tildify.el: Fix matched group indexes in end-regex building

* lisp/textmodes/tildifi.el (tildify-find-env): When looking for
a start of an ignore-environment, the regex is built by
concatenating regexes of all the environments configured in
`tildify-ignored-environments-alist'.  So for example, the following
list could be used to match TeX's \verb and \verb* commands:

    (("\\\\verb\\(.\\)" . (1))
     ("\\\\verb\\*\\(.\\)" . (1)))

This would result in the following regex being used to find the start
of any of the variants of the \verb command:

    \\\\verb\\(.\\)\\|\\\\verb\\*\\(.\\)

But now, if “\\\\verb\\*\\(.\\)” matches, the first capture group
won't match anything, and thus (match-string 1) will be nil, which
will cause building of the end-matching regex to fail.

Fix this by using capture groups from the time when the opening
regexes are matched individually.

* tests/automated/tildify-tests.el (tildify-test-find-env-group-index-bug):
New test validating fix to the above bug.

2 files changed, 38 insertions, 15 deletions

diff --git a/lisp/ChangeLog b/lisp/ChangeLog
index 7bbaf642d3c..936ae225a8b 100644
--- a/lisp/ChangeLog
+++ b/lisp/ChangeLog
@@ -1,5 +1,28 @@
 2014-06-05  Michal Nazarewicz  <mina86@mina86.com>
 
+        * textmodes/tildify.el (tildify-find-env): Fix matched group
+        indexes in end-regex building
+
+        When looking for a start of an ignore-environment, the regex is built
+        by concatenating regexes of all the environments configured in
+        `tildify-ignored-environments-alist'.  So for example, the following
+        list could be used to match TeX's \verb and \verb* commands:
+
+            (("\\\\verb\\(.\\)" . (1))
+             ("\\\\verb\\*\\(.\\)" . (1)))
+
+        This would result in the following regex being used to find the start
+        of any of the variants of the \verb command:
+
+            \\\\verb\\(.\\)\\|\\\\verb\\*\\(.\\)
+
+        But now, if “\\\\verb\\*\\(.\\)” matches, the first capture group
+        won't match anything, and thus (match-string 1) will be nil, which
+        will cause building of the end-matching regex to fail.
+
+        Fix this by using capture groups from the time when the opening
+        regexes are matched individually.
+
         * textmodes/tildify.el (tildify-find-env): Fix end-regex building
         in `tildify-find-env'
 
diff --git a/lisp/textmodes/tildify.el b/lisp/textmodes/tildify.el
index 7e4b39b615a..7aa338ef207 100644
--- a/lisp/textmodes/tildify.el
+++ b/lisp/textmodes/tildify.el
@@ -271,22 +271,22 @@ Return regexp for the end of the environment or nil if no environment was
 found."
   ;; Find environment
   (when (re-search-forward regexp nil t)
-    ;; Build end-env regexp
-    (let ((match (match-string 0))
-          (alist (tildify-mode-alist tildify-ignored-environments-alist)))
-      (save-match-data
+    (save-match-data
+      ;; Build end-env regexp
+      (let ((match (match-string 0))
+            (alist (tildify-mode-alist tildify-ignored-environments-alist)))
         (while (not (eq (string-match (caar alist) match) 0))
-          (setq alist (cdr alist))))
-      (let ((expression (cdar alist)))
-        (if (stringp expression)
-            expression
-          (mapconcat
-           (lambda (expr)
-             (if (stringp expr)
-                 expr
-               (regexp-quote (match-string expr))))
-           expression
-           ""))))))
+          (setq alist (cdr alist)))
+        (let ((expression (cdar alist)))
+          (if (stringp expression)
+              expression
+            (mapconcat
+             (lambda (expr)
+               (if (stringp expr)
+                   expr
+                 (regexp-quote (match-string expr match))))
+             expression
+             "")))))))
 
 (defun tildify-tildify (beg end ask)
   "Add tilde characters in the region between BEG and END.