Add clang-format-diff to github actions

Back again with another attempt at #12446 after 6 years.

Author: sbc100

.clang-format-ignore

@@ -0,0 +1,3 @@
+# ignore third_party code from clang-format checks
+third_party/*
+test/third_party/*

.github/workflows/ci.yml

@@ -98,3 +98,18 @@ jobs:
             echo "-- This failure is only a warning and can be ignored"
             exit 1
           fi
+
+  clang-format-diff:
+    env:
+      LLVM_VERSION: 19
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v4
+      # Fetch all history for all tags and branches
+      with:
+        fetch-depth: 0
+    - name: Install clang-format
+      run: |
+        sudo apt-get install clang-format-19
+        sudo update-alternatives --install /usr/bin/git-clang-format git-clang-format /usr/bin/git-clang-format-19 100
+    - run: tools/maint/clang-format-diff.sh origin/$GITHUB_BASE_REF

system/include/emscripten/emscripten.h

@@ -43,7 +43,7 @@ void emscripten_run_script(const char * _Nonnull script);
 int emscripten_run_script_int(const char * _Nonnull script);
 char *emscripten_run_script_string(const char * _Nonnull script);
 void emscripten_async_run_script(const char * _Nonnull script, int millis);
-void emscripten_async_load_script(const char * _Nonnull script, em_callback_func onload, em_callback_func onerror);
+void emscripten_async_load_script(const char* _Nonnull script, em_callback_func onload, em_callback_func onerror);
 
 void emscripten_set_main_loop(em_callback_func func, int fps, bool simulate_infinite_loop);
 

tools/maint/clang-format-diff.sh

@@ -0,0 +1,22 @@
+#!/bin/bash
+# Based on binaryen/scripts/clang-format-diff.sh
+# TODO(sbc): Switch to pre-packaged github actions once we find one that
+# is mature enough for our needs.
+
+set -o errexit
+set -o pipefail
+set -o xtrace
+
+if [ -n "$1" ]; then
+  BRANCH="$1"
+else
+  BRANCH="@{upstream}"
+fi
+
+MERGE_BASE=$(git merge-base $BRANCH HEAD)
+FORMAT_ARGS=${MERGE_BASE}
+if [ -n "$LLVM_VERSION" ]; then
+  FORMAT_ARGS="--binary=clang-format-${LLVM_VERSION} ${FORMAT_ARGS}"
+fi
+
+git clang-format ${FORMAT_ARGS} --diff