Make DefiningAnchor::Bind only store the opaque types that may be constrained, instead of the current infcx root item.

This makes `Bind` almost always be empty, so we can start forwarding it to queries, allowing us to remove `Bubble` entirely

Author: oli-obk

compiler/rustc_borrowck/src/consumers.rs

@@ -106,7 +106,7 @@ pub fn get_body_with_borrowck_facts(
     options: ConsumerOptions,
 ) -> BodyWithBorrowckFacts<'_> {
     let (input_body, promoted) = tcx.mir_promoted(def);
-    let infcx = tcx.infer_ctxt().with_opaque_type_inference(DefiningAnchor::Bind(def)).build();
+    let infcx = tcx.infer_ctxt().with_opaque_type_inference(DefiningAnchor::bind(tcx, def)).build();
     let input_body: &Body<'_> = &input_body.borrow();
     let promoted: &IndexSlice<_, _> = &promoted.borrow();
     *super::do_mir_borrowck(&infcx, input_body, promoted, Some(options)).1.unwrap()

compiler/rustc_borrowck/src/lib.rs

@@ -127,8 +127,10 @@ fn mir_borrowck(tcx: TyCtxt<'_>, def: LocalDefId) -> &BorrowCheckResult<'_> {
 
     let hir_owner = tcx.local_def_id_to_hir_id(def).owner;
 
-    let infcx =
-        tcx.infer_ctxt().with_opaque_type_inference(DefiningAnchor::Bind(hir_owner.def_id)).build();
+    let infcx = tcx
+        .infer_ctxt()
+        .with_opaque_type_inference(DefiningAnchor::bind(tcx, hir_owner.def_id))
+        .build();
     let promoted: &IndexSlice<_, _> = &promoted.borrow();
     let opt_closure_req = do_mir_borrowck(&infcx, input_body, promoted, None).0;
     debug!("mir_borrowck done");

compiler/rustc_borrowck/src/region_infer/opaque_types.rs

@@ -317,7 +317,7 @@ fn check_opaque_type_well_formed<'tcx>(
     let infcx = tcx
         .infer_ctxt()
         .with_next_trait_solver(next_trait_solver)
-        .with_opaque_type_inference(DefiningAnchor::Bind(parent_def_id))
+        .with_opaque_type_inference(DefiningAnchor::bind(tcx, parent_def_id))
         .build();
     let ocx = ObligationCtxt::new(&infcx);
     let identity_args = GenericArgs::identity_for_item(tcx, def_id);

compiler/rustc_hir_analysis/src/check/check.rs

@@ -346,7 +346,7 @@ fn check_opaque_meets_bounds<'tcx>(
 
     let infcx = tcx
         .infer_ctxt()
-        .with_opaque_type_inference(DefiningAnchor::Bind(defining_use_anchor))
+        .with_opaque_type_inference(DefiningAnchor::bind(tcx, defining_use_anchor))
         .build();
     let ocx = ObligationCtxt::new(&infcx);
 
@@ -1569,7 +1569,7 @@ pub(super) fn check_coroutine_obligations(
         .ignoring_regions()
         // Bind opaque types to type checking root, as they should have been checked by borrowck,
         // but may show up in some cases, like when (root) obligations are stalled in the new solver.
-        .with_opaque_type_inference(DefiningAnchor::Bind(typeck.hir_owner.def_id))
+        .with_opaque_type_inference(DefiningAnchor::bind(tcx, typeck.hir_owner.def_id))
         .build();
 
     let mut fulfillment_cx = <dyn TraitEngine<'_>>::new(&infcx);

compiler/rustc_hir_typeck/src/inherited.rs

@@ -79,7 +79,7 @@ impl<'tcx> Inherited<'tcx> {
         let infcx = tcx
             .infer_ctxt()
             .ignoring_regions()
-            .with_opaque_type_inference(DefiningAnchor::Bind(def_id))
+            .with_opaque_type_inference(DefiningAnchor::bind(tcx, def_id))
             .build();
         let typeck_results = RefCell::new(ty::TypeckResults::new(hir_owner));
 

compiler/rustc_infer/src/infer/mod.rs

@@ -252,7 +252,7 @@ pub struct InferCtxt<'tcx> {
     ///
     /// Its default value is `DefiningAnchor::Error`, this way it is easier to catch errors that
     /// might come up during inference or typeck.
-    pub defining_use_anchor: DefiningAnchor,
+    pub defining_use_anchor: DefiningAnchor<'tcx>,
 
     /// Whether this inference context should care about region obligations in
     /// the root universe. Most notably, this is used during hir typeck as region
@@ -613,7 +613,7 @@ impl fmt::Display for FixupError {
 /// Used to configure inference contexts before their creation.
 pub struct InferCtxtBuilder<'tcx> {
     tcx: TyCtxt<'tcx>,
-    defining_use_anchor: DefiningAnchor,
+    defining_use_anchor: DefiningAnchor<'tcx>,
     considering_regions: bool,
     skip_leak_check: bool,
     /// Whether we are in coherence mode.
@@ -644,7 +644,7 @@ impl<'tcx> InferCtxtBuilder<'tcx> {
     /// It is only meant to be called in two places, for typeck
     /// (via `Inherited::build`) and for the inference context used
     /// in mir borrowck.
-    pub fn with_opaque_type_inference(mut self, defining_use_anchor: DefiningAnchor) -> Self {
+    pub fn with_opaque_type_inference(mut self, defining_use_anchor: DefiningAnchor<'tcx>) -> Self {
         self.defining_use_anchor = defining_use_anchor;
         self
     }

compiler/rustc_infer/src/infer/opaque_types.rs

@@ -368,28 +368,14 @@ impl<'tcx> InferCtxt<'tcx> {
     /// in its defining scope.
     #[instrument(skip(self), level = "trace", ret)]
     pub fn opaque_type_origin(&self, def_id: LocalDefId) -> Option<OpaqueTyOrigin> {
-        let opaque_hir_id = self.tcx.local_def_id_to_hir_id(def_id);
-        let parent_def_id = match self.defining_use_anchor {
+        let defined_opaque_types = match self.defining_use_anchor {
             DefiningAnchor::Bubble | DefiningAnchor::Error => return None,
             DefiningAnchor::Bind(bind) => bind,
         };
 
         let origin = self.tcx.opaque_type_origin(def_id);
-        let in_definition_scope = match origin {
-            // Async `impl Trait`
-            hir::OpaqueTyOrigin::AsyncFn(parent) => parent == parent_def_id,
-            // Anonymous `impl Trait`
-            hir::OpaqueTyOrigin::FnReturn(parent) => parent == parent_def_id,
-            // Named `type Foo = impl Bar;`
-            hir::OpaqueTyOrigin::TyAlias { in_assoc_ty } => {
-                if in_assoc_ty {
-                    self.tcx.opaque_types_defined_by(parent_def_id).contains(&def_id)
-                } else {
-                    may_define_opaque_type(self.tcx, parent_def_id, opaque_hir_id)
-                }
-            }
-        };
-        in_definition_scope.then_some(origin)
+
+        defined_opaque_types.contains(&def_id).then_some(origin)
     }
 }
 
@@ -638,43 +624,3 @@ impl<'tcx> InferCtxt<'tcx> {
         }
     }
 }
-
-/// Returns `true` if `opaque_hir_id` is a sibling or a child of a sibling of `def_id`.
-///
-/// Example:
-/// ```ignore UNSOLVED (is this a bug?)
-/// # #![feature(type_alias_impl_trait)]
-/// pub mod foo {
-///     pub mod bar {
-///         pub trait Bar { /* ... */ }
-///         pub type Baz = impl Bar;
-///
-///         # impl Bar for () {}
-///         fn f1() -> Baz { /* ... */ }
-///     }
-///     fn f2() -> bar::Baz { /* ... */ }
-/// }
-/// ```
-///
-/// Here, `def_id` is the `LocalDefId` of the defining use of the opaque type (e.g., `f1` or `f2`),
-/// and `opaque_hir_id` is the `HirId` of the definition of the opaque type `Baz`.
-/// For the above example, this function returns `true` for `f1` and `false` for `f2`.
-fn may_define_opaque_type(tcx: TyCtxt<'_>, def_id: LocalDefId, opaque_hir_id: hir::HirId) -> bool {
-    let mut hir_id = tcx.local_def_id_to_hir_id(def_id);
-
-    // Named opaque types can be defined by any siblings or children of siblings.
-    let scope = tcx.hir().get_defining_scope(opaque_hir_id);
-    // We walk up the node tree until we hit the root or the scope of the opaque type.
-    while hir_id != scope && hir_id != hir::CRATE_HIR_ID {
-        hir_id = tcx.hir().get_parent_item(hir_id).into();
-    }
-    // Syntactically, we are allowed to define the concrete type if:
-    let res = hir_id == scope;
-    trace!(
-        "may_define_opaque_type(def={:?}, opaque_node={:?}) = {}",
-        tcx.hir_node(hir_id),
-        tcx.hir_node(opaque_hir_id),
-        res
-    );
-    res
-}

compiler/rustc_middle/src/mir/type_foldable.rs

@@ -1,6 +1,7 @@
 //! `TypeFoldable` implementations for MIR types
 
 use rustc_ast::InlineAsmTemplatePiece;
+use rustc_hir::def_id::LocalDefId;
 
 use super::*;
 
@@ -44,6 +45,15 @@ impl<'tcx> TypeFoldable<TyCtxt<'tcx>> for &'tcx [Span] {
     }
 }
 
+impl<'tcx> TypeFoldable<TyCtxt<'tcx>> for &'tcx [LocalDefId] {
+    fn try_fold_with<F: FallibleTypeFolder<TyCtxt<'tcx>>>(
+        self,
+        _folder: &mut F,
+    ) -> Result<Self, F::Error> {
+        Ok(self)
+    }
+}
+
 impl<'tcx> TypeFoldable<TyCtxt<'tcx>> for &'tcx ty::List<PlaceElem<'tcx>> {
     fn try_fold_with<F: FallibleTypeFolder<TyCtxt<'tcx>>>(
         self,

compiler/rustc_middle/src/traits/mod.rs

@@ -12,8 +12,8 @@ pub mod util;
 use crate::infer::canonical::Canonical;
 use crate::mir::ConstraintCategory;
 use crate::ty::abstract_const::NotConstEvaluatable;
-use crate::ty::GenericArgsRef;
 use crate::ty::{self, AdtKind, Ty};
+use crate::ty::{GenericArgsRef, TyCtxt};
 
 use rustc_data_structures::sync::Lrc;
 use rustc_errors::{Applicability, Diag, EmissionGuarantee};
@@ -1001,10 +1001,10 @@ pub enum CodegenObligationError {
 /// opaques are replaced with inference vars eagerly in the old solver (e.g.
 /// in projection, and in the signature during function type-checking).
 #[derive(Debug, PartialEq, Eq, Clone, Copy, Hash, HashStable, TypeFoldable, TypeVisitable)]
-pub enum DefiningAnchor {
-    /// Define opaques which are in-scope of the `LocalDefId`. Also, eagerly
-    /// replace opaque types in `replace_opaque_types_with_inference_vars`.
-    Bind(LocalDefId),
+pub enum DefiningAnchor<'tcx> {
+    /// Define opaques which are in-scope of the current item being analyzed.
+    /// Also, eagerly replace these opaque types in `replace_opaque_types_with_inference_vars`.
+    Bind(&'tcx [LocalDefId]),
     /// In contexts where we don't currently know what opaques are allowed to be
     /// defined, such as (old solver) canonical queries, we will simply allow
     /// opaques to be defined, but "bubble" them up in the canonical response or
@@ -1018,3 +1018,9 @@ pub enum DefiningAnchor {
     /// otherwise reveal opaques (such as [`Reveal::All`] reveal mode).
     Error,
 }
+
+impl<'tcx> DefiningAnchor<'tcx> {
+    pub fn bind(tcx: TyCtxt<'tcx>, item: LocalDefId) -> Self {
+        Self::Bind(tcx.opaque_types_defined_by(item))
+    }
+}

compiler/rustc_middle/src/traits/solve.rs

@@ -115,7 +115,7 @@ impl MaybeCause {
 #[derive(Debug, PartialEq, Eq, Clone, Copy, Hash, HashStable, TypeFoldable, TypeVisitable)]
 pub struct QueryInput<'tcx, T> {
     pub goal: Goal<'tcx, T>,
-    pub anchor: DefiningAnchor,
+    pub anchor: DefiningAnchor<'tcx>,
     pub predefined_opaques_in_body: PredefinedOpaques<'tcx>,
 }
 

compiler/rustc_trait_selection/src/traits/error_reporting/type_err_ctxt_ext.rs

@@ -31,7 +31,7 @@ use rustc_hir::{GenericParam, Item, Node};
 use rustc_infer::infer::error_reporting::TypeErrCtxt;
 use rustc_infer::infer::{InferOk, TypeTrace};
 use rustc_middle::traits::select::OverflowError;
-use rustc_middle::traits::{DefiningAnchor, SignatureMismatchData};
+use rustc_middle::traits::SignatureMismatchData;
 use rustc_middle::ty::abstract_const::NotConstEvaluatable;
 use rustc_middle::ty::error::{ExpectedFound, TypeError};
 use rustc_middle::ty::fold::{BottomUpFolder, TypeFolder, TypeSuperFoldable};
@@ -3373,19 +3373,12 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
             obligation.cause.span,
             format!("cannot check whether the hidden type of {name} satisfies auto traits"),
         );
+
+        err.note(
+            "fetching the hidden types of an opaque inside of the defining scope is not supported. \
+            You can try moving the opaque type and the item that actually registers a hidden type into a new submodule",
+        );
         err.span_note(self.tcx.def_span(def_id), "opaque type is declared here");
-        match self.defining_use_anchor {
-            DefiningAnchor::Bubble | DefiningAnchor::Error => {}
-            DefiningAnchor::Bind(bind) => {
-                err.span_note(
-                    self.tcx.def_ident_span(bind).unwrap_or_else(|| self.tcx.def_span(bind)),
-                    "this item depends on auto traits of the hidden type, \
-                    but may also be registering the hidden type. \
-                    This is not supported right now. \
-                    You can try moving the opaque type and the item that actually registers a hidden type into a new submodule".to_string(),
-                );
-            }
-        };
 
         self.note_obligation_cause(&mut err, &obligation);
         self.point_at_returns_when_relevant(&mut err, &obligation);

compiler/rustc_ty_utils/src/opaque_types.rs

@@ -109,7 +109,9 @@ impl<'tcx> OpaqueTypeCollector<'tcx> {
 
     #[instrument(level = "trace", skip(self))]
     fn collect_taits_declared_in_body(&mut self) {
-        let body = self.tcx.hir().body(self.tcx.hir().body_owned_by(self.item)).value;
+        // Some things not necessarily have bodies, like method declarations in traits.
+        let Some(body_owner) = self.tcx.hir().maybe_body_owned_by(self.item) else { return };
+        let body = self.tcx.hir().body(body_owner).value;
         struct TaitInBodyFinder<'a, 'tcx> {
             collector: &'a mut OpaqueTypeCollector<'tcx>,
         }
@@ -212,12 +214,24 @@ impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for OpaqueTypeCollector<'tcx> {
             ty::Alias(ty::Opaque, alias_ty) if alias_ty.def_id.is_local() => {
                 self.visit_opaque_ty(alias_ty);
             }
+            // Skips type aliases, as they are meant to be transparent.
             ty::Alias(ty::Weak, alias_ty) if alias_ty.def_id.is_local() => {
                 self.tcx
                     .type_of(alias_ty.def_id)
                     .instantiate(self.tcx, alias_ty.args)
                     .visit_with(self)?;
             }
+            // RPITIT are encoded as projections, not opaque types, make sure to handle these special
+            // projections independently of the projection handling below.
+            ty::Alias(ty::Projection, alias_ty)
+                if let Some(ty::ImplTraitInTraitData::Trait { fn_def_id, .. }) =
+                    self.tcx.opt_rpitit_info(alias_ty.def_id)
+                    && fn_def_id == self.item.into() =>
+            {
+                let ty = self.tcx.type_of(alias_ty.def_id).instantiate(self.tcx, alias_ty.args);
+                let ty::Alias(ty::Opaque, alias_ty) = ty.kind() else { bug!("{ty:?}") };
+                self.visit_opaque_ty(alias_ty);
+            }
             ty::Alias(ty::Projection, alias_ty) => {
                 // This avoids having to do normalization of `Self::AssocTy` by only
                 // supporting the case of a method defining opaque types from assoc types

compiler/rustc_ty_utils/src/sig_types.rs

@@ -43,6 +43,12 @@ pub fn walk_types<'tcx, V: SpannedTypeVisitor<'tcx>>(
         // Walk over the type of the item
         DefKind::Static(_) | DefKind::Const | DefKind::AssocConst | DefKind::AnonConst => {
             if let Some(ty) = tcx.hir_node_by_def_id(item).ty() {
+                // If the type of the item uses `_`, we're gonna error out anyway, but
+                // typeck (which type_of invokes below), will call back into opaque_types_defined_by
+                // causing a cycle. So we just bail out in this case.
+                if ty.is_suggestable_infer_ty() {
+                    return ControlFlow::Continue(());
+                }
                 // Associated types in traits don't necessarily have a type that we can visit
                 visitor.visit(ty.span, tcx.type_of(item).instantiate_identity())?;
             }

tests/ui/generic-associated-types/issue-88595.rs

@@ -19,4 +19,5 @@ impl<'a> A<'a> for C {
     type B<'b> = impl Clone;
 
     fn a(&'a self) -> Self::B<'a> {} //~ ERROR: non-defining opaque type use in defining scope
+    //~^ ERROR: non-defining opaque type use in defining scope
 }

tests/ui/generic-associated-types/issue-88595.stderr

@@ -10,5 +10,19 @@ note: for this opaque type
 LL |     type B<'b> = impl Clone;
    |                  ^^^^^^^^^^
 
-error: aborting due to 1 previous error
+error: non-defining opaque type use in defining scope
+  --> $DIR/issue-88595.rs:21:35
+   |
+LL |     fn a(&'a self) -> Self::B<'a> {}
+   |                                   ^^
+   |
+note: lifetime used multiple times
+  --> $DIR/issue-88595.rs:18:6
+   |
+LL | impl<'a> A<'a> for C {
+   |      ^^
+LL |     type B<'b> = impl Clone;
+   |            ^^
+
+error: aborting due to 2 previous errors
 

tests/ui/impl-trait/auto-trait-leak.stderr

@@ -6,16 +6,12 @@ LL |     send(cycle1().clone());
    |     |
    |     required by a bound introduced by this call
    |
+   = note: fetching the hidden types of an opaque inside of the defining scope is not supported. You can try moving the opaque type and the item that actually registers a hidden type into a new submodule
 note: opaque type is declared here
   --> $DIR/auto-trait-leak.rs:11:16
    |
 LL | fn cycle1() -> impl Clone {
    |                ^^^^^^^^^^
-note: this item depends on auto traits of the hidden type, but may also be registering the hidden type. This is not supported right now. You can try moving the opaque type and the item that actually registers a hidden type into a new submodule
-  --> $DIR/auto-trait-leak.rs:17:4
-   |
-LL | fn cycle2() -> impl Clone {
-   |    ^^^^^^
 note: required by a bound in `send`
   --> $DIR/auto-trait-leak.rs:4:12
    |

tests/ui/impl-trait/issues/issue-78722-2.rs

@@ -12,9 +12,9 @@ struct Bug {
             //~^ ERROR future that resolves to `u8`, but it resolves to `()`
             async {}
         }
+        // FIXME(type_alias_impl_trait): inform the user about why `F` is not available here.
         let f: F = async { 1 };
-        //~^ ERROR item constrains opaque type that is not in its signature
-        //~| ERROR `async` blocks are not allowed in constants
+        //~^ ERROR mismatched types
         1
     }],
 }