x/tools/gopls: ctrl-click should jump to source, not to autogenerated code

[guettli]

gopls version

(does not matter here)

go env

(does not matter here)

What did you do?

I use Go, vscode and templ.guide

The tool templ creates Go code from templates.

I am looking at my Go file and I use a function which was auto-generated by templ:

If I ctrl-click on page() then ...

then I get to the autogenerated Go code:

It would be great if I could get to the templ-file instead:

As a user, the experience is not great, because I would like to jump to the original source (the templ template).

Does gpls provide hooks, which templ could implement, so that ctrl-click jumps directly to the templ template?

Related issue: a-h/templ#387

[icholy]

This would require something akin to sourcemaps.

[joerdav]

@icholy templ does in fact maintain sourcemaps, I think the main question is around whether templ can hook in to gopls to override the jump to definition, or if it would require using templ as the main lsp for go code (which I don't think would be ideal)

[findleyr]

So, a while back gopls would maintain two positions for every position: the "compiled" position, and whichever position was referenced by //line directives. As you might imagine, passing two positions throughout the call stack lead to a lot of complication and misuse, and so //line directives were rather buggy. For that reason, we removed them in #55043.

A cleaner solution would be to only handle line directives at API boundaries, for example in a func(protocol.Location) []protocol.Location that expanded or replaced positions based on //line directives. Such a function would not be that hard to write, but we haven't done so yet. In part, we were waiting to see if anyone cared, because we didn't know how anyone could have been relying on the old buggy implementation.

Does templ produce //line directives? Could it?

[joerdav]

Currently templ does not produce line directives. Though, I believe it could quite easily, as a source map is already maintained.

I imagine it would look something like this in a generated file, if I understand correctly (index_templ.go):

//line index.templ:20
func Index() templ.Component {
...

[findleyr]

@joerdav yes, that looks right.

[joerdav]

I'll give this a go in templ. Given that this isn't currently supported in gopls does the compiler directive have any effect at the moment?

[findleyr]

The compiler directive may affect the location of error messages. Since I wouldn't expect generated code to have errors, this may not matter.

Can you point me to an example of templ's current sourcemaps?

[joerdav]

Cool makes sense, ah I think you're talking about some sourcemap files, whereas templ only really holds it in memory for LSP purposes: https://github.com/a-h/templ/blob/main/parser/v2/sourcemap.go

[joerdav]

@findleyr We currently are processing a PR in templ to add //line directives to generated code. To support the potential release of this feature in gopls. a-h/templ#476

I've also done a proof-of-concept to check if this is possible in gopls, I fully would intend to tidy this up and add tests, but just wanted to check if I was on the right track here: joerdav/tools@63456ed

This does work on an example project.