Fix double prompt

If an error is thrown while handling a target event (within
fetch_inferior_event), and, the interpreter is not async (but the
target is), then GDB prints the prompt twice.

One way to see that in action is throw a QUIT while in a pagination
prompt issued from within fetch_inferior_event (or one of its
callees).  E.g. from the test:

 ---Type <return> to continue, or q <return> to quit---
 ^CQuit
 (gdb) (gdb) p 1
 ^^^^^^^^^^^
 $1 = 1
 (gdb)

The issue is that inferior_event_handler swallows errors and notifies
the observers (the interpreters) about the command error, even if the
interpreter is forced sync while we're handling a nested event loop
(for execute_command).  The observers print a prompt, and then when we
get back to the top event loop, we print another (in
start_event_loop).

I see no reason the error should be swallowed here.  Just cancel the
execution related bits and let the error propagate to the top level
(start_event_loop), which re-enables stdin and notifies observers.

gdb/
2014-07-14  Pedro Alves  <palves@redhat.com>

	* inf-loop.c (inferior_event_handler): Use TRY_CATCH instead of
	catch_errors.  Don't re-enable stdin or notify observers where,
	and rethrow error.
	(fetch_inferior_event_wrapper): Delete.

gdb/testsuite/
2014-07-14  Pedro Alves  <palves@redhat.com>

	* gdb.base/double-prompt-target-event-error.c: New file.
	* gdb.base/double-prompt-target-event-error.exp: New file.

1 files changed, 17 insertions, 19 deletions

diff --git a/gdb/inf-loop.c b/gdb/inf-loop.c
index 247e9d6..d4f9a35 100644
--- a/gdb/inf-loop.c
+++ b/gdb/inf-loop.c
@@ -33,8 +33,6 @@
 #include "top.h"
 #include "observer.h"
 
-static int fetch_inferior_event_wrapper (gdb_client_data client_data);
-
 /* General function to handle events in the inferior.  So far it just
    takes care of detecting errors reported by select() or poll(),
    otherwise it assumes that all is OK, and goes on reading data from
@@ -48,19 +46,26 @@ inferior_event_handler (enum inferior_event_type event_type,
   switch (event_type)
     {
     case INF_REG_EVENT:
-      /* Use catch errors for now, until the inner layers of
+      /* Catch errors for now, until the inner layers of
 	 fetch_inferior_event (i.e. readchar) can return meaningful
 	 error status.  If an error occurs while getting an event from
 	 the target, just cancel the current command.  */
-      if (!catch_errors (fetch_inferior_event_wrapper, 
-			 client_data, "", RETURN_MASK_ALL))
-	{
-	  bpstat_clear_actions ();
-	  do_all_intermediate_continuations (1);
-	  do_all_continuations (1);
-	  async_enable_stdin ();
-	  observer_notify_command_error ();
-	}
+      {
+	volatile struct gdb_exception ex;
+
+	TRY_CATCH (ex, RETURN_MASK_ALL)
+	  {
+	    fetch_inferior_event (client_data);
+	  }
+	if (ex.reason < 0)
+	  {
+	    bpstat_clear_actions ();
+	    do_all_intermediate_continuations (1);
+	    do_all_continuations (1);
+
+	    throw_exception (ex);
+	  }
+      }
       break;
 
     case INF_EXEC_COMPLETE:
@@ -140,10 +145,3 @@ inferior_event_handler (enum inferior_event_type event_type,
 
   discard_cleanups (cleanup_if_error);
 }
-
-static int 
-fetch_inferior_event_wrapper (gdb_client_data client_data)
-{
-  fetch_inferior_event (client_data);
-  return 1;
-}