Don't generate exit events for jobs created from within event handlers

Add a new job property from_event_handler, and do not create exit events for
such jobs. This prevents easy accidental infinite recursion.

src/fish.cpp

@@ -520,8 +520,6 @@ int main(int argc, char **argv) {
 
     int exit_status = res ? STATUS_CMD_UNKNOWN : parser.get_last_status();
 
-    // TODO: The generic process-exit event is useless and unused.
-    // Remove this in future.
     event_fire(parser,
                proc_create_event(L"PROCESS_EXIT", event_type_t::exit, getpid(), exit_status));
 

src/parse_execution.cpp

@@ -1243,6 +1243,7 @@ parse_execution_result_t parse_execution_context_t::run_1_job(tnode_t<g::job> jo
     props.wants_terminal = wants_job_control && !ld.is_event;
     props.skip_notification =
         ld.is_subshell || ld.is_block || ld.is_event || !shell_is_interactive();
+    props.from_event_handler = ld.is_event;
 
     shared_ptr<job_t> job = std::make_shared<job_t>(acquire_job_id(), props, block_io, parent_job);
     job->tmodes = tmodes;

src/proc.cpp

@@ -472,9 +472,11 @@ static bool try_clean_process_in_job(process_t *p, job_t *j, std::vector<event_t
 
     auto s = p->status;
 
-    // Add an exit event.
+    // Add an exit event if the process did not come from a job handler.
+    if (!j->from_event_handler()) {
         exit_events->push_back(proc_create_event(L"PROCESS_EXIT", event_type_t::exit, p->pid,
                                                  s.normal_exited() ? s.exit_code() : -1));
+    }
 
     // Ignore SIGPIPE. We issue it ourselves to the pipe writer when the pipe reader dies.
     if (!s.signal_exited() || s.signal_code() == SIGPIPE) {
@@ -600,8 +602,9 @@ static bool process_clean_after_marking(parser_t &parser, bool allow_interactive
             printed = true;
         }
 
-        // Prepare events for completed jobs.
-        if (j->is_completed()) {
+        // Prepare events for completed jobs, except for jobs that themselves came from event
+        // handlers.
+        if (!j->from_event_handler() && j->is_completed()) {
             if (j->pgid != INVALID_PID) {
                 exit_events.push_back(
                     proc_create_event(L"JOB_EXIT", event_type_t::exit, -j->pgid, 0));

src/proc.h

@@ -296,6 +296,9 @@ class job_t {
 
         /// Whether the job wants to own the terminal when in the foreground.
         bool wants_terminal{};
+
+        /// Whether this job was created as part of an event handler.
+        bool from_event_handler{};
     };
 
    private:
@@ -421,6 +424,7 @@ class job_t {
         return !is_completed() && is_constructed() && !get_flag(job_flag_t::DISOWN_REQUESTED);
     };
     bool skip_notification() const { return properties.skip_notification; }
+    bool from_event_handler() const { return properties.from_event_handler; }
 
     /// \return the parent job, or nullptr.
     const std::shared_ptr<job_t> get_parent() const { return parent_job; }