Rollup merge of #99383 - ouz-a:issue_57961, r=oli-obk

Formalize defining_use_anchor

This tackles issue #57961

Introduces new enum called `DefiningAnchor` that replaces `Option<LocalDefId>` of `defining_use_anchor`. Now every use of it is explicit and exhaustively matched, catching errors like one in the linked issue. This is not a perfect fix but it's a step in the right direction.

r? `@oli-obk`

Author: Dylan-DPC

compiler/rustc_borrowck/src/consumers.rs

@@ -2,7 +2,7 @@
 
 use rustc_hir::def_id::LocalDefId;
 use rustc_index::vec::IndexVec;
-use rustc_infer::infer::TyCtxtInferExt;
+use rustc_infer::infer::{DefiningAnchor, TyCtxtInferExt};
 use rustc_middle::mir::Body;
 use rustc_middle::ty::{self, TyCtxt};
 
@@ -31,7 +31,7 @@ pub fn get_body_with_borrowck_facts<'tcx>(
     def: ty::WithOptConstParam<LocalDefId>,
 ) -> BodyWithBorrowckFacts<'tcx> {
     let (input_body, promoted) = tcx.mir_promoted(def);
-    tcx.infer_ctxt().with_opaque_type_inference(def.did).enter(|infcx| {
+    tcx.infer_ctxt().with_opaque_type_inference(DefiningAnchor::Bind(def.did)).enter(|infcx| {
         let input_body: &Body<'_> = &input_body.borrow();
         let promoted: &IndexVec<_, _> = &promoted.borrow();
         *super::do_mir_borrowck(&infcx, input_body, promoted, true).1.unwrap()

compiler/rustc_borrowck/src/lib.rs

@@ -24,7 +24,7 @@ use rustc_hir as hir;
 use rustc_hir::def_id::LocalDefId;
 use rustc_index::bit_set::ChunkedBitSet;
 use rustc_index::vec::IndexVec;
-use rustc_infer::infer::{InferCtxt, TyCtxtInferExt};
+use rustc_infer::infer::{DefiningAnchor, InferCtxt, TyCtxtInferExt};
 use rustc_middle::mir::{
     traversal, Body, ClearCrossCrate, Local, Location, Mutability, Operand, Place, PlaceElem,
     PlaceRef, VarDebugInfoContents,
@@ -130,11 +130,14 @@ fn mir_borrowck<'tcx>(
     debug!("run query mir_borrowck: {}", tcx.def_path_str(def.did.to_def_id()));
     let hir_owner = tcx.hir().local_def_id_to_hir_id(def.did).owner;
 
-    let opt_closure_req = tcx.infer_ctxt().with_opaque_type_inference(hir_owner).enter(|infcx| {
-        let input_body: &Body<'_> = &input_body.borrow();
-        let promoted: &IndexVec<_, _> = &promoted.borrow();
-        do_mir_borrowck(&infcx, input_body, promoted, false).0
-    });
+    let opt_closure_req = tcx
+        .infer_ctxt()
+        .with_opaque_type_inference(DefiningAnchor::Bind(hir_owner))
+        .enter(|infcx| {
+            let input_body: &Body<'_> = &input_body.borrow();
+            let promoted: &IndexVec<_, _> = &promoted.borrow();
+            do_mir_borrowck(&infcx, input_body, promoted, false).0
+        });
     debug!("mir_borrowck done");
 
     tcx.arena.alloc(opt_closure_req)

compiler/rustc_borrowck/src/region_infer/opaque_types.rs

@@ -3,8 +3,8 @@ use rustc_data_structures::vec_map::VecMap;
 use rustc_hir::def_id::LocalDefId;
 use rustc_hir::OpaqueTyOrigin;
 use rustc_infer::infer::error_reporting::unexpected_hidden_region_diagnostic;
-use rustc_infer::infer::InferCtxt;
 use rustc_infer::infer::TyCtxtInferExt as _;
+use rustc_infer::infer::{DefiningAnchor, InferCtxt};
 use rustc_infer::traits::{Obligation, ObligationCause, TraitEngine};
 use rustc_middle::ty::fold::{TypeFolder, TypeSuperFoldable};
 use rustc_middle::ty::subst::{GenericArg, GenericArgKind, InternalSubsts};
@@ -269,59 +269,65 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
             // FIXME(oli-obk): Also do region checks here and then consider removing `check_opaque_meets_bounds` entirely.
             let param_env = self.tcx.param_env(def_id);
             let body_id = self.tcx.local_def_id_to_hir_id(def_id);
-            self.tcx.infer_ctxt().enter(move |infcx| {
-                // Require the hidden type to be well-formed with only the generics of the opaque type.
-                // Defining use functions may have more bounds than the opaque type, which is ok, as long as the
-                // hidden type is well formed even without those bounds.
-                let predicate =
-                    ty::Binder::dummy(ty::PredicateKind::WellFormed(definition_ty.into()))
-                        .to_predicate(infcx.tcx);
-                let mut fulfillment_cx = <dyn TraitEngine<'tcx>>::new(infcx.tcx);
-
-                // Require that the hidden type actually fulfills all the bounds of the opaque type, even without
-                // the bounds that the function supplies.
-                match infcx.register_hidden_type(
-                    OpaqueTypeKey { def_id, substs: id_substs },
-                    ObligationCause::misc(instantiated_ty.span, body_id),
-                    param_env,
-                    definition_ty,
-                    origin,
-                ) {
-                    Ok(infer_ok) => {
-                        for obligation in infer_ok.obligations {
-                            fulfillment_cx.register_predicate_obligation(&infcx, obligation);
+            // HACK This bubble is required for this tests to pass:
+            // type-alias-impl-trait/issue-67844-nested-opaque.rs
+            self.tcx.infer_ctxt().with_opaque_type_inference(DefiningAnchor::Bubble).enter(
+                move |infcx| {
+                    // Require the hidden type to be well-formed with only the generics of the opaque type.
+                    // Defining use functions may have more bounds than the opaque type, which is ok, as long as the
+                    // hidden type is well formed even without those bounds.
+                    let predicate =
+                        ty::Binder::dummy(ty::PredicateKind::WellFormed(definition_ty.into()))
+                            .to_predicate(infcx.tcx);
+                    let mut fulfillment_cx = <dyn TraitEngine<'tcx>>::new(infcx.tcx);
+
+                    // Require that the hidden type actually fulfills all the bounds of the opaque type, even without
+                    // the bounds that the function supplies.
+                    match infcx.register_hidden_type(
+                        OpaqueTypeKey { def_id, substs: id_substs },
+                        ObligationCause::misc(instantiated_ty.span, body_id),
+                        param_env,
+                        definition_ty,
+                        origin,
+                    ) {
+                        Ok(infer_ok) => {
+                            for obligation in infer_ok.obligations {
+                                fulfillment_cx.register_predicate_obligation(&infcx, obligation);
+                            }
+                        }
+                        Err(err) => {
+                            infcx
+                                .report_mismatched_types(
+                                    &ObligationCause::misc(instantiated_ty.span, body_id),
+                                    self.tcx.mk_opaque(def_id.to_def_id(), id_substs),
+                                    definition_ty,
+                                    err,
+                                )
+                                .emit();
                         }
                     }
-                    Err(err) => {
-                        infcx
-                            .report_mismatched_types(
-                                &ObligationCause::misc(instantiated_ty.span, body_id),
-                                self.tcx.mk_opaque(def_id.to_def_id(), id_substs),
-                                definition_ty,
-                                err,
-                            )
-                            .emit();
-                    }
-                }
 
-                fulfillment_cx.register_predicate_obligation(
-                    &infcx,
-                    Obligation::misc(instantiated_ty.span, body_id, param_env, predicate),
-                );
+                    fulfillment_cx.register_predicate_obligation(
+                        &infcx,
+                        Obligation::misc(instantiated_ty.span, body_id, param_env, predicate),
+                    );
 
-                // Check that all obligations are satisfied by the implementation's
-                // version.
-                let errors = fulfillment_cx.select_all_or_error(&infcx);
+                    // Check that all obligations are satisfied by the implementation's
+                    // version.
+                    let errors = fulfillment_cx.select_all_or_error(&infcx);
 
-                let _ = infcx.inner.borrow_mut().opaque_type_storage.take_opaque_types();
+                    // This is still required for many(half of the tests in ui/type-alias-impl-trait)
+                    // tests to pass
+                    let _ = infcx.inner.borrow_mut().opaque_type_storage.take_opaque_types();
 
-                if errors.is_empty() {
-                    definition_ty
-                } else {
-                    infcx.report_fulfillment_errors(&errors, None, false);
-                    self.tcx.ty_error()
-                }
-            })
+                    if errors.is_empty() {
+                        definition_ty
+                    } else {
+                        infcx.report_fulfillment_errors(&errors, None, false);
+                        self.tcx.ty_error()
+                    }
+                },
+            )
         } else {
             definition_ty
         }

compiler/rustc_infer/src/infer/mod.rs

@@ -239,17 +239,31 @@ impl<'tcx> InferCtxtInner<'tcx> {
     }
 }
 
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub enum DefiningAnchor {
+    /// `DefId` of the item.
+    Bind(LocalDefId),
+    /// When opaque types are not resolved, we `Bubble` up, meaning
+    /// return the opaque/hidden type pair from query, for caller of query to handle it.
+    Bubble,
+    /// Used to catch type mismatch errors when handling opaque types.
+    Error,
+}
+
 pub struct InferCtxt<'a, 'tcx> {
     pub tcx: TyCtxt<'tcx>,
 
     /// The `DefId` of the item in whose context we are performing inference or typeck.
     /// It is used to check whether an opaque type use is a defining use.
     ///
-    /// If it is `None`, we can't resolve opaque types here and need to bubble up
+    /// If it is `DefiningAnchor::Bubble`, we can't resolve opaque types here and need to bubble up
     /// the obligation. This frequently happens for
     /// short lived InferCtxt within queries. The opaque type obligations are forwarded
     /// to the outside until the end up in an `InferCtxt` for typeck or borrowck.
-    pub defining_use_anchor: Option<LocalDefId>,
+    ///
+    /// It is 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,
 
     /// During type-checking/inference of a body, `in_progress_typeck_results`
     /// contains a reference to the typeck results being built up, which are
@@ -526,7 +540,7 @@ impl<'tcx> fmt::Display for FixupError<'tcx> {
 pub struct InferCtxtBuilder<'tcx> {
     tcx: TyCtxt<'tcx>,
     fresh_typeck_results: Option<RefCell<ty::TypeckResults<'tcx>>>,
-    defining_use_anchor: Option<LocalDefId>,
+    defining_use_anchor: DefiningAnchor,
 }
 
 pub trait TyCtxtInferExt<'tcx> {
@@ -535,7 +549,11 @@ pub trait TyCtxtInferExt<'tcx> {
 
 impl<'tcx> TyCtxtInferExt<'tcx> for TyCtxt<'tcx> {
     fn infer_ctxt(self) -> InferCtxtBuilder<'tcx> {
-        InferCtxtBuilder { tcx: self, defining_use_anchor: None, fresh_typeck_results: None }
+        InferCtxtBuilder {
+            tcx: self,
+            defining_use_anchor: DefiningAnchor::Error,
+            fresh_typeck_results: None,
+        }
     }
 }
 
@@ -545,7 +563,7 @@ impl<'tcx> InferCtxtBuilder<'tcx> {
     /// Will also change the scope for opaque type defining use checks to the given owner.
     pub fn with_fresh_in_progress_typeck_results(mut self, table_owner: LocalDefId) -> Self {
         self.fresh_typeck_results = Some(RefCell::new(ty::TypeckResults::new(table_owner)));
-        self.with_opaque_type_inference(table_owner)
+        self.with_opaque_type_inference(DefiningAnchor::Bind(table_owner))
     }
 
     /// Whenever the `InferCtxt` should be able to handle defining uses of opaque types,
@@ -554,8 +572,8 @@ impl<'tcx> InferCtxtBuilder<'tcx> {
     /// It is only meant to be called in two places, for typeck
     /// (via `with_fresh_in_progress_typeck_results`) and for the inference context used
     /// in mir borrowck.
-    pub fn with_opaque_type_inference(mut self, defining_use_anchor: LocalDefId) -> Self {
-        self.defining_use_anchor = Some(defining_use_anchor);
+    pub fn with_opaque_type_inference(mut self, defining_use_anchor: DefiningAnchor) -> Self {
+        self.defining_use_anchor = defining_use_anchor;
         self
     }
 

compiler/rustc_infer/src/infer/opaque_types.rs

@@ -1,4 +1,4 @@
-use crate::infer::{InferCtxt, InferOk};
+use crate::infer::{DefiningAnchor, InferCtxt, InferOk};
 use crate::traits;
 use hir::def_id::{DefId, LocalDefId};
 use hir::{HirId, OpaqueTyOrigin};
@@ -101,44 +101,46 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
         let process = |a: Ty<'tcx>, b: Ty<'tcx>| match *a.kind() {
             ty::Opaque(def_id, substs) if def_id.is_local() => {
                 let def_id = def_id.expect_local();
-                let origin = if self.defining_use_anchor.is_some() {
-                    // Check that this is `impl Trait` type is
-                    // declared by `parent_def_id` -- i.e., one whose
-                    // value we are inferring.  At present, this is
-                    // always true during the first phase of
-                    // type-check, but not always true later on during
-                    // NLL. Once we support named opaque types more fully,
-                    // this same scenario will be able to arise during all phases.
-                    //
-                    // Here is an example using type alias `impl Trait`
-                    // that indicates the distinction we are checking for:
-                    //
-                    // ```rust
-                    // mod a {
-                    //   pub type Foo = impl Iterator;
-                    //   pub fn make_foo() -> Foo { .. }
-                    // }
-                    //
-                    // mod b {
-                    //   fn foo() -> a::Foo { a::make_foo() }
-                    // }
-                    // ```
-                    //
-                    // Here, the return type of `foo` references an
-                    // `Opaque` indeed, but not one whose value is
-                    // presently being inferred. You can get into a
-                    // similar situation with closure return types
-                    // today:
-                    //
-                    // ```rust
-                    // fn foo() -> impl Iterator { .. }
-                    // fn bar() {
-                    //     let x = || foo(); // returns the Opaque assoc with `foo`
-                    // }
-                    // ```
-                    self.opaque_type_origin(def_id, cause.span)?
-                } else {
-                    self.opaque_ty_origin_unchecked(def_id, cause.span)
+                let origin = match self.defining_use_anchor {
+                    DefiningAnchor::Bind(_) => {
+                        // Check that this is `impl Trait` type is
+                        // declared by `parent_def_id` -- i.e., one whose
+                        // value we are inferring.  At present, this is
+                        // always true during the first phase of
+                        // type-check, but not always true later on during
+                        // NLL. Once we support named opaque types more fully,
+                        // this same scenario will be able to arise during all phases.
+                        //
+                        // Here is an example using type alias `impl Trait`
+                        // that indicates the distinction we are checking for:
+                        //
+                        // ```rust
+                        // mod a {
+                        //   pub type Foo = impl Iterator;
+                        //   pub fn make_foo() -> Foo { .. }
+                        // }
+                        //
+                        // mod b {
+                        //   fn foo() -> a::Foo { a::make_foo() }
+                        // }
+                        // ```
+                        //
+                        // Here, the return type of `foo` references an
+                        // `Opaque` indeed, but not one whose value is
+                        // presently being inferred. You can get into a
+                        // similar situation with closure return types
+                        // today:
+                        //
+                        // ```rust
+                        // fn foo() -> impl Iterator { .. }
+                        // fn bar() {
+                        //     let x = || foo(); // returns the Opaque assoc with `foo`
+                        // }
+                        // ```
+                        self.opaque_type_origin(def_id, cause.span)?
+                    }
+                    DefiningAnchor::Bubble => self.opaque_ty_origin_unchecked(def_id, cause.span),
+                    DefiningAnchor::Error => return None,
                 };
                 if let ty::Opaque(did2, _) = *b.kind() {
                     // We could accept this, but there are various ways to handle this situation, and we don't
@@ -407,7 +409,10 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
     #[instrument(skip(self), level = "trace")]
     pub fn opaque_type_origin(&self, def_id: LocalDefId, span: Span) -> Option<OpaqueTyOrigin> {
         let opaque_hir_id = self.tcx.hir().local_def_id_to_hir_id(def_id);
-        let parent_def_id = self.defining_use_anchor?;
+        let parent_def_id = match self.defining_use_anchor {
+            DefiningAnchor::Bubble | DefiningAnchor::Error => return None,
+            DefiningAnchor::Bind(bind) => bind,
+        };
         let item_kind = &self.tcx.hir().expect_item(def_id).kind;
 
         let hir::ItemKind::OpaqueTy(hir::OpaqueTy { origin, ..  }) = item_kind else {

compiler/rustc_trait_selection/src/traits/codegen.rs

@@ -3,7 +3,7 @@
 // seems likely that they should eventually be merged into more
 // general routines.
 
-use crate::infer::TyCtxtInferExt;
+use crate::infer::{DefiningAnchor, TyCtxtInferExt};
 use crate::traits::{
     FulfillmentContext, ImplSource, Obligation, ObligationCause, SelectionContext, TraitEngine,
     Unimplemented,
@@ -30,7 +30,9 @@ pub fn codegen_fulfill_obligation<'tcx>(
 
     // Do the initial selection for the obligation. This yields the
     // shallow result we are looking for -- that is, what specific impl.
-    tcx.infer_ctxt().enter(|infcx| {
+    tcx.infer_ctxt().with_opaque_type_inference(DefiningAnchor::Bubble).enter(|infcx| {
+        //~^ HACK `Bubble` is required for
+        // this test to pass: type-alias-impl-trait/assoc-projection-ice.rs
         let mut selcx = SelectionContext::new(&infcx);
 
         let obligation_cause = ObligationCause::dummy();
@@ -69,7 +71,8 @@ pub fn codegen_fulfill_obligation<'tcx>(
 
         // Opaque types may have gotten their hidden types constrained, but we can ignore them safely
         // as they will get constrained elsewhere, too.
-        let _opaque_types = infcx.inner.borrow_mut().opaque_type_storage.take_opaque_types();
+        // (ouz-a) This is required for `type-alias-impl-trait/assoc-projection-ice.rs` to pass
+        let _ = infcx.inner.borrow_mut().opaque_type_storage.take_opaque_types();
 
         debug!("Cache miss: {trait_ref:?} => {impl_source:?}");
         Ok(&*tcx.arena.alloc(impl_source))