stubtest: check Final variables with literal values against runtime (#20858)

Vikash-Kumar-23 · brianschubert · hauntsaninja · web-flow · commit b972d9a7f0a8 · 2026-02-22T23:28:29.000-08:00
Currently, stubtest does not detect discrepancies when a stub uses Final = <value> but the runtime has a different value. While it correctly handles Literal[...] mismatches, it was previously silent on Final assignments. This PR extends the variable verification logic in stubtest to ensure assigned Final values in stubs are compared against the actual runtime value. Fixes #20857 --------- Co-authored-by: Brian Schubert <brianm.schubert@gmail.com> Co-authored-by: Shantanu <12621235+hauntsaninja@users.noreply.github.com>
diff --git a/mypy/stubtest.py b/mypy/stubtest.py
@@ -1323,6 +1323,14 @@ def verify_var(
                 stub,
                 runtime,
             )
+    elif stub.final_value is not None and stub.final_value != runtime:
+        yield Error(
+            object_path,
+            "is inconsistent, stub value for Final var differs from runtime value",
+            stub,
+            runtime,
+            stub_desc=repr(stub.final_value),
+        )
 
 
 @verify.register(nodes.OverloadedFuncDef)
diff --git a/mypy/test/teststubtest.py b/mypy/test/teststubtest.py
@@ -1171,6 +1171,22 @@ def read_write_attr(self, val): self._val = val
             """,
             error=None,
         )
+        yield Case(
+            stub="""
+            from typing import Final
+            X_FINAL: Final = 2
+            """,
+            runtime="X_FINAL = 1",
+            error="X_FINAL",
+        )
+        yield Case(
+            stub="""
+            from typing import Final
+            X_FINAL_OK: Final = 1
+            """,
+            runtime="X_FINAL_OK = 1",
+            error=None,
+        )
 
     @collect_cases
     def test_type_alias(self) -> Iterator[Case]:
