5 files changed, 35 insertions, 7 deletions
diff --git a/compiler/rustc_hir_analysis/src/collect.rs b/compiler/rustc_hir_analysis/src/collect.rs
index 640138a3e5e..9636c614446 100644
--- a/compiler/rustc_hir_analysis/src/collect.rs
+++ b/compiler/rustc_hir_analysis/src/collect.rs
@@ -14,14 +14,11 @@
 //! At present, however, we do run collection across all items in the
 //! crate as a kind of pass. This should eventually be factored away.
 
-use crate::astconv::AstConv;
-use crate::check::intrinsic::intrinsic_operation_unsafety;
-use crate::errors;
-use hir::def::DefKind;
 use rustc_data_structures::captures::Captures;
 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 use rustc_errors::{Applicability, DiagnosticBuilder, ErrorGuaranteed, StashKey};
 use rustc_hir as hir;
+use rustc_hir::def::DefKind;
 use rustc_hir::def_id::{DefId, LocalDefId, LocalModDefId};
 use rustc_hir::intravisit::{self, Visitor};
 use rustc_hir::{GenericParamKind, Node};
@@ -40,6 +37,11 @@ use rustc_trait_selection::traits::ObligationCtxt;
 use std::iter;
 use std::ops::Bound;
 
+use crate::astconv::AstConv;
+use crate::check::intrinsic::intrinsic_operation_unsafety;
+use crate::errors;
+pub use type_of::test_opaque_hidden_types;
+
 mod generics_of;
 mod item_bounds;
 mod predicates_of;
diff --git a/compiler/rustc_hir_analysis/src/collect/type_of.rs b/compiler/rustc_hir_analysis/src/collect/type_of.rs
index 47a412c2110..d7bd2a7b17f 100644
--- a/compiler/rustc_hir_analysis/src/collect/type_of.rs
+++ b/compiler/rustc_hir_analysis/src/collect/type_of.rs
@@ -11,6 +11,7 @@ use rustc_span::{Span, DUMMY_SP};
 
 use super::ItemCtxt;
 use super::{bad_placeholder, is_suggestable_infer_ty};
+pub use opaque::test_opaque_hidden_types;
 
 mod opaque;
 
diff --git a/compiler/rustc_hir_analysis/src/collect/type_of/opaque.rs b/compiler/rustc_hir_analysis/src/collect/type_of/opaque.rs
index 0544c5ca866..e8d5264c2b8 100644
--- a/compiler/rustc_hir_analysis/src/collect/type_of/opaque.rs
+++ b/compiler/rustc_hir_analysis/src/collect/type_of/opaque.rs
@@ -1,12 +1,25 @@
 use rustc_errors::StashKey;
-use rustc_hir::def_id::LocalDefId;
+use rustc_hir::def::DefKind;
+use rustc_hir::def_id::{LocalDefId, CRATE_DEF_ID};
 use rustc_hir::intravisit::{self, Visitor};
 use rustc_hir::{self as hir, def, Expr, ImplItem, Item, Node, TraitItem};
 use rustc_middle::hir::nested_filter;
 use rustc_middle::ty::{self, Ty, TyCtxt, TypeVisitableExt};
-use rustc_span::DUMMY_SP;
+use rustc_span::{sym, DUMMY_SP};
 
-use crate::errors::{TaitForwardCompat, UnconstrainedOpaqueType};
+use crate::errors::{TaitForwardCompat, TypeOf, UnconstrainedOpaqueType};
+
+pub fn test_opaque_hidden_types(tcx: TyCtxt<'_>) {
+    if tcx.has_attr(CRATE_DEF_ID, sym::rustc_hidden_type_of_opaques) {
+        for id in tcx.hir().items() {
+            if matches!(tcx.def_kind(id.owner_id), DefKind::OpaqueTy) {
+                let type_of = tcx.type_of(id.owner_id).instantiate_identity();
+
+                tcx.sess.emit_err(TypeOf { span: tcx.def_span(id.owner_id), type_of });
+            }
+        }
+    }
+}
 
 /// Checks "defining uses" of opaque `impl Trait` types to ensure that they meet the restrictions
 /// laid for "higher-order pattern unification".
diff --git a/compiler/rustc_hir_analysis/src/errors.rs b/compiler/rustc_hir_analysis/src/errors.rs
index 1120585f1aa..189564d4e33 100644
--- a/compiler/rustc_hir_analysis/src/errors.rs
+++ b/compiler/rustc_hir_analysis/src/errors.rs
@@ -468,6 +468,14 @@ pub(crate) struct VariancesOf {
 }
 
 #[derive(Diagnostic)]
+#[diag(hir_analysis_type_of)]
+pub(crate) struct TypeOf<'tcx> {
+    #[primary_span]
+    pub span: Span,
+    pub type_of: Ty<'tcx>,
+}
+
+#[derive(Diagnostic)]
 #[diag(hir_analysis_pass_to_variadic_function, code = "E0617")]
 pub(crate) struct PassToVariadicFunction<'tcx, 'a> {
     #[primary_span]
diff --git a/compiler/rustc_hir_analysis/src/lib.rs b/compiler/rustc_hir_analysis/src/lib.rs
index 88f3db03a4e..0622aa2ee80 100644
--- a/compiler/rustc_hir_analysis/src/lib.rs
+++ b/compiler/rustc_hir_analysis/src/lib.rs
@@ -214,6 +214,10 @@ pub fn check_crate(tcx: TyCtxt<'_>) -> Result<(), ErrorGuaranteed> {
         tcx.hir().for_each_module(|module| tcx.ensure().check_mod_item_types(module))
     });
 
+    if tcx.features().rustc_attrs {
+        tcx.sess.track_errors(|| collect::test_opaque_hidden_types(tcx))?;
+    }
+
     // Freeze definitions as we don't add new ones at this point. This improves performance by
     // allowing lock-free access to them.
     tcx.untracked().definitions.freeze();