When lsp-mode is active, it tries to ensure it's own
lsp-completion-at-point function is listed before any other functions in
completion-at-point-functions.
This however prevents completions for yasnippet snippets and
files/folders from working, as completion never moved on beyond
lsp-completion-at-point. Previously I had managed to fix this by using
the DEPTH option of add-hook to get siren-yasnippet-capf and cape-file
to run before lsp-completion-at-point.
But it seems lsp-mode has changed from using add-hook to a more custom
method of always ensuring lsp-completion-at-point is always first on the
list. Hence we need to the same using the new siren-prepend macro I
recently added.
I opted for accepting copilot completions using C-<tab> /
<backtab> (shift+tab) instead of regular tab, as it was often getting in
the way of yasnippet and lsp completion suggestions. This allows a more
explicit acceptance of Copilot suggestions.
This applies especially in lsp-mode. Yasnippet snippets now show as
completion candidates if the word at point exactly matches a snippet
keyword, otherwise it'll fallback to normal lsp backed completion.
And it also supports completing file/directory names now too while
lsp-mode is active.
All this is done by modifying completion-at-point-functions after
lsp-mode has done it's trickery with it. Along with a dirty hack to
company-yasnippet to make it only activate on exact matches. Without
this hack, lsp backed completion rarely activates as snippets would have
higher priority if there's any partial matches.
