Add error types for visit map and sequence assertions (#2941)

## Why
Used in #2940. Since required
validation queries against a static list of patterns, it's possible that
the pattern it is querying is not defined in the bundle config tree.

## Tests
Existing tests pass.

Author: shreyas-goenka

libs/dyn/pattern.go

@@ -1,6 +1,7 @@
 package dyn
 
 import (
+	"errors"
 	"fmt"
 	"slices"
 )
@@ -66,11 +67,39 @@ func AnyKey() patternComponent {
 	return anyKeyComponent{}
 }
 
+type expectedMapError struct {
+	p Path
+	v Value
+}
+
+func (e expectedMapError) Error() string {
+	return fmt.Sprintf("expected a map at %q, found %s", e.p, e.v.Kind())
+}
+
+func IsExpectedMapError(err error) bool {
+	var target expectedMapError
+	return errors.As(err, &target)
+}
+
+type expectedSequenceError struct {
+	p Path
+	v Value
+}
+
+func (e expectedSequenceError) Error() string {
+	return fmt.Sprintf("expected a sequence at %q, found %s", e.p, e.v.Kind())
+}
+
+func IsExpectedSequenceError(err error) bool {
+	var target expectedSequenceError
+	return errors.As(err, &target)
+}
+
 // This function implements the patternComponent interface.
 func (c anyKeyComponent) visit(v Value, prefix Path, suffix Pattern, opts visitOptions) (Value, error) {
 	m, ok := v.AsMap()
 	if !ok {
-		return InvalidValue, fmt.Errorf("expected a map at %q, found %s", prefix, v.Kind())
+		return InvalidValue, expectedMapError{p: prefix, v: v}
 	}
 
 	m = m.Clone()
@@ -105,7 +134,7 @@ func AnyIndex() patternComponent {
 func (c anyIndexComponent) visit(v Value, prefix Path, suffix Pattern, opts visitOptions) (Value, error) {
 	s, ok := v.AsSequence()
 	if !ok {
-		return InvalidValue, fmt.Errorf("expected a sequence at %q, found %s", prefix, v.Kind())
+		return InvalidValue, expectedSequenceError{p: prefix, v: v}
 	}
 
 	s = slices.Clone(s)

libs/dyn/visit.go

@@ -54,6 +54,34 @@ func IsIndexOutOfBoundsError(err error) bool {
 	return errors.As(err, &target)
 }
 
+type expectedMapToIndexError struct {
+	p Path
+	v Value
+}
+
+func (e expectedMapToIndexError) Error() string {
+	return fmt.Sprintf("expected a map to index %q, found %s", e.p, e.v.Kind())
+}
+
+func IsExpectedMapToIndexError(err error) bool {
+	var target expectedMapToIndexError
+	return errors.As(err, &target)
+}
+
+type expectedSequenceToIndexError struct {
+	p Path
+	v Value
+}
+
+func (e expectedSequenceToIndexError) Error() string {
+	return fmt.Sprintf("expected a sequence to index %q, found %s", e.p, e.v.Kind())
+}
+
+func IsExpectedSequenceToIndexError(err error) bool {
+	var target expectedSequenceToIndexError
+	return errors.As(err, &target)
+}
+
 type visitOptions struct {
 	// The function to apply to the value once found.
 	//
@@ -98,7 +126,7 @@ func (component pathComponent) visit(v Value, prefix Path, suffix Pattern, opts
 		case KindNil:
 			return InvalidValue, cannotTraverseNilError{path}
 		default:
-			return InvalidValue, fmt.Errorf("expected a map to index %q, found %s", path, v.Kind())
+			return InvalidValue, expectedMapToIndexError{p: path, v: v}
 		}
 
 		m := v.MustMap()
@@ -137,7 +165,7 @@ func (component pathComponent) visit(v Value, prefix Path, suffix Pattern, opts
 		case KindNil:
 			return InvalidValue, cannotTraverseNilError{path}
 		default:
-			return InvalidValue, fmt.Errorf("expected a sequence to index %q, found %s", path, v.Kind())
+			return InvalidValue, expectedSequenceToIndexError{p: path, v: v}
 		}
 
 		s := v.MustSequence()