Fix: --line-ranges dedents a # fmt: off in the middle of a decorator (#4084)

Fixes #4068

CHANGES.md

@@ -8,7 +8,8 @@
 
 ### Stable style
 
-<!-- Changes that affect Black's stable style -->
+- Fix bug where `# fmt: off` automatically dedents when used with the `--line-ranges`
+  option, even when it is not within the specified line range. (#4084)
 
 ### Preview style
 

src/black/__init__.py

@@ -1180,7 +1180,7 @@ def _format_str_once(
         for feature in {Feature.PARENTHESIZED_CONTEXT_MANAGERS}
         if supports_feature(versions, feature)
     }
-    normalize_fmt_off(src_node, mode)
+    normalize_fmt_off(src_node, mode, lines)
     if lines:
         # This should be called after normalize_fmt_off.
         convert_unchanged_lines(src_node, lines)

src/black/comments.py

@@ -1,7 +1,7 @@
 import re
 from dataclasses import dataclass
 from functools import lru_cache
-from typing import Final, Iterator, List, Optional, Union
+from typing import Collection, Final, Iterator, List, Optional, Tuple, Union
 
 from black.mode import Mode, Preview
 from black.nodes import (
@@ -161,14 +161,18 @@ def make_comment(content: str) -> str:
     return "#" + content
 
 
-def normalize_fmt_off(node: Node, mode: Mode) -> None:
+def normalize_fmt_off(
+    node: Node, mode: Mode, lines: Collection[Tuple[int, int]]
+) -> None:
     """Convert content between `# fmt: off`/`# fmt: on` into standalone comments."""
     try_again = True
     while try_again:
-        try_again = convert_one_fmt_off_pair(node, mode)
+        try_again = convert_one_fmt_off_pair(node, mode, lines)
 
 
-def convert_one_fmt_off_pair(node: Node, mode: Mode) -> bool:
+def convert_one_fmt_off_pair(
+    node: Node, mode: Mode, lines: Collection[Tuple[int, int]]
+) -> bool:
     """Convert content of a single `# fmt: off`/`# fmt: on` into a standalone comment.
 
     Returns True if a pair was converted.
@@ -213,7 +217,18 @@ def convert_one_fmt_off_pair(node: Node, mode: Mode) -> bool:
                     prefix[:previous_consumed] + "\n" * comment.newlines
                 )
             hidden_value = "".join(str(n) for n in ignored_nodes)
+            comment_lineno = leaf.lineno - comment.newlines
             if comment.value in FMT_OFF:
+                fmt_off_prefix = ""
+                if len(lines) > 0 and not any(
+                    comment_lineno >= line[0] and comment_lineno <= line[1]
+                    for line in lines
+                ):
+                    # keeping indentation of comment by preserving original whitespaces.
+                    fmt_off_prefix = prefix.split(comment.value)[0]
+                    if "\n" in fmt_off_prefix:
+                        fmt_off_prefix = fmt_off_prefix.split("\n")[-1]
+                standalone_comment_prefix += fmt_off_prefix
                 hidden_value = comment.value + "\n" + hidden_value
             if _contains_fmt_skip_comment(comment.value, mode):
                 hidden_value += "  " + comment.value

tests/data/cases/line_ranges_fmt_off_decorator.py

@@ -1,4 +1,4 @@
-# flags: --line-ranges=12-12
+# flags: --line-ranges=12-12 --line-ranges=21-21
 # NOTE: If you need to modify this file, pay special attention to the --line-ranges=
 # flag above as it's formatting specifically these lines.
 
@@ -11,9 +11,19 @@ class MyClass:
     def method():
         print   ( "str" )
 
+    @decor(
+        a=1,
+        # fmt: off
+        b=(2,   3),
+        # fmt: on
+    )
+    def func():
+          pass
+
+
 # output
 
-# flags: --line-ranges=12-12
+# flags: --line-ranges=12-12 --line-ranges=21-21
 # NOTE: If you need to modify this file, pay special attention to the --line-ranges=
 # flag above as it's formatting specifically these lines.
 
@@ -25,3 +35,13 @@ class MyClass:
     # fmt: on
     def method():
         print("str")
+
+    @decor(
+        a=1,
+        # fmt: off
+        b=(2,   3),
+        # fmt: on
+    )
+    def func():
+        pass
+