Improve positional/named pairing

Author: sterliakov

mypy/join.py

@@ -716,6 +716,7 @@ def combine_parameters_with(
         kwarg = arg_transformer(s_kw.typ, t_kw.typ)
         if isinstance(get_proper_type(kwarg), UninhabitedType):
             kwarg = None
+    spent_names: set[str] = set()
     for s_kind, s_a in zip(s.arg_kinds, s.formal_arguments(include_star_args=True)):
         if vararg is not None and s_kind == ArgKind.ARG_STAR:
             args_meet.append(vararg)
@@ -731,17 +732,30 @@ def combine_parameters_with(
             continue
         if s_kind.is_star():
             continue
-        t_a = t.argument_by_position(s_a.pos) or t.argument_by_name(s_a.name)
-        if t_a is None:
+
+        candidates = [t.argument_by_position(s_a.pos)]
+        if s_a.name is not None and s_a.name not in spent_names:
+            candidates.append(t.argument_by_name(s_a.name))
+        candidates = [c for c in candidates if c is not None]
+        if not candidates:
             if s_a.required:
                 return None
             continue
-        typ = arg_transformer(s_a.typ, t_a.typ)
-        if not allow_uninhabited and isinstance(get_proper_type(typ), UninhabitedType):
-            return None
+
+        for t_a in candidates:
+            typ = arg_transformer(s_a.typ, t_a.typ)
+            if not isinstance(get_proper_type(typ), UninhabitedType):
+                break
+        else:
+            if not s_a.required:
+                continue
+            if not allow_uninhabited:
+                return None
+        if t_a.name is not None:
+            spent_names.add(t_a.name)
         args_meet.append(typ)
         arg_names.append(s_a.name if s_a.name == t_a.name else None)
-        kinds = [ArgKind.ARG_POS, ArgKind.ARG_OPT, ArgKind.ARG_NAMED, ArgKind.ARG_NAMED_OPT]
+        kinds = [ArgKind.ARG_OPT, ArgKind.ARG_POS, ArgKind.ARG_NAMED_OPT, ArgKind.ARG_NAMED]
         if s_a.pos != t_a.pos or s_a.pos is None or t_a.pos is None:
             kinds = [k for k in kinds if not k.is_positional()]
         if s_a.name != t_a.name or s_a.name is None or t_a.name is None:

test-data/unit/check-functions.test

@@ -3712,3 +3712,27 @@ reveal_type(join(base, bad2))  # E: Value of type variable "C" of "join" cannot
 reveal_type(join(base, bad3))  # E: Value of type variable "C" of "join" cannot be "function" \
                                # N: Revealed type is "builtins.function"
 [builtins fixtures/tuple.pyi]
+
+[case testCallableJoin5]
+from typing import Callable, TypeVar
+
+C = TypeVar("C", bound=Callable[..., None])
+
+def join(t: C, val: C) -> C:
+    pass
+
+def less1(code, lang, style=None): ...
+def more1(code, lang, suffix="", style=None): ...
+reveal_type(join(less1, more1))  # N: Revealed type is "def (code: Any, lang: Any, Any =) -> Any"
+reveal_type(join(more1, less1))  # N: Revealed type is "def (code: Any, lang: Any, Any =) -> Any"
+
+def less2(code, lang, style: int = 0): ...
+def more2(code, lang, suffix: str = "", style: int = 0): ...
+reveal_type(join(less2, more2))  # N: Revealed type is "def (code: Any, lang: Any, *, style: builtins.int =) -> Any"
+reveal_type(join(more2, less2))  # N: Revealed type is "def (code: Any, lang: Any, *, style: builtins.int =) -> Any"
+
+def less3(code, lang, style: int = 0): ...
+def more3(code, lang, suffix: int = 0, style: str = ""): ...
+reveal_type(join(less3, more3))  # N: Revealed type is "def (code: Any, lang: Any, builtins.int =) -> Any"
+reveal_type(join(more3, less3))  # N: Revealed type is "def (code: Any, lang: Any, builtins.int =) -> Any"
+[builtins fixtures/tuple.pyi]