Add GitHub Action for checking w/ clang-format-10

.github/workflows/clang-format.yml

@@ -0,0 +1,27 @@
+name: clang-format
+
+on: [push, pull_request]
+
+jobs:
+  check:
+    runs-on: ubuntu-18.04
+    env:
+      CLANG_VERSION: 10
+    steps:
+    - uses: actions/checkout@v2
+    - name: Install clang-format
+      run: |
+        sudo tee /etc/apt/sources.list.d/llvm.list >/dev/null <<EOF
+        deb http://apt.llvm.org/bionic/ llvm-toolchain-bionic-${CLANG_VERSION} main
+        deb-src http://apt.llvm.org/bionic/ llvm-toolchain-bionic-${CLANG_VERSION} main
+        EOF
+        wget -O - https://apt.llvm.org/llvm-snapshot.gpg.key | sudo apt-key add
+        sudo apt-get update
+        sudo apt-get install clang-format-${CLANG_VERSION}
+    - name: Format src/ripple
+      run: find src/ripple -type f \( -name '*.cpp' -o -name '*.h' -o -name '*.ipp' \) -print0 | xargs -0 clang-format-${CLANG_VERSION} -i
+    - name: Format src/test
+      run: find src/test -type f \( -name '*.cpp' -o -name '*.h' -o -name '*.ipp' \) -print0 | xargs -0 clang-format-${CLANG_VERSION} -i
+    - name: Check for differences
+      run: git diff --exit-code
+