plugin/resolvergen: respect named return values

codegen/field.go

@@ -3,6 +3,7 @@ package codegen
 import (
 	"errors"
 	"fmt"
+	goast "go/ast"
 	"go/types"
 	"log"
 	"reflect"
@@ -503,6 +504,12 @@ func (f *Field) ResolverType() string {
 }
 
 func (f *Field) ShortResolverDeclaration() string {
+	return f.ShortResolverSignature(nil)
+}
+
+// ShortResolverSignature is identical to ShortResolverDeclaration,
+// but respects previous naming (return) conventions, if any.
+func (f *Field) ShortResolverSignature(ft *goast.FuncType) string {
 	if f.Object.Kind == ast.InputObject {
 		return fmt.Sprintf("(ctx context.Context, obj %s, data %s) error",
 			templates.CurrentImports.LookupType(f.Object.Reference()),
@@ -523,8 +530,17 @@ func (f *Field) ShortResolverDeclaration() string {
 	if f.Object.Stream {
 		result = "<-chan " + result
 	}
-
-	res += fmt.Sprintf(") (%s, error)", result)
+	// Named return.
+	var namedV, namedE string
+	if ft != nil {
+		if ft.Results != nil && len(ft.Results.List) > 0 && len(ft.Results.List[0].Names) > 0 {
+			namedV = ft.Results.List[0].Names[0].Name
+		}
+		if ft.Results != nil && len(ft.Results.List) > 1 && len(ft.Results.List[1].Names) > 0 {
+			namedE = ft.Results.List[1].Names[0].Name
+		}
+	}
+	res += fmt.Sprintf(") (%s %s, %s error)", namedV, result, namedE)
 	return res
 }
 

internal/rewrite/rewriter.go

@@ -68,7 +68,7 @@ func (r *Rewriter) getFile(filename string) string {
 	return r.files[filename]
 }
 
-func (r *Rewriter) GetMethodComment(structname string, methodname string) string {
+func (r *Rewriter) GetPrevDecl(structname string, methodname string) *ast.FuncDecl {
 	for _, f := range r.pkg.Syntax {
 		for _, d := range f.Decls {
 			d, isFunc := d.(*ast.FuncDecl)
@@ -89,48 +89,29 @@ func (r *Rewriter) GetMethodComment(structname string, methodname string) string
 			if !ok {
 				continue
 			}
-
 			if ident.Name != structname {
 				continue
 			}
-			return d.Doc.Text()
+			r.copied[d] = true
+			return d
 		}
 	}
+	return nil
+}
 
+func (r *Rewriter) GetMethodComment(structname string, methodname string) string {
+	d := r.GetPrevDecl(structname, methodname)
+	if d != nil {
+		return d.Doc.Text()
+	}
 	return ""
 }
-func (r *Rewriter) GetMethodBody(structname string, methodname string) string {
-	for _, f := range r.pkg.Syntax {
-		for _, d := range f.Decls {
-			d, isFunc := d.(*ast.FuncDecl)
-			if !isFunc {
-				continue
-			}
-			if d.Name.Name != methodname {
-				continue
-			}
-			if d.Recv == nil || len(d.Recv.List) == 0 {
-				continue
-			}
-			recv := d.Recv.List[0].Type
-			if star, isStar := recv.(*ast.StarExpr); isStar {
-				recv = star.X
-			}
-			ident, ok := recv.(*ast.Ident)
-			if !ok {
-				continue
-			}
 
-			if ident.Name != structname {
-				continue
-			}
-
-			r.copied[d] = true
-
-			return r.getSource(d.Body.Pos()+1, d.Body.End()-1)
-		}
+func (r *Rewriter) GetMethodBody(structname string, methodname string) string {
+	d := r.GetPrevDecl(structname, methodname)
+	if d != nil {
+		return r.getSource(d.Body.Pos()+1, d.Body.End()-1)
 	}
-
 	return ""
 }
 

plugin/resolvergen/resolver.go

@@ -4,6 +4,7 @@ import (
 	_ "embed"
 	"errors"
 	"fmt"
+	"go/ast"
 	"io/fs"
 	"os"
 	"path/filepath"
@@ -67,7 +68,7 @@ func (m *Plugin) generateSingleFile(data *codegen.Data) error {
 				continue
 			}
 
-			resolver := Resolver{o, f, "// foo", `panic("not implemented")`}
+			resolver := Resolver{o, f, nil, "// foo", `panic("not implemented")`}
 			file.Resolvers = append(file.Resolvers, &resolver)
 		}
 	}
@@ -119,16 +120,16 @@ func (m *Plugin) generatePerSchema(data *codegen.Data) error {
 			}
 
 			structName := templates.LcFirst(o.Name) + templates.UcFirst(data.Config.Resolver.Type)
-			implementation := strings.TrimSpace(rewriter.GetMethodBody(structName, f.GoFieldName))
 			comment := strings.TrimSpace(strings.TrimLeft(rewriter.GetMethodComment(structName, f.GoFieldName), `\`))
-			if implementation == "" {
-				implementation = fmt.Sprintf("panic(fmt.Errorf(\"not implemented: %v - %v\"))", f.GoFieldName, f.Name)
-			}
 			if comment == "" {
 				comment = fmt.Sprintf("%v is the resolver for the %v field.", f.GoFieldName, f.Name)
 			}
+			implementation := strings.TrimSpace(rewriter.GetMethodBody(structName, f.GoFieldName))
+			if implementation == "" {
+				implementation = fmt.Sprintf("panic(fmt.Errorf(\"not implemented: %v - %v\"))", f.GoFieldName, f.Name)
+			}
 
-			resolver := Resolver{o, f, comment, implementation}
+			resolver := Resolver{o, f, rewriter.GetPrevDecl(structName, f.GoFieldName), comment, implementation}
 			fn := gqlToResolverName(data.Config.Resolver.Dir(), f.Position.Src.Name, data.Config.Resolver.FilenameTemplate)
 			if files[fn] == nil {
 				files[fn] = &File{}
@@ -215,6 +216,7 @@ func (f *File) Imports() string {
 type Resolver struct {
 	Object         *codegen.Object
 	Field          *codegen.Field
+	PrevDecl       *ast.FuncDecl
 	Comment        string
 	Implementation string
 }

plugin/resolvergen/resolver.gotpl

@@ -20,7 +20,7 @@
 
 {{ range $resolver := .Resolvers -}}
     // {{ $resolver.Comment }}
-	func (r *{{lcFirst $resolver.Object.Name}}{{ucFirst $.ResolverType}}) {{$resolver.Field.GoFieldName}}{{ $resolver.Field.ShortResolverDeclaration }} {
+	func (r *{{lcFirst $resolver.Object.Name}}{{ucFirst $.ResolverType}}) {{$resolver.Field.GoFieldName}}{{ with $resolver.PrevDecl }}{{ $resolver.Field.ShortResolverSignature .Type }}{{ else }}{{ $resolver.Field.ShortResolverDeclaration }}{{ end }}{
 		{{ $resolver.Implementation }}
 	}
 

plugin/resolvergen/resolver_test.go

@@ -37,7 +37,8 @@ func TestLayoutFollowSchema(t *testing.T) {
 	require.NoError(t, err)
 	source := string(b)
 
-	require.Contains(t, source, "// CustomerResolverType.Resolver implementation")
+	require.Contains(t, source, "(_ *customresolver.Resolver, err error)")
+	require.Contains(t, source, "// Named return values are supported.")
 	require.Contains(t, source, "// CustomerResolverType.Name implementation")
 	require.Contains(t, source, "// AUserHelperFunction implementation")
 }