Fix # fmt: skip ignored in deeply nested expressions

CHANGES.md

@@ -30,6 +30,7 @@
   magic trailing commas and intentional multiline formatting (#4865)
 - Fix `fix_fmt_skip_in_one_liners` crashing on `with` statements (#4853)
 - Fix `fix_fmt_skip_in_one_liners` crashing on annotated parameters (#4854)
+- Fix `# fmt: skip` behavior for deeply nested expressions (#4883)
 
 ### Configuration
 

src/black/comments.py

@@ -7,6 +7,7 @@
 from black.mode import Mode, Preview
 from black.nodes import (
     CLOSING_BRACKETS,
+    OPENING_BRACKETS,
     STANDALONE_COMMENT,
     STATEMENT,
     WHITESPACE,
@@ -645,7 +646,46 @@ def _generate_ignored_nodes_from_fmt_skip(
         return
 
     if Preview.fix_fmt_skip_in_one_liners in mode and not prev_sibling and parent:
-        prev_sibling = parent.prev_sibling
+        # If the current leaf doesn't have a previous sibling, it might be deeply nested
+        # (e.g. inside a list, function call, etc.). We need to climb up the tree
+        # to find the previous sibling on the same line.
+
+        # First, find the ancestor node that starts the current line
+        # (has a newline in its prefix, or is at the root)
+        line_start_node = parent
+        while line_start_node.parent is not None:
+            # The comment itself is in the leaf's prefix, so we need to check
+            # if the current node's prefix (before the comment) has a newline
+            node_prefix = (
+                line_start_node.prefix if hasattr(line_start_node, "prefix") else ""
+            )
+            # Skip the comment part if this is the first node (parent)
+            if line_start_node == parent:
+                # The parent node has the comment in its prefix, so we check
+                # what's before the comment
+                comment_start = node_prefix.find(comment.value)
+                if comment_start >= 0:
+                    prefix_before_comment = node_prefix[:comment_start]
+                    if "\n" in prefix_before_comment:
+                        # There's a newline before the comment, so this node
+                        # is at the start of the line
+                        break
+                elif "\n" in node_prefix:
+                    break
+            elif "\n" in node_prefix:
+                # This node starts on a new line, so it's the line start
+                break
+            line_start_node = line_start_node.parent
+
+        # Now find the prev_sibling by climbing from parent up to line_start_node
+        curr = parent
+        while curr is not None and curr != line_start_node.parent:
+            if curr.prev_sibling is not None:
+                prev_sibling = curr.prev_sibling
+                break
+            if curr.parent is None:
+                break
+            curr = curr.parent
 
     if prev_sibling is not None:
         leaf.prefix = leaf.prefix[comment.consumed :]
@@ -746,6 +786,22 @@ def _generate_ignored_nodes_from_fmt_skip(
                 if header_nodes:
                     ignored_nodes = header_nodes + ignored_nodes
 
+        # If the leaf's parent is an atom (parenthesized expression) and we've
+        # captured the opening bracket in our ignored_nodes, we should include
+        # the entire atom (including the closing bracket and the leaf itself)
+        # to avoid partial formatting
+        if (
+            parent is not None
+            and parent.type == syms.atom
+            and len(parent.children) >= 2
+            and parent.children[0].type in OPENING_BRACKETS
+            and parent.children[0] in ignored_nodes
+        ):
+            # Replace the opening bracket and any other captured children of this atom
+            # with the entire atom node
+            ignored_nodes = [node for node in ignored_nodes if node.parent != parent]
+            ignored_nodes.append(parent)
+
         yield from ignored_nodes
     elif (
         parent is not None and parent.type == syms.suite and leaf.type == token.NEWLINE

src/black/lines.py

@@ -863,6 +863,10 @@ def is_line_short_enough(line: Line, *, mode: Mode, line_str: str = "") -> bool:
     for i, leaf in enumerate(line.leaves):
         if max_level_to_update == math.inf:
             had_comma: int | None = None
+            # Skip multiline_string_handling logic for leaves without bracket_depth
+            # (e.g., newly created leaves not yet processed by bracket tracker)
+            if not hasattr(leaf, "bracket_depth"):
+                continue
             if leaf.bracket_depth + 1 > len(commas):
                 commas.append(0)
             elif leaf.bracket_depth + 1 < len(commas):
@@ -878,17 +882,22 @@ def is_line_short_enough(line: Line, *, mode: Mode, line_str: str = "") -> bool:
                     # MLS was in parens with at least one comma - force split
                     return False
 
-        if leaf.bracket_depth <= max_level_to_update and leaf.type == token.COMMA:
-            # Inside brackets, ignore trailing comma
-            # directly after MLS/MLS-containing expression
-            ignore_ctxs: list[LN | None] = [None]
-            ignore_ctxs += multiline_string_contexts
-            if (line.inside_brackets or leaf.bracket_depth > 0) and (
-                i != len(line.leaves) - 1 or leaf.prev_sibling not in ignore_ctxs
-            ):
-                commas[leaf.bracket_depth] += 1
-        if max_level_to_update != math.inf:
-            max_level_to_update = min(max_level_to_update, leaf.bracket_depth)
+        # Skip bracket-depth-dependent processing for leaves without the attribute
+        if not hasattr(leaf, "bracket_depth"):
+            # Still process multiline string detection below
+            pass
+        else:
+            if leaf.bracket_depth <= max_level_to_update and leaf.type == token.COMMA:
+                # Inside brackets, ignore trailing comma
+                # directly after MLS/MLS-containing expression
+                ignore_ctxs: list[LN | None] = [None]
+                ignore_ctxs += multiline_string_contexts
+                if (line.inside_brackets or leaf.bracket_depth > 0) and (
+                    i != len(line.leaves) - 1 or leaf.prev_sibling not in ignore_ctxs
+                ):
+                    commas[leaf.bracket_depth] += 1
+            if max_level_to_update != math.inf:
+                max_level_to_update = min(max_level_to_update, leaf.bracket_depth)
 
         if is_multiline_string(leaf):
             if leaf.parent and (

tests/data/cases/fmtskip_nested_if.py

@@ -0,0 +1,39 @@
+# flags: --preview --no-preview-line-length-1
+class ClassWithALongName:
+    Constant1 = 1
+    Constant2 = 2
+    Constant3 = 3
+
+
+def test():
+    if (
+        "cond1" == "cond1"
+        and "cond2" == "cond2"
+        and 1 in (  # fmt: skip
+            ClassWithALongName.Constant1,
+            ClassWithALongName.Constant2,
+            ClassWithALongName.Constant3,
+        )
+    ):
+        return True
+    return False
+
+# output
+
+class ClassWithALongName:
+    Constant1 = 1
+    Constant2 = 2
+    Constant3 = 3
+
+
+def test():
+    if (
+        "cond1" == "cond1" and "cond2" == "cond2"
+        and 1 in (  # fmt: skip
+        ClassWithALongName.Constant1,
+        ClassWithALongName.Constant2,
+        ClassWithALongName.Constant3,
+    )
+):
+        return True
+    return False