Hard to setup complex include paths for flycheck-clang projects

[stsquad]

I'm trying to improve my use of flycheck-clang with QEMU. The problem is the build includes multiple target binaries and multiple source directories. I've tried manually adding include paths, e.g:

(setq flycheck-clang-include-path '("./include/" "./aarch64-softmmu/" "./target-arm/"))

However this falls down as you go into sub-directories so the pathes need to be relative to the project root.

What would make this easier is if the clang checker supported a config file and then I could modify the the make system to spit out something useful for the particular thing I'm building.

[swsnr]

@stsquad The paths are not relative to the project root. That's documented, actually. You need to use absolute paths, ideally via .dir-locals.el—which is how these options are intended to be used.

Alternatively add a hook to C Mode which automatically computes the absolute include paths by resolving the relative paths against the project root (which you could obtain from Projectile, for instance), e.g. something like this:

(add-hook 'c-mode-hook (lambda () (set flycheck-clang-include-path (mapcar (lambda (p) (expand-file-name p (projectile-project-root)) my-relative-include-paths)

I know that Clang supports “compilation database” files, which appear to be JSON files with flags that common build systems like CMake can generate, but I do not know how to make Clang load such databases, and I do not have the time to find out. I don't use C/C++. Pull requests welcome.

For complex C/C++ packages, you may also want to look at Irony Mode and Flycheck Irony or similar extensions.

I'm closing this issue, since it's more a question than a problem in Flycheck, and in any case not something that I'd fix, for said reasons.

[stsquad]

OK I'm getting there. You can build a compilation database with a tool called bear:

./configure <blah>
bear make

And then check any file using clang-check:

clang-check cputlb.c

So I've started adding another flychecker type:

(flycheck-define-checker c/c++-clang-check
  "A C/C++ syntax checker using Clang.

See URL `http://clang.llvm.org/'."
  :command ("clang-check"
            "--extra-arg=-Wno-unknown-warning-option" ; silence GCC options
            "--extra-arg=-Wno-null-character"         ; silence null
            "--extra-arg=-fno-color-diagnostics"      ; Do not include color codes in output
            "--extra-arg=-fno-caret-diagnostics"      ; Do not visually indicate the source
            "--extra-arg=-fno-diagnostics-show-option" ; Do not show the corresponding
            (eval flycheck-clang-args)
            source)
  :error-patterns
  ((error line-start
          (message "In file included from") " " (file-name) ":" line ":"
          line-end)
   (info line-start (file-name) ":" line ":" column
         ": note: " (optional (message)) line-end)
   (warning line-start (file-name) ":" line ":" column
            ": warning: " (optional (message)) line-end)
   (error line-start (file-name) ":" line ":" column
          ": " (or "fatal error" "error") ": " (optional (message)) line-end))
  :error-filter
  (lambda (errors)
    (let ((errors (flycheck-sanitize-errors errors)))
      (dolist (err errors)
        ;; Clang will output empty messages for #error/#warning pragmas without
        ;; messages.  We fill these empty errors with a dummy message to get
        ;; them past our error filtering
        (setf (flycheck-error-message err)
              (or (flycheck-error-message err) "no message")))
      (flycheck-fold-include-levels errors "In file included from")))
  :modes (c-mode c++-mode)
  :next-checkers ((warning . c/c++-cppcheck)))

Unfortunately this falls over because flycheck has moved the file to be compile checked. Is there any way to suppress this?

[swsnr]

@stsquad source-original. And read the documentation, please.

[stsquad]

@lunaryorn it took some finding, I figured it out from the source eventually. pull req incoming.

[swsnr]

@stsquad It's in the docstring of flycheck-substitute-argument, isn't it?

[stsquad]

@lunaryorn it is, but I missed it from the flycheck-define-checker info. I'll have to re-read because something has gone wrong...

[themattman]

I'd like to use the compilation database as well. I work with large codebases and can't list all include paths for flycheck. Does flycheck support the compile_commands.json format now?

[stsquad]

@themattman see https://github.com/kumar8600/flycheck-clangcheck