vim-patch:8.0.0702: error in a timer can make Vim unusable #9826

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.
https://github.com/vim/vim/commit/c577d813b7978345dec4310b2d8f5d5624a681f6

closes #9826

1 files changed, 21 insertions, 0 deletions

diff --git a/src/nvim/eval.c b/src/nvim/eval.c
index 929304a874..9a67b01307 100644
--- a/src/nvim/eval.c
+++ b/src/nvim/eval.c
@@ -449,6 +449,7 @@ typedef struct {
   int timer_id;
   int repeat_count;
   int refcount;
+  int emsg_count;  ///< Errors in a repeating timer.
   long timeout;
   bool stopped;
   bool paused;
@@ -17160,6 +17161,7 @@ static void f_timer_start(typval_T *argvars, typval_T *rettv, FunPtr fptr)
   timer->refcount = 1;
   timer->stopped = false;
   timer->paused = false;
+  timer->emsg_count = 0;
   timer->repeat_count = repeat;
   timer->timeout = timeout;
   timer->timer_id = last_timer_id++;
@@ -17202,6 +17204,9 @@ static void f_timer_stopall(typval_T *argvars, typval_T *unused, FunPtr fptr)
 static void timer_due_cb(TimeWatcher *tw, void *data)
 {
   timer_T *timer = (timer_T *)data;
+  int save_did_emsg = did_emsg;
+  int save_called_emsg = called_emsg;
+
   if (timer->stopped || timer->paused) {
     return;
   }
@@ -17216,8 +17221,24 @@ static void timer_due_cb(TimeWatcher *tw, void *data)
   argv[0].v_type = VAR_NUMBER;
   argv[0].vval.v_number = timer->timer_id;
   typval_T rettv = TV_INITIAL_VALUE;
+  called_emsg = false;
 
   callback_call(&timer->callback, 1, argv, &rettv);
+
+  // Handle error message
+  if (called_emsg && did_emsg) {
+    timer->emsg_count++;
+    if (current_exception != NULL) {
+      discard_current_exception();
+    }
+  }
+  did_emsg = save_did_emsg;
+  called_emsg = save_called_emsg;
+
+  if (timer->emsg_count >= 3) {
+    timer_stop(timer);
+  }
+
   tv_clear(&rettv);
 
   if (!timer->stopped && timer->timeout == 0) {