About flycheck

Recently I replaced my emacs on-the-fly syntax checker from flymake to flycheck. Flycheck is more well designed so that additional checker can be used without introducing into the other plugins.

For PHP development, I used to use php + phpcs, php for syntax check, phpcs for unused variable check. With flymake, it can only use php by default, and need to install flymake-php etc. for phpcs. While in flycheck, there’s a mechanism called ‘next checker’, in which additional checker can be defined.

After flycheck is installed, php checker works fine while phpcs does not. So I digged a little further into the source code of flycheck, and found out the reason. It turns out that, flycheck will save a copy of the source code to be checked to a tmp folder. In my Mac computer, it is /var/xxx/yyy. This folder is in fact a symbol link to /private/var/xxx/yyy/. The output of phpcs use directory name /private/var/xxx, while flycheck assumed the directory name /var/xxx. The flycheck will use string= tocheck if the origin of the error message is the same as the checked file, the file name is obviously different although they refer to the same place.. As a result, the error message will be discarded and no check result will be output. My solution is customized the temporary-file-directory variable to refer to the real directory name instead of the symbol link, and everything works fine. Also, I customized the flycheck-phpcs-standard to specify the standard of phpcs, and flycheck-php-phpcs-executable to specify the phpcs command path.

How flycheck works?

• Configuration

  • php checker

  flycheck-define-checker php
  

  This says use php to check for error, and after error check is performed check for warnings use phpmd and phpcs.

  • phpcs checker

  flycheck-define-checker php-phpcs
  

  This says that use flycheck-phpcs-standard to check for warnings.

  • workflow
  • flycheck-buffer: checker entry point
  • flycheck-start-checker: start a checker
    • flycheck-checker-executable: extract checker command from checker config
    • flycheck-checker-substitued-arguments: determine the arguments from checker config, also creates temp file for check
    • flycheck-receive-checker-ouput: collects output of checker
    • flycheck-handle-signal: deal with output when process finished with some signal
    • flycheck-finish-syntax-check: finish the check
      • flycheck-relevant-errors: check if error message belong the current buffer
      • flycheck-process-error-functions: actually change the buffer display with error messages
      • next checker: if there’s next checker for the buffer, repeat…