Fix a magical comment caused internal error

CHANGES.md

@@ -12,6 +12,8 @@
 
 - Fix a bug where an illegal trailing comma was added to return type annotations using
   PEP 604 unions (#3735)
+- Fix a bug where multi-line open parenthesis magic comment like `type: ignore` were not
+  correctly parsed (#3740)
 
 ### Preview style
 

src/black/linegen.py

@@ -49,6 +49,7 @@
     is_stub_body,
     is_stub_suite,
     is_tuple_containing_walrus,
+    is_type_ignore_comment_string,
     is_vararg,
     is_walrus_assignment,
     is_yield,
@@ -1399,8 +1400,13 @@ def maybe_make_parens_invisible_in_atom(
     if is_lpar_token(first) and is_rpar_token(last):
         middle = node.children[1]
         # make parentheses invisible
-        first.value = ""
-        last.value = ""
+        if (
+            # If the prefix of `middle` includes a type comment with
+            # ignore annotation, then we do not remove the parentheses
+            not is_type_ignore_comment_string(middle.prefix.strip())
+        ):
+            first.value = ""
+            last.value = ""
         maybe_make_parens_invisible_in_atom(
             middle,
             parent=parent,

src/black/lines.py

@@ -28,6 +28,7 @@
     is_multiline_string,
     is_one_sequence_between,
     is_type_comment,
+    is_type_ignore_comment,
     is_with_or_async_with_stmt,
     replace_child,
     syms,
@@ -251,7 +252,7 @@ def contains_uncollapsable_type_comments(self) -> bool:
             for comment in comments:
                 if is_type_comment(comment):
                     if comment_seen or (
-                        not is_type_comment(comment, " ignore")
+                        not is_type_ignore_comment(comment)
                         and leaf_id not in ignored_ids
                     ):
                         return True
@@ -288,7 +289,7 @@ def contains_unsplittable_type_ignore(self) -> bool:
             # line.
             for node in self.leaves[-2:]:
                 for comment in self.comments.get(id(node), []):
-                    if is_type_comment(comment, " ignore"):
+                    if is_type_ignore_comment(comment):
                         return True
 
         return False

src/black/nodes.py

@@ -816,12 +816,27 @@ def is_async_stmt_or_funcdef(leaf: Leaf) -> bool:
     )
 
 
-def is_type_comment(leaf: Leaf, suffix: str = "") -> bool:
-    """Return True if the given leaf is a special comment.
-    Only returns true for type comments for now."""
+def is_type_comment(leaf: Leaf) -> bool:
+    """Return True if the given leaf is a type comment. This function should only
+    be used for general type comments (excluding ignore annotations, which should
+    use `is_type_ignore_comment`). Note that general type comments are no longer
+    used in modern version of Python, this function may be deprecated in the future."""
     t = leaf.type
     v = leaf.value
-    return t in {token.COMMENT, STANDALONE_COMMENT} and v.startswith("# type:" + suffix)
+    return t in {token.COMMENT, STANDALONE_COMMENT} and v.startswith("# type:")
+
+
+def is_type_ignore_comment(leaf: Leaf) -> bool:
+    """Return True if the given leaf is a type comment with ignore annotation."""
+    t = leaf.type
+    v = leaf.value
+    return t in {token.COMMENT, STANDALONE_COMMENT} and is_type_ignore_comment_string(v)
+
+
+def is_type_ignore_comment_string(value: str) -> bool:
+    """Return True if the given string match with type comment with
+    ignore annotation."""
+    return value.startswith("# type: ignore")
 
 
 def wrap_in_parentheses(parent: Node, child: LN, *, visible: bool = True) -> None:

tests/data/simple_cases/multiline_consecutive_open_parentheses_ignore.py

@@ -0,0 +1,41 @@
+# This is a regression test. Issue #3737
+
+a = (  # type: ignore
+    int(  # type: ignore
+        int(  # type: ignore
+            int(  # type: ignore
+                6
+            )
+        )
+    )
+)
+
+b = (
+    int(
+        6
+    )
+)
+
+print(   "111") # type: ignore
+print(   "111"                         ) # type: ignore
+print(   "111"       ) # type: ignore
+
+
+# output
+
+
+# This is a regression test. Issue #3737
+
+a = (  # type: ignore
+    int(  # type: ignore
+        int(  # type: ignore
+            int(6)  # type: ignore
+        )
+    )
+)
+
+b = int(6)
+
+print("111")  # type: ignore
+print("111")  # type: ignore
+print("111")  # type: ignore