Automatically add project directory to flycheck clang/gcc include path

Question

I want to use syntax checking with Flycheck in my C++ projects, but the Clang checker fails to find the local file includes. For example, when I have:

#include "foo/bar/x.h"

in the file foo2/y.cc, it reports an error that it couldn't find the include file. Both foo/ and foo2/ are in the project root. I can work around this by adding the following to a .dir-locals.el file in the project:

((c++-mode .
     ( (flycheck-clang-include-path . "/home/user/src/myproject") ) )
     ))

However, I have dozens of projects and it would be a lot of work to set this for each directory. I'm using Projectile and I think it should be possible to set the include path based on the project root automatically, but I cannot find any variable or function in Projectile that would return the path to the current project.

Answer 1

Use projectile-project-root to get the root path and add it to the list with a c++-mode-hook

(defun setup-flycheck-clang-project-path ()
  (let ((root (ignore-errors (projectile-project-root))))
    (when root
      (add-to-list 
       (make-variable-buffer-local 'flycheck-clang-include-path)
       root)))

(add-hook 'c++-mode-hook 'setup-flycheck-clang-project-path)

Answer 2

You could wait for this pull request to get merged. This adds a new clang-check based checker to flycheck. The main difference is the tooling supports a compilation database which contains all the include paths (and defines and other compilation controls) for the file. This database can be automatically created with CMAKE or you can use a tool like bear to create it.