1 files changed, 77 insertions, 0 deletions
diff --git a/vendor/tracing-subscriber/src/registry/stack.rs b/vendor/tracing-subscriber/src/registry/stack.rs
new file mode 100644
index 000000000..4a3f7e59d
--- /dev/null
+++ b/vendor/tracing-subscriber/src/registry/stack.rs
@@ -0,0 +1,77 @@
+pub(crate) use tracing_core::span::Id;
+
+#[derive(Debug)]
+struct ContextId {
+    id: Id,
+    duplicate: bool,
+}
+
+/// `SpanStack` tracks what spans are currently executing on a thread-local basis.
+///
+/// A "separate current span" for each thread is a semantic choice, as each span
+/// can be executing in a different thread.
+#[derive(Debug, Default)]
+pub(crate) struct SpanStack {
+    stack: Vec<ContextId>,
+}
+
+impl SpanStack {
+    #[inline]
+    pub(super) fn push(&mut self, id: Id) -> bool {
+        let duplicate = self.stack.iter().any(|i| i.id == id);
+        self.stack.push(ContextId { id, duplicate });
+        !duplicate
+    }
+
+    #[inline]
+    pub(super) fn pop(&mut self, expected_id: &Id) -> bool {
+        if let Some((idx, _)) = self
+            .stack
+            .iter()
+            .enumerate()
+            .rev()
+            .find(|(_, ctx_id)| ctx_id.id == *expected_id)
+        {
+            let ContextId { id: _, duplicate } = self.stack.remove(idx);
+            return !duplicate;
+        }
+        false
+    }
+
+    #[inline]
+    pub(crate) fn iter(&self) -> impl Iterator<Item = &Id> {
+        self.stack
+            .iter()
+            .rev()
+            .filter_map(|ContextId { id, duplicate }| if !*duplicate { Some(id) } else { None })
+    }
+
+    #[inline]
+    pub(crate) fn current(&self) -> Option<&Id> {
+        self.iter().next()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::{Id, SpanStack};
+
+    #[test]
+    fn pop_last_span() {
+        let mut stack = SpanStack::default();
+        let id = Id::from_u64(1);
+        stack.push(id.clone());
+
+        assert!(stack.pop(&id));
+    }
+
+    #[test]
+    fn pop_first_span() {
+        let mut stack = SpanStack::default();
+        stack.push(Id::from_u64(1));
+        stack.push(Id::from_u64(2));
+
+        let id = Id::from_u64(1);
+        assert!(stack.pop(&id));
+    }
+}