patch 8.0.0702: an error in a timer can make Vim unusable

Problem:    An error in a timer can make Vim unusable.
Solution:   Don't set the error flag or exception from a timer.  Stop a timer
            if it causes an error 3 out of 3 times.  Discard an exception
            caused inside a timer.

Author: brammool

runtime/doc/eval.txt

@@ -1,4 +1,4 @@
-*eval.txt*	For Vim version 8.0.  Last change: 2017 Jun 25
+*eval.txt*	For Vim version 8.0.  Last change: 2017 Jul 08
 
 
 		  VIM REFERENCE MANUAL	  by Bram Moolenaar
@@ -4189,14 +4189,14 @@ getchar([expr])						*getchar()*
 			not consumed.  Return zero if no character available.
 
 		Without [expr] and when [expr] is 0 a whole character or
-		special key is returned.  If it is an 8-bit character, the
+		special key is returned.  If it is a single character, the
 		result is a number.  Use nr2char() to convert it to a String.
 		Otherwise a String is returned with the encoded character.
-		For a special key it's a sequence of bytes starting with 0x80
-		(decimal: 128).  This is the same value as the string
-		"\<Key>", e.g., "\<Left>".  The returned value is also a
-		String when a modifier (shift, control, alt) was used that is
-		not included in the character.
+		For a special key it's a String with a sequence of bytes
+		starting with 0x80 (decimal: 128).  This is the same value as
+		the String "\<Key>", e.g., "\<Left>".  The returned value is
+		also a String when a modifier (shift, control, alt) was used
+		that is not included in the character.
 
 		When [expr] is 0 and Esc is typed, there will be a short delay
 		while Vim waits to see if this is the start of an escape
@@ -8017,6 +8017,10 @@ timer_start({time}, {callback} [, {options}])
 		   "repeat"	Number of times to repeat calling the
 				callback.  -1 means forever.  When not present
 				the callback will be called once.
+				If the timer causes an error three times in a
+				row the repeat is cancelled.  This avoids that
+				Vim becomes unusable because of all the error
+				messages.
 
 		Example: >
 			func MyHandler(timer)

src/ex_cmds2.c

@@ -1197,11 +1197,13 @@ check_due_timer(void)
     long	current_id = last_timer_id;
 # ifdef WIN3264
     LARGE_INTEGER   fr;
+# endif
 
-    /* Don't run any timers while exiting. */
-    if (exiting)
+    /* Don't run any timers while exiting or dealing with an error. */
+    if (exiting || aborting())
 	return next_due;
 
+# ifdef WIN3264
     QueryPerformanceFrequency(&fr);
 # endif
     profile_start(&now);
@@ -1216,20 +1218,33 @@ check_due_timer(void)
 	{
 	    int save_timer_busy = timer_busy;
 	    int save_vgetc_busy = vgetc_busy;
+	    int did_emsg_save = did_emsg;
+	    int called_emsg_save = called_emsg;
+	    int did_throw_save = did_throw;
 
 	    timer_busy = timer_busy > 0 || vgetc_busy > 0;
 	    vgetc_busy = 0;
+	    called_emsg = FALSE;
 	    timer->tr_firing = TRUE;
 	    timer_callback(timer);
 	    timer->tr_firing = FALSE;
 	    timer_next = timer->tr_next;
 	    did_one = TRUE;
 	    timer_busy = save_timer_busy;
 	    vgetc_busy = save_vgetc_busy;
+	    if (called_emsg)
+	    {
+		++timer->tr_emsg_count;
+		if (!did_throw_save && current_exception != NULL)
+		    discard_current_exception();
+	    }
+	    did_emsg = did_emsg_save;
+	    called_emsg = called_emsg_save;
 
 	    /* Only fire the timer again if it repeats and stop_timer() wasn't
 	     * called while inside the callback (tr_id == -1). */
-	    if (timer->tr_repeat != 0 && timer->tr_id != -1)
+	    if (timer->tr_repeat != 0 && timer->tr_id != -1
+		    && timer->tr_emsg_count < 3)
 	    {
 		profile_setlimit(timer->tr_interval, &timer->tr_due);
 		this_due = GET_TIMEDIFF(timer, now);

src/structs.h

@@ -3243,6 +3243,7 @@ struct timer_S
     long	tr_interval;	    /* msec */
     char_u	*tr_callback;	    /* allocated */
     partial_T	*tr_partial;
+    int		tr_emsg_count;
 #endif
 };
 

src/testdir/test_timers.vim

@@ -189,4 +189,22 @@ func Test_input_in_timer()
   call assert_equal('hello', g:val)
 endfunc
 
+func FuncWithError(timer)
+  let g:call_count += 1
+  if g:call_count == 4
+    return
+  endif
+  doesnotexist
+endfunc
+
+func Test_timer_errors()
+  let g:call_count = 0
+  let timer = timer_start(10, 'FuncWithError', {'repeat': -1})
+  " Timer will be stopped after failing 3 out of 3 times.
+  call WaitFor('g:call_count == 3')
+  sleep 50m
+  call assert_equal(3, g:call_count)
+endfunc
+
+
 " vim: shiftwidth=2 sts=2 expandtab

src/version.c

@@ -764,6 +764,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    702,
 /**/
     701,
 /**/