Fix crash on partial type inference within a lambda

mypy/checker.py

@@ -7031,6 +7031,9 @@ def is_valid_inferred_type(typ: Type, is_lvalue_final: bool = False) -> bool:
         return is_lvalue_final
     elif isinstance(proper_type, UninhabitedType):
         return False
+    elif mypy.checkexpr.has_erased_component(typ):
+        # This can happen inside a lambda.
+        return False
     return not typ.accept(NothingSeeker())
 
 

test-data/unit/check-incremental.test

@@ -6286,3 +6286,29 @@ class C: ...
 [out]
 [out2]
 [out3]
+
+[case testNoCrashOnPartialLambdaInference]
+import m
+[file m.py]
+from typing import TypeVar, Callable
+
+V = TypeVar("V")
+def apply(val: V, func: Callable[[V], None]) -> None:
+    return func(val)
+
+xs = []
+apply(0, lambda a: xs.append(a))
+[file m.py.2]
+from typing import TypeVar, Callable
+
+V = TypeVar("V")
+def apply(val: V, func: Callable[[V], None]) -> None:
+    return func(val)
+
+xs = []
+apply(0, lambda a: xs.append(a))
+reveal_type(xs)
+[builtins fixtures/list.pyi]
+[out]
+[out2]
+tmp/m.py:9: note: Revealed type is "builtins.list[builtins.int]"