Add CI to check trailing whitespace

Author: bondhugula

.github/workflows/build_and_test.yml

@@ -1,4 +1,4 @@
-name: Build and Test Pluto
+name: Build and test Pluto
 
 on:
   push:

.github/workflows/find_trailing_whitespace.yml

@@ -0,0 +1,71 @@
+name: Check trailing whitespaces
+
+on:
+  push:
+    branches: [master]
+    paths-ignore:
+    - '**.png'
+  pull_request:
+    branches: [master]
+    paths-ignore:
+    - '**.png'
+
+
+jobs:
+  check-trailing-whitespace:
+    name: Check trailing whitespaces
+    runs-on: [self-hosted]
+    steps:
+      - uses: actions/checkout@v2
+
+        # Choose the git commit to diff against for the purposes of diff-check.
+        # Since this workflow is triggered on both pushes and pull requests, we
+        # have to determine if the pull request target branch is set (which it
+        # will only be on the PR triggered flow). If it's not, then compare
+        # against the last commit.
+      - name: choose-commit
+        if: ${{ always() }}
+        env:
+          # Base ref is the target branch, in text form (not hash)
+          PR_BASE: ${{ github.base_ref }}
+        run: |
+          # Determine diff commit name.
+          if [[ -z "$PR_BASE" ]]; then
+            DIFF_COMMIT_NAME="HEAD^"
+          else
+            DIFF_COMMIT_NAME="$PR_BASE"
+          fi
+          echo "DIFF_COMMIT_NAME=$DIFF_COMMIT_NAME" >> $GITHUB_ENV
+
+      # Since we did a shallow fetch for this repo, we must fetch the commit
+      # upon which we be diff'ing. The last step set the ref name in the
+      # $DIFF_COMMIT_NAME environment variable. When running the fetch, resolve
+      # it to the commit hash and pass that hash along to subsequent steps.
+      - name: git fetch base commit
+        continue-on-error: true
+        run: |
+          if [[ ! "$DIFF_COMMIT_NAME" == *"HEAD"* ]]; then
+            git fetch --recurse-submodules=no origin $DIFF_COMMIT_NAME
+            DIFF_COMMIT_SHA=$( git rev-parse origin/$DIFF_COMMIT_NAME )
+          else
+            DIFF_COMMIT_SHA=$( git rev-parse $DIFF_COMMIT_NAME )
+          fi
+          echo "DIFF_COMMIT=$DIFF_COMMIT_SHA" >> $GITHUB_ENV
+
+      # Run 'git diff --check', comparing against the target commit hash. If
+      # diff check fixed anything, fail and output a patch.
+      - name: diff-check
+        shell: bash
+        working-directory: ${{github.workspace}}
+        run: |
+          git diff --ignore-submodules --check $DIFF_COMMIT
+          echo "git diff --check found no whitespace problems"
+          exit 0
+
+# Cancel workflows when new commit is pushed to a branch other than master.
+concurrency:
+  # Use github.run_id on master branch.
+  # Use github.event.pull_request.number on pull requests, so it's unique per pull request.
+  # Use github.ref on other branches, so it's unique per branch.
+  group: ${{ github.workflow }}-${{ github.ref == 'refs/heads/master' && github.run_id || github.event.pull_request.number || github.ref }}
+  cancel-in-progress: true

README.md

@@ -54,6 +54,8 @@ test](https://github.com/bondhugula/pluto/actions/workflows/build_and_test.yml/b
 
 [![Check format with clang-format](https://github.com/bondhugula/pluto/actions/workflows/clang_format.yml/badge.svg)](https://github.com/bondhugula/pluto/actions/workflows/clang_format.yml)
 
+[![Find trailing whitespace](https://github.com/bondhugula/pluto/actions/workflows/find_trailing_whitespace.yml/badge.svg)](https://github.com/bondhugula/pluto/actions/workflows/find_trailing_whitespace.yml)
+
 ## License
 
 Pluto and libpluto are available under the MIT LICENSE. Please see the file