go/token: add (*File).String method

[adonovan]

Proposal Details

Background: This behavior is not helpful:

	f := token.NewFileSet().AddFile("foo.go", -1, 0)
	fmt.Println(f) // "&{foo.go 1 0 {{} {0 0}} [0] []}"

Proposal: We propose to add this String method to token.File:

package token // "go/token"

// String returns a brief description of the file.
func (f *File) String() string {
        return fmt.Sprintf("%s(%d-%d)", f.Name(), f.Base(), f.End())
}

[Edited Nov 13 to return more than just the name.]

[gabyhelp]

Related Issues

• proposal: go/token: add File.End method #75849
• proposal: archive/zip: *File should implement fmt.Stringer #23260 (closed)
• proposal: os/exec: add String() to *exec.Cmd #21707 (closed)
• go/token: add a (*File).Lines method #57708 (closed)
• go/token: add (*FileSet).AddExistingFiles method to add files out of order #73205 (closed)
• fs: standard implementations of FileInfo and DirEntry should implement fmt.Stringer #54451 (closed)

_{(Emoji vote if this was helpful or unhelpful; more detailed feedback welcome in this discussion.)}

[Agent-Hellboy]

Hi @adonovan , let me do this, I would learn a lot looking at unittest for token and all.

[adonovan]

Hi @adonovan , let me do this, I would learn a lot looking at unittest for token and all.

Thanks for the offer, but the code is already written: see above. ;-) The main obstacle here is waiting for the proposal to be approved, which could take weeks.

[mvdan]

Should the string method say anything about the other file info, like its size? If someone just wants the filename, they can always just call the Name method.

[adonovan]

If someone just wants the filename, they can always just call the Name method.

That's true, but one often forgets when hastily adding a log.Println(fset.File(pos)) statement, and is then confronted with a dump of a massive line-offset table.

Should the string method say anything about the other file info, like its size?

Usually the filename is all one wants, but you're right that we have an opportunity here to do better. More useful than size would be the Pos-End extent. So how about ("%s(%d-%d)", Name, Pos, End)?

[mvdan]

That format sounds good to me. I didn't mean to say we should not be adding a String method, but rather, that we have the opportunity to make it a bit more well-rounded than just a copy of Name.

[mateusz834]

Should the string method say anything about the other file info, like its size? If someone just wants the filename, they can always just call the Name method.

We could define a GoString for that i guess? i.e. fmt.GoStringer

[odeke-em]

I have moved the milestone to Go1.27 as we haven’t yet gotten a review but in the end cycle for Go1.26.