Add ccls/cquery (language server) to c-c++ layer

[MaskRay]

tl;dr Jump to the bottom to see the demo.

"cquery is a highly-scalable, low-latency language server for C/C++/Objective-C". There are uses on indexing Chromium, LLVM projects, and Linux kernel. It provides similar features with venerable rtags, like finding definitions/references.

https://github.com/MaskRay/ccls libclang + Clang C++
https://github.com/cquery-project/cquery libclang

You can take this issue as a "seeking for help". There are many pieces need customizing (cquery.el lsp-mode lsp-ui) to provide a kinda satisfying code assistant UI. spacemacs is used by many and to me a suitable place to combine these efforts. I leave some notes at https://github.com/jacobdufault/cquery/wiki/Emacs but my elisp-fu is incapable to create a robust layer.

I'd also like to know if there is interest to incorporate lsp-mode through which we can provide a unified interface for C++, Rust and many other languages. I have used rls (Rust) and cquery (C++) and many features can and should be shared and be provided by a common library (lsp-mode lsp-ui). cquery.el provides a LSP plugin for cquery and it also has some extensions not included in LSP:

;; emacs-ccls https://melpa.org/#/ccls
(ccls-xref-find-custom "$ccls/base")
(ccls-xref-find-custom "$ccls/callers")
;; No "$ccls/derived", use lsp-goto-implementation from  lsp-mode instead
(ccls-xref-find-custom "$ccls/vars")

;; Alternatively, use lsp-ui-peek interface
(lsp-ui-peek-find-custom 'base "$ccls/base")
(lsp-ui-peek-find-custom 'callers "$ccls/callers")

;; ...... emacs-cquery https://melpa.org/#/cquery
;; the cquery counterparts are similar
(cquery-xref-find-custom "$cquery/base")
(cquery-xref-find-custom "$cquery/callers")
(cquery-xref-find-custom "$cquery/derived")
(cquery-xref-find-custom "$cquery/vars")

;; Alternatively, use lsp-ui-peek interface
(lsp-ui-peek-find-custom 'base "$cquery/base")
(lsp-ui-peek-find-custom 'callers "$cquery/callers")
;; ......

There are still useful features that are missing or can be improved in cquery.el. And it is also nice to learn from users using other code assistants to know what can be improved generally about cquery.

I might be biased regarding rtags because I am a contributor of cquery. What bothered me a lot when I was using rtags was its query performance Andersbakken/rtags#1007

See also:
cquery.el: https://github.com/cquery-project/emacs-cquery/blob/master/cquery.el
lsp-mode https://github.com/emacs-lsp/lsp-mode
lsp-ui https://github.com/emacs-lsp/lsp-ui

A brief list of what can be improved

• semantic highlighting More granular symbol kinds for semantic highlighting jacobdufault/cquery#239
• Visualization of $cquery/typeHierarchyTree
• With (setq cquery-extra-init-params '(:enableComments 2 :cacheFormat "msgpack"), comments are not nicely rendered in eldoc [hover] Display the last MarkedString when there are multiple. emacs-lsp/lsp-mode#224
• Polish before publishing jacobdufault/cquery#30 some entries lean to VSCode, but many apply also to Emacs
• Some cases where libclang is incapable to provide all desired information "Go to Definition" does not work for enumeration used as type of non-type template parameter jacobdufault/cquery#252
• Something possible technically but entails a complicated implementation Hover over variable (esp. a constant) could show its initial value jacobdufault/cquery#260
• Niche codelens-style argument names in calls jacobdufault/cquery#85 support workspace/executeCommand jacobdufault/cquery#283

If you speak Chinese, I've written an article introducing cquery and my configuration http://maskray.me/blog/2017-12-03-c++-language-server-cquery

[MaskRay]

Adding a bunch of people who may be interested in better Emacs user experience of C/C++ or general LSP support.

@scturtle @jiegec @topisani @danielmartin @DeltaEvo @acowley

Sorry if that bothers you...

For integration of lsp-mode lsp-ui, please contact @vibhavp @sebastiencs

cquery @jacobdufault

[danielmartin]

I don't particularly use Spacemacs, only vanilla GNU Emacs, so I don't know what the requirements are for including a package in a particular layer. I think cquery.el is already pretty stable and provides a lot of functionality so it can be a good candidate for inclusion. Also, with cquery everything is in one place, and it implements a well-known protocol. Without LSP it is typical to have to install several specialized packages to have an IDE experience (rtags for code navigation and irony-mode/ycm for code completion, for example).

[sebastiencs]

I'm not using spacemacs either but if you're willing to integrate lsp-ui I can help :)
An integration with lsp-rust would be nice too @bkchr

[bkchr]

I currently maintain my rust language server layer here: https://github.com/bkchr/rustrls
It would be nice if the interface could be unified across languages, but I don't have any idea up to now.

[scturtle]

If you want to have a try, I have a personal lsp-cquery layer with some customizations.

Agree with @bkchr. If there is a lsp layer with common configurations, it would be easier to integrate lsp client into each language layer.

[MaskRay]

I have also cleaned my lsp-mode/lsp-ui based config. The cquery specific stuff is very simple now.

# cquery cache files
% du -sh .vscode/cquery_cached_index 
96M     .vscode/cquery_cached_index
ray @ hacking >>= ~/Dev/Bin/radare2 

# rtags cache files
% du -sh ~/.cache/rtags/_home_ray_Dev_Bin_radare2_
600M    /home/ray/.cache/rtags/_home_ray_Dev_Bin_radare2_

[MaskRay]

Created #10211 and emacs-cquery is now in Melpa

@syl20bnr

[cormacc]

@MaskRay I spent a few hours on a train journey today comparing your cquery and my-code layers with the existing c-c++ layer, paying attention to how ycmd and rtags are integrated in the latter. Have refactored some of the functionality into a reasonably coherent set of additions to the lsp layer with some of the common keybindings, a new cquery layer and some minimal additions to the c-c++ layer in a new branch forked from spacemacs/develop.

Think it's fairly close, but certainly not suitable for a a single PR -- not sure if it's of any use to you, or where to go with it from here, but it's here;
https://github.com/cormacc/spacemacs/tree/cquery-layer