Replace ScopedPush with scoped_push which is underpinned by ScopeGuard

This allows us to use the scoped push in more scenarios by appeasing the
borrow checker.

Use it in a couple of places instead of ScopeGuard. Hopefully this is makes
porting easier.

fish-rust/src/common.rs

@@ -1855,38 +1855,44 @@ impl<T, F: FnOnce(&mut T), C> Drop for ScopeGuard<T, F, C> {
     }
 }
 
-/// A scoped manager to save the current value of some variable, and optionally set it to a new
-/// value. When dropped, it restores the variable to its old value.
-///
-/// This can be handy when there are multiple code paths to exit a block. Note that this can only be
-/// used if the code does not access the captured variable again for the duration of the scope. If
-/// that's not the case (the code will refuse to compile), use a [`ScopeGuard`] instance instead.
-pub struct ScopedPush<'a, T> {
-    var: &'a mut T,
-    saved_value: Option<T>,
-}
-
-impl<'a, T> ScopedPush<'a, T> {
-    pub fn new(var: &'a mut T, new_value: T) -> Self {
-        let saved_value = mem::replace(var, new_value);
-
-        Self {
-            var,
-            saved_value: Some(saved_value),
-        }
+/// A scoped manager to save the current value of some variable, and set it to a new value. When
+/// dropped, it restores the variable to its old value.
+#[allow(clippy::type_complexity)] // Not sure how to extract the return type.
+pub fn scoped_push<Context, Accessor, T>(
+    mut ctx: Context,
+    accessor: Accessor,
+    new_value: T,
+) -> ScopeGuard<(Context, Accessor, T), fn(&mut (Context, Accessor, T)), Context>
+where
+    Accessor: Fn(&mut Context) -> &mut T,
+    T: Copy,
+{
+    fn restore_saved_value<Context, Accessor, T: Copy>(data: &mut (Context, Accessor, T))
+    where
+        Accessor: Fn(&mut Context) -> &mut T,
+    {
+        let (ref mut ctx, ref accessor, saved_value) = data;
+        *accessor(ctx) = *saved_value;
     }
-
-    pub fn restore(&mut self) {
-        if let Some(saved_value) = self.saved_value.take() {
-            *self.var = saved_value;
-        }
+    fn view_context<Context, Accessor, T>(data: &(Context, Accessor, T)) -> &Context
+    where
+        Accessor: Fn(&mut Context) -> &mut T,
+    {
+        &data.0
     }
-}
-
-impl<'a, T> Drop for ScopedPush<'a, T> {
-    fn drop(&mut self) {
-        self.restore()
+    fn view_context_mut<Context, Accessor, T>(data: &mut (Context, Accessor, T)) -> &mut Context
+    where
+        Accessor: Fn(&mut Context) -> &mut T,
+    {
+        &mut data.0
     }
+    let saved_value = mem::replace(accessor(&mut ctx), new_value);
+    ScopeGuard::with_view(
+        (ctx, accessor, saved_value),
+        view_context,
+        view_context_mut,
+        restore_saved_value,
+    )
 }
 
 pub const fn assert_send<T: Send>() {}

fish-rust/src/event.rs

@@ -13,7 +13,7 @@ use std::sync::{Arc, Mutex};
 use widestring_suffix::widestrs;
 
 use crate::builtins::shared::io_streams_t;
-use crate::common::{escape_string, replace_with, EscapeFlags, EscapeStringStyle, ScopeGuard};
+use crate::common::{escape_string, scoped_push, EscapeFlags, EscapeStringStyle, ScopeGuard};
 use crate::ffi::{self, block_t, parser_t, signal_check_cancel, signal_handle, Repin};
 use crate::flog::FLOG;
 use crate::signal::Signal;
@@ -676,13 +676,17 @@ fn fire_internal(parser: &mut parser_t, event: &Event) {
     );
 
     // Suppress fish_trace during events.
-    let saved_is_event = replace_with(&mut parser.libdata_pod().is_event, |old| old + 1);
-    let saved_suppress_fish_trace =
-        std::mem::replace(&mut parser.libdata_pod().suppress_fish_trace, true);
-    let mut parser = ScopeGuard::new(parser, |parser| {
-        parser.libdata_pod().is_event = saved_is_event;
-        parser.libdata_pod().suppress_fish_trace = saved_suppress_fish_trace;
-    });
+    let is_event = parser.libdata_pod().is_event;
+    let mut parser = scoped_push(
+        parser,
+        |parser| &mut parser.libdata_pod().is_event,
+        is_event + 1,
+    );
+    let mut parser = scoped_push(
+        &mut *parser,
+        |parser| &mut parser.libdata_pod().suppress_fish_trace,
+        true,
+    );
 
     // Capture the event handlers that match this event.
     let fire: Vec<_> = EVENT_HANDLERS
@@ -717,7 +721,7 @@ fn fire_internal(parser: &mut parser_t, event: &Event) {
         let saved_is_interactive =
             std::mem::replace(&mut parser.libdata_pod().is_interactive, false);
         let saved_statuses = parser.get_last_statuses().within_unique_ptr();
-        let mut parser = ScopeGuard::new(&mut parser, |parser| {
+        let mut parser = ScopeGuard::new(&mut *parser, |parser| {
             parser.pin().set_last_statuses(saved_statuses);
             parser.libdata_pod().is_interactive = saved_is_interactive;
         });
@@ -731,14 +735,14 @@ fn fire_internal(parser: &mut parser_t, event: &Event) {
             "'"
         );
 
-        let b = parser
+        let b = (*parser)
             .pin()
             .push_block(block_t::event_block((event as *const Event).cast()).within_unique_ptr());
-        parser
+        (*parser)
             .pin()
             .eval_string_ffi1(&buffer.to_ffi())
             .within_unique_ptr();
-        parser.pin().pop_block(b);
+        (*parser).pin().pop_block(b);
 
         handler.fired.store(true, Ordering::Relaxed);
         fired_one_shot |= handler.is_one_shot();