Show deprecation warning in completion list

[TonalidadeHidrica]

Is your feature request related to a problem? Please describe.
When I choose an item from a completion list, not until a warning is shown that I realize that the selected item is actually deprecated.

Describe the solution you'd like
I want a deprecation mark like ⚠️ shown before the item, or a strikethrough over the item name.

Describe alternatives you've considered
We may alternatively (or also) show that it is deprecated in the docs window shown when we pre-select the completion.

Additional context
Specifically I want this feature for rust-analyzer. I first asked rust-analyzer for this feature to be informed that the LSP already provides such diagnostic and is available in VSCode. (A screenshot is included in that issue.)

[oblitum]

coc.nvim already does this, if it comes as diagnostics warning/info, you can check that with typescript + coc-tsserver for example.

What it doesn't do is this:

• fix(diagnostic): highlight hints, deprecated and unused text with their own unique hlgroups #3188 (comment)

rust-analyzer uses semantic tokens and/or completion tags, and coc doesn't yet fully provide that.

[TonalidadeHidrica]

I realized that I wrote a little bit confusing description, sorry for that. So let me summarize; let me know if I said something wrong.

There are at least three ways for Language Servers to tell that an item is deprecated:

• Through diagnostics. LS points out through diagnostics that some part of a code is using deprecated function etc..
  • This can also be viewed in :CocList diagnostics.
  • You pointed out that it is already available in typescript + coc-tsserver, right? Yes, it indeed works in coc-rust-analyzer, too.
• Through semantic tokens. That is a concept I have never heard of, but perhaps that is an additional information attached to tokens which are sent from LS as a result of its tokenization, isn't it?
• Through completion tags. I didn't know that either, but probably this is what I want, which probably comes with each entry in completion list given from LS.

And you said that the latter two is not entirely supported by coc.nvim.

Is there already an issue that specifically ask for this kind of features in completion list? If there is, please close the issue; otherwise I'll leave it as a ticket of feature request.

[oblitum]

You can keep the ticket, there isn't an specific issue that covers either of the two latter ones.

perhaps that is an additional information attached to tokens which are sent from LS as a result of its tokenization, isn't it?

Yes, it's that, and comes as "deprecated" semantic token "modifier".

You most probably is pointing for completion tag, as the semantic token modifier would present itself in source code strikethrough highlighting.

[TonalidadeHidrica]

@oblitum Thanks. I additionally filed another issue on semantic tokens in #3481.

[oblitum]

@TonalidadeHidrica okay. Notice a strikethrough over some pum items is in fact not possible due to vim/nvim limitation, pum doesn't support syntax highlighting. So the only way out (with pum) is by means of a glyph mark.

[oblitum]

To have that with completion you have to ditch vim/nvim native completion system and reimplement it through vim-popups/nvim-floating-windows, like nvim-cmp has done.

[chemzqm]

Not too hard to implement completion pum by using float window or popup, but lots of details and break changes of how completion works.

Vote for the feature if you really like it.