Use PEP 604 syntax for TypeStrVisitor (#19179)

Author: cdce8p

mypy/types.py

@@ -3489,8 +3489,9 @@ def visit_literal_type(self, t: LiteralType, /) -> str:
         return f"Literal[{t.value_repr()}]"
 
     def visit_union_type(self, t: UnionType, /) -> str:
-        s = self.list_str(t.items)
-        return f"Union[{s}]"
+        use_or_syntax = self.options.use_or_syntax()
+        s = self.list_str(t.items, use_or_syntax=use_or_syntax)
+        return s if use_or_syntax else f"Union[{s}]"
 
     def visit_partial_type(self, t: PartialType, /) -> str:
         if t.type is None:
@@ -3523,14 +3524,15 @@ def visit_type_alias_type(self, t: TypeAliasType, /) -> str:
     def visit_unpack_type(self, t: UnpackType, /) -> str:
         return f"Unpack[{t.type.accept(self)}]"
 
-    def list_str(self, a: Iterable[Type]) -> str:
+    def list_str(self, a: Iterable[Type], *, use_or_syntax: bool = False) -> str:
         """Convert items of an array to strings (pretty-print types)
         and join the results with commas.
         """
         res = []
         for t in a:
             res.append(t.accept(self))
-        return ", ".join(res)
+        sep = ", " if not use_or_syntax else " | "
+        return sep.join(res)
 
 
 class TrivialSyntheticTypeTranslator(TypeTranslator, SyntheticTypeVisitor[Type]):

test-data/unit/fine-grained.test

@@ -10436,14 +10436,14 @@ D = "y"
 C = str
 D = int
 [out]
-a.py:4: note: Revealed type is "Union[builtins.int, builtins.str]"
+a.py:4: note: Revealed type is "builtins.int | builtins.str"
 ==
 a.py:2: error: Unsupported left operand type for | ("str")
 a.py:3: error: Variable "a.A" is not valid as a type
 a.py:3: note: See https://mypy.readthedocs.io/en/stable/common_issues.html#variables-vs-type-aliases
 a.py:4: note: Revealed type is "A?"
 ==
-a.py:4: note: Revealed type is "Union[builtins.str, builtins.int]"
+a.py:4: note: Revealed type is "builtins.str | builtins.int"
 
 [case testUnionOfSimilarCallablesCrash]
 import b

test-data/unit/pythoneval.test

@@ -1632,8 +1632,8 @@ def foo(x: T) -> T:
     return x
 [out]
 _testTypeAliasWithNewStyleUnion.py:5: note: Revealed type is "typing._SpecialForm"
-_testTypeAliasWithNewStyleUnion.py:25: note: Revealed type is "Union[type[builtins.int], builtins.str]"
-_testTypeAliasWithNewStyleUnion.py:28: note: Revealed type is "Union[type[builtins.int], builtins.str]"
+_testTypeAliasWithNewStyleUnion.py:25: note: Revealed type is "type[builtins.int] | builtins.str"
+_testTypeAliasWithNewStyleUnion.py:28: note: Revealed type is "type[builtins.int] | builtins.str"
 
 [case testTypeAliasWithNewStyleUnionInStub]
 import m
@@ -1711,7 +1711,7 @@ reveal_type(e.foo)
 reveal_type(E.Y.foo)
 [out]
 _testEnumNameWorkCorrectlyOn311.py:11: note: Revealed type is "builtins.str"
-_testEnumNameWorkCorrectlyOn311.py:12: note: Revealed type is "Union[Literal[1]?, Literal[2]?]"
+_testEnumNameWorkCorrectlyOn311.py:12: note: Revealed type is "Literal[1]? | Literal[2]?"
 _testEnumNameWorkCorrectlyOn311.py:13: note: Revealed type is "Literal['X']?"
 _testEnumNameWorkCorrectlyOn311.py:14: note: Revealed type is "builtins.int"
 _testEnumNameWorkCorrectlyOn311.py:15: note: Revealed type is "builtins.int"
@@ -1780,9 +1780,9 @@ WrongEllipsis = tuple[float, float, ...] | str  # Error
 
 reveal_type(tuple[int, str]((1, "x")))
 [out]
-_testTupleWithDifferentArgsPy310.py:15: note: Revealed type is "Union[builtins.str, tuple[builtins.float, builtins.float, builtins.str]]"
-_testTupleWithDifferentArgsPy310.py:16: note: Revealed type is "Union[tuple[builtins.float], builtins.str]"
-_testTupleWithDifferentArgsPy310.py:17: note: Revealed type is "Union[builtins.tuple[builtins.float, ...], builtins.str]"
+_testTupleWithDifferentArgsPy310.py:15: note: Revealed type is "builtins.str | tuple[builtins.float, builtins.float, builtins.str]"
+_testTupleWithDifferentArgsPy310.py:16: note: Revealed type is "tuple[builtins.float] | builtins.str"
+_testTupleWithDifferentArgsPy310.py:17: note: Revealed type is "builtins.tuple[builtins.float, ...] | builtins.str"
 _testTupleWithDifferentArgsPy310.py:18: note: Revealed type is "tuple[builtins.float, builtins.str]"
 _testTupleWithDifferentArgsPy310.py:19: note: Revealed type is "builtins.tuple[builtins.float, ...]"
 _testTupleWithDifferentArgsPy310.py:20: note: Revealed type is "builtins.list[tuple[builtins.int, builtins.str]]"