git pre-commit hook for format fix (#1730) - ux only

bin/clang-format-fix

@@ -14,6 +14,7 @@ fi
 set -euo pipefail
 
 GIT_LS_FILES_FLAGS=""
+# -g scopes formatting to tracked files currently modified in git status.
 if [[ "${1:-}" == "-g" ]]; then
   GIT_LS_FILES_FLAGS="--modified"
 fi
@@ -21,6 +22,7 @@ fi
 CLANG_FORMAT_VERSION_RAW="$(${CLANG_FORMAT_BIN} --version)"
 CLANG_FORMAT_MAJOR="$(printf '%s\n' "${CLANG_FORMAT_VERSION_RAW}" | grep -oE '[0-9]+' | head -n1)"
 
+# Guard against local binaries older than the repo formatting config.
 if [[ -z "${CLANG_FORMAT_MAJOR}" || "${CLANG_FORMAT_MAJOR}" -lt 21 ]]; then
   echo "Error: ${CLANG_FORMAT_BIN} is too old: ${CLANG_FORMAT_VERSION_RAW}"
   echo "This repository's .clang-format requires clang-format 21 or newer."
@@ -37,9 +39,14 @@ fi
 # --exclude-standard: ignores files in .gitignore
 # Additionally exclude files in 'lib/EpdFont/builtinFonts/' as they are script-generated.
 # Also exclude files in 'lib/Epub/Epub/hyphenation/generated/' as they are script-generated.
+# Keep the no-match case non-fatal: grep returns 1 when no files match,
+# which is expected when there are no modified C/C++ files.
+set +o pipefail
 git ls-files  --exclude-standard ${GIT_LS_FILES_FLAGS} \
     | grep -E '\.(c|cpp|h|hpp)$' \
     | grep -v -E '^lib/EpdFont/builtinFonts/' \
     | grep -v -E '^lib/Epub/Epub/hyphenation/generated/' \
     | grep -v -E '^lib/uzlib/' \
     | xargs -r "${CLANG_FORMAT_BIN}" -style=file -i
+# Restore strict pipeline failure handling for the rest of the script.
+set -o pipefail