Error on define_opaques entries without any opaques actually referenced

Author: oli-obk

compiler/rustc_ast_lowering/src/item.rs

@@ -11,6 +11,7 @@ use rustc_index::{IndexSlice, IndexVec};
 use rustc_middle::span_bug;
 use rustc_middle::ty::{ResolverAstLowering, TyCtxt};
 use rustc_span::edit_distance::find_best_match_for_name;
+use rustc_span::source_map::{Spanned, respan};
 use rustc_span::{DUMMY_SP, DesugaringKind, Ident, Span, Symbol, kw, sym};
 use smallvec::{SmallVec, smallvec};
 use thin_vec::ThinVec;
@@ -1678,7 +1679,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
     pub(super) fn lower_define_opaques(
         &mut self,
         define_opaques: &Option<ThinVec<(NodeId, Path)>>,
-    ) -> Option<&'hir [LocalDefId]> {
+    ) -> Option<&'hir [Spanned<LocalDefId>]> {
         define_opaques.as_ref().map(|d| {
             &*self.arena.alloc_from_iter(d.iter().filter_map(|(id, path)| {
                 let res = self.resolver.get_partial_res(*id).unwrap();
@@ -1693,7 +1694,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                     );
                     return None;
                 };
-                Some(did)
+                Some(respan(self.lower_span(path.span), did))
             }))
         })
     }

compiler/rustc_hir/src/hir.rs

@@ -704,7 +704,7 @@ pub struct Generics<'hir> {
     pub has_where_clause_predicates: bool,
     pub where_clause_span: Span,
     pub span: Span,
-    pub define_opaques: Option<&'hir [LocalDefId]>,
+    pub define_opaques: Option<&'hir [Spanned<LocalDefId>]>,
 }
 
 impl<'hir> Generics<'hir> {
@@ -1436,7 +1436,7 @@ pub struct Closure<'hir> {
     /// The span of the argument block `|...|`
     pub fn_arg_span: Option<Span>,
     pub kind: ClosureKind,
-    pub define_opaques: Option<&'hir [LocalDefId]>,
+    pub define_opaques: Option<&'hir [Spanned<LocalDefId>]>,
 }
 
 #[derive(Clone, PartialEq, Eq, Debug, Copy, Hash, HashStable_Generic, Encodable, Decodable)]
@@ -4087,7 +4087,7 @@ pub enum ItemKind<'hir> {
     Use(&'hir UsePath<'hir>, UseKind),
 
     /// A `static` item.
-    Static(&'hir Ty<'hir>, Mutability, BodyId, Option<&'hir [LocalDefId]>),
+    Static(&'hir Ty<'hir>, Mutability, BodyId, Option<&'hir [Spanned<LocalDefId>]>),
     /// A `const` item.
     Const(&'hir Ty<'hir>, &'hir Generics<'hir>, BodyId),
     /// A function declaration.
@@ -4619,7 +4619,7 @@ impl<'hir> Node<'hir> {
         }
     }
 
-    pub fn define_opaques(&self) -> Option<&'hir [LocalDefId]> {
+    pub fn define_opaques(&self) -> Option<&'hir [Spanned<LocalDefId>]> {
         match self {
             Node::Item(Item { kind: ItemKind::Static(.., define_opaques), .. }) => *define_opaques,
             Node::Expr(Expr { kind: ExprKind::Closure(c), .. }) => c.define_opaques,

compiler/rustc_ty_utils/src/opaque_types.rs

@@ -181,11 +181,13 @@ impl<'tcx> OpaqueTypeCollector<'tcx> {
             return;
         };
         for &define in defines {
-            // TODO: check that `define` is a type alias (and add tests)
             trace!(?define);
             let mode = std::mem::replace(&mut self.mode, CollectionMode::Taits);
-            // TODO: check that opaque types were introduced and error otherwise (also add tests)
-            super::sig_types::walk_types(self.tcx, define, self);
+            let n = self.opaques.len();
+            super::sig_types::walk_types(self.tcx, define.node, self);
+            if n == self.opaques.len() {
+                self.tcx.dcx().span_err(define.span, "item does not contain any opaque types");
+            }
             self.mode = mode;
         }
         // Allow using `#[defines]` on assoc methods and type aliases to override the default collection mode in

tests/ui/type-alias-impl-trait/define_opaques_attr/no_opaque.rs

@@ -1,8 +1,7 @@
-//@ check-pass
-
 #![feature(type_alias_impl_trait)]
 
 type Thing = ();
 
 #[define_opaques(Thing)]
+//~^ ERROR item does not contain any opaque types
 fn main() {}

tests/ui/type-alias-impl-trait/define_opaques_attr/no_opaque.stderr

@@ -0,0 +1,8 @@
+error: item does not contain any opaque types
+  --> $DIR/no_opaque.rs:5:18
+   |
+LL | #[define_opaques(Thing)]
+   |                  ^^^^^
+
+error: aborting due to 1 previous error
+