Reset trailing comma handling

diff --git a/src/black/__init__.py b/src/black/__init__.py
index d251136942a37a86c8304c341408167ea4dc3f10..2250943665ad21e0cc18ca0efa8edd7288a9329f 100644 (file)
--- a/src/black/__init__.py
+++ b/src/black/__init__.py
@@ -1494,69 +1494,6 @@ class Line:
             Leaf(token.DOT, ".") for _ in range(3)
         ]
 
-    @property
-    def is_collection_with_optional_trailing_comma(self) -> bool:
-        """Is this line a collection literal with a trailing comma that's optional?
-
-        Note that the trailing comma in a 1-tuple is not optional.
-        """
-        if not self.leaves or len(self.leaves) < 4:
-            return False
-
-        # Look for and address a trailing colon.
-        if self.leaves[-1].type == token.COLON:
-            closer = self.leaves[-2]
-            close_index = -2
-        else:
-            closer = self.leaves[-1]
-            close_index = -1
-        if closer.type not in CLOSING_BRACKETS or self.inside_brackets:
-            return False
-
-        if closer.type == token.RPAR:
-            # Tuples require an extra check, because if there's only
-            # one element in the tuple removing the comma unmakes the
-            # tuple.
-            #
-            # We also check for parens before looking for the trailing
-            # comma because in some cases (eg assigning a dict
-            # literal) the literal gets wrapped in temporary parens
-            # during parsing. This case is covered by the
-            # collections.py test data.
-            opener = closer.opening_bracket
-            for _open_index, leaf in enumerate(self.leaves):
-                if leaf is opener:
-                    break
-
-            else:
-                # Couldn't find the matching opening paren, play it safe.
-                return False
-
-            commas = 0
-            comma_depth = self.leaves[close_index - 1].bracket_depth
-            for leaf in self.leaves[_open_index + 1 : close_index]:
-                if leaf.bracket_depth == comma_depth and leaf.type == token.COMMA:
-                    commas += 1
-            if commas > 1:
-                # We haven't looked yet for the trailing comma because
-                # we might also have caught noop parens.
-                return self.leaves[close_index - 1].type == token.COMMA
-
-            elif commas == 1:
-                return False  # it's either a one-tuple or didn't have a trailing comma
-
-            if self.leaves[close_index - 1].type in CLOSING_BRACKETS:
-                close_index -= 1
-                closer = self.leaves[close_index]
-                if closer.type == token.RPAR:
-                    # TODO: this is a gut feeling. Will we ever see this?
-                    return False
-
-        if self.leaves[close_index - 1].type != token.COMMA:
-            return False
-
-        return True
-
     @property
     def is_def(self) -> bool:
         """Is this a function definition? (Also returns True for async defs.)"""
@@ -1683,40 +1620,60 @@ class Line:
 
     def maybe_remove_trailing_comma(self, closing: Leaf) -> bool:
         """Remove trailing comma if there is one and it's safe."""
-        if not (self.leaves and self.leaves[-1].type == token.COMMA):
-            return False
-
-        # We remove trailing commas only in the case of importing a
-        # single name from a module.
         if not (
             self.leaves
-            and self.is_import
-            and len(self.leaves) > 4
             and self.leaves[-1].type == token.COMMA
             and closing.type in CLOSING_BRACKETS
-            and self.leaves[-4].type == token.NAME
-            and (
-                # regular `from foo import bar,`
-                self.leaves[-4].value == "import"
-                # `from foo import (bar as baz,)
-                or (
-                    len(self.leaves) > 6
-                    and self.leaves[-6].value == "import"
-                    and self.leaves[-3].value == "as"
-                )
-                # `from foo import bar as baz,`
-                or (
-                    len(self.leaves) > 5
-                    and self.leaves[-5].value == "import"
-                    and self.leaves[-3].value == "as"
-                )
-            )
-            and closing.type == token.RPAR
         ):
             return False
 
-        self.remove_trailing_comma()
-        return True
+        if closing.type == token.RBRACE:
+            self.remove_trailing_comma()
+            return True
+
+        if closing.type == token.RSQB:
+            comma = self.leaves[-1]
+            if comma.parent and comma.parent.type == syms.listmaker:
+                self.remove_trailing_comma()
+                return True
+
+        # For parens let's check if it's safe to remove the comma.
+        # Imports are always safe.
+        if self.is_import:
+            self.remove_trailing_comma()
+            return True
+
+        # Otherwise, if the trailing one is the only one, we might mistakenly
+        # change a tuple into a different type by removing the comma.
+        depth = closing.bracket_depth + 1
+        commas = 0
+        opening = closing.opening_bracket
+        for _opening_index, leaf in enumerate(self.leaves):
+            if leaf is opening:
+                break
+
+        else:
+            return False
+
+        for leaf in self.leaves[_opening_index + 1 :]:
+            if leaf is closing:
+                break
+
+            bracket_depth = leaf.bracket_depth
+            if bracket_depth == depth and leaf.type == token.COMMA:
+                commas += 1
+                if leaf.parent and leaf.parent.type in {
+                    syms.arglist,
+                    syms.typedargslist,
+                }:
+                    commas += 1
+                    break
+
+        if commas > 1:
+            self.remove_trailing_comma()
+            return True
+
+        return False
 
     def append_comment(self, comment: Leaf) -> bool:
         """Add an inline or standalone comment to the line."""
@@ -2686,7 +2643,6 @@ def transform_line(
     if (
         not line.contains_uncollapsable_type_comments()
         and not line.should_explode
-        and not line.is_collection_with_optional_trailing_comma
         and (
             is_line_short_enough(line, line_length=mode.line_length, line_str=line_str)
             or line.contains_unsplittable_type_ignore()