add validateProjectRoot() goroutine

`validateProjectRoot()` goroutine is used to validate a single
ProjectRoot at a time.

manifest.go

@@ -158,31 +158,32 @@ func validateManifest(s string) ([]error, error) {
 	return warns, nil
 }
 
-// ValidateProjectRoots validates the project roots present in manifest.
-func ValidateProjectRoots(c *Ctx, m *Manifest, sm gps.SourceManager) error {
-	projectRoots := make([]gps.ProjectRoot, 0, len(m.Constraints)+len(m.Ovr))
-	for pr := range m.Constraints {
-		projectRoots = append(projectRoots, pr)
-	}
-	for pr := range m.Ovr {
-		projectRoots = append(projectRoots, pr)
+// validateProjectRoot validates ProjectRoot. It it used as a goroutine for
+// concurrent validation of ProjectRoot(s).
+func validateProjectRoot(pr gps.ProjectRoot, sm gps.SourceManager, wg *sync.WaitGroup, errorCh chan<- error) {
+	defer wg.Done()
+	origPR, err := sm.DeduceProjectRoot(string(pr))
+	if err != nil {
+		errorCh <- err
+	} else if origPR != pr {
+		errorCh <- fmt.Errorf("the name for %q should be changed to %q", pr, origPR)
 	}
+}
 
+// ValidateProjectRoots validates the project roots present in manifest.
+func ValidateProjectRoots(c *Ctx, m *Manifest, sm gps.SourceManager) error {
 	// Channel to receive all the errors
-	errorCh := make(chan error, len(projectRoots))
+	errorCh := make(chan error, len(m.Constraints)+len(m.Ovr))
 
 	var wg sync.WaitGroup
-	for _, pr := range projectRoots {
+
+	for pr := range m.Constraints {
 		wg.Add(1)
-		go func(pr gps.ProjectRoot) {
-			defer wg.Done()
-			origPR, err := sm.DeduceProjectRoot(string(pr))
-			if err != nil {
-				errorCh <- err
-			} else if origPR != pr {
-				errorCh <- fmt.Errorf("the name for %q should be changed to %q", pr, origPR)
-			}
-		}(pr)
+		go validateProjectRoot(pr, sm, &wg, errorCh)
+	}
+	for pr := range m.Ovr {
+		wg.Add(1)
+		go validateProjectRoot(pr, sm, &wg, errorCh)
 	}
 
 	wg.Wait()