rerere: Skip mismatched marker sizes like git-rerere does

git-rerere strictly ignores conflict markers that are not exactly the
expected length. For `<` and `>`, it also requires them to end in a
space.

See git/rerere.c:is_cmarker

gitrevise/merge.py

@@ -375,7 +375,7 @@ def normalize_conflict(
         line = next(lines, None)
         if line is None:
             raise ConflictParseFailed("unexpected eof")
-        if line.startswith(b"<<<<<<<"):
+        if line.startswith(b"<<<<<<< "):
             # parse recursive conflicts, including their processed output in the current hunk
             conflict = normalize_conflict(lines, None)
             if cur_hunk is not None:
@@ -393,7 +393,7 @@ def normalize_conflict(
                     raise ConflictParseFailed("unexpected ======= conflict marker")
                 other_hunk = cur_hunk
             cur_hunk = b""
-        elif line.startswith(b">>>>>>>"):
+        elif line.startswith(b">>>>>>> "):
             # end of conflict. update hasher, and return a normalized conflict
             if cur_hunk is None or other_hunk is None:
                 raise ConflictParseFailed("unexpected >>>>>>> conflict marker")
@@ -426,7 +426,7 @@ def normalize_conflicted_file(body: bytes) -> Tuple[bytes, str]:
         line = next(lines, None)
         if line is None:
             return (normalized, hasher.hexdigest())
-        if line.startswith(b"<<<<<<<"):
+        if line.startswith(b"<<<<<<< "):
             normalized += normalize_conflict(lines, hasher)
         else:
             normalized += line

tests/test_rerere.py

@@ -236,7 +236,7 @@ def test_normalize_conflicted_file() -> None:
             c
             ==========
             d
-            >>>>>>>>>> longer conflict marker, to be trimmed
+            >>>>>>>>>> longer conflict marker, to be ignored
             """
         )
     ) == (
@@ -250,14 +250,14 @@ def test_normalize_conflicted_file() -> None:
 
             unrelated line
 
-            <<<<<<<
+            <<<<<<<<<< HEAD
             c
-            =======
+            ==========
             d
-            >>>>>>>
+            >>>>>>>>>> longer conflict marker, to be ignored
             """
         ),
-        "3d7cdc2948951408412cc64f3816558407f77e18",
+        "0630df854874fc5ffb92a197732cce0d8928e898",
     )
 
     # Discard original-text-marker from merge.conflictStyle diff3.
@@ -315,18 +315,18 @@ def test_normalize_conflicted_file() -> None:
         normalize_conflicted_file(
             dedent(
                 """\
-            <<<<<<<
+            <<<<<<< ours (outer)
             outer left
-            <<<<<<<<<<<
+            <<<<<<< ours (inner)
             inner left
-            |||||||||||
+            |||||||
             inner diff3 original section
-            ===========
+            =======
             inner right
-            >>>>>>>>>>>
+            >>>>>>> theirs (inner)
             =======
             outer right
-            >>>>>>>
+            >>>>>>> theirs (outer)
             """
             )
         )[0]