On recursive ADT, provide indirection structured suggestion

[rust.git] / src / librustc_typeck / check / mod.rs

diff --git a/src/librustc_typeck/check/mod.rs b/src/librustc_typeck/check/mod.rs
index 275581318f75d58c4fc1db75f52525a93a84d53f..1e8a149d7d9ec35bad99fbe645bbe23fa3c700d7 100644 (file)
--- a/src/librustc_typeck/check/mod.rs
+++ b/src/librustc_typeck/check/mod.rs
@@ -31,9 +31,6 @@
   final assignments of the various region variables if there is some
   flexibility.
 
-- vtable: find and records the impls to use for each trait bound that
-  appears on a type parameter.
-
 - writeback: writes the final types within a function body, replacing
   type variables with their final inferred types.  These final types
   are written into the `tcx.node_types` table, which should *never* contain
@@ -1623,12 +1620,17 @@ fn check_opaque_for_inheriting_lifetimes(tcx: TyCtxt<'tcx>, def_id: LocalDefId,
     struct ProhibitOpaqueVisitor<'tcx> {
         opaque_identity_ty: Ty<'tcx>,
         generics: &'tcx ty::Generics,
+        ty: Option<Ty<'tcx>>,
     };
 
     impl<'tcx> ty::fold::TypeVisitor<'tcx> for ProhibitOpaqueVisitor<'tcx> {
         fn visit_ty(&mut self, t: Ty<'tcx>) -> bool {
             debug!("check_opaque_for_inheriting_lifetimes: (visit_ty) t={:?}", t);
-            if t == self.opaque_identity_ty { false } else { t.super_visit_with(self) }
+            if t != self.opaque_identity_ty && t.super_visit_with(self) {
+                self.ty = Some(t);
+                return true;
+            }
+            false
         }
 
         fn visit_region(&mut self, r: ty::Region<'tcx>) -> bool {
@@ -1651,46 +1653,61 @@ fn visit_const(&mut self, c: &'tcx ty::Const<'tcx>) -> bool {
         }
     }
 
-    let prohibit_opaque = match item.kind {
-        ItemKind::OpaqueTy(hir::OpaqueTy {
-            origin: hir::OpaqueTyOrigin::AsyncFn | hir::OpaqueTyOrigin::FnReturn,
-            ..
-        }) => {
-            let mut visitor = ProhibitOpaqueVisitor {
-                opaque_identity_ty: tcx.mk_opaque(
-                    def_id.to_def_id(),
-                    InternalSubsts::identity_for_item(tcx, def_id.to_def_id()),
-                ),
-                generics: tcx.generics_of(def_id),
-            };
-            debug!("check_opaque_for_inheriting_lifetimes: visitor={:?}", visitor);
-
-            tcx.predicates_of(def_id)
-                .predicates
-                .iter()
-                .any(|(predicate, _)| predicate.visit_with(&mut visitor))
-        }
-        _ => false,
-    };
-
-    debug!("check_opaque_for_inheriting_lifetimes: prohibit_opaque={:?}", prohibit_opaque);
-    if prohibit_opaque {
-        let is_async = match item.kind {
-            ItemKind::OpaqueTy(hir::OpaqueTy { origin, .. }) => match origin {
-                hir::OpaqueTyOrigin::AsyncFn => true,
-                _ => false,
-            },
-            _ => unreachable!(),
+    if let ItemKind::OpaqueTy(hir::OpaqueTy {
+        origin: hir::OpaqueTyOrigin::AsyncFn | hir::OpaqueTyOrigin::FnReturn,
+        ..
+    }) = item.kind
+    {
+        let mut visitor = ProhibitOpaqueVisitor {
+            opaque_identity_ty: tcx.mk_opaque(
+                def_id.to_def_id(),
+                InternalSubsts::identity_for_item(tcx, def_id.to_def_id()),
+            ),
+            generics: tcx.generics_of(def_id),
+            ty: None,
         };
+        let prohibit_opaque = tcx
+            .predicates_of(def_id)
+            .predicates
+            .iter()
+            .any(|(predicate, _)| predicate.visit_with(&mut visitor));
+        debug!(
+            "check_opaque_for_inheriting_lifetimes: prohibit_opaque={:?}, visitor={:?}",
+            prohibit_opaque, visitor
+        );
 
-        tcx.sess.span_err(
-            span,
-            &format!(
-            "`{}` return type cannot contain a projection or `Self` that references lifetimes from \
+        if prohibit_opaque {
+            let is_async = match item.kind {
+                ItemKind::OpaqueTy(hir::OpaqueTy { origin, .. }) => match origin {
+                    hir::OpaqueTyOrigin::AsyncFn => true,
+                    _ => false,
+                },
+                _ => unreachable!(),
+            };
+
+            let mut err = struct_span_err!(
+                tcx.sess,
+                span,
+                E0760,
+                "`{}` return type cannot contain a projection or `Self` that references lifetimes from \
              a parent scope",
-            if is_async { "async fn" } else { "impl Trait" },
-        ),
-        );
+                if is_async { "async fn" } else { "impl Trait" },
+            );
+
+            if let Ok(snippet) = tcx.sess.source_map().span_to_snippet(span) {
+                if snippet == "Self" {
+                    if let Some(ty) = visitor.ty {
+                        err.span_suggestion(
+                            span,
+                            "consider spelling out the type instead",
+                            format!("{:?}", ty),
+                            Applicability::MaybeIncorrect,
+                        );
+                    }
+                }
+            }
+            err.emit();
+        }
     }
 }
 
@@ -2373,11 +2390,7 @@ fn check_representable(tcx: TyCtxt<'_>, sp: Span, item_def_id: LocalDefId) -> bo
     // caught by case 1.
     match rty.is_representable(tcx, sp) {
         Representability::SelfRecursive(spans) => {
-            let mut err = recursive_type_with_infinite_size_error(tcx, item_def_id.to_def_id());
-            for span in spans {
-                err.span_label(span, "recursive without indirection");
-            }
-            err.emit();
+            recursive_type_with_infinite_size_error(tcx, item_def_id.to_def_id(), spans);
             return false;
         }
         Representability::Representable | Representability::ContainsRecursive => (),
@@ -3389,8 +3402,7 @@ pub fn node_ty(&self, id: hir::HirId) -> Ty<'tcx> {
         }
     }
 
-    /// Registers an obligation for checking later, during regionck, that the type `ty` must
-    /// outlive the region `r`.
+    /// Registers an obligation for checking later, during regionck, that `arg` is well-formed.
     pub fn register_wf_obligation(
         &self,
         arg: subst::GenericArg<'tcx>,
@@ -3794,7 +3806,7 @@ fn self_type_matches_expected_vid(
         trait_ref: ty::PolyTraitRef<'tcx>,
         expected_vid: ty::TyVid,
     ) -> bool {
-        let self_ty = self.shallow_resolve(trait_ref.self_ty());
+        let self_ty = self.shallow_resolve(trait_ref.skip_binder().self_ty());
         debug!(
             "self_type_matches_expected_vid(trait_ref={:?}, self_ty={:?}, expected_vid={:?})",
             trait_ref, self_ty, expected_vid
@@ -4051,7 +4063,7 @@ fn check_argument_types(
             debug!("check_closures={}", check_closures);
 
             // More awful hacks: before we check argument types, try to do
-            // an "opportunistic" vtable resolution of any trait bounds on
+            // an "opportunistic" trait resolution of any trait bounds on
             // the call. This helps coercions.
             if check_closures {
                 self.select_obligations_where_possible(false, |errors| {