Add clang-tidy-diff hook to Travis CI (#2060)

This adds clang-tidy hook to Travis CI. This runs clang-tidy to the diff
between the current HEAD and master. (It takes very long time to run
clang-tidy on the whole repo, so it is not feasible anyway.)

Author: aheejin

.travis.yml

@@ -64,7 +64,9 @@ jobs:
         - ./scripts/gen-s-parser.py | diff src/gen-s-parser.inc -
         - BUILD_SUBDIR=${BUILD_SUBDIR:-.}
         - mkdir -p ${BUILD_SUBDIR} && cd ${BUILD_SUBDIR}
-        - cmake ${TRAVIS_BUILD_DIR} -DCMAKE_C_FLAGS="$COMPILER_FLAGS" -DCMAKE_CXX_FLAGS="$COMPILER_FLAGS" -DCMAKE_INSTALL_PREFIX=install
+        - cmake ${TRAVIS_BUILD_DIR} -DCMAKE_C_FLAGS="$COMPILER_FLAGS" -DCMAKE_CXX_FLAGS="$COMPILER_FLAGS" -DCMAKE_INSTALL_PREFIX=install -DCMAKE_EXPORT_COMPILE_COMMANDS=ON
+        # clang-tidy-diff.sh may not exist when BUILD_SUBDIR is a subdirectory
+        - if [ -f clang-tidy-diff.sh ]; then ./clang-tidy-diff.sh; fi
         - make -j2 install
         - cd ${TRAVIS_BUILD_DIR}
         - ./check.py --binaryen-bin=${BUILD_SUBDIR}/install/bin

clang-tidy-diff.sh

@@ -0,0 +1,13 @@
+#!/bin/bash
+CLANG_DIR=$(dirname $(dirname $(which clang-tidy)))
+CLANG_TIDY_DIFF=$CLANG_DIR/share/clang/clang-tidy-diff.py
+MERGE_BASE=$(git merge-base master HEAD)
+TIDY_MSG=$(git diff -U0 $MERGE_BASE | $CLANG_TIDY_DIFF -quiet -p1 2> /dev/null)
+if [ -n "$TIDY_MSG" -a "$TIDY_MSG" != "No relevant changes found." ]
+then
+  echo "Fix clang-tidy errors before committing!"
+  echo
+  # Run clang-tidy once again to show the error
+  git diff -U0 $MERGE_BASE | $CLANG_TIDY_DIFF -quiet -p1
+  exit 1
+fi