Throw a `search-failed' derived error in Info search

The original fix for Bug#6106 switched from signalling `search-failed'
to `user-error'.  However, this breaks incremental searching over
multiple nodes because the isearch code doesn't expect a `user-error'.

* src/search.c (syms_of_search): New error, `user-search-failed',
with `user-error' and `search-failed' as parents.
* doc/lispref/errors.texi (Standard Errors): Document it.
* etc/NEWS: Announce it.
* lisp/info.el (Info-search): Use it instead of `user-error' so that
isearch will handle failed searches correctly.

1 files changed, 10 insertions, 0 deletions

diff --git a/src/search.c b/src/search.c
index 33cb02aa7af..c0deb57213c 100644
--- a/src/search.c
+++ b/src/search.c
@@ -3389,6 +3389,10 @@ syms_of_search (void)
   /* Error condition used for failing searches.  */
   DEFSYM (Qsearch_failed, "search-failed");
 
+  /* Error condition used for failing searches started by user, i.e.,
+     where failure should not invoke the debugger.  */
+  DEFSYM (Quser_search_failed, "user-search-failed");
+
   /* Error condition signaled when regexp compile_pattern fails.  */
   DEFSYM (Qinvalid_regexp, "invalid-regexp");
 
@@ -3397,6 +3401,12 @@ syms_of_search (void)
   Fput (Qsearch_failed, Qerror_message,
         build_pure_c_string ("Search failed"));
 
+  Fput (Quser_search_failed, Qerror_conditions,
+        listn (CONSTYPE_PURE, 4,
+               Quser_search_failed, Quser_error, Qsearch_failed, Qerror));
+  Fput (Quser_search_failed, Qerror_message,
+        build_pure_c_string ("Search failed"));
+
   Fput (Qinvalid_regexp, Qerror_conditions,
         listn (CONSTYPE_PURE, 2, Qinvalid_regexp, Qerror));
   Fput (Qinvalid_regexp, Qerror_message,