Completion for variables in C using company-gtags, or not Semantic

Question

I have a working C IDE without Semantic (too slow for me), from instructions here, with completion provided by company-gtags (I think. Maybe clang does something too?).

Completion at point works for functions throughout the project, but not for variable names. I.e., if param_n is a global variable, I get no completions for param, even when I force completions. I expect that gtags knows about param_n, because it shows all of the references to it when I call global -sx param_n from the command line.

How do I get completion, without Semantic, for local and global variables, whenever they are in scope?

Answer 1

I have followed the directions at this blog which supplements the C ide stuff by Tudho to install rtags and irony (as suggested by Dmitry) and it provides the features I asked for.

I'll expand with a summary of steps I had to take to get it all working on a Mac:

• Install a recent version of the clang compiler with macports (likely optional)
• Set environment variable CC=clang so that the most basic cmake files will call clang
• make and install rtags v2.3 from rtags the repository. Detailed instructions and quick start guide worked but not with Apple XCode's clang (which lacked a link to libclang). follow instructions at the repository to check it works. Not clear to me whether you need to install rtags package in emacs from melpa, but I did that too.
• write a very basic cmake file. If you are a cmake newbie like me you might have a simple C project with no libraries, with a root directory structured like this:

~~~~

% tree . 
└── src
    ├── bar
    │   ├── bar.c
    │   └── bar.h
    └── foo
        ├── foo.c
        └── foo.h

In this case, perhaps the following cmake file will work for you. Call it CMakeLists.txt and put it in the top directory.

cmake_minimum_required(VERSION 3.5)
project(myProjectName)
file(GLOB_RECURSE SRC_FILES src/*.c)
add_executable(myProjectName ${SRC_FILES})

Put build commands for the project in the directory ./build by calling

cmake -H. -Bbuild

Then export the compile command to a file that rtags will use

cmake build -DCMAKE_EXPORT_COMPILE_COMMANDS=1

And build the project

cmake --build build

Now, to make sure things are working cleanly, clear projects and quit the rdm daemon if it was running with

rc -C
rc -q

and restart the daemon

rdm &

and read that .json file you exported from cmake

rc -J build

You should see output like this:

% rc -J build                                                                                                                                                         Cprogrammingglanguage/wtf (hcn ⚡) alejandro
[Server] Compilation database loading...
 % [  3%] 1/35 23:40:23 ~/Google Drive/Work Cloud/... in 211ms. (549 syms, 780 symNames, 28 includes, 17 of 22 files, symbols: 792 of 1445, 1840 cursors, 21 queried 86ms) (37/111/49ms). (priority 0)
[  6%] 2/35 23:40:24 ~/Google Drive/Work Cloud/.../code/main/src/inrflow/reporting.c in 226ms. (1354 syms, 521 symNames, 15 includes, 6 of 87 files, symbols: 1714 of 4676, 7220 cursors, 5 queried 2ms) (119/61/25ms). (priority 0)

Note the following pitfall: can't have spaces in the path to the project. I worked around this by symlinking to the project folder from a space-less path.

Now you are finally able to start following the rest of the instructions in 1 about configuring rtags, company-rtags, rtags + helm, irony-mode, company-irony, company-irony-c-headers, and flycheck-rtags, and cmake-ide, which mostly follows the documentation for each package.

I tend to fumble through these things and would like to help other users, so constructive comments are welcome.