Fix crash on unnormalized tuples in deferred type alias

mypy/semanal.py

@@ -5904,7 +5904,9 @@ def visit_type_alias_stmt(self, s: TypeAliasStmt) -> None:
                 python_3_12_type_alias=True,
             )
             alias_node.default_depends = default_depends
-            s.alias_node = alias_node
+            if s.alias_node is None:
+                # If there is an existing node, it will be modified in-place.
+                s.alias_node = alias_node
 
             updated = False
             if (
@@ -6329,9 +6331,11 @@ def analyze_type_application(self, expr: IndexExpr) -> None:
         if types is None:
             return
         base = expr.base
-        expr.analyzed = TypeApplication(base, types)
-        expr.analyzed.line = expr.line
-        expr.analyzed.column = expr.column
+        if not isinstance(expr.analyzed, TypeAliasExpr):
+            # Do not re-point r.h.s. of a type alias, it is all set.
+            expr.analyzed = TypeApplication(base, types)
+            expr.analyzed.line = expr.line
+            expr.analyzed.column = expr.column
 
         if isinstance(base, RefExpr) and base.fullname == "librt.vecs.vec":
             # Apply restrictions specific to vec

test-data/unit/check-python312.test

@@ -2401,3 +2401,14 @@ reveal_type(baz(objs))  # N: Revealed type is "builtins.list[__main__.B | __main
 reveal_type(baz(objs_a))  # N: Revealed type is "builtins.list[__main__.B | __main__.C]"
 [builtins fixtures/tuple.pyi]
 [typing fixtures/typing-full.pyi]
+
+[case testDeferredNestedTupleAliasNewSyntax]
+type Inner = tuple[int, str]
+type Outer = tuple[bool, *Inner]
+
+class K(Base):
+    q: list[Outer] = list()
+
+class Base: ...
+reveal_type(K.q)  # N: Revealed type is "builtins.list[tuple[builtins.bool, builtins.int, builtins.str]]"
+[builtins fixtures/tuple.pyi]

test-data/unit/check-typevar-tuple.test

@@ -3232,3 +3232,16 @@ def foo(x, *args):
 def test(f: Callable[[object], object]) -> None: ...
 test(foo)  # E: Argument 1 to "test" has incompatible type overloaded function; expected "Callable[[object], object]"
 [builtins fixtures/tuple.pyi]
+
+[case testDeferredNestedTupleAlias]
+from typing import Unpack
+
+Inner = tuple[int, str]
+Outer = tuple[bool, Unpack[Inner]]
+
+class K(Base):
+    q: list[Outer] = list()
+
+class Base: ...
+reveal_type(K.q)  # N: Revealed type is "builtins.list[tuple[builtins.bool, builtins.int, builtins.str]]"
+[builtins fixtures/tuple.pyi]