perf: use CoW (copy-on-write) cloning for directory copies

.github/workflows/lint.yml

@@ -20,6 +20,15 @@ jobs:
         run: |
           shellcheck bin/gtr bin/git-gtr lib/*.sh lib/commands/*.sh adapters/editor/*.sh adapters/ai/*.sh
 
+  completions:
+    name: Completions
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Verify completion files are up to date
+        run: ./scripts/generate-completions.sh --check
+
   test:
     name: Tests
     runs-on: ubuntu-latest

lib/copy.sh

@@ -75,6 +75,40 @@ merge_copy_patterns() {
   fi
 }
 
+# Copy a directory using CoW (copy-on-write) when available, falling back to standard cp.
+# macOS APFS: cp -cRP (clone); Linux Btrfs/XFS: cp --reflink=auto -RP
+# Callers must guard the return value with `if` or `|| true` (set -e safe).
+# Usage: _fast_copy_dir src dest
+# Cached OS value for _fast_copy_dir; set on first call.
+_fast_copy_os=""
+
+_fast_copy_dir() {
+  local src="$1" dest="$2"
+  if [ -z "$_fast_copy_os" ]; then
+    _fast_copy_os=$(detect_os)
+  fi
+  local os="$_fast_copy_os"
+
+  case "$os" in
+    darwin)
+      # Try CoW clone first; if unsupported, fall back to regular copy
+      if cp -cRP "$src" "$dest" 2>/dev/null; then
+        return 0
+      fi
+      # Clean up any partial clone output before fallback
+      local _clone_target="${dest%/}/$(basename "$src")"
+      if [ -e "$_clone_target" ]; then rm -rf "$_clone_target"; fi
+      cp -RP "$src" "$dest"
+      ;;
+    linux)
+      cp --reflink=auto -RP "$src" "$dest"
+      ;;
+    *)
+      cp -RP "$src" "$dest"
+      ;;
+  esac
+}
+
 # Copy a single file to destination, handling exclusion, path preservation, and dry-run
 # Usage: _copy_pattern_file file dst_root excludes preserve_paths dry_run
 # Returns: 0 if file was copied (or would be in dry-run), 1 if skipped/failed
@@ -295,6 +329,13 @@ copy_directories() {
 
     # Find directories matching the pattern
     # Use -path for patterns with slashes (e.g., vendor/bundle), -name for basenames
+    # Note: case inside $() inside heredocs breaks Bash 3.2, so compute first
+    local find_results
+    case "$pattern" in
+      */*) find_results=$(find . -type d -path "./$pattern" 2>/dev/null) ;;
+      *)   find_results=$(find . -type d -name "$pattern" 2>/dev/null) ;;
+    esac
+
     while IFS= read -r dir_path; do
       [ -z "$dir_path" ] && continue
       dir_path="${dir_path#./}"
@@ -307,16 +348,16 @@ copy_directories() {
       dest_parent=$(dirname "$dest_dir")
       mkdir -p "$dest_parent"
 
-      # Copy directory (cp -RP preserves symlinks as symlinks)
-      if cp -RP "$dir_path" "$dest_parent/" 2>/dev/null; then
+      # Copy directory using CoW when available (preserves symlinks as symlinks)
+      if _fast_copy_dir "$dir_path" "$dest_parent/"; then
         log_info "Copied directory $dir_path"
         copied_count=$((copied_count + 1))
         _apply_directory_excludes "$dest_parent" "$dir_path" "$excludes"
       else
         log_warn "Failed to copy directory $dir_path"
       fi
     done <<EOF
-$(case "$pattern" in */*) find . -type d -path "./$pattern" 2>/dev/null ;; *) find . -type d -name "$pattern" 2>/dev/null ;; esac)
+$find_results
 EOF
   done <<EOF
 $dir_patterns

tests/copy_safety.bats

@@ -2,9 +2,17 @@
 
 setup() {
   load test_helper
+  _fast_copy_os=""
+  source "$PROJECT_ROOT/lib/platform.sh"
   source "$PROJECT_ROOT/lib/copy.sh"
 }
 
+teardown() {
+  if [ -n "${_test_tmpdir:-}" ]; then
+    rm -rf "$_test_tmpdir"
+  fi
+}
+
 # --- _is_unsafe_path tests ---
 
 @test "absolute path is unsafe" {
@@ -82,3 +90,37 @@ setup() {
   excludes=$(printf '%s\n' "*.log" "dist/*")
   ! is_excluded "src/app.js" "$excludes"
 }
+
+# --- _fast_copy_dir tests ---
+
+@test "_fast_copy_dir copies directory contents" {
+  _test_tmpdir=$(mktemp -d)
+  local src="$_test_tmpdir/src" dst="$_test_tmpdir/dst"
+  mkdir -p "$src" "$dst"
+  mkdir -p "$src/mydir/sub"
+  echo "hello" > "$src/mydir/sub/file.txt"
+
+  _fast_copy_dir "$src/mydir" "$dst/"
+
+  [ -f "$dst/mydir/sub/file.txt" ]
+  [ "$(cat "$dst/mydir/sub/file.txt")" = "hello" ]
+}
+
+@test "_fast_copy_dir preserves symlinks" {
+  _test_tmpdir=$(mktemp -d)
+  local src="$_test_tmpdir/src" dst="$_test_tmpdir/dst"
+  mkdir -p "$src" "$dst"
+  mkdir -p "$src/mydir"
+  echo "target" > "$src/mydir/real.txt"
+  ln -s real.txt "$src/mydir/link.txt"
+
+  _fast_copy_dir "$src/mydir" "$dst/"
+
+  [ -L "$dst/mydir/link.txt" ]
+  [ "$(readlink "$dst/mydir/link.txt")" = "real.txt" ]
+}
+
+@test "_fast_copy_dir fails on nonexistent source" {
+  _test_tmpdir=$(mktemp -d)
+  ! _fast_copy_dir "/nonexistent/path" "$_test_tmpdir/"
+}