Factor out Travis 'install' sections for use with GitHub Actions (#7988)

.github/workflows/jenkins.yml

@@ -17,7 +17,7 @@ jobs:
       - name: Checkout repository
         uses: actions/checkout@v1
         with:
-          fetch-depth: 1
+          fetch-depth: 0
       - name: Run Jenkins Tests
         shell: bash -e -o pipefail -l {0}
         env:

.github/workflows/main.yml

@@ -11,48 +11,38 @@ jobs:
       matrix:
         # Useful info: https://help.github.com/en/articles/workflow-syntax-for-github-actions
         include:
-          - name: ubuntu-clang
+          - name: ubuntu
             os: ubuntu-16.04
-            compiler: clang
-          - name: windows-clang
+          - name: windows
             os: windows-2019
-            compiler: clang-cl
-          - name: macos-clang
+          - name: macos
             os: macos-10.15
-            compiler: clang
+    env:
+      PYTHON: 3.6
     steps:
-    - name: Configure Git
+    - name: Pre-checkout system configuration
       # We add -l to process .bashrc, but need -e -o pipefail for consistency with GitHub Actions's default behavior.
       shell: bash -e -o pipefail -l {0}
       run: |
+        # Note: only configure settings here that are required _before_ the repository is cloned (such as Git settings).
+        if [ ! -f ~/.profile ] && [ ! -f ~/.bash_profile ]; then  # missing on some machines, but needed for ~/.bashrc
+          echo 'if [ -n "${BASH_VERSION}" ] && [ -f ~/.bashrc ]; then . ~/.bashrc; fi' >> ~/.profile
+        fi
         git config --global core.symlinks true && git config --global core.autocrlf false
         if command -v dpkg > /dev/null; then sudo dpkg-reconfigure debconf -f noninteractive -p high; fi
     - name: Checkout repository
       uses: actions/checkout@v2
       with:
-        fetch-depth: 1
-    - name: Setup Bazel
+        # we need full history to diff against the original for linting etc.
+        fetch-depth: 0
+    - name: Run CI script
       shell: bash -e -o pipefail -l {0}
       env:
         BAZEL_CACHE_CREDENTIAL_B64: ${{ secrets.BAZEL_CACHE_CREDENTIAL_B64 }}
         GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
-      run: ./ci/travis/install-bazel.sh
-    - name: Install C/C++ toolchains
-      shell: bash -e -o pipefail -l {0}
-      env:
-        CC: ${{ matrix.compiler }}
-      run: ./ci/travis/install-toolchains.sh "${CC%%-*}"
-    - name: Install MSYS2 (only needed if some shell commands are missing)
-      if: false && runner.os == 'Windows'
-      uses: numworks/setup-msys2@v1
-      with:
-        update: false
-    - name: Perform build
-      shell: bash -e -o pipefail -l {0}
       run: |
-        bazel build \
-          --keep_going \
-          "//:*"
+        . ./ci/travis/ci.sh init
+        . ./ci/travis/ci.sh build
     - name: Run Clang Include-What-You-Use
       continue-on-error: true
       if: runner.os == 'Linux'