fix abi3 interpreter discovery on Windows

[davidhewitt]

This is an attempt to fix #2325 (comment)

(Not tested yet, I wanted to push and see how this runs on CI as well as test locally.)

[davidhewitt]

Looks like this is working well.

Without generate-import-lib enabled, setting 3.13t:

~\Dev\maturin> cargo run -- build --manifest-path ../pyo3-scratch/Cargo.toml -i 3.13t
   Compiling maturin v1.7.6 (C:\Users\david\Dev\maturin)
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 4.28s
     Running `target\debug\maturin.exe build --manifest-path ../pyo3-scratch/Cargo.toml -i 3.13t`
🔗 Found pyo3 bindings with abi3 support for Python ≥ 3.8
⚠️  Warning: Failed to determine python platform
💥 maturin failed
  Caused by: Need a Python interpreter to compile for Windows without PyO3's `generate-import-lib` feature
  Caused by: Python interpreter `3.13t` doesn't exist
error: process didn't exit successfully: `target\debug\maturin.exe build --manifest-path ../pyo3-scratch/Cargo.toml -i 3.13t` (exit code: 1)

... and the same if I enable the generate-import-lib feature:

~\Dev\maturin> cargo run -- build --manifest-path ../pyo3-scratch/Cargo.toml -i 3.13t
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.23s
     Running `target\debug\maturin.exe build --manifest-path ../pyo3-scratch/Cargo.toml -i 3.13t`
🔗 Found pyo3 bindings with abi3 support for Python ≥ 3.8
⚠️  Warning: Failed to determine python platform
🐍 Not using a specific python interpreter (automatically generating windows import library)
⚠️ Warning: CPython 3.13t does not yet support abi3 so the build artifacts will be version-specific.
   Compiling pyo3-build-config v0.23.2 (C:\Users\david\Dev\pyo3\pyo3-build-config)
   Compiling pyo3-macros-backend v0.23.2 (C:\Users\david\Dev\pyo3\pyo3-macros-backend)
   Compiling pyo3-ffi v0.23.2 (C:\Users\david\Dev\pyo3\pyo3-ffi)
   Compiling pyo3 v0.23.2 (C:\Users\david\Dev\pyo3)
   Compiling pyo3-macros v0.23.2 (C:\Users\david\Dev\pyo3\pyo3-macros)
   Compiling pyo3-scratch v0.1.0 (C:\Users\david\Dev\pyo3-scratch)
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 3.76s
📦 Built wheel for CPython 3.13t to C:\Users\david\Dev\pyo3-scratch\target\wheels\pyo3_scratch-0.1.0-cp313-cp313t-win_amd64.whl

Copilot reviewed 3 out of 3 changed files in this pull request and generated no suggestions.

Comments skipped due to low confidence (2)

src/build_options.rs:413

• The capitalization of 'automatically' has been corrected.

eprintln!("🐍 Not using a specific python interpreter (automatically generating windows import library)");

src/build_context.rs:237

• The to_string method for interp does not include the major and minor versions, which could lead to incorrect output. Consider using format!("{}{}{}", interp, interp.major, interp.minor) to ensure the correct format.

.map(|interp| interp.to_string())

[messense]

Thanks!

[messense]

Tested in nh3 and it works great!

[davidhewitt]

Great!

[ravenexp]

Looks like this is working well.

Without generate-import-lib enabled, setting 3.13t:

  Caused by: Need a Python interpreter to compile for Windows without PyO3's `generate-import-lib` feature
  Caused by: Python interpreter `3.13t` doesn't exist

... and the same if I enable the generate-import-lib feature:

📦 Built wheel for CPython 3.13t to C:\Users\david\Dev\pyo3-scratch\target\wheels\pyo3_scratch-0.1.0-cp313-cp313t-win_amd64.whl

But does setting just PYO3_CROSS_LIB_DIR in cross-compile scenarios still work when generate-import-lib feature is not enabled?
From the diff it looks like it will now fail at https://github.com/PyO3/maturin/pull/2333/files#diff-d2936347274858bda2ad31e68e259a54467b075b0532f87a27e52b4b73366762R369. (I have not tested this.)

I'm not using this configuration myself since generate-import-lib had been merged, but it is documented and used to work for a long time.

[davidhewitt]

Oof, good spot, I think you might be right. I'll try to circle back here and cover with some tests at the same time.