From 6094fc46d12904eaec42c3e622645551b549e7e5 Mon Sep 17 00:00:00 2001
From: Charlie Denton <charlie@meshy.co.uk>
Date: Sun, 12 Mar 2023 23:25:29 +0000
Subject: [PATCH] Prove possibly-undefined errors disappear

This test fails with the error:

    AssertionError: Command 3 (dmypy check -- bar.py) did not give expected output
    --- Captured stderr call ---
    Expected:
      bar.py:4: error: Name "a" may be undefined  [possibly-undefined] (diff)
      == Return code: 1                             (diff)
    Actual:
      (empty)

This test illustrates that possibly-undefined errors currently disappear
in the same way that 'Unused "type: ignore"' errors do as described in #9655.

Ref: https://github.com/python/mypy/issues/9655
---
 test-data/unit/daemon.test | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/test-data/unit/daemon.test b/test-data/unit/daemon.test
index dcc7ec86309f0..d4ec103db8818 100644
--- a/test-data/unit/daemon.test
+++ b/test-data/unit/daemon.test
@@ -556,3 +556,22 @@ bar.py:2: error: "type: ignore" comment without error code  [ignore-without-code
 [file bar.py]
 from foo.empty import *
 a = 1  # type: ignore
+
+[case testPossiblyUndefinedVarsPreservedAfterUpdate]
+-- Regression test for https://github.com/python/mypy/issues/9655
+$ dmypy start -- --enable-error-code possibly-undefined --no-error-summary
+Daemon started
+$ dmypy check -- bar.py
+bar.py:4: error: Name "a" may be undefined  [possibly-undefined]
+== Return code: 1
+$ dmypy check -- bar.py
+bar.py:4: error: Name "a" may be undefined  [possibly-undefined]
+== Return code: 1
+
+[file foo/__init__.py]
+[file foo/empty.py]
+[file bar.py]
+from foo.empty import *
+if False:
+    a = 1
+a