Fix crash on class using itself as a type variable (#22219)

Fixes #21549

Fix is straightforward. New syntax test added just in case for
completeness.

Author: ilevkivskyi

mypy/semanal.py

@@ -2463,7 +2463,10 @@ def analyze_unbound_tvar_impl(
         assert not is_unpacked or not is_typealias_param, "Mutually exclusive conditions"
         sym = self.lookup_qualified(t.name, t)
         if sym and isinstance(sym.node, PlaceholderNode):
-            self.record_incomplete_ref()
+            if self.final_iteration:
+                self.cannot_resolve_name(t.name, "name", t)
+            else:
+                self.record_incomplete_ref()
         if not is_unpacked and sym and isinstance(sym.node, ParamSpecExpr):
             if sym.fullname and not self.tvar_scope.allow_binding(sym.fullname):
                 # It's bound by our type variable scope

test-data/unit/check-newsemanal.test

@@ -3316,3 +3316,20 @@ class D: ...
 
 x: A
 reveal_type(x)  # N: Revealed type is "builtins.str | __main__.D"
+
+[case testBrokenClassUsingItselfAsTypeVarNoCrash]
+from typing import Generic
+
+class C(Generic[C]):  # E: Free type variable expected in Generic[...] \
+                      # E: Cannot resolve name "C" (possible cyclic definition)
+    pass
+
+class D(Generic[E]):  # E: Free type variable expected in Generic[...] \
+                      # E: Cannot resolve name "E" (possible cyclic definition)
+    pass
+
+class E(Generic[DD]):  # E: Free type variable expected in Generic[...] \
+                       # E: Cannot resolve name "DD" (possible cyclic definition)
+    pass
+
+DD = D  # E: Cannot resolve name "DD" (possible cyclic definition)

test-data/unit/check-python312.test

@@ -2439,6 +2439,12 @@ def test[*Us](*xs: *Us) -> None:
     reveal_type(print_args(2, *xs, 4))  # N: Revealed type is "__main__.C[[Literal[2]?, *args: *tuple[*Us, Literal[4]?]], tuple[Literal[2]?, *Us, Literal[4]?]]"
 [builtins fixtures/paramspec.pyi]
 
+[case testBrokenClassUsingItselfAsTypeVarNoCrashNewSyntax]
+class C[C]:
+    x: C
+c: C[int]
+reveal_type(c.x)  # N: Revealed type is "builtins.int"
+
 [case testDoubleTypeVarTupleNoCrashNewSyntax]
 class C[*T, *U](T, U):  # E: Can only use one TypeVarTuple in a class definition \
                         # E: TypeVarTuple "T" is only valid with an unpack \