Add python-arch support (#1079)

Windows ARM64 jobs may need x64 Python independently of their Python
version pin. Add `python-arch` to export `UV_PYTHON_ARCH` for subsequent
steps and include the selected architecture in the uv and managed-Python
cache keys. The input takes precedence over an inherited environment
value, and unsupported uv versions fail before environment creation.

Requires a uv release with `UV_PYTHON_ARCH` support.

README.md

@@ -15,6 +15,7 @@ Set up your GitHub Actions workflow with a specific version of [uv](https://docs
   - [Inputs](#inputs)
   - [Outputs](#outputs)
   - [Python version](#python-version)
+  - [Python architecture](#python-architecture)
   - [Working directory](#working-directory)
 - [Advanced Configuration](#advanced-configuration)
 - [How it works](#how-it-works)
@@ -56,6 +57,9 @@ Have a look under [Advanced Configuration](#advanced-configuration) for detailed
     # The version of Python to set UV_PYTHON to (overrides the Python version from .tool-versions)
     python-version: ""
 
+    # The Python architecture to set UV_PYTHON_ARCH to, e.g., x86_64 or aarch64
+    python-arch: ""
+
     # Use uv venv to activate a venv ready to be used by later steps
     activate-environment: "false"
 
@@ -193,6 +197,25 @@ jobs:
         run: uv run --frozen pytest
 ```
 
+### Python architecture
+
+Use `python-arch` to set `UV_PYTHON_ARCH` for the rest of the job. This selects the Python
+architecture independently of the version, including versions requested by `.python-version`.
+An explicit architecture or interpreter path in a Python request takes precedence.
+
+```yaml
+- uses: astral-sh/setup-uv@main
+  with:
+    python-version: "3.14"
+    python-arch: x86_64
+- run: uv run --frozen pytest
+```
+
+The input overrides an existing `UV_PYTHON_ARCH` value. When it is omitted, the action respects
+`UV_PYTHON_ARCH` from the environment. Both forms require a uv version that supports the variable;
+the action reports an error if the installed version does not support it. The selected architecture
+is included in the [cache key](docs/caching.md#cache-key).
+
 ### Working directory
 
 You can set the working directory with the `working-directory` input.