Update pre-commit hook for clang-format

pre-commit-clang

-#!/bin/bash
-
-# Installation:
-#   cp pre-commit-clang .git/hooks/pre-commit
-#   chmod +x .git/hooks/pre-commit
-
-# Source: https://gist.github.com/wangkuiyi/7379a242f0d4089eaa75
-
-# git pre-commit hook that runs an clang-format stylecheck.
-# Features:
-#  - abort commit when commit does not comply with the style guidelines
-#  - create a patch of the proposed style changes
-
-# modifications for clang-format by rene.milk@wwu.de
-# This file is part of a set of unofficial pre-commit hooks available
-# at github.
-# Link:    https://github.com/githubbrowser/Pre-commit-hooks
-# Contact: David Martin, david.martin.mailbox@googlemail.com
-
-
-##################################################################
-# SETTINGS
-# set path to clang-format binary
-CLANG_FORMAT="clang-format"
-
-# remove any older patches from previous commits. Set to true or false.
-DELETE_OLD_PATCHES=false
-
-# only parse files with the extensions in FILE_EXTS. Set to true or false.
-# if false every changed file in the commit will be parsed with clang-format.
-# if true only files matching one of the extensions are parsed with clang-format.
-# PARSE_EXTS=true
-PARSE_EXTS=true
-
-# file types to parse. Only effective when PARSE_EXTS is true.
-{ILE_EXTS=".c .h .cpp .hpp .cc .hh .cxx .m"
-
-##################################################################
-# There should be no need to change anything below this line.
-
-# Reference: http://stackoverflow.com/questions/1055671/how-can-i-get-the-behavior-of-gnus-readlink-f-on-a-mac
-canonicalize_filename () {
-    local target_file=$1
-    local physical_directory=""
-    local result=""
-
-    # Need to restore the working directory after work.
-    pushd `pwd` > /dev/null
-
-    cd "$(dirname "$target_file")"
-    target_file=`basename $target_file`
-
-    # Iterate down a (possible) chain of symlinks
-    while [ -L "$target_file" ]
-    do
-        target_file=$(readlink "$target_file")
-        cd "$(dirname "$target_file")"
-        target_file=$(basename "$target_file")
-    done
-
-    # Compute the canonicalized name by finding the physical path
-    # for the directory we're in and appending the target file.
-    physical_directory=`pwd -P`
-    result="$physical_directory"/"$target_file"
-
-    # restore the working directory after work.
-    popd > /dev/null
-
-    echo "$result"
-}
-
-# exit on error
-set -e
-
-# check whether the given file matches any of the set extensions
-matches_extension() {
-    local filename=$(basename "$1")
-    local extension=".${filename##*.}"
-    local ext
-
-    for ext in $FILE_EXTS; do [[ "$ext" == "$extension" ]] && return 0; done
-
-    return 1
+#!/usr/bin/env bash
+#
+# Runs clang-format on changed regions before commit.
+#
+# To install this, copy it to .git/hooks/pre-commit in your repo.
+# Remaining installation checks/instructions will be printed when you commit.
+#
+
+read -d '' help <<- EOF
+This repository requires you to install the clang-format command. This hook has
+been tested with clang-format-10, so remove all previous versions and reinstall:
+$ sudo apt-get remove clang-format-*
+$ sudo apt-get install clang-format-10
+You should now have clang-format-10 installed. Then, update the configuration
+as follows:
+$ git config --global clangFormat.binary clang-format-10
+$ git config --global clangFormat.style file
+$ git config --global alias.clang-format clang-format-10
+EOF
+
+check_clang_format() {
+  if hash git clang-format 2>/dev/null; then
+    return
+  else
+    echo "SETUP ERROR: no git clang-format executable found, or it is not executable"
+    echo "$help"
+    exit 1
+  fi
 }
 
-# necessary check for initial commit
-if git rev-parse --verify HEAD >/dev/null 2>&1 ; then
-    against=HEAD
-else
-    # Initial commit: diff against an empty tree object
-    against=4b825dc642cb6eb9a060e54bf8d69288fbee4904
-fi
-
-if [ ! -x "$CLANG_FORMAT" ] ; then
-    printf "Error: clang-format executable not found.\n"
-    printf "Set the correct path in $(canonicalize_filename "$0").\n"
+check_git_config() {
+  if [[ "$(git config --get clangFormat.binary)" != "clang-format-10" ]]; then
+    echo "SETUP ERROR: git config clangFormat.binary should be \"clang-format-10\"."
+    echo "$help"
     exit 1
-fi
-
-# create a random filename to store our generated patch
-prefix="pre-commit-clang-format"
-suffix="$(date +%s)"
-patch="/tmp/$prefix-$suffix.patch"
-
-# clean up any older clang-format patches
-$DELETE_OLD_PATCHES && rm -f /tmp/$prefix*.patch
-
-# create one patch containing all changes to the files
-git diff-index --cached --diff-filter=ACMR --name-only $against -- | while read file;
-do
-    # ignore file if we do check for file extensions and the file
-    # does not match any of the extensions specified in $FILE_EXTS
-    if $PARSE_EXTS && ! matches_extension "$file"; then
-        continue;
   fi
+  if [[ "$(git config --get clangFormat.style)" != "file" ]]; then
+    echo "SETUP ERROR: git config clangFormat.style should be \"file\"."
+    echo "$help"
+    exit 1
+  fi
+}
 
-    # clang-format our sourcefile, create a patch with diff and append it to our $patch
-    # The sed call is necessary to transform the patch from
-    #    --- $file timestamp
-    #    +++ - timestamp
-    # to both lines working on the same file and having a a/ and b/ prefix.
-    # Else it can not be applied with 'git apply'.
-    "$CLANG_FORMAT" -style=file "$file" | \
-        diff -u "$file" - | \
-        sed -e "1s|--- |--- a/|" -e "2s|+++ -|+++ b/$file|" >> "$patch"
-done
-
-# if no patch has been generated all is ok, clean up the file stub and exit
-if [ ! -s "$patch" ] ; then
-    printf "Files in this commit comply with the clang-format rules.\n"
-    rm -f "$patch"
-    exit 0
-fi
+check_clang_format
+check_git_config
 
-# a patch has been created, notify the user and exit
-printf "\nThe following differences were found between the code to commit "
-printf "and the clang-format rules:\n\n"
-cat "$patch"
+readonly out=$(git clang-format -v --diff)
 
-printf "\nYou can apply these changes with:\n git apply $patch\n"
-printf "(may need to be called from the root directory of your repository)\n"
-printf "Aborting commit. Apply changes and commit again or skip checking with"
-printf " --no-verify (not recommended).\n"
+if [[ "$out" == *"no modified files to format"* ]]; then exit 0; fi
+if [[ "$out" == *"clang-format did not modify any files"* ]]; then exit 0; fi
 
+echo "ERROR: the code to be committed is not formatted properly"
+echo "you need to run \"git clang-format\" on your commit"
 exit 1