add entry in CHANGES.md, make the style change only in preview mode

CHANGES.md

@@ -12,6 +12,9 @@
 
 ### Preview style
 
+- Long type hints are now wrapped in parentheses and properly indented when split across
+  multiple lines (#3899)
+
 <!-- Changes that affect Black's preview style -->
 
 ### Configuration

src/black/linegen.py

@@ -408,9 +408,10 @@ def foo(a: int, b: float = 7): ...
 
         def foo(a: (int), b: (float) = 7): ...
         """
-        assert len(node.children) == 3
-        if maybe_make_parens_invisible_in_atom(node.children[2], parent=node):
-            wrap_in_parentheses(node, node.children[2], visible=False)
+        if Preview.parenthesize_long_type_hints in self.mode:
+            assert len(node.children) == 3
+            if maybe_make_parens_invisible_in_atom(node.children[2], parent=node):
+                wrap_in_parentheses(node, node.children[2], visible=False)
 
         yield from self.visit_default(node)
 
@@ -515,7 +516,14 @@ def __post_init__(self) -> None:
         self.visit_except_clause = partial(v, keywords={"except"}, parens={"except"})
         self.visit_with_stmt = partial(v, keywords={"with"}, parens={"with"})
         self.visit_classdef = partial(v, keywords={"class"}, parens=Ø)
-        self.visit_expr_stmt = partial(v, keywords=Ø, parens=ASSIGNMENTS)
+
+        # When this is moved out of preview, add ":" directly to ASSIGNMENTS in nodes.py
+        if Preview.parenthesize_long_type_hints in self.mode:
+            assignments = ASSIGNMENTS | {":"}
+        else:
+            assignments = ASSIGNMENTS
+        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"})

src/black/mode.py

@@ -180,6 +180,7 @@ class Preview(Enum):
     # for https://github.com/psf/black/issues/3117 to be fixed.
     string_processing = auto()
     parenthesize_conditional_expressions = auto()
+    parenthesize_long_type_hints = auto()
     skip_magic_trailing_comma_in_subscript = auto()
     wrap_long_dict_values_in_parens = auto()
     wrap_multiple_context_managers_in_parens = auto()

src/black/nodes.py

@@ -121,8 +121,6 @@
     ">>=",
     "**=",
     "//=",
-    # also handle annassign
-    ":",
 }
 
 IMPLICIT_TUPLE: Final = {syms.testlist, syms.testlist_star_expr, syms.exprlist}

tests/data/miscellaneous/long_strings_flag_disabled.py

@@ -254,9 +254,7 @@
     + CONCATENATED
     + "using the '+' operator."
 )
-annotated_variable: (
-    Final
-) = "This is a large string that has a type annotation attached to it. A type annotation should NOT stop a long string from being wrapped."
+annotated_variable: Final = "This is a large string that has a type annotation attached to it. A type annotation should NOT stop a long string from being wrapped."
 annotated_variable: Literal[
     "fakse_literal"
 ] = "This is a large string that has a type annotation attached to it. A type annotation should NOT stop a long string from being wrapped."

tests/data/py_310/pep604_union_types_line_breaks.py → tests/data/preview_py_310/pep604_union_types_line_breaks.py

@@ -149,13 +149,11 @@ def f(
 
 
 # remove unnecessary paren
-def foo(i: int) -> None:
-    ...
+def foo(i: int) -> None: ...
 
 
 # this is a syntax error in the type annotation according to mypy, but it's not invalid *python* code, so make sure we don't mess with it and make it so.
-def foo(i: (int,)) -> None:
-    ...
+def foo(i: (int,)) -> None: ...
 
 
 def foo(
@@ -186,5 +184,4 @@ def f(
         None, help="Maximum number of jobs to launch. And some additional text."
     ),
     another_option: bool = False,
-):
-    ...
+): ...