ccls is a rewrite of cquery (originally written by Jacob Dufault), a C/C++/Objective-C language server.
- code completion (with both signature help and snippets)
- definition/references, and other cross references
- call (caller/callee) hierarchy, inheritance (base/derived) hierarchy, member hierarchy
- symbol rename
- document symbols and approximate search of workspace symbol
- hover information
- diagnostics
- code actions (clang FixIts)
- preprocessor skipped regions
- semantic highlighting, including support for rainbow semantic highlighting
It makes use of C++17 features, has less third-party dependencies and slimmed-down code base. Cross reference features are strenghened, (see wiki/FAQ. It currently uses libclang to index C++ code but will switch to Clang C++ API. Refactoring and formatting are non-goals as they can be provided by clang-format, clang-include-fixer and other Clang based tools.
The comparison with cquery as noted on 2018-07-09:
| cquery | ccls | |
|---|---|---|
| third_party | more | fewer |
| C++ | C++14 | C++17 |
| clang API | libclang (C) | libclang + clang/llvm C++ |
| Filesystem | AbsolutePath + custom routines | llvm/Support |
| index | libclang | clangIndex, some enhancement |
| pipeline | index merge+id remapping | simpler and more robust |
cquery has system include path detection (through running the compiler driver) while ccls does not.