Installer: verify the interpreter version the py launcher resolves to

[MrDix]

Problem

On a machine whose py launcher resolves the -3.13/-3.12 tag to a wrong interpreter (e.g. a stale registry registration left behind by a Python upgrade or uninstall), the Windows installers hand that interpreter straight to uv sync --python, which then aborts:

Using CPython 3.10.11 interpreter at: C:\Users\...\Python310\python.exe
error: The requested interpreter resolved to Python 3.10.11, which is
incompatible with the project's Python requirement: '>=3.12, <3.14'
Error during uv sync

This happened after uv lock had already succeeded, so the run failed at the very last step.

Root cause

The py-launcher discovery block only checked the launcher's exit code, never the version of the interpreter it actually returned. The PATH fallback right below it already verifies sys.version_info before accepting a candidate — the launcher block was the one discovery path without that check, and it is also the only path that can produce a full interpreter path, which matches the failure output above.

Fix

Verify the major.minor version of the interpreter the launcher resolves (same check the PATH fallback uses). On mismatch, discovery falls through to the PATH fallback and finally to the portable uv-managed Python 3.12, so the installer now self-heals on such machines instead of aborting.

Applied to both install/CPU/windows_cpu.bat and install/CUDA/windows_cuda_gpu.bat (identical block).

Testing

• Extracted the discovery block into a standalone test script: on a healthy machine it still picks the launcher-resolved Python 3.12 (verified path + version).
• Simulated a mismatching launcher (requested tag differs from the returned version): the candidate is rejected and discovery correctly continues to the PATH fallback.

Summary by CodeRabbit

• Bug Fixes
  • Improved Python version detection during Windows CPU and CUDA GPU installations.
  • Installers now verify that the Python interpreter selected by the launcher matches the requested major and minor version.
  • If a mismatch is detected, the installer continues searching for a compatible interpreter instead of selecting an incorrect one.
  • This helps prevent installation failures and compatibility issues caused by using the wrong Python version.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: e3b4b805-cd84-49b3-8940-d0c101ae2217

📥 Commits

Reviewing files that changed from the base of the PR and between 02ee3db and 9fabd36.

📒 Files selected for processing (2)

• install/CPU/windows_cpu.bat
• install/CUDA/windows_cuda_gpu.bat

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📝 Walkthrough

Walkthrough

The Windows CPU and CUDA installer scripts now compute and compare the resolved interpreter’s major.minor version with the requested py launcher tag before setting PYTHON_EXE and completing Python discovery.

Changes

Windows Python validation

Layer / File(s)	Summary
Validate Python launcher resolution install/CPU/windows_cpu.bat, install/CUDA/windows_cuda_gpu.bat	The installer loops compute each candidate interpreter’s major.minor version and only accept matching versions before capturing sys.executable and jumping to :found_python.

Estimated code review effort: 2 (Simple) | ~10 minutes

Possibly related PRs

• MrDix/UltraSinger#111: Modifies the Windows CPU/CUDA installer scripts’ Python provisioning and interpreter-selection logic.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly summarizes the main change: validating the Python version resolved by the Windows installer’s py launcher.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/installer-verify-py-launcher-version

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