Panel Completions

[kassick]

Copilot support a textDocument/copilotPanelCompletion call that generates a number of code suggestions at point. Unlike inline completions, these completions are supposed to be displayed in a separate window, so the user can inspect the suggestions more thoroughly.

Also unlike inline completions, textDocument/copilotPanelCompletion is a client-to-server notification -- there's no response. The code suggestions are provided via $/progress server-to-client notifications. It's up to us to collect these suggestions to then display them.

I've implemented this in lsp-copilot and the results can be seen below:

Gravacao.de.tela.de.2024-12-27.11-20-54.mp4

• I've fixed the progress callback of copilot-ls to actually integrate with the LSP native progress reports (notice the progress in the status line)
• Completions are shown in a read-only org buffer, so the user can interact with it, copy only the parts they find relevant, etc.
• Navigation with C-n/C-p -- next / previous suggestion
• Emacs buttons available for accepting or copying the suggestion. Tab jumps to the next button
• C-<return> on any part of a suggestion accepts it
• Some buffer-state handling to avoid inserting stuff on modified buffers -- the server takes its sweet time providing the responses.

I'm not too sure if this functionality should live inside lsp-mode's implementation of copilot itself or if it should be provided as some extra package, being so copilot-specific (though other clients implement some server-specific features, so that would not be too way off).

As I see, we can either:

• Bring this functionality to lsp-mode
• Update copilot-ls's progress function to call a hook -- so we can implement the panel functionality in a separate, copilot-specific package

What do you folks think? Specially @kiennq , who has so kindly reviewed all my copilot PRs so far :)

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BTW big kudos for the folks of https://github.com/copilot-emacs/copilot.el who implemented this functionality before -- it saved me a lot of time understanding how to communicate with the server and what the payloads should be like ❤️

[kassick]

Also: We could use this same panel code to have a "Pop to Panel" functionality in inline completions -- so the user can further study the suggestion before accepting or rejecting it.