Support LSP tab stops like ${1}

[muirdm]

The LSP spec ("Snippet Syntax") says tab stops can optionally have curlies: tabstop ::= '$' int | '${' int '}'. Currently yasnippet seems to support $1 but not ${1} (expanding ${1} inserts a literal "1"). Can ${1} be supported in a backwards compatible way, or is the current behavior intended?

[npostavs]

yasnippet doesn't implement the LSP Snippet Syntax, but the current handling of ${1} doesn't seem to make much sense (it creates a tab stop with default contents of 1), so I'd say changing it is not out of the question.

Related: #979 "Handle curly braces with LSP-style escaping"

[xendk]

The PHPactor language server, for one, insists on using ${0} on a lot of completions, so it turns annoying fast.

A workaround until it's decided if yasnippet or eglot should handle it:

(define-advice eglot--snippet-expansion-fn (:override (&rest args) xen-eglot--snippet-expansion-fn)
    (and (fboundp 'yas-minor-mode)
         (lambda (&rest args)
           (with-no-warnings
             (unless (bound-and-true-p yas-minor-mode) (yas-minor-mode 1))
             (apply #'yas-expand-snippet (list (replace-regexp-in-string "\\${\\([[:digit:]]+\\)}" "$\\1" (car args))))))))

[monnier]

I just pushed to master a patch which seems to make YASnippet accept this. I'm not familiar with this part of the code at all, so knock on wood. If you can try it (e.g. via GNU-devel ELPA where it should appear this afternoon) and confirm that it works for you, that would be great.

[xendk]

I'm using elpaca, so I just pulled and commented my advice. Seems to work fine here. :+1: