[mypyc] Enable free threading when compiling multiple modules #19541
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p-sawicki
approved these changes
Jul 30, 2025
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Previously we used multi-phase initialization to enable free threading on Python builds that support it, but only if a single module was compiled in a group.
Implements it also for multiple modules in a group. Add support for multi-phase initialization in module shims and the shared library. It's still only used on free-threaded builds, and we fall back to the old approach on other Python versions/builds.
This enables compiling mypy and mypyc on free-threaded Python builds. At least almost all mypy and mypyc tests now pass when compiled and on 3.14.0b4 with free threading (only tested on macOS so far).