Fix: Warn about files with too-long lines

Fixes #63.  Or works around it.  There's only so much we can do.
These tend to be e.g. minified JavaScript files, which shouldn't be
scanned, and the user will have to exclude them.

Author: alphapapa

README.org

@@ -131,6 +131,9 @@ Helm and Ivy are also supported.  Note that the =helm= and =ivy= packages are no
 *Added*
 +  Commands =helm-magit-todos= and =ivy-magit-todos=, which display items with Helm and Ivy.  (Note that Helm and Ivy are not required, nor does this package depend on them; they are only used if present.)
 
+*Fixed*
++  Warn about files containing lines too long for Emacs's regexp matcher to handle, rather than aborting the scan ([[https://github.com/alphapapa/magit-todos/issues/63][#63]]).
+
 *Updated*
 +  Use =magit-setup-buffer= instead of =magit-mode-setup=.
 

magit-todos.el

@@ -517,12 +517,22 @@ Match items are a list of `magit-todos-item' found in PROCESS's buffer for RESUL
 
 (defun magit-todos--buffer-items (results-regexp)
   "Return list of `magit-todos-item' found in current buffer for RESULTS-REGEXP."
-  (save-excursion
-    (goto-char (point-min))
-    (cl-loop for item = (magit-todos--line-item results-regexp)
-             while item
-             collect item
-             do (forward-line 1))))
+  (let ((items))
+    (save-excursion
+      (goto-char (point-min))
+      (while (not (eobp))
+        (--when-let (condition-case err
+                        (magit-todos--line-item results-regexp)
+                      ;; Files with very, very long lines may cause Emacs's regexp matcher to overflow.
+                      ;; Rather than abort the whole scan and raise an error, try to handle it gracefully.
+                      ;; FIXME: This may raise multiple warnings per file.
+                      (error (if (string= "Stack overflow in regexp matcher" (error-message-string err))
+                                 (let ((filename (buffer-substring (point) (1- (re-search-forward ":")))))
+                                   (display-warning 'magit-todos (concat "File has lines too long for Emacs to search.  Consider excluding it from scans: " filename)))
+                               (signal (car err) (cdr err)))))
+          (push it items))
+        (forward-line 1)))
+    (nreverse items)))
 
 (cl-defun magit-todos--git-diff-callback (&key magit-status-buffer results-regexp search-regexp-elisp process heading
                                                &allow-other-keys)