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Fix incremental issue with namespace packages (option 2) #18908

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@hauntsaninja hauntsaninja commented Apr 11, 2025

Fixes #12664

See #18907 which is another possible fix

I'm not sure why this logic is actually needed given that we should record the dependency from import analysis in fastparse... maybe just because it adjusts priority?

Relevant history:

I can't write a good test for this because it requires something in site_packages, but here's a minimal repro:

set -eux
rm -rf repro
mkdir repro
cd repro

SITEPACK=env/site-packages
mkdir -p $SITEPACK

mkdir $SITEPACK/ruamel
mkdir $SITEPACK/ruamel/yaml

printf 'from ruamel.yaml.main import *' > $SITEPACK/ruamel/yaml/__init__.py
printf 'import ruamel.yaml' > $SITEPACK/ruamel/yaml/main.py
printf '' > $SITEPACK/ruamel/yaml/py.typed

printf 'import ruamel.yaml' > a.py
printf 'import a' > main.py

rm -rf .mypy_cache
PYTHONPATH=$SITEPACK mypy main.py
PYTHONPATH=$SITEPACK mypy main.py

Fixes python#12664

See python#18907 which is another possible fix

I'm not sure why this logic is actually needed given that we should
record the dependency from import analysis in fastparse... maybe just
because it adjusts priority?

I can't write a good test for this because it requires something in site_packages, but here's a minimal repro:
```
set -eux
rm -rf repro
mkdir repro
cd repro

SITEPACK=env/site-packages
mkdir -p $SITEPACK

mkdir $SITEPACK/ruamel
mkdir $SITEPACK/ruamel/yaml

printf 'from ruamel.yaml.main import *' > $SITEPACK/ruamel/yaml/__init__.py
printf 'import ruamel.yaml' > $SITEPACK/ruamel/yaml/main.py
printf '' > $SITEPACK/ruamel/yaml/py.typed

printf 'import ruamel.yaml' > a.py
printf 'import a' > main.py

rm -rf .mypy_cache
PYTHONPATH=$SITEPACK mypy main.py
PYTHONPATH=$SITEPACK mypy main.py
```
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According to mypy_primer, this change doesn't affect type check results on a corpus of open source code. ✅

@hauntsaninja hauntsaninja changed the title Fix incremental issue with namespace packages Fix incremental issue with namespace packages (option 2) Apr 11, 2025
hauntsaninja added a commit that referenced this pull request Apr 11, 2025
Fixes #12664

A root cause is there is this stateful `_update_ns_ancestors` thing in
`modulefinder`, so if things get called in the wrong order, you can get
incorrect results.

See also the logic in `all_imported_modules_in_file` where we've fixed
several bugs like this previously, like #13124 and #10937

As a result of (seemingly accidentally) reusing imports across modules,
we can end up in a situation where the namespace gets added as a
dependency to all other modules and so on the cached run we attempt to
find namespace before package, which does not work

I am not sure this `imports` code path is even needed, so I will open an
alternate PR, see #18908.

Relevant history:
- #6582
- #6179

I can't write a good test for this because it requires something in
site_packages, but here's a minimal repro:
```
set -eux
rm -rf repro
mkdir repro
cd repro

SITEPACK=env/site-packages
mkdir -p $SITEPACK

mkdir $SITEPACK/ruamel
mkdir $SITEPACK/ruamel/yaml

printf 'from ruamel.yaml.main import *' > $SITEPACK/ruamel/yaml/__init__.py
printf 'import ruamel.yaml' > $SITEPACK/ruamel/yaml/main.py
printf '' > $SITEPACK/ruamel/yaml/py.typed

printf 'import ruamel.yaml' > a.py
printf 'import a' > main.py

rm -rf .mypy_cache
PYTHONPATH=$SITEPACK mypy main.py
PYTHONPATH=$SITEPACK mypy main.py
```
@hauntsaninja
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Going with #18907 on Ivan's recommendation

@hauntsaninja hauntsaninja deleted the ruamelfix2 branch April 11, 2025 20:02
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Incremental parsing issue with namespace packages
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