Add clang-format-diff hook (#2057)

This adds a commit hook to Travis CI that errors out if incoming PRs'
diffs are not clang-formatted. Turns out clang-format is also capable of
formatting JavaScript, but we haven't agreed on a style for JS yet, this
PR disables JavaScript formatting for now. This also adds clang-format
exempt header/footer to a generated source file.

Author: aheejin

.clang-format

@@ -1,3 +1,5 @@
+---
+Language: Cpp
 BasedOnStyle: LLVM
 PointerAlignment: Left
 IndentCaseLabels: true
@@ -6,3 +8,7 @@ ConstructorInitializerIndentWidth: 2
 SpaceAfterTemplateKeyword: false
 BinPackArguments: false
 BinPackParameters: false
+---
+Language: JavaScript
+DisableFormat: true
+---

.travis.yml

@@ -59,6 +59,7 @@ jobs:
       script:
         - set -o errexit
         - flake8
+        - ./clang-format-diff.sh
         # ensure generated parser is up to date
         - ./scripts/gen-s-parser.py | diff src/gen-s-parser.inc -
         - BUILD_SUBDIR=${BUILD_SUBDIR:-.}

clang-format-diff.sh

@@ -0,0 +1,11 @@
+#!/bin/bash
+MERGE_BASE=$(git merge-base master HEAD)
+FORMAT_MSG=$(git clang-format $MERGE_BASE -q --diff -- src/)
+if [ -n "$FORMAT_MSG" -a "$FORMAT_MSG" != "no modified files to format" ]
+then
+  echo "Run git clang-format before committing!"
+  echo
+  # Run git clang-format once again to show the error
+  git clang-format $MERGE_BASE -q --diff -- src/
+  exit 1
+fi

scripts/gen-s-parser.py

@@ -533,6 +533,11 @@ def emit(node, idx=0):
 
 def print_header():
   print("// DO NOT EDIT! This file generated by scripts/gen-s-parser.py\n")
+  print("// clang-format off\n")
+
+
+def print_footer():
+  print("\n// clang-format on")
 
 
 def generate_with_guard(generator, guard):
@@ -549,6 +554,7 @@ def main():
     sys.exit(1)
   print_header()
   generate_with_guard(instruction_parser, "INSTRUCTION_PARSER")
+  print_footer()
 
 
 if __name__ == "__main__":

src/gen-s-parser.inc

@@ -1,5 +1,7 @@
 // DO NOT EDIT! This file generated by scripts/gen-s-parser.py
 
+// clang-format off
+
 #ifdef INSTRUCTION_PARSER
 #undef INSTRUCTION_PARSER
 char op[27] = {'\0'};
@@ -2260,3 +2262,5 @@ switch (op[0]) {
 parse_error:
   throw ParseException(std::string(op));
 #endif // INSTRUCTION_PARSER
+
+// clang-format on