Allow t as a catch-all condition-case handler (Bug#24618)

* src/eval.c (find_handler_clause): Accept a handler of t as always
matching.
(Fcondition_case):
* doc/lispref/control.texi (Handling Errors): Document this.
* etc/NEWS: Announce it.

1 files changed, 6 insertions, 4 deletions

diff --git a/src/eval.c b/src/eval.c
index 50de60c936c..1011fc888b5 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -1215,9 +1215,9 @@ Executes BODYFORM and returns its value if no error happens.
 Each element of HANDLERS looks like (CONDITION-NAME BODY...)
 where the BODY is made of Lisp expressions.
 
-A handler is applicable to an error
-if CONDITION-NAME is one of the error's condition names.
-If an error happens, the first applicable handler is run.
+A handler is applicable to an error if CONDITION-NAME is one of the
+error's condition names.  A CONDITION-NAME of t applies to any error
+symbol.  If an error happens, the first applicable handler is run.
 
 The car of a handler may be a list of condition names instead of a
 single condition name; then it handles all of them.  If the special
@@ -1854,7 +1854,9 @@ find_handler_clause (Lisp_Object handlers, Lisp_Object conditions)
   for (h = handlers; CONSP (h); h = XCDR (h))
     {
       Lisp_Object handler = XCAR (h);
-      if (!NILP (Fmemq (handler, conditions)))
+      if (!NILP (Fmemq (handler, conditions))
+          /* t is also used as a catch-all by Lisp code.  */
+          || EQ (handler, Qt))
         return handlers;
     }