How to make gf replace "res://" prefix with project root?

Question

Godot scripts sometimes contain lines like:

extends "res://cars/driveable.gd"

If my project is in c:/project, then that line refers to the path c:/project/cars/car_base.gd.

How can I make gf work with this root substitution scheme?

I would expect this to work, but it does not:

let &includeexpr = "substitute(v:fname, 'res:/', substitute(fnamemodify(findfile('project.godot', '.;'), ':h'), '\\', '/', 'g'), '')"

---

As a test, I can't get res:// paths to be affected by 'includeexpr' at all:

let &includeexpr = "substitute(v:fname, '.*', '~/.vimrc', '')"

Doing gf on my res:// line edits "res://cars/driveable.gd" (a nonexistent file, but no E447). If I change res: to res_, then that 'includeexpr' works. So it seems like vim thinks res:// is a real filepath and doesn't care that it doesn't exist.

I saw the question open salt://whatever as somedir/whatever and it seems close, but findfile("project.godot", ".;") returns res://cars/project.godot inside my BufReadCmd instead of the actual path. The returned path should be c:/code/project/project.godot and definitely shouldn't have the "cars" directory in it. (Neither resolve() nor expand() are helpful.)

I have netrw disabled, but I get similar results with gvim --clean.

Answer 1

For some reason (possibly Netrw integration), Vim seems to treat all paths that start with a scheme-like foo:// as legitimate paths so includeexpr, which is invoked when the path can't be found, is never invoked. If these tests are not enough, one can test this empirically with this file:

" filename.ext
"patapouf://sdsgifd/sdjfghsd/sdgfisd"
"sdsgifd/sdjfghsd/sdgfisd"

" no netrw, no vimrc, no defaults.vim
$ vim -Nu NONE filename.ext
:1normal gf
<opens buffer for patapouf://sdsgifd/sdjfghsd/sdgfisd>
:b#
:2normal gf
E447: Can't find file "sdsgifd/sdjfghsd/sdgfisd" in 'path

This is not a satisfying situation, IMO, which creates similar problems in other filetypes (./foo/bar should resolve to ./foo/bar.ext and ./foo/bar/index.ext in JavaScript but only the former is possible because Vim thinks ./foo/bar/ is a legitimate path).

The workaround I've used is to map gf and friends to a custom function:

nnoremap <silent> <buffer> gf      :<C-u>call GF('n', 0, 0, v:count1)<CR>
nnoremap <silent> <buffer> <C-w>f  :<C-u>call GF('n', 1, 0, v:count1)<CR>
nnoremap <silent> <buffer> <C-w>gf :<C-u>call GF('n', 1, 1, v:count1)<CR>
xnoremap <silent> <buffer> gf      <C-c>:call GF('v', 0, 0, v:count1)<CR>
xnoremap <silent> <buffer> <C-w>f  <C-c>:call GF('v', 1, 0, v:count1)<CR>
xnoremap <silent> <buffer> <C-w>gf <C-c>:call GF('v', 1, 1, v:count1)<CR>

function! GF(mode, split, tab, count) abort
    if a:mode == "n"
        let fname = expand('<cfile>')
    else
        let old_reg = getreg("v")
        normal! gv"vy
        let fname = getreg("v")
        call setreg("v", old_reg)
    endif

    let transformed_name = SomeFunction(fname)    " your implementation here
    let found_file = findfile(transformed_name, &path, a:count)

    if empty(found_file)
        echohl Error
        echo "E447: Can't find file \"" . fname . "\" in path"
        echohl None
        return 0
    endif

    let cmds = {
                \ "00": "silent edit ",
                \ "10": "silent split ",
                \ "11": "silent tab split ",
                \ }

    execute cmds[a:split . a:tab] . found_file
endfunction