bug#65518: 30.0.50; [FR Eglot] Completions over all workspace symbols

[João Távora]

Gerd Möllmann <gerd.moellmann@gmail.com> writes:

> I'm in a C buffer with Eglot running, and I want to go to the definition
> of something whose name I know, but point is not on an identifier naming
> that thing.  For instance, I want to go the definition of Lisp_Package
> (in an obsure branch having a struct Lisp_Package), while point is
> somewhere.

>
> C-u M-. offers some completions, but Lisp_Package is not among them.
> Not using a completion and entering Lisp_Package works.

Like I explained in bug#65517 (which see), this too is based on the
'workspace/symbol' request.  You can check your Eglot events buffer (M-x
eglot-events-buffer) around the time you press C-u M-. to get a feel of
how the server responds to these queries.

You'll see Eglot sends the widest possible 'query' to the LSP server
which returns a limited number of names (clangd caps at exactly 100 by
default).  In large projects it's unlikely the symbol you're looking for
is there, but as you type more text into the prompt, further
'workspace/symbol' requests are made.

Note that, similarly to many other LSP situations, Eglot and Emacs has
no control over _how_ the server interprets the 'query' string, so there
is no control over the "completion style" and your setting of
'completion-style' has no effect here. The clangd LSP server in
particular seems to use a somewhat "flex" or "fuzzy" completion style.

You didn't specify exactly how you entered input into your search box,
and what completion package, if any, you are using.  So, whereas in
bug#65517 it was simple to understand the root cause of the observed
behavior, in this particular case, I'm afraid I'm going to have to refer
you to the usual checklist on making reproducible bug reports for Eglot:

  https://joaotavora.github.io/eglot/#Troubleshooting-Eglot

Here, for your specific example, I'm guessing the project is Emacs
itself (checked out in your CL packages branch).  I'm also guessing
you're using the `clangd` server and some of compile_commands.json.

Confirming this data and specifying versions etc should be enough for me
to reproduce the problem exactly as it appeared to you.  I'm also
guessing (or at least hoping), you don't use complicated third party
completion packages and everything can be experimented with via Emacs
-Q.

For reference, C-u M-. works fairly well here in my projects when used
with clangd 15.0.7 and the compile_commands.json file generated by the
CMake system.  I don't yet fully understand how clangd's sorting
heuristics and completion pattern matching work, but I seem to
eventually reach the name I want.

João