Make is_recursive and has_recursive_types() more consistent (#14147)

While working on another PR I noticed that current behavior of
`has_recursive_types()` is inconsistent, it returns `False` is there is
a recursive type nested as an argument to a generic non-recursive alias.
I wasn't able to find any situation where this actually matters, but I
think it is better if this function behaves consistently.

Author: ilevkivskyi

mypy/test/testtypes.py

@@ -31,6 +31,7 @@
     UninhabitedType,
     UnionType,
     get_proper_type,
+    has_recursive_types,
 )
 
 
@@ -157,6 +158,12 @@ def test_type_alias_expand_all(self) -> None:
             [self.fx.a, self.fx.a], Instance(self.fx.std_tuplei, [self.fx.a])
         )
 
+    def test_recursive_nested_in_non_recursive(self) -> None:
+        A, _ = self.fx.def_alias_1(self.fx.a)
+        NA = self.fx.non_rec_alias(Instance(self.fx.gi, [UnboundType("T")]), ["T"], [A])
+        assert not NA.is_recursive
+        assert has_recursive_types(NA)
+
     def test_indirection_no_infinite_recursion(self) -> None:
         A, _ = self.fx.def_alias_1(self.fx.a)
         visitor = TypeIndirectionVisitor()

mypy/test/typefixture.py

@@ -339,9 +339,13 @@ def def_alias_2(self, base: Instance) -> tuple[TypeAliasType, Type]:
         A.alias = AN
         return A, target
 
-    def non_rec_alias(self, target: Type) -> TypeAliasType:
-        AN = TypeAlias(target, "__main__.A", -1, -1)
-        return TypeAliasType(AN, [])
+    def non_rec_alias(
+        self, target: Type, alias_tvars: list[str] | None = None, args: list[Type] | None = None
+    ) -> TypeAliasType:
+        AN = TypeAlias(target, "__main__.A", -1, -1, alias_tvars=alias_tvars)
+        if args is None:
+            args = []
+        return TypeAliasType(AN, args)
 
 
 class InterfaceTypeFixture(TypeFixture):

mypy/types.py

@@ -278,30 +278,42 @@ def _expand_once(self) -> Type:
             self.alias.target, self.alias.alias_tvars, self.args, self.line, self.column
         )
 
-    def _partial_expansion(self) -> tuple[ProperType, bool]:
+    def _partial_expansion(self, nothing_args: bool = False) -> tuple[ProperType, bool]:
         # Private method mostly for debugging and testing.
         unroller = UnrollAliasVisitor(set())
-        unrolled = self.accept(unroller)
+        if nothing_args:
+            alias = self.copy_modified(args=[UninhabitedType()] * len(self.args))
+        else:
+            alias = self
+        unrolled = alias.accept(unroller)
         assert isinstance(unrolled, ProperType)
         return unrolled, unroller.recursed
 
-    def expand_all_if_possible(self) -> ProperType | None:
+    def expand_all_if_possible(self, nothing_args: bool = False) -> ProperType | None:
         """Attempt a full expansion of the type alias (including nested aliases).
 
         If the expansion is not possible, i.e. the alias is (mutually-)recursive,
-        return None.
+        return None. If nothing_args is True, replace all type arguments with an
+        UninhabitedType() (used to detect recursively defined aliases).
         """
-        unrolled, recursed = self._partial_expansion()
+        unrolled, recursed = self._partial_expansion(nothing_args=nothing_args)
         if recursed:
             return None
         return unrolled
 
     @property
     def is_recursive(self) -> bool:
+        """Whether this type alias is recursive.
+
+        Note this doesn't check generic alias arguments, but only if this alias
+        *definition* is recursive. The property value thus can be cached on the
+        underlying TypeAlias node. If you want to include all nested types, use
+        has_recursive_types() function.
+        """
         assert self.alias is not None, "Unfixed type alias"
         is_recursive = self.alias._is_recursive
         if is_recursive is None:
-            is_recursive = self.expand_all_if_possible() is None
+            is_recursive = self.expand_all_if_possible(nothing_args=True) is None
             # We cache the value on the underlying TypeAlias node as an optimization,
             # since the value is the same for all instances of the same alias.
             self.alias._is_recursive = is_recursive
@@ -3259,7 +3271,7 @@ def __init__(self) -> None:
         super().__init__(any)
 
     def visit_type_alias_type(self, t: TypeAliasType) -> bool:
-        return t.is_recursive
+        return t.is_recursive or self.query_types(t.args)
 
 
 def has_recursive_types(typ: Type) -> bool: