mach: adopt uv and avoid system python (#34632)

This allows us to use `uv` for:
1. Installing a pinned Python version
2. Installing the dependency packages using `uv`'s pip compatible interface.
4. Bootstrapping `mach` without a Python installion on the host, using `uv
   run`

This change also introduces a new 'composite' GitHub action to setup
python in the different CI workflows. There is no support for externally
managed python installations and virtual environments. These could be
added in the future.

Fixes #34095, #34547

Signed-off-by: Mukilan Thiyagarajan <mukilan@igalia.com>

.github/actions/setup-python/action.yml

@@ -0,0 +1,20 @@
+name: Setup Python and uv
+inputs:
+  skip-python-setup:
+    required: false
+    description: "Whether to skip installing python using Github's `setup-python` action"
+    default: false
+runs:
+  using: "composite"
+  steps:
+    # Use the setup-python action to take advantage of the cache. uv will
+    # symlink to this version.
+    - name: Setup system python
+      if: ${{ inputs.skip-python-setup != 'true' }}
+      uses: actions/setup-python@v5
+      with:
+        python-version-file: '.python-version'
+    - name: Install uv
+      uses: astral-sh/setup-uv@v4
+      with:
+        version: "0.5.6"

.github/workflows/android.yml

@@ -61,8 +61,8 @@ jobs:
         uses: mozilla-actions/sccache-action@v0.0.7
       - name: Install crown
         run: cargo install --path support/crown
-      - name: Bootstrap Python
-        run: python3 -m pip install --upgrade pip virtualenv
+      - name: Setup Python
+        uses: ./.github/actions/setup-python
       - name: Bootstrap dependencies
         run: sudo apt update && python3 ./mach bootstrap --skip-lints
       - name: Set up JDK 17

.github/workflows/docs.yml

@@ -13,9 +13,10 @@ jobs:
     runs-on: ubuntu-22.04
     steps:
       - uses: actions/checkout@v4
+      - name: Setup Python
+        uses: ./.github/actions/setup-python
       - name: Bootstrap
         run: |
-          python3 -m pip install --upgrade pip
           sudo apt update
           python3 ./mach bootstrap --skip-lints
       - name: Set LIBCLANG_PATH # This is needed for bindgen in mozangle.

.github/workflows/lint.yml

@@ -33,9 +33,8 @@ jobs:
         uses: mozilla-actions/sccache-action@v0.0.6
       - name: Set LIBCLANG_PATH env # needed for bindgen in mozangle
         run: echo "LIBCLANG_PATH=/usr/lib/llvm-14/lib" >> $GITHUB_ENV
-      - uses: actions/setup-python@v5
-        with:
-          python-version: '3.10'
+      - name: Setup Python
+        uses: ./.github/actions/setup-python
       - name: Install taplo
         uses: baptiste0928/cargo-install@v3
         with:
@@ -46,8 +45,6 @@ jobs:
         with:
           crate: cargo-deny
           locked: true
-      - name: Bootstrap Python
-        run: python3 -m pip install --upgrade pip
       - name: Bootstrap dependencies
         run: |
           sudo apt update
@@ -57,4 +54,4 @@ jobs:
         run: |
           python3 ./mach clippy --use-crown --locked -- -- --deny warnings
       - name: Tidy
-        run: python3 ./mach test-tidy --no-progress --all
+        run: python3 ./mach test-tidy --no-progress --all

.github/workflows/linux-bencher.yml

@@ -35,9 +35,10 @@ jobs:
           path: release-binary-linux
       - name: unPackage binary
         run: tar -xzf release-binary-linux/target.tar.gz
+      - name: Setup Python
+        uses: ./.github/actions/setup-python
       - name: Bootstrap dependencies
         run: |
-          python3 -m pip install --upgrade pip
           sudo apt update
           sudo apt install -qy --no-install-recommends mesa-vulkan-drivers
           python3 ./mach bootstrap --skip-lints

.github/workflows/linux-wpt.yml

@@ -52,9 +52,10 @@ jobs:
           path: ${{ inputs.profile }}-binary-linux
       - name: unPackage binary
         run: tar -xzf ${{ inputs.profile }}-binary-linux/target.tar.gz
+      - name: Setup Python
+        uses: ./.github/actions/setup-python
       - name: Bootstrap dependencies
         run: |
-          python3 -m pip install --upgrade pip
           sudo apt update
           sudo apt install -qy --no-install-recommends mesa-vulkan-drivers
           python3 ./mach bootstrap --skip-lints

.github/workflows/linux.yml

@@ -141,13 +141,10 @@ jobs:
       - name: Set LIBCLANG_PATH env # needed for bindgen in mozangle
         if: ${{ ! fromJSON(needs.runner-select.outputs.is-self-hosted) && !inputs.upload }} # not needed on ubuntu 20.04 used for nightly
         run: echo "LIBCLANG_PATH=/usr/lib/llvm-14/lib" >> $GITHUB_ENV
-      - uses: actions/setup-python@v5
-        if: ${{ ! fromJSON(needs.runner-select.outputs.is-self-hosted) }}
+      - name: Setup Python
+        uses: ./.github/actions/setup-python
         with:
-          python-version: '3.10'
-      - name: Bootstrap Python
-        if: ${{ ! fromJSON(needs.runner-select.outputs.is-self-hosted) }}
-        run: python3 -m pip install --upgrade pip
+          skip-python-setup: ${{ fromJSON(needs.runner-select.outputs.is-self-hosted) }}
       - name: Bootstrap dependencies
         if: ${{ ! fromJSON(needs.runner-select.outputs.is-self-hosted) }}
         run: |

.github/workflows/mac-wpt.yml

@@ -41,15 +41,11 @@ jobs:
       - uses: actions/download-artifact@v4
         with:
           name: ${{ inputs.profile }}-binary-macos
-      # Python 3.13 breaks wptrunner, so pin the version until
-      # web-platform-tests/wpt#48585 is fixed.
-      - uses: actions/setup-python@v5
-        with:
-          python-version: '3.12'
+      - name: Setup Python
+        uses: ./.github/actions/setup-python
       - name: Prep test environment
         run: |
           gtar -xzf target.tar.gz
-          python3 -m pip install --upgrade pip
           python3 ./mach bootstrap --skip-lints
       - name: Smoketest
         run: python3 ./mach smoketest --${{ inputs.profile }}

.github/workflows/mac.yml

@@ -79,18 +79,14 @@ jobs:
         if: github.event_name == 'pull_request_target'
         with:
           ref: ${{ github.event.pull_request.head.sha }}
-      # Python 3.13 breaks wptrunner, so pin the version until
-      # web-platform-tests/wpt#48585 is fixed.
-      - uses: actions/setup-python@v5
-        with:
-          python-version: '3.12'
+      - name: Setup Python
+        uses: ./.github/actions/setup-python
       - name: Run sccache-cache
         uses: mozilla-actions/sccache-action@v0.0.6
       - name: Install crown
         run: cargo install --path support/crown
       - name: Bootstrap
         run: |
-          python3 -m pip install --upgrade pip
           python3 ./mach bootstrap --skip-lints
           brew install gnu-tar
       - name: Build (${{ inputs.profile }})

.github/workflows/main.yml

@@ -20,15 +20,16 @@ jobs:
     outputs:
       configuration: ${{ steps.configuration.outputs.result }}
     steps:
-      - uses: actions/setup-python@v5
-        with:
-          python-version: '3.10'
       - uses: actions/checkout@v4
         with:
           fetch-depth: 1
           sparse-checkout: |
             python/servo/try_parser.py
+            .github/actions/setup-python
+            .python-version
           sparse-checkout-cone-mode: false
+      - name: Setup Python
+        uses: ./.github/actions/setup-python
       - name: Get Configuration
         id: configuration
         run: |

.github/workflows/ohos.yml

@@ -55,8 +55,8 @@ jobs:
         uses: mozilla-actions/sccache-action@v0.0.6
       - name: Install crown
         run: cargo install --path support/crown
-      - name: Bootstrap Python
-        run: python3 -m pip install --upgrade pip virtualenv
+      - name: Setup Python
+        uses: ./.github/actions/setup-python
       - name: Bootstrap dependencies
         run: sudo apt update && python3 ./mach bootstrap --skip-lints
       - name: Setup OpenHarmony SDK

.github/workflows/pull-request-wpt-export.yml

@@ -28,10 +28,16 @@ jobs:
           # using the token specified here.
           # See https://github.com/actions/checkout/issues/162.
           token: ${{ secrets.WPT_SYNC_TOKEN }}
+      - name: Setup Python
+        uses: ./servo/.github/actions/setup-python
       - name: Install requirements
-        run: pip install -r servo/python/requirements.txt
+        run: |
+          uv venv
+          uv pip install -r servo/python/requirements.txt
       - name: Process pull request
-        run: servo/python/wpt/export.py
+        run: |
+         source .venv/bin/activate
+         servo/python/wpt/export.py
         env:
           GITHUB_CONTEXT: ${{ toJson(github) }}
           WPT_SYNC_TOKEN: ${{ secrets.WPT_SYNC_TOKEN }}

.github/workflows/scheduled-wpt-import.yml

@@ -35,9 +35,10 @@ jobs:
       - uses: actions/download-artifact@v4
         with:
           name: wpt-full-logs-linux-layout-2020
+      - name: Setup Python
+        uses: ./.github/actions/setup-python
       - name: Prep environment
         run: |
-          python3 -m pip install --upgrade pip
           sudo apt update
           python3 ./mach bootstrap
       - name: Add upstream remote

.github/workflows/try-label.yml

@@ -77,14 +77,15 @@ jobs:
             }
 
             return try_string;
-      - uses: actions/setup-python@v5
-        with:
-          python-version: '3.10'
       - uses: actions/checkout@v4
         with:
           sparse-checkout: |
             python/servo/try_parser.py
+            .github/actions/setup-python
+            .python-version
           sparse-checkout-cone-mode: false
+      - name: Setup Python
+        uses: ./.github/actions/setup-python
       - name: Parse Labels
         if: ${{ steps.try_string.outputs.result }}
         id: configuration

.github/workflows/try.yml

@@ -32,15 +32,16 @@ jobs:
     outputs:
       configuration: ${{ steps.configuration.outputs.result }}
     steps:
-      - uses: actions/setup-python@v5
-        with:
-          python-version: '3.10'
       - uses: actions/checkout@v4
         with:
           fetch-depth: 1
           sparse-checkout: |
             python/servo/try_parser.py
+            .github/actions/setup-python
+            .python-version
           sparse-checkout-cone-mode: false
+      - name: Setup Python
+        uses: ./.github/actions/setup-python
       - name: Get Full Configuration
         id: full_config
         run: |

.github/workflows/windows.yml

@@ -114,13 +114,13 @@ jobs:
           choco install wixtoolset
           echo "C:\\Program Files (x86)\\WiX Toolset v3.11\\bin" | Out-File -FilePath $env:GITHUB_PATH -Encoding utf8 -Append
       - uses: actions/setup-python@v5
-        if: ${{ ! fromJSON(needs.runner-select.outputs.is-self-hosted) }}
+      - name: Setup Python
+        uses: ./.github/actions/setup-python
         with:
-          python-version: "3.10"
+          skip-python-setup: ${{ fromJSON(needs.runner-select.outputs.is-self-hosted) }}
       - name: Bootstrap
         if: ${{ ! fromJSON(needs.runner-select.outputs.is-self-hosted) }}
         run: |
-          python -m pip install --upgrade pip
           python mach fetch
           python mach bootstrap-gstreamer
       # For some reason WiX isn't currently on the GitHub runner path. This is a