Block Comment Handling Regression in gogen (v1.19.7 → v1.20.2) Produces Invalid Go Code

[luoliwoshang]

Description

After upgrading github.com/goplus/gogen from v1.19.7 to v1.20.2, I noticed a regression in how block comments (/* ... */) are handled when attached to a function.

In the previous version (v1.19.7), the generated Go source code was valid and could compile normally.

However, in the new version (v1.20.2), the same input produces malformed output where an extra */ is inserted before the function declaration, resulting in Go code that cannot be compiled.

---

Environment

• Package: github.com/goplus/gogen
• Working version: v1.19.7
• Broken version: v1.20.2
• Go version: (please fill in if needed)

---

Reproduction Code

package main

import (
    "go/ast"
    "go/token"
    "os"
    "strings"

    "github.com/goplus/gogen"
)

func main() {
    pkg := gogen.NewPackage("", "main", nil)

    commentGroup := &ast.CommentGroup{
        List: []*ast.Comment{
            {
                Slash: token.NoPos,
                Text:  "/* returns the version of cJSON as a string */\n",
            },
        },
    }

    fn := pkg.NewFunc(nil, "main", nil, nil, false)
    fn.SetComments(pkg, commentGroup)

    fn.BodyStart(pkg).End()

    var buf strings.Builder
    pkg.WriteTo(&buf, "")

    os.WriteFile("./temp/test.go", []byte(buf.String()), os.ModePerm)
}

---

Output in v1.19.7 (Correct)

package main

/* returns the version of cJSON as a string */

func main() {
}

This file compiles successfully.

---

Output in v1.20.2 (Incorrect)

package main

/* returns the version of cJSON as a string */
*/func main() {
}

Notice the unexpected extra */ before the function declaration.

---

Compilation Error

Running the generated file:

go run test.go

Produces:

# command-line-arguments
./test.go:3:1: syntax error: non-declaration statement outside function body

So the generated Go file is no longer valid and fails to compile.

---

Expected Behavior

The comment should be emitted cleanly above the function declaration, as in v1.19.7, without introducing invalid tokens.

---

Actual Behavior

In v1.20.2, block comments passed through fn.SetComments are incorrectly terminated, producing malformed Go code.

---

Request

Could you please check if there was a recent change in comment formatting logic between v1.19.7 and v1.20.2?

This appears to be a regression that breaks code generation when using block comments.

Thanks!

[luoliwoshang]

this behavior is the go/printer 's change lead

package main

import (
	"bytes"
	"fmt"
	"go/ast"
	"go/printer"
	"go/token"
)

func main() {
	fset := token.NewFileSet()
	f := &ast.File{
		Name: ast.NewIdent("main"),
		Decls: []ast.Decl{
			&ast.FuncDecl{
				Doc: &ast.CommentGroup{List: []*ast.Comment{{
					Slash: token.NoPos,
					Text:  "/* returns the version of cJSON as a string */\n",
				}}},
				Name: ast.NewIdent("main"),
				Type: &ast.FuncType{Params: &ast.FieldList{}},
				Body: &ast.BlockStmt{},
			},
		},
	}
	var b bytes.Buffer
	cfg := printer.Config{Mode: printer.UseSpaces | printer.TabIndent, Tabwidth: 8}
	if err := cfg.Fprint(&b, fset, f); err != nil {
		panic(err)
	}
	fmt.Print(b.String())
}

llcppg/_demo/printf on  main [$!?⇕] via 🐹 v1.24.10 
❯ go run main.go
package main
/* returns the version of cJSON as a string */
*/func main() {
}