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Re: maintain flymake.el

From: Sebastian Wiesner
Subject: Re: maintain flymake.el
Date: Mon, 16 Dec 2013 17:48:12 +0100

2013/12/16 Jan Djärv <address@hidden>:
> Hello.
> 16 dec 2013 kl. 15:32 skrev Ted Zlatanov <address@hidden>:
>> On Sun, 15 Dec 2013 19:31:46 +0100 Sebastian Wiesner <address@hidden> wrote:
>> SW> 2013/12/14 Sebastian Wiesner <address@hidden>:
>>>> I hope to finish the document by tomorrow evening, and will come back
>>>> if it's done.
>> SW> I have completed the document now.  The final version is to be found
>> SW> at https://github.com/flycheck/flycheck/wiki/Flycheck-versus-Flymake.
>> SW> It's a thorough write-up of the differences and similarities between
>> SW> Flycheck and Flymake, and probably also a comprehensive summary of the
>> SW> current issues and weaknesses in Flymake.
>> SW> Again, it's probably unfairly biased towards Flycheck.  I tried my
>> SW> best to be neutral, but I consider Flycheck superior and think that
>> SW> the design and implementation of Flymake are somewhat broken, so I may
>> SW> have failed to properly account for Flymake's features and strengths.
>> SW> Please excuse this, and feel free to correct any mistakes I may have
>> SW> made.
>> SW> Please also suggest improvements, such as additional aspects which
>> SW> should be covered, or report issues, such as missing details in the
>> SW> comparsion.
> You are missing the big think that separates flymake and flycheck. Flymake 
> uses makefiles, flycheck does not.  This means to be able to use flycheck on 
> a large C/C++ project you have to maintain includes and defined in both 
> makefiles and as lisp variables for flycheck.  Flymake does not have that 
> problem, you just add one rule for it in the makefiles, re-using all 
> definitions and include paths.
> This is really a showstopper for flycheck, even if it has some nicer GUI 
> stuff.  It is really only usable for small projects.

You can easily define your own syntax checker:

(flycheck-define-checker 'c-makefile-checker
  :command ("make" "CC=clang" "build")
  ((info line-start (file-name) ":" line ":" column
            ": note: " (message) line-end)
   (warning line-start (file-name) ":" line ":" column
            ": warning: " (message) line-end)
   (error line-start (file-name) ":" line ":" column
          ": " (or "fatal error" "error") ": " (message) line-end))
  :modes (c-mode)
  :predicate (lambda () (not (buffer-modified-p)))

The error patterns are for Clang.  Adapt the accordingly, if you are
using a different compiler.  The predicate makes sure that Flycheck
only uses this syntax checker after the buffer was saved, because
calling out to the build system after every change is probably not a
good idea.

Then just register the new syntax checker, and disable the built-in
Clang checker to avoid conflicting error messages:

(add-to-list 'flycheck-checkers 'c-make-file-checker)
(setq-default flycheck-disabled-checkers '(c/c++-clang))

Feel free to copy this to your "init.el".

Flycheck does not include this syntax checker for two reasons:

- No one contributed it :)
- It's hard, if not impossible, to get this right in a generic way.

There is simply no standard for Makefiles and compiler messages, so
Flycheck has no chance to call a Makefile in a portable way, that
works identically across all build systems, from CMake and Autotools,
to custom ad-hoc Makefiles, which don't even use generic rules, to the
strangest and most exotic compiler flags, especially if it does not
want to conduct a full build (which could take minutes, if not ours),
but only a syntax check of the file being edited.

But again, you know your projects, and nothing stops you from
definining your own syntax checker just for these projects.  Try it.
Really.  It's easy.

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