Change the way we aggregate path for errors

Author: Antoine Pelisse

typed/helpers.go

@@ -64,15 +64,32 @@ func (errs ValidationErrors) WithPath(p string) ValidationErrors {
 	return errs
 }
 
-// Prefix all errors path with the given pathelement. This is useful
-// when unwinding the stack on errors.
+// WithPrefix prefixes all errors path with the given pathelement. This
+// is useful when unwinding the stack on errors.
 func (errs ValidationErrors) WithPrefix(prefix string) ValidationErrors {
 	for i := range errs {
 		errs[i].Path = prefix + errs[i].Path
 	}
 	return errs
 }
 
+// WithLazyPrefix prefixes all errors path with the given pathelement.
+// This is useful when unwinding the stack on errors. Prefix is
+// computed lazily only if there is an error.
+func (errs ValidationErrors) WithLazyPrefix(fn func() string) ValidationErrors {
+	if len(errs) == 0 {
+		return errs
+	}
+	prefix := ""
+	if fn != nil {
+		prefix = fn()
+	}
+	for i := range errs {
+		errs[i].Path = prefix + errs[i].Path
+	}
+	return errs
+}
+
 func errorf(format string, args ...interface{}) ValidationErrors {
 	return ValidationErrors{{
 		ErrorMessage: fmt.Sprintf(format, args...),

typed/merge.go

@@ -68,7 +68,7 @@ var (
 )
 
 // merge sets w.out.
-func (w *mergingWalker) merge() (errs ValidationErrors) {
+func (w *mergingWalker) merge(prefixFn func() string) (errs ValidationErrors) {
 	if w.lhs == nil && w.rhs == nil {
 		// check this condidition here instead of everywhere below.
 		return errorf("at least one of lhs and rhs must be provided")
@@ -91,7 +91,7 @@ func (w *mergingWalker) merge() (errs ValidationErrors) {
 	if !w.inLeaf && w.postItemHook != nil {
 		w.postItemHook(w)
 	}
-	return errs
+	return errs.WithLazyPrefix(prefixFn)
 }
 
 // doLeaf should be called on leaves before descending into children, if there
@@ -223,9 +223,8 @@ func (w *mergingWalker) visitListItems(t *schema.List, lhs, rhs value.List) (err
 			if rchild, ok := observedRHS.Get(pe); ok {
 				w2.rhs = rchild
 			}
-			if newErrs := w2.merge(); len(newErrs) > 0 {
-				errs = append(errs, newErrs.WithPrefix(pe.String())...)
-			} else if w2.out != nil {
+			errs = append(errs, w2.merge(pe.String)...)
+			if w2.out != nil {
 				out = append(out, *w2.out)
 			}
 			w.finishDescent(w2)
@@ -239,9 +238,8 @@ func (w *mergingWalker) visitListItems(t *schema.List, lhs, rhs value.List) (err
 		value, _ := observedRHS.Get(pe)
 		w2 := w.prepareDescent(pe, t.ElementType)
 		w2.rhs = value
-		if newErrs := w2.merge(); len(newErrs) > 0 {
-			errs = append(errs, newErrs.WithPrefix(pe.String())...)
-		} else if w2.out != nil {
+		errs = append(errs, w2.merge(pe.String)...)
+		if w2.out != nil {
 			out = append(out, *w2.out)
 		}
 		w.finishDescent(w2)
@@ -302,13 +300,12 @@ func (w *mergingWalker) visitMapItem(t *schema.Map, out map[string]interface{},
 	w2 := w.prepareDescent(pe, fieldType)
 	w2.lhs = lhs
 	w2.rhs = rhs
-	if newErrs := w2.merge(); len(newErrs) > 0 {
-		errs = append(errs, newErrs.WithPrefix(pe.String())...)
-	} else if w2.out != nil {
+	errs = append(errs, w2.merge(pe.String)...)
+	if w2.out != nil {
 		out[key] = *w2.out
 	}
 	w.finishDescent(w2)
-	return nil
+	return errs
 }
 
 func (w *mergingWalker) visitMapItems(t *schema.Map, lhs, rhs value.Map) (errs ValidationErrors) {

typed/typed.go

@@ -70,7 +70,7 @@ func (tv TypedValue) AsValue() value.Value {
 func (tv TypedValue) Validate() error {
 	w := tv.walker()
 	defer w.finished()
-	if errs := w.validate(); len(errs) != 0 {
+	if errs := w.validate(nil); len(errs) != 0 {
 		return errs
 	}
 	return nil
@@ -239,7 +239,7 @@ func merge(lhs, rhs *TypedValue, rule, postRule mergeRule) (*TypedValue, error)
 	mw.rule = rule
 	mw.postItemHook = postRule
 
-	errs := mw.merge()
+	errs := mw.merge(nil)
 	if len(errs) > 0 {
 		return nil, errs
 	}

typed/validate.go

@@ -73,8 +73,8 @@ func (v *validatingObjectWalker) finishDescent(v2 *validatingObjectWalker) {
 	*v.spareWalkers = append(*v.spareWalkers, v2)
 }
 
-func (v *validatingObjectWalker) validate() ValidationErrors {
-	return resolveSchema(v.schema, v.typeRef, v.value, v)
+func (v *validatingObjectWalker) validate(prefixFn func() string) ValidationErrors {
+	return resolveSchema(v.schema, v.typeRef, v.value, v).WithLazyPrefix(prefixFn)
 }
 
 func validateScalar(t *schema.Scalar, v value.Value, prefix string) (errs ValidationErrors) {
@@ -133,9 +133,7 @@ func (v *validatingObjectWalker) visitListItems(t *schema.List, list value.List)
 		}
 		v2 := v.prepareDescent(t.ElementType)
 		v2.value = child
-		if newErrs := v2.validate(); len(newErrs) != 0 {
-			errs = append(errs, newErrs.WithPrefix(pe.String())...)
-		}
+		errs = append(errs, v2.validate(pe.String)...)
 		v.finishDescent(v2)
 	}
 	return errs
@@ -168,7 +166,8 @@ func (v *validatingObjectWalker) visitMapItems(t *schema.Map, m value.Map) (errs
 		}
 		v2 := v.prepareDescent(tr)
 		v2.value = val
-		errs = append(errs, v2.validate()...)
+		// Giving pe.String as a parameter actually increases the allocations.
+		errs = append(errs, v2.validate(func() string { return pe.String() })...)
 		v.finishDescent(v2)
 		return true
 	})