Add clang-format specific pre-commit hook

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" == "$extension" ]] && return 0; done
+
+    return 1
+}
+
+# necessary check for initial commit
+if git rev-parse --verify HEAD >/dev/null 2>&1 ; then
+    against=HEAD
+else
+    # Initial commit: diff against an empty tree object
+    against=4b825dc642cb6eb9a060e54bf8d69288fbee4904
+fi
+
+if [ ! -x "$CLANG_FORMAT" ] ; then
+    printf "Error: clang-format executable not found.\n"
+    printf "Set the correct path in $(canonicalize_filename "$0").\n"
+    exit 1
+fi
+
+# create a random filename to store our generated patch
+prefix="pre-commit-clang-format"
+suffix="$(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
+
+    # 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
+
+# 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"
+
+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"
+
+exit 1