tools/checkpatch.sh: Add support for breaking change commit message enforcement

- Introduced a new flag '-b' to enforce breaking change format in commit messages.
- Added checks to ensure that breaking change commits start with '!' and contain 'BREAKING CHANGE:' in the body before 'Signed-off-by'.
- Updated usage instructions to reflect the new breaking change option.

Signed-off-by: Arjav Patel <arjav1528@gmail.com>

tools/checkpatch.sh

@@ -32,6 +32,7 @@ range=0
 spell=0
 encoding=0
 message=0
+breaking_change=0
 
 # CMake
 cmake_warning_once=0
@@ -57,6 +58,7 @@ usage() {
   echo "-r range check only (coupled with -p or -g)"
   echo "-p <patch file names> (default)"
   echo "-m Check commit message (coupled with -g)"
+  echo "-b Enforce breaking change format when checking commit message (requires -m -g; use when PR has breaking change label)"
   echo "-g <commit list>"
   echo "-f <file list>"
   echo "-x format supported files (only .py, requires: pip install black)"
@@ -286,13 +288,14 @@ check_msg() {
   num_lines=0
   max_line_len=80
   min_num_lines=5
+  breaking_change_found=0
 
   first=$(head -n1 <<< "$msg")
 
   # check for Merge line and remove from parsed string
   if [[ $first == *Merge* ]]; then
       msg="$(echo "$msg" | tail -n +2)"
-      first=$(head -n2 <<< "$msg")
+      first=$(head -n1 <<< "$msg")
   fi
 
   while IFS= read -r REPLY; do
@@ -311,7 +314,15 @@ check_msg() {
       fail=1
     fi
 
+    if [[ $REPLY =~  ^BREAKING\ CHANGE: ]]; then
+      breaking_change_found=1
+    fi
+
     if [[ $REPLY =~  ^Signed-off-by ]]; then
+      if [ $breaking_change != 0 ] && [ $breaking_change_found == 0 ]; then
+        echo "❌ BREAKING CHANGE: must appear in the commit body before Signed-off-by (see CONTRIBUTING.md 1.13)"
+        fail=1
+      fi
       signedoffby_found=1
     fi
 
@@ -328,6 +339,23 @@ check_msg() {
     fail=1
   fi
 
+  second=$(echo "$msg" | sed -n '2p')
+  if [ $num_lines -ge 2 ] && ! [[ "$second" =~ ^[[:space:]]*$ ]]; then
+    echo "❌ Commit subject must be followed by a blank line"
+    fail=1
+  fi
+
+  if [ $breaking_change != 0 ]; then
+    if [[ "${first:0:1}" != "!" ]]; then
+      echo "❌ Breaking change commit subject must start with '!' (e.g. '!subsystem: description')"
+      fail=1
+    fi
+    if [ $breaking_change_found == 0 ]; then
+      echo "❌ Breaking change commit must contain 'BREAKING CHANGE:' in the body before Signed-off-by (see CONTRIBUTING.md 1.13)"
+      fail=1
+    fi
+  fi
+
   if ! [ $signedoffby_found == 1 ]; then
     echo "❌ Missing Signed-off-by"
     fail=1
@@ -383,6 +411,9 @@ while [ ! -z "$1" ]; do
   -m )
     message=1
     ;;
+  -b )
+    breaking_change=1
+    ;;
   -g )
     check=check_commit
     ;;