Enable Windows on Arm GitHub runners

.github/workflows/build.yml

@@ -164,10 +164,12 @@ jobs:
           - false
           - true
         include:
-          - os: windows-latest # FIXME(diegorusso): change to os: windows-aarch64
+          # Forks don't have access to Windows on Arm runners. These jobs are skipped below:
+          - os: ${{ github.repository_owner == 'python' && 'windows-aarch64' || 'windows-latest' }}
             arch: arm64
             free-threading: false
-          - os: windows-latest # FIXME(diegorusso): change to os: windows-aarch64
+          # Forks don't have access to Windows on Arm runners. These jobs are skipped below:
+          - os: ${{ github.repository_owner == 'python' && 'windows-aarch64' || 'windows-latest' }}
             arch: arm64
             free-threading: true
           - os: windows-latest
@@ -187,12 +189,18 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
+        os:
+        - windows-latest
         arch:
         - x86
         - x64
-        - arm64
+        include:
+          # Forks don't have access to Windows on Arm runners. These jobs are skipped below:
+          - os: ${{ github.repository_owner == 'python' && 'windows-aarch64' || 'windows-latest' }}
+            arch: arm64
     uses: ./.github/workflows/reusable-windows-msi.yml
     with:
+      os: ${{ matrix.os }}
       arch: ${{ matrix.arch }}
 
   build-macos:

.github/workflows/jit.yml

@@ -74,7 +74,8 @@ jobs:
             runner: windows-latest
           - target: aarch64-pc-windows-msvc/msvc
             architecture: ARM64
-            runner: windows-latest
+            # Forks don't have access to Windows on Arm runners. These jobs are skipped below:
+            runner: ${{ github.repository_owner == 'python' && 'windows-aarch64' || 'windows-latest' }}
           - target: x86_64-apple-darwin/clang
             architecture: x86_64
             runner: macos-13
@@ -96,19 +97,13 @@ jobs:
           python-version: '3.11'
 
       - name: Native Windows
-        if: runner.os == 'Windows' && matrix.architecture != 'ARM64'
+        # Forks don't have access to Windows on Arm runners. Skip those:
+        if: runner.os == 'Windows' && (matrix.architecture != 'ARM64' || github.repository_owner == 'python')
         run: |
           choco install llvm --allow-downgrade --no-progress --version ${{ matrix.llvm }}.1.0
           ./PCbuild/build.bat --experimental-jit ${{ matrix.debug && '-d' || '' }} -p ${{ matrix.architecture }}
           ./PCbuild/rt.bat ${{ matrix.debug && '-d' || '' }} -p ${{ matrix.architecture }} -q --multiprocess 0 --timeout 4500 --verbose2 --verbose3
 
-      # No tests (yet):
-      - name: Emulated Windows
-        if: runner.os == 'Windows' && matrix.architecture == 'ARM64'
-        run: |
-          choco install llvm --allow-downgrade --no-progress --version ${{ matrix.llvm }}.1.0
-          ./PCbuild/build.bat --experimental-jit ${{ matrix.debug && '-d' || '' }} -p ${{ matrix.architecture }}
-
         # The `find` line is required as a result of https://github.com/actions/runner-images/issues/9966.
         # This is a bug in the macOS runner image where the pre-installed Python is installed in the same
         # directory as the Homebrew Python, which causes the build to fail for macos-13. This line removes

.github/workflows/reusable-windows-msi.yml

@@ -3,6 +3,10 @@ name: Reusable Windows MSI
 on:
   workflow_call:
     inputs:
+      os:
+        description: OS to run on
+        required: true
+        type: string
       arch:
         description: CPU architecture
         required: true
@@ -17,7 +21,7 @@ env:
 jobs:
   build:
     name: installer for ${{ inputs.arch }}
-    runs-on: windows-latest
+    runs-on: ${{ inputs.os }}
     timeout-minutes: 60
     env:
       ARCH: ${{ inputs.arch }}
@@ -27,5 +31,7 @@ jobs:
       with:
         persist-credentials: false
     - name: Build CPython installer
+      # Forks don't have access to Windows on Arm runners. Skip those:
+      if: inputs.arch != 'arm64' || github.repository_owner == 'python'
       run: ./Tools/msi/build.bat --doc -"${ARCH}"
       shell: bash

.github/workflows/reusable-windows.yml

@@ -24,7 +24,7 @@ env:
 
 jobs:
   build:
-    name: ${{ inputs.arch == 'arm64' && 'build' || 'build and test' }} (${{ inputs.arch }})
+    name: Build and test (${{ inputs.arch }})
     runs-on: ${{ inputs.os }}
     timeout-minutes: 60
     env:
@@ -37,17 +37,21 @@ jobs:
       if: inputs.arch != 'Win32'
       run: echo "::add-matcher::.github/problem-matchers/msvc.json"
     - name: Build CPython
+      # Forks don't have access to Windows on Arm runners. Skip those:
+      if: inputs.arch != 'arm64' || github.repository_owner == 'python'
       run: >-
         .\\PCbuild\\build.bat
         -e -d -v
         -p "${ARCH}"
         ${{ fromJSON(inputs.free-threading) && '--disable-gil' || '' }}
       shell: bash
-    - name: Display build info  # FIXME(diegorusso): remove the `if`
-      if: inputs.arch != 'arm64'
+    - name: Display build info
+      # Forks don't have access to Windows on Arm runners. Skip those:
+      if: inputs.arch != 'arm64' || github.repository_owner == 'python'
       run: .\\python.bat -m test.pythoninfo
-    - name: Tests  # FIXME(diegorusso): remove the `if`
-      if: inputs.arch != 'arm64'
+    - name: Tests
+      # Forks don't have access to Windows on Arm runners. Skip those:
+      if: inputs.arch != 'arm64' || github.repository_owner == 'python'
       run: >-
         .\\PCbuild\\rt.bat
         -p "${ARCH}"