Respect force-union-syntax flag in error hint (#20165)

The error hint for `Need type annotations for ...` should defer to
`options.use_union_syntax` when evaluating if `Union` or `|` should be
used. This will also make it easier to eventually upgrade all tests to
use the PEP 604 syntax.

Author: cdce8p

mypy/checker.py

@@ -4449,7 +4449,7 @@ def infer_variable_type(
             # partial type which will be made more specific later. A partial type
             # gets generated in assignment like 'x = []' where item type is not known.
             if name.name != "_" and not self.infer_partial_type(name, lvalue, init_type):
-                self.msg.need_annotation_for_var(name, context, self.options.python_version)
+                self.msg.need_annotation_for_var(name, context, self.options)
                 self.set_inference_error_fallback_type(name, lvalue, init_type)
         elif (
             isinstance(lvalue, MemberExpr)
@@ -4459,7 +4459,7 @@ def infer_variable_type(
             and not is_same_type(self.inferred_attribute_types[lvalue.def_var], init_type)
         ):
             # Multiple, inconsistent types inferred for an attribute.
-            self.msg.need_annotation_for_var(name, context, self.options.python_version)
+            self.msg.need_annotation_for_var(name, context, self.options)
             name.type = AnyType(TypeOfAny.from_error)
         else:
             # Infer type of the target.
@@ -4656,9 +4656,7 @@ def check_simple_assignment(
                     rvalue, type_context=lvalue_type, always_allow_any=always_allow_any
                 )
                 if not is_valid_inferred_type(rvalue_type, self.options) and inferred is not None:
-                    self.msg.need_annotation_for_var(
-                        inferred, context, self.options.python_version
-                    )
+                    self.msg.need_annotation_for_var(inferred, context, self.options)
                     rvalue_type = rvalue_type.accept(SetNothingToAny())
 
             if (
@@ -7680,7 +7678,7 @@ def enter_partial_types(
                     var.type = NoneType()
                 else:
                     if var not in self.partial_reported and not permissive:
-                        self.msg.need_annotation_for_var(var, context, self.options.python_version)
+                        self.msg.need_annotation_for_var(var, context, self.options)
                         self.partial_reported.add(var)
                     if var.type:
                         fixed = fixup_partial_type(var.type)
@@ -7707,9 +7705,7 @@ def handle_partial_var_type(
                 if in_scope:
                     context = partial_types[node]
                     if is_local or not self.options.allow_untyped_globals:
-                        self.msg.need_annotation_for_var(
-                            node, context, self.options.python_version
-                        )
+                        self.msg.need_annotation_for_var(node, context, self.options)
                         self.partial_reported.add(node)
                 else:
                     # Defer the node -- we might get a better type in the outer scope

mypy/messages.py

@@ -1803,18 +1803,17 @@ def unimported_type_becomes_any(self, prefix: str, typ: Type, ctx: Context) -> N
         )
 
     def need_annotation_for_var(
-        self, node: SymbolNode, context: Context, python_version: tuple[int, int] | None = None
+        self, node: SymbolNode, context: Context, options: Options | None = None
     ) -> None:
         hint = ""
-        pep604_supported = not python_version or python_version >= (3, 10)
         # type to recommend the user adds
         recommended_type = None
         # Only gives hint if it's a variable declaration and the partial type is a builtin type
-        if python_version and isinstance(node, Var) and isinstance(node.type, PartialType):
+        if options and isinstance(node, Var) and isinstance(node.type, PartialType):
             type_dec = "<type>"
             if not node.type.type:
                 # partial None
-                if pep604_supported:
+                if options.use_or_syntax():
                     recommended_type = f"{type_dec} | None"
                 else:
                     recommended_type = f"Optional[{type_dec}]"

mypy/suggestions.py

@@ -890,7 +890,8 @@ def visit_typeddict_type(self, t: TypedDictType) -> str:
 
     def visit_union_type(self, t: UnionType) -> str:
         if len(t.items) == 2 and is_overlapping_none(t):
-            return f"Optional[{remove_optional(t).accept(self)}]"
+            s = remove_optional(t).accept(self)
+            return f"{s} | None" if self.options.use_or_syntax() else f"Optional[{s}]"
         else:
             return super().visit_union_type(t)
 

mypy/test/testcheck.py

@@ -140,7 +140,7 @@ def run_case_once(
             options.hide_error_codes = False
         if "abstract" not in testcase.file:
             options.allow_empty_bodies = not testcase.name.endswith("_no_empty")
-        if "union-error" not in testcase.file:
+        if "union-error" not in testcase.file and "Pep604" not in testcase.name:
             options.force_union_syntax = True
 
         if incremental_step and options.incremental:

test-data/unit/check-inference.test

@@ -3548,7 +3548,7 @@ if x:
 [builtins fixtures/dict.pyi]
 
 [case testSuggestPep604AnnotationForPartialNone]
-# flags: --local-partial-types --python-version 3.10
+# flags: --local-partial-types --python-version 3.10 --no-force-union-syntax
 x = None # E: Need type annotation for "x" (hint: "x: <type> | None = ...")
 
 [case testTupleContextFromIterable]