Fix an Isearch var to be a string (Bug#23038)

* isearch.el (isearch--describe-regexp-mode): The `description' var
  needs to always be a string.  Add the missing default case for the
  cond form that ensures that.

Before this bug fix, for the events when `regexp-function' and
`search-default-mode' both were nil, `description' also stayed nil.  So
when `space-before' was non-nil, the "non-string" `description'
(with a value of nil) got passed as an argument to
`replace-regexp-in-string' (where a string was expected).  That caused
the error described in Bug#23038.

1 files changed, 11 insertions, 8 deletions

diff --git a/lisp/isearch.el b/lisp/isearch.el
index 988503eaa4f..48354d39d48 100644
--- a/lisp/isearch.el
+++ b/lisp/isearch.el
@@ -2585,16 +2585,19 @@ the word mode."
                     (eq search-default-mode isearch-regexp))) "")
           ;; 2. Use the `isearch-message-prefix' set for
           ;;    `regexp-function' if available.
-               (regexp-function
-                (and (symbolp regexp-function)
-                     (or (get regexp-function 'isearch-message-prefix)
-                         "")))
+          (regexp-function
+           (and (symbolp regexp-function)
+                (or (get regexp-function 'isearch-message-prefix)
+                    "")))
           ;; 3. Else if `isearch-regexp' is non-nil, set description
           ;;    to "regexp ".
-               (isearch-regexp "regexp ")
-          ;; 4. And finally, if we're in literal mode (and if the
-          ;;    default mode is also not literal), describe it.
-               ((functionp search-default-mode) "literal "))))
+          (isearch-regexp "regexp ")
+          ;; 4. Else if we're in literal mode (and if the default
+          ;;    mode is also not literal), describe it.
+          ((functionp search-default-mode) "literal ")
+          ;; 5. And finally, if none of the above is true, set the
+          ;;    description to an empty string.
+          (t ""))))
     (if space-before
         ;; Move space from the end to the beginning.
         (replace-regexp-in-string "\\(.*\\) \\'" " \\1" description)