Run LLVM install script on Linux runners (#146)

* Run LLVM install script on Linux runners

This will add the relevant LLVM PPA to the runner's package manager
which provides versions of clang-format and clang-tidy that may not yet
be available in the official Ubuntu repositories (e.g. LLVM 16 on Ubuntu
22.04 at the time this commit was authored).

* Only use LLVM script after failure from Ubuntu repos

This also separates the steps of installing the dependencies on Linux
runners from the dependencies on other runners.

* Remove unnecessary apt-get update

* Combine dependency installation into 1 step

* Update action.yml

* nest the call to instal script in a conditional statement

---------

Co-authored-by: Brendan <[email protected]>

Author: mirenradia

action.yml

@@ -90,14 +90,23 @@ runs:
       run: |
         if [[ "${{runner.os}}"  == "Linux" ]]; then
           sudo apt-get update
-          sudo apt-get install clang-format-${{ inputs.version }} clang-tidy-${{ inputs.version }} || true
+          # First try installing from default Ubuntu repositories before trying LLVM script
+          if ! sudo apt-get install clang-format-${{ inputs.version }} clang-tidy-${{ inputs.version }}; then
+            # This LLVM script will add the relevant LLVM PPA: https://apt.llvm.org/
+            wget https://apt.llvm.org/llvm.sh -O $GITHUB_ACTION_PATH/llvm_install.sh
+            chmod +x $GITHUB_ACTION_PATH/llvm_install.sh
+            if sudo $GITHUB_ACTION_PATH/llvm_install.sh ${{ inputs.version }}; then
+              sudo apt-get install clang-format-${{ inputs.version }} clang-tidy-${{ inputs.version }}
+            fi
+          fi
         fi
-        if [[ "${{runner.os}}"  == "macOS" ]];then
+        if [[ "${{runner.os}}"  == "macOS" ]]; then
           python3 -m venv '${{ github.action_path }}/venv'
           source '${{ github.action_path }}/venv/bin/activate'
         fi
         python3 -m pip install -r '${{ github.action_path }}/requirements.txt'
         clang-tools -i ${{ inputs.version }} -b
+
     - name: Run cpp-linter
       id: cpp-linter
       shell: bash