Fix the handling of # fmt: skip when it's at a colon line (#3148)

When the Leaf node with `# fmt: skip` is a NEWLINE inside a `suite`
Node, the nodes to ignore should be from the siblings of the parent
`suite` Node.

There is a also a special case for the ASYNC token, where it expands
to the grandparent Node where the ASYNC token is.

This fixes GH-2646, GH-3126, GH-2680, GH-2421, GH-2339, and GH-2138.

CHANGES.md

@@ -10,6 +10,7 @@
 
 <!-- Changes that affect Black's stable style -->
 
+- Fix incorrect handling of `# fmt: skip` on colon `:` lines. (#3148)
 - Comments are no longer deleted when a line had spaces removed around power operators
   (#2874)
 

src/black/comments.py

@@ -9,7 +9,7 @@
 else:
     from typing_extensions import Final
 
-from blib2to3.pytree import Node, Leaf
+from blib2to3.pytree import Node, Leaf, type_repr
 from blib2to3.pgen2 import token
 
 from black.nodes import first_leaf_column, preceding_leaf, container_of
@@ -174,6 +174,11 @@ def convert_one_fmt_off_pair(node: Node, *, preview: bool) -> bool:
                 first.prefix = prefix[comment.consumed :]
             if comment.value in FMT_SKIP:
                 first.prefix = ""
+                standalone_comment_prefix = prefix
+            else:
+                standalone_comment_prefix = (
+                    prefix[:previous_consumed] + "\n" * comment.newlines
+                )
             hidden_value = "".join(str(n) for n in ignored_nodes)
             if comment.value in FMT_OFF:
                 hidden_value = comment.value + "\n" + hidden_value
@@ -195,7 +200,7 @@ def convert_one_fmt_off_pair(node: Node, *, preview: bool) -> bool:
                 Leaf(
                     STANDALONE_COMMENT,
                     hidden_value,
-                    prefix=prefix[:previous_consumed] + "\n" * comment.newlines,
+                    prefix=standalone_comment_prefix,
                 ),
             )
             return True
@@ -211,26 +216,10 @@ def generate_ignored_nodes(
     If comment is skip, returns leaf only.
     Stops at the end of the block.
     """
-    container: Optional[LN] = container_of(leaf)
     if comment.value in FMT_SKIP:
-        prev_sibling = leaf.prev_sibling
-        # Need to properly format the leaf prefix to compare it to comment.value,
-        # which is also formatted
-        comments = list_comments(leaf.prefix, is_endmarker=False, preview=preview)
-        if comments and comment.value == comments[0].value and prev_sibling is not None:
-            leaf.prefix = ""
-            siblings = [prev_sibling]
-            while (
-                "\n" not in prev_sibling.prefix
-                and prev_sibling.prev_sibling is not None
-            ):
-                prev_sibling = prev_sibling.prev_sibling
-                siblings.insert(0, prev_sibling)
-            for sibling in siblings:
-                yield sibling
-        elif leaf.parent is not None:
-            yield leaf.parent
+        yield from _generate_ignored_nodes_from_fmt_skip(leaf, comment, preview=preview)
         return
+    container: Optional[LN] = container_of(leaf)
     while container is not None and container.type != token.ENDMARKER:
         if is_fmt_on(container, preview=preview):
             return
@@ -246,6 +235,51 @@ def generate_ignored_nodes(
             container = container.next_sibling
 
 
+def _generate_ignored_nodes_from_fmt_skip(
+    leaf: Leaf, comment: ProtoComment, *, preview: bool
+) -> Iterator[LN]:
+    """Generate all leaves that should be ignored by the `# fmt: skip` from `leaf`."""
+    prev_sibling = leaf.prev_sibling
+    parent = leaf.parent
+    # Need to properly format the leaf prefix to compare it to comment.value,
+    # which is also formatted
+    comments = list_comments(leaf.prefix, is_endmarker=False, preview=preview)
+    if not comments or comment.value != comments[0].value:
+        return
+    if prev_sibling is not None:
+        leaf.prefix = ""
+        siblings = [prev_sibling]
+        while "\n" not in prev_sibling.prefix and prev_sibling.prev_sibling is not None:
+            prev_sibling = prev_sibling.prev_sibling
+            siblings.insert(0, prev_sibling)
+        for sibling in siblings:
+            yield sibling
+    elif (
+        parent is not None
+        and type_repr(parent.type) == "suite"
+        and leaf.type == token.NEWLINE
+    ):
+        # The `# fmt: skip` is on the colon line of the if/while/def/class/...
+        # statements. The ignored nodes should be previous siblings of the
+        # parent suite node.
+        leaf.prefix = ""
+        ignored_nodes: List[LN] = []
+        parent_sibling = parent.prev_sibling
+        while parent_sibling is not None and type_repr(parent_sibling.type) != "suite":
+            ignored_nodes.insert(0, parent_sibling)
+            parent_sibling = parent_sibling.prev_sibling
+        # Special case for `async_stmt` where the ASYNC token is on the
+        # grandparent node.
+        grandparent = parent.parent
+        if (
+            grandparent is not None
+            and grandparent.prev_sibling is not None
+            and grandparent.prev_sibling.type == token.ASYNC
+        ):
+            ignored_nodes.insert(0, grandparent.prev_sibling)
+        yield from iter(ignored_nodes)
+
+
 def is_fmt_on(container: LN, preview: bool) -> bool:
     """Determine whether formatting is switched on within a container.
     Determined by whether the last `# fmt:` comment is `on` or `off`.

src/black/linegen.py

@@ -220,7 +220,9 @@ def visit_async_stmt(self, node: Node) -> Iterator[Line]:
         for child in children:
             yield from self.visit(child)
 
-            if child.type == token.ASYNC:
+            if child.type == token.ASYNC or child.type == STANDALONE_COMMENT:
+                # STANDALONE_COMMENT happens when `# fmt: skip` is applied on the async
+                # line.
                 break
 
         internal_stmt = next(children)

tests/data/simple_cases/fmtskip8.py

@@ -0,0 +1,62 @@
+# Make sure a leading comment is not removed.
+def some_func(  unformatted,  args  ):  # fmt: skip
+    print("I am some_func")
+    return 0
+    # Make sure this comment is not removed.
+
+
+# Make sure a leading comment is not removed.
+async def some_async_func(  unformatted,   args):  # fmt: skip
+    print("I am some_async_func")
+    await asyncio.sleep(1)
+
+
+# Make sure a leading comment is not removed.
+class SomeClass(  Unformatted,  SuperClasses  ):  # fmt: skip
+    def some_method(  self,  unformatted,  args  ):  # fmt: skip
+        print("I am some_method")
+        return 0
+
+    async def some_async_method(  self,  unformatted,  args  ):  # fmt: skip
+        print("I am some_async_method")
+        await asyncio.sleep(1)
+
+
+# Make sure a leading comment is not removed.
+if  unformatted_call(  args  ):  # fmt: skip
+    print("First branch")
+    # Make sure this is not removed.
+elif  another_unformatted_call(  args  ):  # fmt: skip
+    print("Second branch")
+else  :  # fmt: skip
+    print("Last branch")
+
+
+while  some_condition(  unformatted,  args  ):  # fmt: skip
+    print("Do something")
+
+
+for  i  in  some_iter(  unformatted,  args  ):  # fmt: skip
+    print("Do something")
+
+
+async def test_async_for():
+    async  for  i  in  some_async_iter(  unformatted,  args  ):  # fmt: skip
+        print("Do something")
+
+
+try  :  # fmt: skip
+    some_call()
+except  UnformattedError  as  ex:  # fmt: skip
+    handle_exception()
+finally  :  # fmt: skip
+    finally_call()
+
+
+with  give_me_context(  unformatted,  args  ):  # fmt: skip
+    print("Do something")
+
+
+async def test_async_with():
+    async  with  give_me_async_context(  unformatted,  args  ):  # fmt: skip
+        print("Do something")