diff git index line with a trailing mode `index abc..def 100644`
 RE_DIFF_GIT_INDEX = re.compile(
     r'^index [0-9a-f]+\.\.[0-9a-f]+ (?P<mode>\d+)$')

unidiff/patch.py

@@ -46,6 +46,8 @@
     RE_DIFF_GIT_NEW_FILE,
     RE_DIFF_GIT_NEW_MODE,
     RE_DIFF_GIT_OLD_MODE,
+    RE_DIFF_GIT_RENAME_FROM,
+    RE_DIFF_GIT_RENAME_TO,
     RE_HUNK_BODY_LINE,
     RE_HUNK_EMPTY_BODY_LINE,
     RE_HUNK_HEADER,
@@ -225,6 +227,9 @@ def __init__(self, patch_info: Optional[PatchInfo] = None,
         # 1-based line number in the diff where this file entry starts; useful
         # to locate files that have no hunks (e.g. binary changes)
         self.diff_line_no = diff_line_no
+        # paths from git `rename from` / `rename to` lines; None if missing
+        self.rename_from: Optional[str] = None
+        self.rename_to: Optional[str] = None
 
     def __repr__(self) -> str:
         return "<PatchedFile: %s>" % self.path
@@ -366,6 +371,10 @@ def _append_trailing_empty_line(self) -> None:
     @property
     def path(self) -> str:
         """Return the file path abstracted from VCS."""
+        if self.rename_to is not None:
+            # git states the new path explicitly, without any prefix
+            return self.rename_to
+
         filepath = self.source_file
         if filepath in (None, DEV_NULL) or (
                 self.is_rename and self.target_file not in (None, DEV_NULL)):
@@ -396,6 +405,8 @@ def removed(self) -> int:
 
     @property
     def is_rename(self) -> bool:
+        if self.rename_from is not None and self.rename_to is not None:
+            return True
         return (self.source_file != DEV_NULL
             and self.target_file != DEV_NULL
             and self.source_file[2:] != self.target_file[2:])
@@ -531,6 +542,18 @@ def _parse(self, diff: Iterable, encoding: Optional[str],
                     patch_info.append(line)
                     continue
 
+                is_diff_git_rename_from = RE_DIFF_GIT_RENAME_FROM.match(line)
+                if is_diff_git_rename_from:
+                    current_file.rename_from = is_diff_git_rename_from.group('filename')
+                    patch_info.append(line)
+                    continue
+
+                is_diff_git_rename_to = RE_DIFF_GIT_RENAME_TO.match(line)
+                if is_diff_git_rename_to:
+                    current_file.rename_to = is_diff_git_rename_to.group('filename')
+                    patch_info.append(line)
+                    continue
+
                 is_diff_git_index = RE_DIFF_GIT_INDEX.match(line)
                 if is_diff_git_index:
                     # an unchanged index mode applies to both source and target