Fix internal error when FORCE_OPTIONAL_PARENTHESES feature is enabled (…

…#2332)

Fixes #2313.

CHANGES.md

@@ -5,6 +5,7 @@
 ### _Black_
 
 - Add primer support and test for code piped into black via STDIN (#2315)
+- Fix internal error when `FORCE_OPTIONAL_PARENTHESES` feature is enabled (#2332)
 
 ## 21.6b0
 

src/black/linegen.py

@@ -961,14 +961,19 @@ def run_transformer(
 
         result.extend(transform_line(transformed_line, mode=mode, features=features))
 
-    if not (
-        transform.__name__ == "rhs"
-        and line.bracket_tracker.invisible
-        and not any(bracket.value for bracket in line.bracket_tracker.invisible)
-        and not line.contains_multiline_strings()
-        and not result[0].contains_uncollapsable_type_comments()
-        and not result[0].contains_unsplittable_type_ignore()
-        and not is_line_short_enough(result[0], line_length=mode.line_length)
+    if (
+        transform.__name__ != "rhs"
+        or not line.bracket_tracker.invisible
+        or any(bracket.value for bracket in line.bracket_tracker.invisible)
+        or line.contains_multiline_strings()
+        or result[0].contains_uncollapsable_type_comments()
+        or result[0].contains_unsplittable_type_ignore()
+        or is_line_short_enough(result[0], line_length=mode.line_length)
+        # If any leaves have no parents (which _can_ occur since
+        # `transform(line)` potentially destroys the line's underlying node
+        # structure), then we can't proceed. Doing so would cause the below
+        # call to `append_leaves()` to fail.
+        or any(leaf.parent is None for leaf in line.leaves)
     ):
         return result
 

tests/data/long_strings__regression.py

@@ -518,6 +518,12 @@ async def foo(self):
     "\N{BLACK RIGHT-POINTING TRIANGLE WITH DOUBLE VERTICAL BAR}\N{VARIATION SELECTOR-16}"
 )
 
+xxxxxx_xxx_xxxx_xx_xxxxx_xxxxxxxx_xxxxxxxx_xxxxxxxxxx_xxxx_xxxx_xxxxx = xxxx.xxxxxx.xxxxxxxxx.xxxxxxxxxxxxxxxxxxxx(
+    xx_xxxxxx={
+        "x3_xxxxxxxx": "xxx3_xxxxx_xxxxxxxx_xxxxxxxx_xxxxxxxxxx_xxxxxxxx_xxxxxx_xxxxxxx",
+    },
+)
+
 
 # output
 
@@ -1150,3 +1156,11 @@ async def foo(self):
 x = (
     "\N{BLACK RIGHT-POINTING TRIANGLE WITH DOUBLE VERTICAL BAR}\N{VARIATION SELECTOR-16}"
 )
+
+xxxxxx_xxx_xxxx_xx_xxxxx_xxxxxxxx_xxxxxxxx_xxxxxxxxxx_xxxx_xxxx_xxxxx = xxxx.xxxxxx.xxxxxxxxx.xxxxxxxxxxxxxxxxxxxx(
+    xx_xxxxxx={
+        "x3_xxxxxxxx": (
+            "xxx3_xxxxx_xxxxxxxx_xxxxxxxx_xxxxxxxxxx_xxxxxxxx_xxxxxx_xxxxxxx"
+        ),
+    },
+)