From ceb4d7fd687ddbb94dc6c62fb6a2c46c383da54f Mon Sep 17 00:00:00 2001
From: Ivan Levkivskyi <levkivskyi@gmail.com>
Date: Thu, 15 Jun 2023 21:32:37 +0100
Subject: [PATCH] Fix re-added file with errors in mypy daemon (#15440)

Fixes #5343
Fixes #12249

This can potentially slow down runs in situations where multiple
unchanged files are re-added to source list. Potentially, we can track
whether modules had errors permanently (not just from previous run), and
then only re-check those unchanged re-added files that had errors
before. I am not sure if this is important.
---
 mypy/dmypy_server.py             | 15 +++++++++++++++
 test-data/unit/daemon.test       | 22 ++++++++++++++++++++++
 test-data/unit/fine-grained.test | 21 +++++++++++++++++++++
 3 files changed, 58 insertions(+)

diff --git a/mypy/dmypy_server.py b/mypy/dmypy_server.py
index 631aab4ccbc8..54544f4c01ce 100644
--- a/mypy/dmypy_server.py
+++ b/mypy/dmypy_server.py
@@ -857,6 +857,21 @@ def _find_changed(
             assert path
             removed.append((source.module, path))
 
+        # Always add modules that were (re-)added, since they may be detected as not changed by
+        # fswatcher (if they were actually not changed), but they may still need to be checked
+        # in case they had errors before they were deleted from sources on previous runs.
+        previous_modules = {source.module for source in self.previous_sources}
+        changed_set = set(changed)
+        changed.extend(
+            [
+                (source.module, source.path)
+                for source in sources
+                if source.path
+                and source.module not in previous_modules
+                and (source.module, source.path) not in changed_set
+            ]
+        )
+
         # Find anything that has had its module path change because of added or removed __init__s
         last = {s.path: s.module for s in self.previous_sources}
         for s in sources:
diff --git a/test-data/unit/daemon.test b/test-data/unit/daemon.test
index 424fc6d2b167..1fae1514111c 100644
--- a/test-data/unit/daemon.test
+++ b/test-data/unit/daemon.test
@@ -62,6 +62,28 @@ Daemon started
 \[mypy]
 files = ./foo.py
 
+[case testDaemonRunMultipleStrict]
+$ dmypy run -- foo.py --strict --follow-imports=error
+Daemon started
+foo.py:1: error: Function is missing a return type annotation
+foo.py:1: note: Use "-> None" if function does not return a value
+Found 1 error in 1 file (checked 1 source file)
+== Return code: 1
+$ dmypy run -- bar.py --strict --follow-imports=error
+bar.py:1: error: Function is missing a return type annotation
+bar.py:1: note: Use "-> None" if function does not return a value
+Found 1 error in 1 file (checked 1 source file)
+== Return code: 1
+$ dmypy run -- foo.py --strict --follow-imports=error
+foo.py:1: error: Function is missing a return type annotation
+foo.py:1: note: Use "-> None" if function does not return a value
+Found 1 error in 1 file (checked 1 source file)
+== Return code: 1
+[file foo.py]
+def f(): pass
+[file bar.py]
+def f(): pass
+
 [case testDaemonRunRestart]
 $ dmypy run -- foo.py --follow-imports=error
 Daemon started
diff --git a/test-data/unit/fine-grained.test b/test-data/unit/fine-grained.test
index 88a11be31f34..a0d7d302fd08 100644
--- a/test-data/unit/fine-grained.test
+++ b/test-data/unit/fine-grained.test
@@ -10340,3 +10340,24 @@ reveal_type(x)
 [out]
 ==
 a.py:3: note: Revealed type is "Union[def (x: builtins.int) -> builtins.int, def (*x: builtins.int) -> builtins.int]"
+
+[case testErrorInReAddedModule]
+# flags: --disallow-untyped-defs --follow-imports=error
+# cmd: mypy a.py
+# cmd2: mypy b.py
+# cmd3: mypy a.py
+
+[file a.py]
+def f(): pass
+[file b.py]
+def f(): pass
+[file unrelated.txt.3]
+[out]
+a.py:1: error: Function is missing a return type annotation
+a.py:1: note: Use "-> None" if function does not return a value
+==
+b.py:1: error: Function is missing a return type annotation
+b.py:1: note: Use "-> None" if function does not return a value
+==
+a.py:1: error: Function is missing a return type annotation
+a.py:1: note: Use "-> None" if function does not return a value