Fix staleness on changed follow imports options#20773
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ilevkivskyi merged 2 commits intoFeb 12, 2026
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Not a full review, but I measured performance on a huge internal codebase, and I couldn't see any regression. So performance impact looks minimal. |
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According to mypy_primer, this change doesn't affect type check results on a corpus of open source code. ✅ |
JukkaL
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Feb 12, 2026
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Thanks for fixing this old but quite annoying issue! The approach looks good.
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May 8, 2026
In mypy 1.19, re-running `mypy` with a saved cache and a file containing
an inline configuration comment (e.g. `# mypy:
disable-error-code="import-not-found"`) acted 'correctly', i.e. the same
behaviour on the first run vs subsequent runs.
In mypy 1.20 and newer, this is no longer the case. Running `mypy` with
a pre-existing cache fails to respect inline configuration comments for
stale modules, leading to confusing false-positive errors that can be
hard to debug.
This PR introduces a failing test as at current master, and then a fix
for the issue. I believe this is the right fix, though happy to change
as suggested by the maintainers, I'm not nearly as familiar with mypy
internals.
Notably also from L2376-80, it's by design that file-level comments
aren't cached:
```python
# Note that the options we store in the cache are the options as
# specified by the command line/config file and *don't* reflect
# updates made by inline config directives in the file. This is
# important, or otherwise the options would never match when
# verifying the cache.
```
I believe that this regression was introduced in #20773
A
Co-authored-by: Adam Turner <turner@hudson-trading.com>
JukkaL
pushed a commit
that referenced
this pull request
May 10, 2026
In mypy 1.19, re-running `mypy` with a saved cache and a file containing
an inline configuration comment (e.g. `# mypy:
disable-error-code="import-not-found"`) acted 'correctly', i.e. the same
behaviour on the first run vs subsequent runs.
In mypy 1.20 and newer, this is no longer the case. Running `mypy` with
a pre-existing cache fails to respect inline configuration comments for
stale modules, leading to confusing false-positive errors that can be
hard to debug.
This PR introduces a failing test as at current master, and then a fix
for the issue. I believe this is the right fix, though happy to change
as suggested by the maintainers, I'm not nearly as familiar with mypy
internals.
Notably also from L2376-80, it's by design that file-level comments
aren't cached:
```python
# Note that the options we store in the cache are the options as
# specified by the command line/config file and *don't* reflect
# updates made by inline config directives in the file. This is
# important, or otherwise the options would never match when
# verifying the cache.
```
I believe that this regression was introduced in #20773
A
Co-authored-by: Adam Turner <turner@hudson-trading.com>
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This fixes the coarse grained part of #7777. I do not change semantics for daemon for two reasons:
Some notes:
follow_imports = skip <-> normal), or there is no effect on the caller/importer (e.g. whenfollow_imports = normal <-> silent).CacheMetabut good new is I have an idea how to get rid of another entry I added in one of recent PRs. Essentially I will need to record early (import) errors anyway to send to parallel workers after we switch to parallel parsing, and if we do this we won't need theimports_ignoredentry.