runner: add Stack type

A Stack guarantees that elements are dropped in reverse push order.

2 files changed, 26 insertions, 0 deletions

diff --git a/crates/runner/src/util/mod.rs b/crates/runner/src/util/mod.rs
index 1f89592..0fbe3b5 100644
--- a/crates/runner/src/util/mod.rs
+++ b/crates/runner/src/util/mod.rs
@@ -2,5 +2,6 @@ pub mod checkable;
 pub mod cjson;
 pub mod clone;
 pub mod fs;
+pub mod stack;
 pub mod steal;
 pub mod unix;
diff --git a/crates/runner/src/util/stack.rs b/crates/runner/src/util/stack.rs
new file mode 100644
index 0000000..15d5daf
--- /dev/null
+++ b/crates/runner/src/util/stack.rs
@@ -0,0 +1,25 @@
+use std::mem;
+
+/// Simple inefficient datastructure with guaranteed drop order
+#[derive(Debug)]
+pub enum Stack<T> {
+	Cons(Box<(T, Stack<T>)>),
+	Empty,
+}
+
+impl<T> Default for Stack<T> {
+	fn default() -> Self {
+		Self::Empty
+	}
+}
+
+impl<T> Stack<T> {
+	pub fn new() -> Self {
+		Self::Empty
+	}
+
+	pub fn push(&mut self, value: T) {
+		let tmp = mem::take(self);
+		*self = Stack::Cons(Box::new((value, tmp)));
+	}
+}