Improve ResolverImplementer.Implment (#2850)

* improve resolver implement render

* add error when multiple implementors

* add initial test

plugin/plugin.go

@@ -3,10 +3,9 @@
 package plugin
 
 import (
-	"github.com/vektah/gqlparser/v2/ast"
-
 	"github.com/99designs/gqlgen/codegen"
 	"github.com/99designs/gqlgen/codegen/config"
+	"github.com/vektah/gqlparser/v2/ast"
 )
 
 type Plugin interface {
@@ -31,7 +30,7 @@ type LateSourceInjector interface {
 	InjectSourceLate(schema *ast.Schema) *ast.Source
 }
 
-// Implementer is used to generate code inside resolvers
+// ResolverImplementer is used to generate code inside resolvers
 type ResolverImplementer interface {
 	Implement(field *codegen.Field) string
 }

plugin/resolvergen/resolver.go

@@ -68,7 +68,7 @@ func (m *Plugin) generateSingleFile(data *codegen.Data) error {
 				continue
 			}
 
-			resolver := Resolver{o, f, nil, "", `panic("not implemented")`}
+			resolver := Resolver{o, f, nil, "", `panic("not implemented")`, nil}
 			file.Resolvers = append(file.Resolvers, &resolver)
 		}
 	}
@@ -130,29 +130,24 @@ func (m *Plugin) generatePerSchema(data *codegen.Data) error {
 
 			structName := templates.LcFirst(o.Name) + templates.UcFirst(data.Config.Resolver.Type)
 			comment := strings.TrimSpace(strings.TrimLeft(rewriter.GetMethodComment(structName, f.GoFieldName), `\`))
-
 			implementation := strings.TrimSpace(rewriter.GetMethodBody(structName, f.GoFieldName))
 			if implementation == "" {
-				// Check for Implementer Plugin
-				var resolver_implementer plugin.ResolverImplementer
-				var exists bool
-				for _, p := range data.Plugins {
-					if p_cast, ok := p.(plugin.ResolverImplementer); ok {
-						resolver_implementer = p_cast
-						exists = true
-						break
-					}
+				// use default implementation, if no implementation was previously used
+				implementation = fmt.Sprintf("panic(fmt.Errorf(\"not implemented: %v - %v\"))", f.GoFieldName, f.Name)
+			}
+			resolver := Resolver{o, f, rewriter.GetPrevDecl(structName, f.GoFieldName), comment, implementation, nil}
+			var implExists bool
+			for _, p := range data.Plugins {
+				rImpl, ok := p.(plugin.ResolverImplementer)
+				if !ok {
+					continue
 				}
-
-				if exists {
-					implementation = resolver_implementer.Implement(f)
-				} else {
-					implementation = fmt.Sprintf("panic(fmt.Errorf(\"not implemented: %v - %v\"))", f.GoFieldName, f.Name)
+				if implExists {
+					return fmt.Errorf("multiple plugins implement ResolverImplementer")
 				}
-
+				implExists = true
+				resolver.ImplementationRender = rImpl.Implement
 			}
-
-			resolver := Resolver{o, f, rewriter.GetPrevDecl(structName, f.GoFieldName), comment, implementation}
 			fnCase := gqlToResolverName(data.Config.Resolver.Dir(), f.Position.Src.Name, data.Config.Resolver.FilenameTemplate)
 			fn := strings.ToLower(fnCase)
 			if files[fn] == nil {
@@ -257,11 +252,19 @@ func (f *File) Imports() string {
 }
 
 type Resolver struct {
-	Object         *codegen.Object
-	Field          *codegen.Field
-	PrevDecl       *ast.FuncDecl
-	Comment        string
-	Implementation string
+	Object               *codegen.Object
+	Field                *codegen.Field
+	PrevDecl             *ast.FuncDecl
+	Comment              string
+	ImplementationStr    string
+	ImplementationRender func(r *codegen.Field) string
+}
+
+func (r *Resolver) Implementation() string {
+	if r.ImplementationRender != nil {
+		return r.ImplementationRender(r.Field)
+	}
+	return r.ImplementationStr
 }
 
 func gqlToResolverName(base string, gqlname, filenameTmpl string) string {

plugin/resolvergen/resolver_test.go

@@ -84,6 +84,24 @@ func TestOmitTemplateComment(t *testing.T) {
 	assertNoErrors(t, "github.com/99designs/gqlgen/plugin/resolvergen/testdata/omit_template_comment/out")
 }
 
+func TestResolver_Implementation(t *testing.T) {
+	_ = syscall.Unlink("testdata/resolver_implementor/resolver.go")
+
+	cfg, err := config.LoadConfig("testdata/resolver_implementor/gqlgen.yml")
+	require.NoError(t, err)
+	p := Plugin{}
+
+	require.NoError(t, cfg.Init())
+
+	data, err := codegen.BuildData(cfg, &implementorTest{})
+	if err != nil {
+		panic(err)
+	}
+
+	require.NoError(t, p.GenerateCode(data))
+	assertNoErrors(t, "github.com/99designs/gqlgen/plugin/resolvergen/testdata/resolver_implementor/out")
+}
+
 func TestCustomResolverTemplate(t *testing.T) {
 	_ = syscall.Unlink("testdata/resolvertemplate/out/resolver.go")
 	cfg, err := config.LoadConfig("testdata/resolvertemplate/gqlgen.yml")
@@ -142,3 +160,9 @@ func assertNoErrors(t *testing.T, pkg string) {
 		t.Fatal("see compilation errors above")
 	}
 }
+
+type implementorTest struct{}
+
+func (i *implementorTest) Implement(field *codegen.Field) string {
+	return "panic(\"implementor implemented me\")"
+}

plugin/resolvergen/testdata/resolver_implementor/gqlgen.yml

@@ -0,0 +1,15 @@
+schema:
+  - "testdata/schema.graphql"
+
+exec:
+  filename: testdata/resolver_implementor/out/ignored.go
+model:
+  filename: testdata/resolver_implementor/out/generated.go
+resolver:
+  type: CustomResolverType
+  layout: follow-schema
+  dir: testdata/resolver_implementor/out
+
+models:
+  Resolver:
+    model: github.com/99designs/gqlgen/plugin/resolvergen/testdata/resolver_implementor/out.Resolver

plugin/resolvergen/testdata/resolver_implementor/out/model.go

@@ -0,0 +1,13 @@
+package customresolver
+
+import "context"
+
+type Resolver struct{}
+
+type QueryResolver interface {
+	Resolver(ctx context.Context) (*Resolver, error)
+}
+
+type ResolverResolver interface {
+	Name(ctx context.Context, obj *Resolver) (string, error)
+}

plugin/resolvergen/testdata/resolver_implementor/out/resolver.go

@@ -0,0 +1,7 @@
+package customresolver
+
+// This file will not be regenerated automatically.
+//
+// It serves as dependency injection for your app, add any dependencies you require here.
+
+type CustomResolverType struct{}