Closes #318: now checks for circular parenthood in snippet dirs

yasnippet-tests.el

@@ -312,6 +312,22 @@ TODO: correct this bug!"
      (yas-reload-all)
      (yas--basic-jit-loading-1))))
 
+(ert-deftest loading-with-cyclic-parenthood ()
+  "Test loading when cyclic parenthood is setup."
+  (yas-saving-variables
+   (yas-with-snippet-dirs '((".emacs.d/snippets"
+                             ("c-mode"
+                              (".yas-parents" . "cc-mode"))
+                             ("cc-mode"
+                              (".yas-parents" . "yet-another-c-mode"))
+                             ("yet-another-c-mode"
+                              (".yas-parents" . "c-mode"))))
+     (yas-reload-all)
+     (condition-case nil
+         (yas--all-parents 'c-mode)
+       (error
+        (ert-fail "cyclic parenthood test failed"))))))
+
 (defun yas--basic-jit-loading-1 (&optional compile)
   (with-temp-buffer
     (should (= 4 (hash-table-count yas--scheduled-jit-loads)))

yasnippet.el

@@ -660,6 +660,11 @@ There might be additional parenting information stored in the
 `derived-mode-parent' property of some mode symbols, but that is
 not recorded here.")
 
+(defvar yas--ancestors (make-hash-table)
+  "A hash table of mode symbols do lists of all parent mode symbols.
+
+A cache managed by `yas--all-parents'")
+
 (defvar yas--direct-keymaps (list)
   "Keymap alist supporting direct snippet keybindings.
 
@@ -1151,9 +1156,21 @@ conditions to filter out potential expansions."
 
 (defun yas--all-parents (mode)
   "Returns a list of all parent modes of MODE."
-  (let ((parents (gethash mode yas--parents)))
-    (append parents
-            (mapcan #'yas--all-parents parents))))
+  (or (gethash mode yas--ancestors)
+      (let ((seen '()))
+        (labels ((yas--all-parents-1
+                  (m)
+                  (cond ((memq m seen)
+                         (yas--message 1
+                                       "Cyclic parenthood: mode %s has already seen as a parent of mode %s"
+                                       m mode)
+                         nil)
+                        (t
+                         (let* ((parents (gethash m yas--parents)))
+                           (setq seen (append seen parents))
+                           (append parents (mapcan #'yas--all-parents-1 parents)))))))
+          (puthash mode (yas--all-parents-1 mode)
+                   yas--ancestors)))))
 
 (defun yas--table-templates (table)
   (when table
@@ -1866,6 +1883,7 @@ loading."
       ;;
       (setq yas--tables (make-hash-table))
       (setq yas--parents (make-hash-table))
+      (setq yas--ancestors (make-hash-table))
 
       ;; Before killing `yas--menu-table' use its keys to cleanup the
       ;; mode menu parts of `yas--minor-mode-menu' (thus also cleaning
@@ -2531,7 +2549,7 @@ neither do the elements of PARENTS."
                                     (buffer-substring-no-properties (point-min)
                                                                     (point-max))))))))
     (when major-mode-sym
-      (cons major-mode-sym parents))))
+      (cons major-mode-sym (remove major-mode-sym parents)))))
 
 (defvar yas--editing-template nil
   "Supporting variable for `yas-load-snippet-buffer' and `yas--visit-snippet'.")