Port scoped_push to Rust

fish-rust/src/common.rs

@@ -0,0 +1,33 @@
+use std::mem;
+
+/// 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.
+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),
+        }
+    }
+
+    pub fn restore(&mut self) {
+        if let Some(saved_value) = self.saved_value.take() {
+            *self.var = saved_value;
+        }
+    }
+}
+
+impl<'a, T> Drop for ScopedPush<'a, T> {
+    fn drop(&mut self) {
+        self.restore()
+    }
+}

fish-rust/src/lib.rs

@@ -4,6 +4,7 @@
 #![allow(clippy::needless_return)]
 #![allow(clippy::manual_is_ascii_check)]
 
+mod common;
 mod fd_readable_set;
 mod fds;
 #[allow(rustdoc::broken_intra_doc_links)]