Don't clobber match data in timer

Fixes flycheck#1805

flycheck.el

@@ -3377,16 +3377,17 @@ or a list of them.)
 
 The syntax check is deferred if FORCE-DEFERRED is non-nil, or if
 `flycheck-must-defer-check' returns t."
- (when (and flycheck-mode (if (listp condition)
- (apply #'flycheck-may-check-automatically
- condition)
- (flycheck-may-check-automatically condition)))
- (flycheck--clear-idle-trigger-timer)
- (setq flycheck--idle-trigger-conditions nil)
- (if (or force-deferred (flycheck-must-defer-check))
- (flycheck-buffer-deferred)
- (with-demoted-errors "Error while checking syntax automatically: %S"
- (flycheck-buffer)))))
+ (save-match-data
+ (when (and flycheck-mode (if (listp condition)
+ (apply #'flycheck-may-check-automatically
+ condition)
+ (flycheck-may-check-automatically condition)))
+ (flycheck--clear-idle-trigger-timer)
+ (setq flycheck--idle-trigger-conditions nil)
+ (if (or force-deferred (flycheck-must-defer-check))
+ (flycheck-buffer-deferred)
+ (with-demoted-errors "Error while checking syntax automatically: %S"
+ (flycheck-buffer))))))
 
 (defun flycheck--clear-idle-trigger-timer ()
  "Clear the idle trigger timer."
@@ -3397,17 +3398,18 @@ The syntax check is deferred if FORCE-DEFERRED is non-nil, or if
 (defun flycheck--handle-idle-trigger (buffer)
  "Run a syntax check in BUFFER if appropriate.
 This function is called by `flycheck--idle-trigger-timer'."
- (let ((current-buffer (current-buffer)))
- (when (buffer-live-p buffer)
- (with-current-buffer buffer
- (unless (or flycheck-buffer-switch-check-intermediate-buffers
- (eq buffer current-buffer))
- (setq flycheck--idle-trigger-conditions
- (delq 'idle-buffer-switch
- flycheck--idle-trigger-conditions)))
- (when flycheck--idle-trigger-conditions
- (flycheck-buffer-automatically flycheck--idle-trigger-conditions)
- (setq flycheck--idle-trigger-conditions nil))))))
+ (save-match-data
+ (let ((current-buffer (current-buffer)))
+ (when (buffer-live-p buffer)
+ (with-current-buffer buffer
+ (unless (or flycheck-buffer-switch-check-intermediate-buffers
+ (eq buffer current-buffer))
+ (setq flycheck--idle-trigger-conditions
+ (delq 'idle-buffer-switch
+ flycheck--idle-trigger-conditions)))
+ (when flycheck--idle-trigger-conditions
+ (flycheck-buffer-automatically flycheck--idle-trigger-conditions)
+ (setq flycheck--idle-trigger-conditions nil)))))))
 
 (defun flycheck-handle-change (beg end _len)
  "Handle a buffer change between BEG and END.