How to change flycheck symbol?, like spacemacs

Question

Flycheck has a symbol that tells in which line an error or warning have been encountered. I have seen spacemacs has its flycheck symbol changed. Default symbol is a double arrow; while spacemacs's symbol is a dot. I can't find a function to change it. How did spacemacs do that?

Answer 1

After reading flycheck source code..

1) You must define a fringe bitmap (the "symbol") with 'define-fringe-bitmap' function.

2) Use 'flycheck-define-error-level' function to load the new bitman

3) Enable Flycheck mode

Example:

(define-fringe-bitmap 'flycheck-fringe-bitmap-ball
    (vector #b00000000
            #b00000000
            #b00000000
            #b00000000
            #b00000000
            #b00111000
            #b01111100
            #b11111110
            #b11111110
            #b01111100
            #b00111000
            #b00000000
            #b00000000
            #b00000000
            #b00000000
            #b00000000
            #b00000000)))

(flycheck-define-error-level 'error
  :severity 100
  :compilation-level 2
  :overlay-category 'flycheck-error-overlay
  :fringe-bitmap 'flycheck-fringe-bitmap-ball
  :fringe-face 'flycheck-fringe-error
  :error-list-face 'flycheck-error-list-error)