lsp: Support goToDefinition from a Go file to a templ file

[guettli]

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:

[a-h]

Yes, that would be much more useful!

If you're in a *.templ file, then the templ LSP is operating and will carry out a remapping operation from templ position -> go file position -> gopls -> templ position, as per here:

templ/cmd/templ/lspcmd/proxy/server.go

Lines 507 to 512 in c674f64

	for i := 0; i < len(result); i++ {
	if isTemplGoFile, templURI := convertTemplGoToTemplURI(result[i].URI); isTemplGoFile {
	result[i].URI = templURI
	result[i].Range = p.convertGoRangeToTemplRange(templURI, result[i].Range)
	}
	}

But currently, if you start from a *.go file, then gopls is operating and there's no templ code running at all. To rewrite the responses from gopls, templ would have to proxy all Go LSP operations (i.e. for all *.go files) and work out that if a _templ.go file was being referenced, then, it should look up the various source code mapping positions and switch it to *.templ instead. I'm not sure if replacing (as a proxy) gopls for all projects is ideal (higher risk?), but it would work.

It may also possible for the templ LSP to capture *_templ.go file usage too, and be able to ctrl+click on the function name to get to the *.templ file. (Worse UX, but maybe a good first step)

[joerdav]

I know you can have multiple LSPs attached to a file, but I wonder what would happen if you had 2 trying to respond to a jump to definition request.

[guettli]

I asked the gopls maintainers. Maybe they know a hook which templ could implement: golang/go#65001

[joerdav]

We have the following issue to implement the line directive #415, and then I think it's a case of closing this ticket and helping the gopls team implement golang/go#65001

[guettli]

@joerdav thank you for your work! This is great!

[joerdav]

Thank @af-md !

[meistertigran]

Here's a quick and dirty fix for anyone using neovim. It doesn't go directly to the location of the definition in the file, but at least it opens the correct file.

local go_to_definition = function()
    if vim.bo.filetype == "go" then
        vim.lsp.buf.definition({
            on_list = function(options)
                if options == nil or options.items == nil or #options.items == 0 then
                    return
                end

                local targetFile = options.items[1].filename
                local prefix = string.match(targetFile, "(.-)_templ%.go$")

                if prefix then
                    options.items[1].filename = prefix .. ".templ"
                end

                vim.fn.setqflist({}, ' ', options)
                vim.api.nvim_command('cfirst')
            end
        })
    else
        vim.lsp.buf.definition()
    end
end

and then in your key map

vim.keymap.set("n", "gd", go_to_definition)

Note that the check for being in a go buffer will run every time you try to go to definition. You probably would want to add this modification only if you are using templ a lot and should remember to remove it once the actual fix is implemented.