Hello,
I wanted my emacs to parse messages from IAR Embedded workbench compiler so I added following lines into my .emacs file:

;; To parse "IAR Embedded workbench 4.21A for Atmel AVR" messages
;; Load compile.el library
(require 'compile)
;;Store new item "iar-avr" into compilation-error-regexp-alist variable
(setq compilation-error-regexp-alist
(cons 'iar-avr compilation-error-regexp-alist))
;; Store iar-avr regexp into compilation-error-regexp-alist-alist variable
(setq compilation-error-regexp-alist-alist
(cons '(iar-avr
"^\\(?:.*\\\\\\)\\(.*\\)(\\([0-9]+\\)) : \\(?:Error\\|Warnin\\(g\\)\\)\\[Pe[0-9]+\\]:"
1 2 nil (3)) compilation-error-regexp-alist-alist))

It works all right, but when I start customize and try to customize compilation-error-regexp-alist, it shows "mismatch". At first before i modified .emacs as shown above, I put there just "compilation-error-regexp-alist-alist" but this didn't work, emacs reported "compilation-error-regexp-alist-alist is void" after start-up. To solve this I added "(require 'compile)" line. Error message disappeared but parsing of compiler messages didn't work, so I added setting of "compilation-error-regexp-alist" to contain name of my compiler (iar-avr). This solved the problem, but issue with "customize" appeared.

Parsing works, that's fine but "mismatch" message from customize bothers me. I don't want to modify compile.el (where compilation-error-regexp-alist is defined) directly, which probably would solve the problem.

Could anyone help, please?

Regards,
Jiri