Some usability improvements to formatting script (#6153)

* Sharpen the requirements for formatting

* Add option to only format files changed since a given revision

* Avoid divison-by-zero when total is zero

* format code

---------

Co-authored-by: slangbot <186143334+slangbot@users.noreply.github.com>

extras/formatting.sh

@@ -4,6 +4,7 @@ set -e
 
 script_dir="$(cd "$(dirname "${BASH_SOURCE[0]}")" >/dev/null 2>&1 && pwd)"
 source_dir="$(dirname "$script_dir")"
+since_rev=""
 
 check_only=0
 no_version_check=0
@@ -30,6 +31,7 @@ Options:
     --md              Format only markdown files
     --sh              Format only shell script files
     --cmake           Format only CMake files
+    --since <rev>     Only format files since Git revision <rev>
 EOF
 }
 
@@ -65,6 +67,10 @@ while [[ "$#" -gt 0 ]]; do
     source_dir="$2"
     shift
     ;;
+  --since)
+    since_rev="$2"
+    shift
+    ;;
   *)
     echo "unrecognized argument: $1"
     show_help
@@ -108,23 +114,31 @@ require_bin() {
 }
 
 require_bin "git" "1.8"
-require_bin "gersemi" "0.17"
-require_bin "xargs" "3"
+((run_all || run_cmake)) && require_bin "gersemi" "0.17"
+((run_all || run_cpp)) && require_bin "xargs" "3"
 require_bin "diff" "2"
-require_bin "clang-format" "17" "18"
-require_bin "prettier" "3"
-require_bin "shfmt" "3"
+((run_all || run_cpp)) && require_bin "clang-format" "17" "18"
+((run_all || run_yaml || run_markdown)) && require_bin "prettier" "3"
+((run_all || run_sh)) && require_bin "shfmt" "3"
 
 if [ "$missing_bin" ]; then
   exit 1
 fi
 
 exit_code=0
 
+function list_files() {
+  if [ "$since_rev" ]; then
+    git diff --name-only "$since_rev" HEAD $@
+  else
+    git ls-files $@
+  fi
+}
+
 cmake_formatting() {
   echo "Formatting CMake files..." >&2
 
-  readarray -t files < <(git ls-files '*.cmake' 'CMakeLists.txt' '**/CMakeLists.txt')
+  readarray -t files < <(list_files '*.cmake' 'CMakeLists.txt' '**/CMakeLists.txt')
 
   common_args=(
     # turn on warning when this is fixed https://github.com/BlankSpruce/gersemi/issues/39
@@ -150,7 +164,7 @@ track_progress() {
   local total=$1
   local current=0
 
-  while IFS= read -r _; do
+  ((total)) && while IFS= read -r _; do
     ((current++)) || :
     percent=$((current * 100 / total))
     printf '\rProgress: [%-50s] %d%%' "$(printf '#%.0s' $(seq 1 $((percent / 2))))" "$percent" >&2
@@ -161,7 +175,7 @@ track_progress() {
 cpp_formatting() {
   echo "Formatting cpp files..." >&2
 
-  readarray -t files < <(git ls-files '*.cpp' '*.hpp' '*.c' '*.h' ':!external/**')
+  readarray -t files < <(list_files '*.cpp' '*.hpp' '*.c' '*.h' ':!external/**')
 
   # The progress reporting is a bit sneaky, we use `--verbose` with xargs which
   # prints a line to stderr for each command, and we simply count these...
@@ -211,23 +225,23 @@ prettier_formatting() {
 yaml_json_formatting() {
   echo "Formatting yaml and json files..." >&2
 
-  readarray -t files < <(git ls-files "*.yaml" "*.yml" "*.json" ':!external/**')
+  readarray -t files < <(list_files "*.yaml" "*.yml" "*.json" ':!external/**')
 
   prettier_formatting
 }
 
 markdown_formatting() {
   echo "Formatting markdown files..." >&2
 
-  readarray -t files < <(git ls-files "*.md" ':!external/**')
+  readarray -t files < <(list_files "*.md" ':!external/**')
 
   prettier_formatting
 }
 
 sh_formatting() {
   echo "Formatting sh files..." >&2
 
-  readarray -t files < <(git ls-files "*.sh")
+  readarray -t files < <(list_files "*.sh")
 
   common_args=(
     # default 8 is way too wide