chore: merge fields that are duplicated across subgraphs (#554)

pkg/federation/sdlmerge/merge_duplicated_fields.go

@@ -0,0 +1,62 @@
+package sdlmerge
+
+import (
+	"github.com/wundergraph/graphql-go-tools/pkg/ast"
+	"github.com/wundergraph/graphql-go-tools/pkg/astvisitor"
+	"github.com/wundergraph/graphql-go-tools/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)
+}

pkg/federation/sdlmerge/object_type_extending_test.go

@@ -209,4 +209,30 @@ func TestExtendObjectType(t *testing.T) {
 			}
 		`, nonEntityExtensionErrorMessage("Mammal"))
 	})
+
+	t.Run("", func(t *testing.T) {
+		run(t, newExtendObjectTypeDefinition(newTestNormalizer(true)), `
+			 type Mammal @key(fields: "name") {
+				name: String!
+				age: Int!
+			}
+			
+			extend type Mammal @key(fields: "name") {
+				name: String! @external
+				age: Int!
+			}
+		`, `
+			type Mammal @key(fields: "name") @key(fields: "name") {
+				name: String!
+				age: Int!
+				name: String! @external
+				age: Int!
+			}
+
+			extend type Mammal @key(fields: "name") {
+				name: String! @external
+				age: Int!
+			}
+		`)
+	})
 }

pkg/federation/sdlmerge/sdlmerge.go

@@ -136,6 +136,7 @@ func (m *normalizer) setupWalkers() {
 			newRemoveFieldDefinitions("external"),
 			newRemoveDuplicateFieldedSharedTypesVisitor(),
 			newRemoveDuplicateFieldlessSharedTypesVisitor(),
+			newMergeDuplicatedFieldsVisitor(),
 			newRemoveInterfaceDefinitionDirective("key"),
 			newRemoveObjectTypeDefinitionDirective("key"),
 			newRemoveFieldDefinitionDirective("provides", "requires"),

pkg/federation/sdlmerge/sdlmerge_test.go

@@ -143,6 +143,100 @@ func TestMergeSDLs(t *testing.T) {
 		emptyTypeBodyErrorMessage("object", "Message"),
 		accountSchema, negativeTestingProductSchema,
 	))
+
+	t.Run("Fields should merge successfully", runMergeTest(
+		`
+			type Mammal {
+				name: String!
+				age: Int!
+			}
+		`,
+		`
+			type Mammal @key(fields: "name") {
+				name: String!
+				age: Int!
+			}
+		`, `
+			extend type Mammal @key(fields: "name") {
+				name: String! @external
+				age: Int!
+			}
+		`,
+	))
+
+	t.Run("Operation fields should merge successfully", runMergeTest(
+		`
+			type Query {
+			  _service: _Service!
+			}
+
+			type _Service {
+			  sdl: String
+			}
+		`,
+		`
+			type Query {
+			  _service: _Service!
+			}
+
+			type _Service {
+			  sdl: String
+			}
+		`, `
+			type Query {
+		  		_service: _Service!
+			}
+
+			type _Service {
+			  sdl: String
+			}
+		`,
+	))
+
+	t.Run("Non-identical fields should fail to merge #1", runMergeTestAndExpectError(
+		unmergableDuplicateFieldsErrorMessage("age", "Mammal", "Int", "String"),
+		`
+			type Mammal @key(fields: "name") {
+				name: String!
+				age: Int
+			}
+		`, `
+			extend type Mammal @key(fields: "name") {
+				name: String! @external
+				age: String
+			}
+		`,
+	))
+
+	t.Run("Non-identical fields should fail to merge #2", runMergeTestAndExpectError(
+		unmergableDuplicateFieldsErrorMessage("age", "Mammal", "Int!", "String!"),
+		`
+			type Mammal @key(fields: "name") {
+				name: String!
+				age: Int!
+			}
+		`, `
+			extend type Mammal @key(fields: "name") {
+				name: String! @external
+				age: String!
+			}
+		`,
+	))
+
+	t.Run("Non-dentical fields should fail to merge #3", runMergeTestAndExpectError(
+		unmergableDuplicateFieldsErrorMessage("ages", "Mammal", "[Int!]!", "[String!]!"),
+		`
+			type Mammal @key(fields: "name") {
+				name: String!
+				ages: [Int!]!
+			}
+		`, `
+			extend type Mammal @key(fields: "name") {
+				name: String! @external
+				ages: [String!]!
+			}
+		`,
+	))
 }
 
 const (
@@ -672,6 +766,12 @@ func duplicateEntityErrorMessage(typeName string) string {
 	return fmt.Sprintf("the entity named '%s' is defined in the subgraph(s) more than once", typeName)
 }
 
+func unmergableDuplicateFieldsErrorMessage(fieldName, parentName, typeOne, typeTwo string) string {
+	return fmt.Sprintf("field '%s' on type '%s' is defined in multiple subgraphs "+
+		"but the fields cannot be merged because the types of the fields are non-identical:\n"+
+		"first subgraph: type '%s'\n second subgraph: type '%s'", fieldName, parentName, typeOne, typeTwo)
+}
+
 func Test_validateSubgraphs(t *testing.T) {
 	basePath := filepath.Join(".", "testdata", "validate-subgraph")
 

pkg/operationreport/externalerror.go

@@ -475,3 +475,10 @@ func ErrExtensionWithKeyDirectiveMustExtendEntity(typeName string) (err External
 	err.Message = fmt.Sprintf("the extension named '%s' has a key directive but there is no entity of the same name", typeName)
 	return err
 }
+
+func ErrDuplicateFieldsMustBeIdentical(fieldName, parentName, typeOne, typeTwo string) (err ExternalError) {
+	err.Message = fmt.Sprintf("field '%s' on type '%s' is defined in multiple subgraphs "+
+		"but the fields cannot be merged because the types of the fields are non-identical:\n"+
+		"first subgraph: type '%s'\n second subgraph: type '%s'", fieldName, parentName, typeOne, typeTwo)
+	return err
+}