1 files changed, 45 insertions, 0 deletions
diff --git a/src/librustdoc/passes/propagate_doc_cfg.rs b/src/librustdoc/passes/propagate_doc_cfg.rs
new file mode 100644
index 000000000..0c5d83655
--- /dev/null
+++ b/src/librustdoc/passes/propagate_doc_cfg.rs
@@ -0,0 +1,45 @@
+//! Propagates [`#[doc(cfg(...))]`](https://github.com/rust-lang/rust/issues/43781) to child items.
+use std::sync::Arc;
+
+use crate::clean::cfg::Cfg;
+use crate::clean::{Crate, Item};
+use crate::core::DocContext;
+use crate::fold::DocFolder;
+use crate::passes::Pass;
+
+pub(crate) const PROPAGATE_DOC_CFG: Pass = Pass {
+    name: "propagate-doc-cfg",
+    run: propagate_doc_cfg,
+    description: "propagates `#[doc(cfg(...))]` to child items",
+};
+
+pub(crate) fn propagate_doc_cfg(cr: Crate, _: &mut DocContext<'_>) -> Crate {
+    CfgPropagator { parent_cfg: None }.fold_crate(cr)
+}
+
+struct CfgPropagator {
+    parent_cfg: Option<Arc<Cfg>>,
+}
+
+impl DocFolder for CfgPropagator {
+    fn fold_item(&mut self, mut item: Item) -> Option<Item> {
+        let old_parent_cfg = self.parent_cfg.clone();
+
+        let new_cfg = match (self.parent_cfg.take(), item.cfg.take()) {
+            (None, None) => None,
+            (Some(rc), None) | (None, Some(rc)) => Some(rc),
+            (Some(mut a), Some(b)) => {
+                let b = Arc::try_unwrap(b).unwrap_or_else(|rc| Cfg::clone(&rc));
+                *Arc::make_mut(&mut a) &= b;
+                Some(a)
+            }
+        };
+        self.parent_cfg = new_cfg.clone();
+        item.cfg = new_cfg;
+
+        let result = self.fold_item_recur(item);
+        self.parent_cfg = old_parent_cfg;
+
+        Some(result)
+    }
+}