split long del statements into multiple lines (#698)

Fixes #693

README.md

@@ -944,10 +944,12 @@ More details can be found in [CONTRIBUTING](CONTRIBUTING.md).
 
 ### 19.2b0
 
-* *Black* no longer normalizes numeric literals to include `_` separators.
+* long `del` statements are now split into multiple lines (#698)
+
+* *Black* no longer normalizes numeric literals to include `_` separators (#696)
 
 * new option `--target-version` to control which Python versions
-  *Black*-formatted code should target
+  *Black*-formatted code should target (#618)
 
 ### 18.9b0
 

black.py

@@ -1646,6 +1646,7 @@ def __attrs_post_init__(self) -> None:
         self.visit_expr_stmt = partial(v, keywords=Ø, parens=ASSIGNMENTS)
         self.visit_return_stmt = partial(v, keywords={"return"}, parens={"return"})
         self.visit_import_from = partial(v, keywords=Ø, parens={"import"})
+        self.visit_del_stmt = partial(v, keywords=Ø, parens={"del"})
         self.visit_async_funcdef = self.visit_async_stmt
         self.visit_decorated = self.visit_decorators
 
@@ -3350,7 +3351,16 @@ def _v(node: ast.AST, depth: int = 0) -> Iterator[str]:
 
             if isinstance(value, list):
                 for item in value:
-                    if isinstance(item, ast.AST):
+                    # Ignore nested tuples within del statements, because we may insert
+                    # parentheses and they change the AST.
+                    if (
+                        field == "targets"
+                        and isinstance(node, ast.Delete)
+                        and isinstance(item, ast.Tuple)
+                    ):
+                        for item in item.elts:
+                            yield from _v(item, depth + 2)
+                    elif isinstance(item, ast.AST):
                         yield from _v(item, depth + 2)
 
             elif isinstance(value, ast.AST):

tests/data/cantfit.py

@@ -36,6 +36,7 @@
     if key in self.connect_kwargs:
         raise ValueError(err.format(key))
 concatenated_strings = "some strings that are" "concatenated implicitly, so if you put them on separate" "lines it will fit"
+del concatenated_strings, string_variable_name, normal_function_name, normal_name, need_more_to_make_the_line_long_enough
 
 
 # output
@@ -91,3 +92,10 @@
     "concatenated implicitly, so if you put them on separate"
     "lines it will fit"
 )
+del (
+    concatenated_strings,
+    string_variable_name,
+    normal_function_name,
+    normal_name,
+    need_more_to_make_the_line_long_enough,
+)