refactor(astfile): add generated code comment to output files

README.md

@@ -8,6 +8,10 @@
 
 `moldable` builds precise interfaces from any package so you can plug in `mockery`, `gomock`, `moq`, or any other mock tool you like.
 
+| ![Example](./.github/example.png) |
+| :--: |
+| *Example: every exported AWS S3 struct becomes its own ready-to-use interface.* |
+
 > [!WARNING]
 > This project is in active development and may contain bugs or breaking changes. We recommend testing thoroughly in your environment before using in production. Issues and contributions are welcome!
 
@@ -105,7 +109,6 @@ moldable version
 
 Re-run `moldable` whenever the upstream code changes; imports and file lists are recalculated automatically.
 
---------------------------------------------------
 ## Configuration
 
 The file `moldable.yaml` is created by `moldable init` command.

go.mod

@@ -11,7 +11,6 @@ require (
 	github.com/spf13/cobra v1.10.1
 	github.com/spf13/pflag v1.0.10
 	github.com/stretchr/testify v1.11.1
-	golang.org/x/exp v0.0.0-20250911091902-df9299821621
 	golang.org/x/tools v0.37.0
 )
 
@@ -37,6 +36,7 @@ require (
 	github.com/rivo/uniseg v0.4.7 // indirect
 	github.com/xo/terminfo v0.0.0-20220910002029-abceb7e1c41e // indirect
 	go.yaml.in/yaml/v3 v3.0.4 // indirect
+	golang.org/x/exp v0.0.0-20250911091902-df9299821621 // indirect
 	golang.org/x/mod v0.28.0 // indirect
 	golang.org/x/sync v0.17.0 // indirect
 	golang.org/x/sys v0.36.0 // indirect

go.sum

@@ -66,8 +66,6 @@ github.com/xo/terminfo v0.0.0-20220910002029-abceb7e1c41e h1:JVG44RsyaB9T2KIHavM
 github.com/xo/terminfo v0.0.0-20220910002029-abceb7e1c41e/go.mod h1:RbqR21r5mrJuqunuUZ/Dhy/avygyECGrLceyNeo4LiM=
 go.yaml.in/yaml/v3 v3.0.4 h1:tfq32ie2Jv2UxXFdLJdh3jXuOzWiL1fo0bu/FbuKpbc=
 go.yaml.in/yaml/v3 v3.0.4/go.mod h1:DhzuOOF2ATzADvBadXxruRBLzYTpT36CKvDb3+aBEFg=
-golang.org/x/exp v0.0.0-20250819193227-8b4c13bb791b h1:DXr+pvt3nC887026GRP39Ej11UATqWDmWuS99x26cD0=
-golang.org/x/exp v0.0.0-20250819193227-8b4c13bb791b/go.mod h1:4QTo5u+SEIbbKW1RacMZq1YEfOBqeXa19JeshGi+zc4=
 golang.org/x/exp v0.0.0-20250911091902-df9299821621 h1:2id6c1/gto0kaHYyrixvknJ8tUK/Qs5IsmBtrc+FtgU=
 golang.org/x/exp v0.0.0-20250911091902-df9299821621/go.mod h1:TwQYMMnGpvZyc+JpB/UAuTNIsVJifOlSkrZkhcvpVUk=
 golang.org/x/mod v0.28.0 h1:gQBtGhjxykdjY9YhZpSlZIsbnaE2+PgjfLWUQTnoZ1U=

internal/astfile/file.go

@@ -22,13 +22,15 @@ type InterfaceSpec struct {
 }
 
 type File struct {
+	fset        *token.FileSet
 	packageName string
 	imports     []*ImportSpec
 	interfaces  []*InterfaceSpec
 }
 
-func New(packageName string) *File {
+func New(fset *token.FileSet, packageName string) *File {
 	return &File{
+		fset:        fset,
 		packageName: packageName,
 		imports:     make([]*ImportSpec, 0),
 		interfaces:  make([]*InterfaceSpec, 0),
@@ -61,8 +63,15 @@ func (f *File) Build(qual types.Qualifier) (*ast.File, error) {
 	decls = append(decls, interfaces...)
 
 	return &ast.File{
-		Name:  ast.NewIdent(f.packageName),
-		Decls: decls,
+		Doc: &ast.CommentGroup{
+			List: []*ast.Comment{{
+				Slash: 1,
+				Text:  "// Code generated by moldable; DO NOT EDIT.",
+			}},
+		},
+		Package: 2,
+		Name:    ast.NewIdent(f.packageName),
+		Decls:   decls,
 	}, nil
 }
 

internal/astfile/writer.go

@@ -18,13 +18,11 @@ func NewWriter() *Writer {
 	return &Writer{}
 }
 
-func (Writer) Write(file *ast.File, path string) error {
+func (Writer) Write(fset *token.FileSet, file *ast.File, path string) error {
 	if err := os.MkdirAll(filepath.Dir(path), 0755); err != nil {
 		return fmt.Errorf("creating directory: %w", err)
 	}
 
-	fset := token.NewFileSet()
-
 	var buf bytes.Buffer
 
 	if err := format.Node(&buf, fset, file); err != nil {

internal/generator/generator.go

@@ -2,6 +2,7 @@ package generator
 
 import (
 	"fmt"
+	"go/token"
 	"go/types"
 	"path/filepath"
 	"strings"
@@ -57,7 +58,13 @@ func (g Generator) Generate() error {
 func (g Generator) processPackage(pkg *types.Package) error {
 	g.reporter.ProcessingPackage(pkg.Path())
 
-	builder := astfile.New(g.config.Output.Package)
+	filename := strings.ReplaceAll(g.config.Output.Filename, "{package}", pkg.Name())
+
+	fset := token.NewFileSet()
+
+	fset.AddFile(filename, fset.Base(), 1)
+
+	builder := astfile.New(fset, g.config.Output.Package)
 
 	is := importset.New()
 	is.Import(pkg)
@@ -106,12 +113,9 @@ func (g Generator) processPackage(pkg *types.Package) error {
 		return fmt.Errorf("building ast file: %w", err)
 	}
 
-	path := filepath.Join(
-		g.config.Output.Dir,
-		strings.ReplaceAll(g.config.Output.Filename, "{package}", pkg.Name()),
-	)
+	output := filepath.Join(g.config.Output.Dir, filename)
 
-	if err := g.writer.Write(file, path); err != nil {
+	if err := g.writer.Write(fset, file, output); err != nil {
 		return fmt.Errorf("writing file: %w", err)
 	}