Tooling: Skip pnpm install when lockfile unchanged

vdavid · vdavid · commit 8d2b39b84709 · 2026-03-24T17:49:33.000+01:00
- Store `pnpm-lock.yaml` mtime in `node_modules/.pnpm-install-marker` after successful install
- On next run, skip install if mtime matches (saves ~20s and heavy CPU)
- Always runs in CI mode (`--ci`)
- Marker is auto-invalidated when `node_modules` is deleted
diff --git a/scripts/check/CLAUDE.md b/scripts/check/CLAUDE.md
@@ -202,6 +202,12 @@ Use `CommandExists()` to check if a tool is installed, and auto-install if possi
 **Decision**: Auto-fix locally, check-only in CI.
 **Why**: Developers get instant fixes locally (less friction), CI ensures code is properly formatted before merge. Controlled by the `--ci` flag.
 
+**Decision**: Skip `pnpm install` when lockfile is unchanged.
+**Why**: `pnpm install` takes ~20s and pegs all CPUs even when deps haven't changed. A marker file
+(`node_modules/.pnpm-install-marker`) stores `pnpm-lock.yaml`'s mtime after each successful install.
+On the next run, if the mtime matches, install is skipped. The marker lives inside `node_modules/` so
+it's automatically invalidated if `node_modules` is deleted. Always runs in CI (`--ci`).
+
 ## Dependencies
 
 `golang.org/x/term`, `golang.org/x/sys` (transitive). Go 1.25.
diff --git a/scripts/check/checks/common.go b/scripts/check/checks/common.go
@@ -222,8 +222,25 @@ func indentOutput(output string) string {
 }
 
 // EnsurePnpmDependencies runs pnpm install to ensure all dependencies are installed.
-// In CI mode, uses --frozen-lockfile to fail if lockfile is out of sync.
-func EnsurePnpmDependencies(ctx *CheckContext) error {
+// Skips the install if pnpm-lock.yaml hasn't changed since the last successful run.
+// In CI mode, uses --frozen-lockfile and always runs (never skips).
+// Returns true if the install was skipped.
+func EnsurePnpmDependencies(ctx *CheckContext) (skipped bool, err error) {
+	lockfilePath := filepath.Join(ctx.RootDir, "pnpm-lock.yaml")
+	markerPath := filepath.Join(ctx.RootDir, "node_modules", ".pnpm-install-marker")
+
+	if !ctx.CI {
+		if lockInfo, lockErr := os.Stat(lockfilePath); lockErr == nil {
+			if markerContent, markerErr := os.ReadFile(markerPath); markerErr == nil {
+				recorded := string(markerContent)
+				current := lockInfo.ModTime().UTC().Format("2006-01-02T15:04:05.000000000Z")
+				if recorded == current {
+					return true, nil
+				}
+			}
+		}
+	}
+
 	args := []string{"install"}
 	if ctx.CI {
 		args = append(args, "--frozen-lockfile")
@@ -233,9 +250,16 @@ func EnsurePnpmDependencies(ctx *CheckContext) error {
 	cmd.Dir = ctx.RootDir
 	output, err := RunCommand(cmd, true)
 	if err != nil {
-		return fmt.Errorf("pnpm install failed:\n%s", indentOutput(output))
+		return false, fmt.Errorf("pnpm install failed:\n%s", indentOutput(output))
 	}
-	return nil
+
+	// Write marker with lockfile's current mtime
+	if lockInfo, lockErr := os.Stat(lockfilePath); lockErr == nil {
+		mtime := lockInfo.ModTime().UTC().Format("2006-01-02T15:04:05.000000000Z")
+		_ = os.WriteFile(markerPath, []byte(mtime), 0644)
+	}
+
+	return false, nil
 }
 
 // Pluralize returns singular if count is 1, plural otherwise.
diff --git a/scripts/check/main.go b/scripts/check/main.go
@@ -280,13 +280,18 @@ func ensurePnpmDependencies(ctx *checks.CheckContext) error {
 	fmt.Print("📦 Ensuring pnpm dependencies are installed... ")
 	startTime := time.Now()
 
-	if err := checks.EnsurePnpmDependencies(ctx); err != nil {
+	skipped, err := checks.EnsurePnpmDependencies(ctx)
+	if err != nil {
 		fmt.Printf("%sFAILED%s\n", colorRed, colorReset)
 		return err
 	}
 
 	duration := time.Since(startTime)
-	fmt.Printf("%sOK%s (%s)\n\n", colorGreen, colorReset, formatDuration(duration))
+	if skipped {
+		fmt.Printf("%sOK%s (skipped, lockfile unchanged)\n\n", colorGreen, colorReset)
+	} else {
+		fmt.Printf("%sOK%s (%s)\n\n", colorGreen, colorReset, formatDuration(duration))
+	}
 	return nil
 }
 
