What version of Go are you using (go version)?

$ go version
go version go1.17 linux/amd64

Does this issue reproduce with the latest release?

Yes

What did you do?

1. Parse the following source code with mode parser.ImportsOnly|parser.ParseComments:

// Package main
package main

import (
	// fmt import
	_ "fmt"
	_ "github.com/pkg/errors" // errors import
)

// F func
func F() {}

// B func
func B() {}

// Hello const
const Hello = "word"

func main() {
}

2. Print *ast.File.Comments

The Go Playground link: https://play.golang.org/p/w0yK1K_q4tr

What did you expect to see?

3 comments:

"Package main\n"
"fmt import\n"
"errors import\n"

What did you see instead?

4 comments:

"Package main\n"
"fmt import\n"
"errors import\n"
"F func\n"

"F func\n" is an extra comment because the documentation for parser.ImportsOnly says stop parsing after import declarations. However, if an import declaration is followed by any code without comments, there will be no extra comments. For example:

// Package main
package main

import (
	_ "fmt" // fmt import
)

var A = 1

// F func
func F() {}

This bug was originally discovered in #47436 (comment)