1 files changed, 71 insertions, 1 deletions
diff --git a/compiler/rustc_lint/src/builtin.rs b/compiler/rustc_lint/src/builtin.rs
index cd19e65b6fc..d6de6e70ead 100644
--- a/compiler/rustc_lint/src/builtin.rs
+++ b/compiler/rustc_lint/src/builtin.rs
@@ -25,6 +25,7 @@ use crate::{
     types::{transparent_newtype_field, CItemKind},
     EarlyContext, EarlyLintPass, LateContext, LateLintPass, LintContext,
 };
+use hir::IsAsync;
 use rustc_ast::attr;
 use rustc_ast::tokenstream::{TokenStream, TokenTree};
 use rustc_ast::visit::{FnCtxt, FnKind};
@@ -40,7 +41,10 @@ use rustc_feature::{deprecated_attributes, AttributeGate, BuiltinAttribute, Gate
 use rustc_hir as hir;
 use rustc_hir::def::{DefKind, Res};
 use rustc_hir::def_id::{DefId, LocalDefId, LocalDefIdSet, CRATE_DEF_ID};
-use rustc_hir::{ForeignItemKind, GenericParamKind, HirId, Node, PatKind, PredicateOrigin};
+use rustc_hir::intravisit::FnKind as HirFnKind;
+use rustc_hir::{
+    Body, FnDecl, ForeignItemKind, GenericParamKind, HirId, Node, PatKind, PredicateOrigin,
+};
 use rustc_index::vec::Idx;
 use rustc_middle::lint::in_external_macro;
 use rustc_middle::ty::layout::{LayoutError, LayoutOf};
@@ -1371,6 +1375,72 @@ impl<'tcx> LateLintPass<'tcx> for UnstableFeatures {
 }
 
 declare_lint! {
+    /// The `ungated_async_fn_track_caller` lint warns when the
+    /// `#[track_caller]` attribute is used on an async function, method, or
+    /// closure, without enabling the corresponding unstable feature flag.
+    ///
+    /// ### Example
+    ///
+    /// ```rust
+    /// #[track_caller]
+    /// async fn foo() {}
+    /// ```
+    ///
+    /// {{produces}}
+    ///
+    /// ### Explanation
+    ///
+    /// The attribute must be used in conjunction with the
+    /// [`closure_track_caller` feature flag]. Otherwise, the `#[track_caller]`
+    /// annotation will function as as no-op.
+    ///
+    /// [`closure_track_caller` feature flag]: https://doc.rust-lang.org/beta/unstable-book/language-features/closure-track-caller.html
+    UNGATED_ASYNC_FN_TRACK_CALLER,
+    Warn,
+    "enabling track_caller on an async fn is a no-op unless the closure_track_caller feature is enabled"
+}
+
+declare_lint_pass!(
+    /// Explains corresponding feature flag must be enabled for the `#[track_caller] attribute to
+    /// do anything
+    UngatedAsyncFnTrackCaller => [UNGATED_ASYNC_FN_TRACK_CALLER]
+);
+
+impl<'tcx> LateLintPass<'tcx> for UngatedAsyncFnTrackCaller {
+    fn check_fn(
+        &mut self,
+        cx: &LateContext<'_>,
+        fn_kind: HirFnKind<'_>,
+        _: &'tcx FnDecl<'_>,
+        _: &'tcx Body<'_>,
+        span: Span,
+        hir_id: HirId,
+    ) {
+        if fn_kind.asyncness() == IsAsync::Async
+            && !cx.tcx.features().closure_track_caller
+            && let attrs = cx.tcx.hir().attrs(hir_id)
+            // Now, check if the function has the `#[track_caller]` attribute
+            && let Some(attr) = attrs.iter().find(|attr| attr.has_name(sym::track_caller))
+            {
+                cx.struct_span_lint(
+                    UNGATED_ASYNC_FN_TRACK_CALLER,
+                    attr.span,
+                    fluent::lint_ungated_async_fn_track_caller,
+                    |lint| {
+                        lint.span_label(span, fluent::label);
+                        rustc_session::parse::add_feature_diagnostics(
+                            lint,
+                            &cx.tcx.sess.parse_sess,
+                            sym::closure_track_caller,
+                        );
+                        lint
+                    },
+                );
+            }
+    }
+}
+
+declare_lint! {
     /// The `unreachable_pub` lint triggers for `pub` items not reachable from
     /// the crate root.
     ///