Lsp-mode: Error when selecting 'fill match arms' code action: (void-function yas-expand-snippet)

[jimblandy]

In lsp-mode-20201021.1658, clicking on the light bulb in the mode line to fill in a match statement raises an error saying that yas-expand-snippet is not defined, at the backtrace below.

I do not have yasnippet installed.

Debugger entered--Lisp error: (void-function yas-expand-snippet)
  yas-expand-snippet("\\{\n            Some(${0:_}) => \\{}\n            Non..." 4829 4894 nil)
  lsp--expand-snippet("{\n            Some(${0:_}) => {}\n            None ..." 4829 4894)
  #f(compiled-function (edit) #<bytecode 0xdcf815>)(#<hash-table equal 3/3 0xe649e1>)
  mapc(#f(compiled-function (edit) #<bytecode 0xdcf815>) [#<hash-table equal 3/3 0xe649e1>])
  lsp--apply-text-edits([#<hash-table equal 3/3 0xe649e1>])
  lsp--apply-text-document-edit(#<hash-table equal 2/2 0xe64989>)
  mapc(lsp--apply-text-document-edit (#<hash-table equal 2/2 0xe64989>))
  seq-do(lsp--apply-text-document-edit (#<hash-table equal 2/2 0xe64989>))
  lsp--apply-workspace-edit(#<hash-table equal 1/1 0xe64951>)
  lsp-execute-code-action(#<hash-table equal 3/3 0xe648f9>)
  #f(compiled-function () (interactive nil) #<bytecode 0xe6b869>)()
  funcall-interactively(#f(compiled-function () (interactive nil) #<bytecode 0xe6b869>))
  call-interactively(#f(compiled-function () (interactive nil) #<bytecode 0xe6b869>) nil nil)
  command-execute(#f(compiled-function () (interactive nil) #<bytecode 0xe6b869>))

[jcs090218]

I think we are calling external function yas-expand-snippet without ensuring the function existence. I think the error is cause by the line here.

https://github.com/emacs-lsp/lsp-mode/blob/9116389c96b2f7ddd537d2842550d2f3bc140119/lsp-mode.el#L3964

I will mark this as bug for now! Thank you for reporting this issue to us!

[yyoncho]

The issue here is server-side - Rust Analyzer does not support running without snippets which we try to enforce. The only option ATM to fix that client-side is the user to install yasnippet package.

[jimblandy]

@yyoncho At the moment, lsp-mode.el says:

(require 'yasnippet nil t)

If yasnippet is a hard requirement, then shouldn't that be an ordinary require form? And shouldn't it be listed in lsp-mode-pkg.el?

[jcs090218]

IMO, we should still fix this issue in the client sider; unless the server is fixed.

@jimblandy Has a good point here. Or maybe we can just simply add yasnippet as a package dependency? 😕

[yyoncho]

If yasnippet is a hard requirement, then shouldn't that be an ordinary require form? And shouldn't it be listed in lsp-mode-pkg.el?

it is not a hard dependency but soft. You can run perfectly fine without it when the server follows the spec.

[yyoncho]

We might change the error message though

[jimblandy]

Okay - I didn't understand that it is rust-analyzer that is misbehaving, and sending Emacs things that it should not.

Do you happen to know if there is an issue filed against rust-analyzer for this problem? I would file one myself, but I don't know the protocol, so I'm not sure how to explain the issue.

[yyoncho]

They have closed the server side issue - https://github.com/rust-analyzer/rust-analyzer/issues/2518 . I tried it on my side and with snippets being off it all works fine. How do you get that error?

[nbfalcon]

Isn't that issue about snippet completion, not fill-match-arms?

[yyoncho]

Ah, actually, the issue is not in the completion. I will do the proper fix client side.

[yyoncho]

see https://github.com/emacs-lsp/lsp-mode/commit/a9c5fec385e089463ffb5a310ed333d95cd5449c

[yyoncho]

Just want to mention that now, if you don't have yasnippet the code actions that require snippets (e. g. Add derive) won't work at all.

[nbfalcon]

@yyoncho is a good error message provided in that case? If not, we might want to fix that.

[yyoncho]

Hitting the error won't be possible due to the fact that the server will no longer send snippets. When there are no snippets we will behave like in #1907