Properle space complex expressions in default values of typed arguments

Fixes #60

README.md

@@ -311,6 +311,9 @@ More details can be found in [CONTRIBUTING](CONTRIBUTING.md).
 * automatic detection of deprecated Python 2 forms of print statements
   and exec statements in the formatted file (#49)
 
+* use proper spaces for complex expressions in default values of typed
+  function arguments (#60)
+
 * only return exit code 1 when --check is used (#50)
 
 * don't remove single trailing commas from square bracket indexing

black.py

@@ -419,7 +419,7 @@ def any_open_brackets(self) -> bool:
         """Returns True if there is an yet unmatched open bracket on the line."""
         return bool(self.bracket_match)
 
-    def max_priority(self, exclude: Iterable[LeafID] =()) -> int:
+    def max_priority(self, exclude: Iterable[LeafID] = ()) -> int:
         """Returns the highest priority of a delimiter found on the line.
 
         Values are consistent with what `is_delimiter()` returns.
@@ -885,14 +885,17 @@ def whitespace(leaf: Leaf) -> str:  # noqa C901
             return SPACE if prevp.type == token.COMMA else NO
 
         if prevp.type == token.EQUAL:
-            if prevp.parent and prevp.parent.type in {
-                syms.arglist,
-                syms.argument,
-                syms.parameters,
-                syms.typedargslist,
-                syms.varargslist,
-            }:
-                return NO
+            if prevp.parent:
+                if prevp.parent.type in {
+                    syms.arglist, syms.argument, syms.parameters, syms.varargslist
+                }:
+                    return NO
+
+                elif prevp.parent.type == syms.typedargslist:
+                    # A bit hacky: if the equal sign has whitespace, it means we
+                    # previously found it's a typed argument.  So, we're using
+                    # that, too.
+                    return prevp.prefix
 
         elif prevp.type == token.DOUBLESTAR:
             if prevp.parent and prevp.parent.type in {
@@ -938,7 +941,7 @@ def whitespace(leaf: Leaf) -> str:  # noqa C901
         if not prev or prev.type != token.COMMA:
             return NO
 
-    if p.type == syms.varargslist:
+    elif p.type == syms.varargslist:
         # lambdas
         if t == token.RPAR:
             return NO

tests/function.py

@@ -31,6 +31,7 @@ def function_signature_stress_test(number:int,no_annotation=None,text:str="defau
 def spaces(a=1, b=(), c=[], d={}, e=True, f=-1, g=1 if False else 2, h="", i=r''):
  offset = attr.ib(default=attr.Factory( lambda: _r.uniform(10000, 200000)))
  assert task._cancel_stack[:len(old_stack)] == old_stack
+def spaces_types(a: int = 1, b: tuple = (), c: list = [], d: dict = {}, e: bool = True, f: int = -1, g: int = 1 if False else 2, h: str = "", i: str = r''): ...
 def spaces2(result= _core.Value(None)):
  ...
 def example(session):
@@ -123,6 +124,20 @@ def spaces(a=1, b=(), c=[], d={}, e=True, f=-1, g=1 if False else 2, h="", i=r''
     assert task._cancel_stack[:len(old_stack)] == old_stack
 
 
+def spaces_types(
+    a: int = 1,
+    b: tuple = (),
+    c: list = [],
+    d: dict = {},
+    e: bool = True,
+    f: int = -1,
+    g: int = 1 if False else 2,
+    h: str = "",
+    i: str = r'',
+):
+    ...
+
+
 def spaces2(result=_core.Value(None)):
     ...