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[another approach] Prevent crash with Unpack of a fixed tuple in PEP695 type alias#18452

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sterliakov wants to merge 3 commits into
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[another approach] Prevent crash with Unpack of a fixed tuple in PEP695 type alias#18452
sterliakov wants to merge 3 commits into
python:masterfrom
sterliakov:bugfix/st-type-alias-analyzed

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Fixes #18309.

This PR offers an alternative approach following #18451. Changes here align the processing of TypeAlias and PEP695 type statement closer, introducing the same "backlinks" to typealias from the RHS. Since those constructs are very similar in semantics, this might be more reasonable than my previous suggestion.

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Diff from mypy_primer, showing the effect of this PR on open source code:

schemathesis (https://github.com/schemathesis/schemathesis)
-   File "/tmp/mypy_primer/old_mypy/venv/bin/mypy", line 8, in <module>
+   File "/tmp/mypy_primer/new_mypy/venv/bin/mypy", line 8, in <module>
-   File "/tmp/mypy_primer/old_mypy/venv/lib/python3.12/site-packages/mypy/__main__.py", line 15, in console_entry
+   File "/tmp/mypy_primer/new_mypy/venv/lib/python3.12/site-packages/mypy/__main__.py", line 15, in console_entry
-   File "/tmp/mypy_primer/old_mypy/venv/lib/python3.12/site-packages/mypy/main.py", line 119, in main
+   File "/tmp/mypy_primer/new_mypy/venv/lib/python3.12/site-packages/mypy/main.py", line 119, in main
-   File "/tmp/mypy_primer/old_mypy/venv/lib/python3.12/site-packages/mypy/main.py", line 203, in run_build
+   File "/tmp/mypy_primer/new_mypy/venv/lib/python3.12/site-packages/mypy/main.py", line 203, in run_build
-   File "/tmp/mypy_primer/old_mypy/venv/lib/python3.12/site-packages/mypy/build.py", line 191, in build
+   File "/tmp/mypy_primer/new_mypy/venv/lib/python3.12/site-packages/mypy/build.py", line 191, in build
-   File "/tmp/mypy_primer/old_mypy/venv/lib/python3.12/site-packages/mypy/build.py", line 267, in _build
+   File "/tmp/mypy_primer/new_mypy/venv/lib/python3.12/site-packages/mypy/build.py", line 267, in _build
-   File "/tmp/mypy_primer/old_mypy/venv/lib/python3.12/site-packages/mypy/build.py", line 2947, in dispatch
+   File "/tmp/mypy_primer/new_mypy/venv/lib/python3.12/site-packages/mypy/build.py", line 2947, in dispatch
-   File "/tmp/mypy_primer/old_mypy/venv/lib/python3.12/site-packages/mypy/build.py", line 976, in write_deps_cache
+   File "/tmp/mypy_primer/new_mypy/venv/lib/python3.12/site-packages/mypy/build.py", line 976, in write_deps_cache

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Now I tend to prefer this version as it does not change how aliases are interpreted and there's no clear winner between those alternatives in #18451. Is this approach unifying type and TypeAlias further reasonable?

@sterliakov sterliakov closed this Jun 8, 2025
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I can not assign a value to variable of a type built from the unpacking of another type with the new pythong 3.13 generic syntax

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