Flymake for JS Hint tool

Abstract

First, I tried to implement own jshint invocation and handling tool. It was pretty fun, but later I found flymake package designed to work with syntax checking tools.

This article is based, and describes JS-Hint mode. It can be treated as development log and tips, as well as short tutorial on how to customize flymake mode.

Flymake

Flymake allows us to define interface to check files, tools to run these checks from time to time, and regexp based tools to highlight broken parts of the files.

Invoke

The entry point of flymake is how to invoke check program:

01 (defun flymake-js-hint-init ()
02   (let* ((temp-file (flymake-init-create-temp-buffer-copy
03                      'flymake-create-temp-inplace))
04          (local-file (file-relative-name
05                       temp-file
06                       (file-name-directory buffer-file-name))))
07     (list "jshint" (list "--verbose" local-file))))

This code, as well as most of the other code is taken from  Example—Configuring a tool called via make.

This function makes a copy of current buffer state into temporary file with unique name, and returns line to be called by flymake. The output usually contains errors and warnings, which is parsed and corresponding lines are highlighted.

Highlight

Flymake uses special list to hold all possible highlights -  flymake-err-line-patterns. Each entry in this list is a list of next format:
(REGEXP FILE-ID [LINE-ID [COLUMN-ID [ERROR-TEXT-ID]]])
where:
REGEXP - what kind of lines to match, with groups,
FILE-ID - id of group in match containing file name with error/warning,
LINE-ID - id of group in match containing line in the file with error/warning,
COLUMN-ID - id of group in match containing column in line
ERROR-TEXT-ID - id of group in match containing message to display against corresponding line.
Example for jshint:

01 (add-to-list 'flymake-err-line-patterns
02              '("^\\(.+\\): line \\([0-9]+\\), col \\([0-9]+\\), \\(.+\\)$" 1 2 3 4))

This code adds new rule to flymake list of rules. Next time flymake find line with error corresponding to this regexp - it will highlight it.

Register for flymake

When we have required parts of running and highlighting, we can link this all together and configure flymake:

01 (add-to-list 'flymake-allowed-file-name-masks
02              '(".+\\.js$"
03               flymake-js-hint-init 
04               flymake-simple-cleanup 
05               flymake-get-real-file-name))

flymake-allowed-file-name-masks - is a list of rules for flymake. Each entry is of the form:
(REGEXP INIT-FUNCTION CLEANUP-FUNCTION GETFNAME-FUNCTION)
where:
REGEXP - is used to match a file,
INIT-FUNCTION - initializes a temporary file with current buffer context and returns specialized function as list,
CLEANUP-FUNCITON - removes temporary file and does other clean up functions,
GETFNAME-FUNCTION - maps temporary file names to real ones.

Links

[1] Flymake mode