Fix the expansion of the Linux host arch matrix

Author: jakepetroules

.github/workflows/pull_request.yml

@@ -26,7 +26,7 @@ jobs:
     with:
       # Linux
       linux_os_versions: '["jammy", "rhel-ubi9", "amazonlinux2"]'
-      linux_host_archs: '["x86_64", "aarch64"]'
+      linux_host_archs: '["x86_64"]'
       linux_build_command: |
         cd tests/TestPackage
         swift build

.github/workflows/swift_package_test.yml

@@ -302,9 +302,29 @@ jobs:
         run: ${{ inputs.ios_build_command }} ${{ (contains(matrix.swift_version, 'nightly') && inputs.swift_nightly_flags) || inputs.swift_flags }}
         timeout-minutes: 60
 
+  define-linux-matrix:
+    runs-on: ubuntu-latest
+    outputs:
+      runner_map: ${{ steps.runners.outputs.runners }}
+    steps:
+      - name: Define Linux Runners
+        id: runners
+        run: |
+          archs='${{ inputs.linux_host_archs }}'
+          full_map='{
+            "x86_64": "ubuntu-24.04",
+            "aarch64": "ubuntu-24.04-arm",
+          }'
+          # Build dynamic map for only selected archs
+          runner_map=$(jq -c --argjson archs "$archs" --argjson full "$full_map" '
+            reduce $archs[] as $a ({}; .[$a] = $full[$a])
+          ' <<< '{}')
+          echo "runner_map=$runner_map" >> $GITHUB_OUTPUT
+
   linux-build:
     name: Linux (${{ matrix.swift_version }} - ${{ matrix.os_version }} - ${{ matrix.arch }})
-    runs-on: ${{ matrix.runner }}
+    needs: define-linux-matrix
+    runs-on: ${{ fromJson(needs.define-linux-matrix.outputs.runner_map)[matrix.arch] }}
     strategy:
       fail-fast: false
       matrix:
@@ -316,11 +336,6 @@ jobs:
           - ${{ fromJson((!inputs.enable_linux_checks && inputs.linux_swift_versions) || '[]') }}
           - ${{ fromJson((!inputs.enable_linux_checks && inputs.linux_os_versions) || '[]') }}
           - ${{ fromJson((!inputs.enable_linux_checks && inputs.linux_host_archs) || '[]') }}
-        include:
-          - arch: x86_64
-            runner: ubuntu-24.04
-          - arch: aarch64
-            runner: ubuntu-24.04-arm
     container:
       image: ${{ (contains(matrix.swift_version, 'nightly') && 'swiftlang/swift') || 'swift' }}:${{ matrix.swift_version }}-${{ matrix.os_version }}
     steps:
@@ -378,7 +393,8 @@ jobs:
 
   linux-static-sdk-build:
     name: Static Linux Swift SDK Build (${{ matrix.swift_version }} - ${{ matrix.os_version }} - ${{ matrix.arch }})
-    runs-on: ${{ matrix.runner }}
+    needs: define-linux-matrix
+    runs-on: ${{ fromJson(needs.define-linux-matrix.outputs.runner_map)[matrix.arch] }}
     strategy:
       fail-fast: false
       matrix:
@@ -390,11 +406,6 @@ jobs:
           - ${{ fromJson((!inputs.enable_linux_static_sdk_build && inputs.linux_static_sdk_versions) || '[]') }}
           - ${{ fromJson((!inputs.enable_linux_static_sdk_build && inputs.linux_os_versions) || '[]') }}
           - ${{ fromJson((!inputs.enable_linux_static_sdk_build && inputs.linux_host_archs) || '[]') }}
-        include:
-          - arch: x86_64
-            runner: ubuntu-24.04
-          - arch: aarch64
-            runner: ubuntu-24.04-arm
     container:
       image: ${{ (contains(matrix.swift_version, 'nightly') && 'swiftlang/swift') || 'swift' }}:${{ matrix.swift_version }}-${{ matrix.os_version }}
     steps: