feat(sdlmerge): add shared types for GraphQL schema handling

Introduce types for managing fielded, enum, union, and scalar shared types.
Implement functionality for comparing values and creating field sets.
Enhance schema extensions by integrating new visitors for enum types.

sdlmerge/merge_duplicated_fields.go

@@ -0,0 +1,62 @@
+package sdlmerge
+
+import (
+	"github.com/wundergraph/graphql-go-tools/v2/pkg/ast"
+	"github.com/wundergraph/graphql-go-tools/v2/pkg/astvisitor"
+	"github.com/wundergraph/graphql-go-tools/v2/pkg/operationreport"
+)
+
+type mergeDuplicatedFieldsVisitor struct {
+	*astvisitor.Walker
+	document *ast.Document
+}
+
+func newMergeDuplicatedFieldsVisitor() *mergeDuplicatedFieldsVisitor {
+	return &mergeDuplicatedFieldsVisitor{
+		nil,
+		nil,
+	}
+}
+
+func (m *mergeDuplicatedFieldsVisitor) Register(walker *astvisitor.Walker) {
+	m.Walker = walker
+	walker.RegisterEnterDocumentVisitor(m)
+	walker.RegisterLeaveObjectTypeDefinitionVisitor(m)
+}
+
+func (m *mergeDuplicatedFieldsVisitor) EnterDocument(document, _ *ast.Document) {
+	m.document = document
+}
+
+func (m *mergeDuplicatedFieldsVisitor) LeaveObjectTypeDefinition(ref int) {
+	var refsForDeletion []int
+	fieldByTypeRefSet := make(map[string]int)
+	for _, fieldRef := range m.document.ObjectTypeDefinitions[ref].FieldsDefinition.Refs {
+		fieldName := m.document.FieldDefinitionNameString(fieldRef)
+		newTypeRef := m.document.FieldDefinitions[fieldRef].Type
+		if oldTypeRef, ok := fieldByTypeRefSet[fieldName]; ok {
+			if m.document.TypesAreEqualDeep(oldTypeRef, newTypeRef) {
+				refsForDeletion = append(refsForDeletion, fieldRef)
+				continue
+			}
+			oldFieldTypeNameBytes, err := m.document.PrintTypeBytes(oldTypeRef, nil)
+			if err != nil {
+				m.Walker.StopWithInternalErr(err)
+				return
+			}
+			newFieldTypeNameBytes, err := m.document.PrintTypeBytes(newTypeRef, nil)
+			if err != nil {
+				m.Walker.StopWithInternalErr(err)
+				return
+			}
+			m.Walker.StopWithExternalErr(operationreport.ErrDuplicateFieldsMustBeIdentical(
+				fieldName, m.document.ObjectTypeDefinitionNameString(ref), string(oldFieldTypeNameBytes), string(newFieldTypeNameBytes),
+			))
+			return
+		}
+
+		fieldByTypeRefSet[fieldName] = newTypeRef
+	}
+
+	m.document.RemoveFieldDefinitionsFromObjectTypeDefinition(refsForDeletion, ref)
+}