Cache python installs (#621)

This pull request introduces support for caching Python installs in the
GitHub Action, allowing users to cache not only dependencies but also
the Python interpreter itself.

This works by setting the `UV_PYTHON_INSTALL_DIR` to a subdirectory of
the dependency cache path so that Python installs are directed there.

Fixes #135

---------

Co-authored-by: Kevin Stillhammer <kevin.stillhammer@gmail.com>

.github/workflows/test.yml

@@ -25,7 +25,7 @@ jobs:
         with:
           persist-credentials: false
       - name: Actionlint
-        uses: eifinger/actionlint-action@23c85443d840cd73bbecb9cddfc933cc21649a38  # v1.9.1
+        uses: eifinger/actionlint-action@23c85443d840cd73bbecb9cddfc933cc21649a38 # v1.9.1
       - name: Run zizmor
         uses: zizmorcore/zizmor-action@e673c3917a1aef3c65c972347ed84ccd013ecda4 # v0.2.0
       - uses: actions/setup-node@a0853c24544627f65ddf259abe73b1d18a591444 # v5.0.0
@@ -269,13 +269,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        os:
-          [
-            ubuntu-latest,
-            macos-latest,
-            macos-14,
-            windows-latest,
-          ]
+        os: [ubuntu-latest, macos-latest, macos-14, windows-latest]
     steps:
       - uses: actions/checkout@08c6903cd8c0fde910a37f88322edcfb5dd907a8 # v5.0.0
         with:
@@ -334,7 +328,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        os: [ ubuntu-latest, macos-latest, windows-latest ]
+        os: [ubuntu-latest, macos-latest, windows-latest]
     steps:
       - uses: actions/checkout@08c6903cd8c0fde910a37f88322edcfb5dd907a8 # v5.0.0
         with:
@@ -371,8 +365,8 @@ jobs:
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        enable-cache: [ "true", "false", "auto" ]
-        os: [ "ubuntu-latest", "selfhosted-ubuntu-arm64", "windows-latest" ]
+        enable-cache: ["true", "false", "auto"]
+        os: ["ubuntu-latest", "selfhosted-ubuntu-arm64", "windows-latest"]
     steps:
       - uses: actions/checkout@08c6903cd8c0fde910a37f88322edcfb5dd907a8 # v5.0.0
         with:
@@ -389,8 +383,8 @@ jobs:
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        enable-cache: [ "true", "false", "auto" ]
-        os: [ "ubuntu-latest", "selfhosted-ubuntu-arm64", "windows-latest" ]
+        enable-cache: ["true", "false", "auto"]
+        os: ["ubuntu-latest", "selfhosted-ubuntu-arm64", "windows-latest"]
     needs: test-setup-cache
     steps:
       - uses: actions/checkout@08c6903cd8c0fde910a37f88322edcfb5dd907a8 # v5.0.0
@@ -836,6 +830,68 @@ jobs:
             exit 1
           fi
 
+  test-cache-python-installs:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@08c6903cd8c0fde910a37f88322edcfb5dd907a8 # v5.0.0
+        with:
+          persist-credentials: false
+      - name: Verify Python install dir is not populated
+        run: |
+          if [ -d ~/.local/share/uv/python ]; then
+            echo "Python install dir should not exist"
+            exit 1
+          fi
+      - name: Setup uv with cache
+        uses: ./
+        with:
+          enable-cache: true
+          cache-python: true
+          cache-suffix: ${{ github.run_id }}-${{ github.run_attempt }}-test-cache-python-installs
+      - run: uv sync --managed-python
+        working-directory: __tests__/fixtures/uv-project
+      - name: Verify Python install dir exists
+        run: |
+          if [ ! -d ~/.local/share/uv/python ]; then
+            echo "Python install dir should exist"
+            exit 1
+          fi
+  test-restore-python-installs:
+    runs-on: ubuntu-latest
+    needs: test-cache-python-installs
+    steps:
+      - uses: actions/checkout@08c6903cd8c0fde910a37f88322edcfb5dd907a8 # v5.0.0
+        with:
+          persist-credentials: false
+      - name: Verify Python install dir does not exist
+        run: |
+          if [ -d ~/.local/share/uv/python ]; then
+            echo "Python install dir should not exist"
+            exit 1
+          fi
+      - name: Restore with cache
+        id: restore
+        uses: ./
+        with:
+          enable-cache: true
+          cache-python: true
+          cache-suffix: ${{ github.run_id }}-${{ github.run_attempt }}-test-cache-python-installs
+      - name: Verify Python install dir exists
+        run: |
+          if [ ! -d ~/.local/share/uv/python ]; then
+            echo "Python install dir should exist"
+            exit 1
+          fi
+      - name: Cache was hit
+        run: |
+          if [ "$CACHE_HIT" != "true" ]; then
+            exit 1
+          fi
+        env:
+          CACHE_HIT: ${{ steps.restore.outputs.cache-hit }}
+      - run: uv sync --managed-python
+        working-directory: __tests__/fixtures/uv-project
+
   all-tests-passed:
     runs-on: ubuntu-latest
     needs:
@@ -878,6 +934,8 @@ jobs:
       - test-relative-path
       - test-cache-prune-force
       - test-cache-dir-from-file
+      - test-cache-python-installs
+      - test-restore-python-installs
     if: always()
     steps:
       - name: All tests passed