feat: Add custom variable for max lines

CHANGELOG.md

@@ -12,6 +12,7 @@ Check [Keep a Changelog](http://keepachangelog.com/) for recommendations on how
 * Rerender sideline after `flycheck-mode` is disabled (52801f817c257955f82a37108044b68ae8833190)
 * Add face text property according to error level (793f7dbf5f9bb1899d741394a48605f1aa4a5ade)
 * Add option to display checker name (1f2f82d4383718a8dd2aff40cffafce4a8d0aca1)
+* feat: Add custom variable for max lines (#3)
 
 ## 0.1.0
 > Released Jun 14, 2022

README.md

@@ -24,7 +24,8 @@
 #### 🧪 Variables
 
 - `sideline-flycheck-inhibit-functions` - Functions to inhibit display of sideline flycheck.
-- `sideline-flycheck-show-checker-name` - If non-nil, show checker name at the back.
+- `sideline-flycheck-show-checker-name` - If non-nil, show the checker's name at the back.
+- `sideline-flycheck-max-lines` - Maximum number of lines to show.
 
 ## Contribute
 

sideline-flycheck.el

@@ -57,10 +57,15 @@
   :group 'sideline-flycheck)
 
 (defcustom sideline-flycheck-show-checker-name nil
-  "If non-nil, show checker name at the back."
+  "If non-nil, show the checker's name at the back."
   :type 'boolean
   :group 'sideline-flycheck)
 
+(defcustom sideline-flycheck-max-lines 1
+  "Maximum number of lines to show."
+  :type 'integer
+  :group 'sideline-flycheck)
+
 (defvar-local sideline-flycheck--old-display-function nil
   "The former value of `flycheck-display-errors-function'.")
 
@@ -90,6 +95,9 @@ Argument COMMAND is required in sideline backend."
         (let* ((level (flycheck-error-level err))
                (face (if (eq level 'info) 'success level))
                (msg (flycheck-error-message err))
+               (lines (split-string msg "\n"))
+               (lines (butlast lines (- (length lines) sideline-flycheck-max-lines)))
+               (msg (mapconcat #'identity lines "\n"))
                (checker (flycheck-error-checker err)))
           (when sideline-flycheck-show-checker-name
             (setq msg (format "%s (%s)" msg checker)))