Make parser.libdata.is_event a bool instead of an int

Contrary to the comment, this can and should be a bool.

src/event.rs

@@ -460,16 +460,10 @@ pub fn get_function_handlers(name: &wstr) -> EventHandlerList {
 /// event handler, we make sure to optimize the 'no matches' path. This means that nothing is
 /// allocated/initialized unless needed.
 fn fire_internal(parser: &Parser, event: &Event) {
-    assert!(
-        parser.libdata().is_event >= 0,
-        "is_event should not be negative"
-    );
-
     // Suppress fish_trace during events.
-    let is_event = parser.libdata().is_event;
-    let _inc_event = scoped_push_replacer(
+    let _set_event = scoped_push_replacer(
         |new_value| std::mem::replace(&mut parser.libdata_mut().is_event, new_value),
-        is_event + 1,
+        true,
     );
     let _suppress_trace = scoped_push_replacer(
         |new_value| std::mem::replace(&mut parser.libdata_mut().suppress_fish_trace, new_value),
@@ -539,7 +533,7 @@ pub fn fire_delayed(parser: &Parser) {
         let ld = &parser.libdata();
 
         // Do not invoke new event handlers from within event handlers.
-        if ld.is_event != 0 {
+        if ld.is_event {
             return;
         };
     }

src/parse_execution.rs

@@ -1625,8 +1625,8 @@ fn run_1_job(
             let parser = ctx.parser();
             let ld = &parser.libdata();
             props.skip_notification =
-                ld.is_subshell || parser.is_block() || ld.is_event != 0 || !parser.is_interactive();
-            props.from_event_handler = ld.is_event != 0;
+                ld.is_subshell || parser.is_block() || ld.is_event || !parser.is_interactive();
+            props.from_event_handler = ld.is_event;
         }
 
         let mut job = Job::new(props, self.node_source_owned(job_node));
@@ -1887,7 +1887,7 @@ fn setup_group(&self, ctx: &OperationContext<'_>, j: &mut Job) {
         } else {
             // This is a "real job" that gets its own pgroup.
             j.processes_mut()[0].leads_pgrp = true;
-            let wants_terminal = ctx.parser().libdata().is_event == 0;
+            let wants_terminal = !ctx.parser().libdata().is_event;
             j.group = Some(JobGroup::create_with_job_control(
                 j.command().to_owned(),
                 wants_terminal,

src/parser.rs

@@ -269,9 +269,8 @@ pub struct LibraryData {
     /// Whether we are running a subshell command.
     pub is_subshell: bool,
 
-    /// Whether we are running an event handler. This is not a bool because we keep count of the
-    /// event nesting level.
-    pub is_event: i32,
+    /// Whether we are running an event handler.
+    pub is_event: bool,
 
     /// Whether we are currently interactive.
     pub is_interactive: bool,