feat(emacs/lean-flycheck): override flycheck-try-parse-error-with-pattern

For lean-mode, we override flycheck-try-parse-error-with-pattern to
increase column number by 1. It uses defadvice.

src/emacs/lean-flycheck.el

@@ -68,4 +68,33 @@
 (add-hook 'lean-mode-hook '(lambda ()
              (when lean-flycheck-use (lean-flycheck-turn-on))))
 
+(defun lean-flycheck-try-parse-error-with-pattern (err pattern)
+    "Try to parse a single ERR with a PATTERN.
+
+Return the parsed error if PATTERN matched ERR, or nil
+otherwise."
+    (let ((regexp (car pattern))
+          (level (cdr pattern)))
+      (when (string-match regexp err)
+        (let ((filename (match-string 1 err))
+              (line (match-string 2 err))
+              (column (match-string 3 err))
+              (message (match-string 4 err)))
+          (flycheck-error-new
+           :filename (unless (string-empty-p filename) filename)
+           :line (flycheck-string-to-number-safe line)
+           :column (let ((col (flycheck-string-to-number-safe column)))
+                     (if (= col 0) 1 col))
+           :message (unless (string-empty-p message) message)
+           :level level)))))
+
+(eval-after-load "flycheck.el"
+  '(defadvice flycheck-try-parse-error-with-pattern
+     (after lean-flycheck-try-parse-error-with-pattern activate)
+     "Add 1 to error-column."
+     (let* ((err ad-return-value)
+            (col (flycheck-error-column err)))
+       (when (and (string= major-mode "lean-mode") col)
+         (setf (flycheck-error-column ad-return-value) (1+ col))))))
+
 (provide 'lean-flycheck)