Report opaque type mismatches directly during borrowck of the function instead of within the type_of query.

This allows us to only store a single hidden type per opaque type instead of having to store one per set of substitutions.

Author: oli-obk

compiler/rustc_borrowck/src/nll.rs

@@ -1,14 +1,15 @@
 //! The entry point of the NLL borrow checker.
 
 use rustc_data_structures::vec_map::VecMap;
+use rustc_hir::def_id::DefId;
 use rustc_index::vec::IndexVec;
 use rustc_infer::infer::InferCtxt;
 use rustc_middle::mir::{create_dump_file, dump_enabled, dump_mir, PassWhere};
 use rustc_middle::mir::{
     BasicBlock, Body, ClosureOutlivesSubject, ClosureRegionRequirements, LocalKind, Location,
     Promoted,
 };
-use rustc_middle::ty::{self, OpaqueHiddenType, OpaqueTypeKey, Region, RegionVid};
+use rustc_middle::ty::{self, OpaqueHiddenType, Region, RegionVid};
 use rustc_span::symbol::sym;
 use std::env;
 use std::fmt::Debug;
@@ -43,7 +44,7 @@ pub type PoloniusOutput = Output<RustcFacts>;
 /// closure requirements to propagate, and any generated errors.
 crate struct NllOutput<'tcx> {
     pub regioncx: RegionInferenceContext<'tcx>,
-    pub opaque_type_values: VecMap<OpaqueTypeKey<'tcx>, OpaqueHiddenType<'tcx>>,
+    pub opaque_type_values: VecMap<DefId, OpaqueHiddenType<'tcx>>,
     pub polonius_input: Option<Box<AllFacts>>,
     pub polonius_output: Option<Rc<PoloniusOutput>>,
     pub opt_closure_req: Option<ClosureRegionRequirements<'tcx>>,
@@ -372,7 +373,7 @@ pub(super) fn dump_annotation<'a, 'tcx>(
     body: &Body<'tcx>,
     regioncx: &RegionInferenceContext<'tcx>,
     closure_region_requirements: &Option<ClosureRegionRequirements<'_>>,
-    opaque_type_values: &VecMap<OpaqueTypeKey<'tcx>, OpaqueHiddenType<'tcx>>,
+    opaque_type_values: &VecMap<DefId, OpaqueHiddenType<'tcx>>,
     errors: &mut crate::error::BorrowckErrors<'tcx>,
 ) {
     let tcx = infcx.tcx;

compiler/rustc_borrowck/src/region_infer/opaque_types.rs

@@ -1,5 +1,6 @@
 use rustc_data_structures::fx::FxHashMap;
 use rustc_data_structures::vec_map::VecMap;
+use rustc_hir::def_id::DefId;
 use rustc_hir::OpaqueTyOrigin;
 use rustc_infer::infer::InferCtxt;
 use rustc_middle::ty::subst::GenericArgKind;
@@ -54,8 +55,8 @@ impl<'tcx> RegionInferenceContext<'tcx> {
         &self,
         infcx: &InferCtxt<'_, 'tcx>,
         opaque_ty_decls: VecMap<OpaqueTypeKey<'tcx>, (OpaqueHiddenType<'tcx>, OpaqueTyOrigin)>,
-    ) -> VecMap<OpaqueTypeKey<'tcx>, OpaqueHiddenType<'tcx>> {
-        let mut result: VecMap<OpaqueTypeKey<'tcx>, OpaqueHiddenType<'tcx>> = VecMap::new();
+    ) -> VecMap<DefId, OpaqueHiddenType<'tcx>> {
+        let mut result: VecMap<DefId, OpaqueHiddenType<'tcx>> = VecMap::new();
         for (opaque_type_key, (concrete_type, origin)) in opaque_ty_decls {
             let substs = opaque_type_key.substs;
             debug!(?concrete_type, ?substs);
@@ -124,21 +125,31 @@ impl<'tcx> RegionInferenceContext<'tcx> {
             // back to the opaque type definition. E.g. we may have `OpaqueType<X, Y>` mapped to `(X, Y)`
             // and `OpaqueType<Y, X>` mapped to `(Y, X)`, and those are the same, but we only know that
             // once we convert the generic parameters to those of the opaque type.
-            if let Some(prev) = result.get_mut(&opaque_type_key) {
+            if let Some(prev) = result.get_mut(&opaque_type_key.def_id) {
                 if prev.ty != ty {
-                    let mut err = infcx.tcx.sess.struct_span_err(
-                        concrete_type.span,
-                        &format!("hidden type `{}` differed from previous `{}`", ty, prev.ty),
-                    );
-                    err.span_note(prev.span, "previous hidden type bound here");
-                    err.emit();
+                    if !ty.references_error() {
+                        let mut err = infcx.tcx.sess.struct_span_err(
+                            concrete_type.span,
+                            "concrete type differs from previous defining opaque type use",
+                        );
+                        err.span_label(prev.span, format!("expected `{}`, got `{}`", prev.ty, ty));
+                        if prev.span == concrete_type.span {
+                            err.span_label(prev.span, "this expression supplies two conflicting concrete types for the same opaque type");
+                        } else {
+                            err.span_note(prev.span, "previous use here");
+                        }
+                        err.emit();
+                    }
                     prev.ty = infcx.tcx.ty_error();
                 }
                 // Pick a better span if there is one.
                 // FIXME(oli-obk): collect multiple spans for better diagnostics down the road.
                 prev.span = prev.span.substitute_dummy(concrete_type.span);
             } else {
-                result.insert(opaque_type_key, OpaqueHiddenType { ty, span: concrete_type.span });
+                result.insert(
+                    opaque_type_key.def_id,
+                    OpaqueHiddenType { ty, span: concrete_type.span },
+                );
             }
         }
         result

compiler/rustc_middle/src/mir/query.rs

@@ -9,7 +9,6 @@ use rustc_hir as hir;
 use rustc_hir::def_id::{DefId, LocalDefId};
 use rustc_index::bit_set::BitMatrix;
 use rustc_index::vec::IndexVec;
-use rustc_middle::ty::OpaqueTypeKey;
 use rustc_span::Span;
 use rustc_target::abi::VariantIdx;
 use smallvec::SmallVec;
@@ -242,7 +241,7 @@ pub struct BorrowCheckResult<'tcx> {
     /// All the opaque types that are restricted to concrete types
     /// by this function. Unlike the value in `TypeckResults`, this has
     /// unerased regions.
-    pub concrete_opaque_types: VecMap<OpaqueTypeKey<'tcx>, OpaqueHiddenType<'tcx>>,
+    pub concrete_opaque_types: VecMap<DefId, OpaqueHiddenType<'tcx>>,
     pub closure_requirements: Option<ClosureRegionRequirements<'tcx>>,
     pub used_mut_upvars: SmallVec<[Field; 8]>,
     pub tainted_by_errors: Option<ErrorGuaranteed>,

compiler/rustc_typeck/src/collect/type_of.rs

@@ -356,7 +356,7 @@ pub(super) fn type_of(tcx: TyCtxt<'_>, def_id: DefId) -> Ty<'_> {
                     let concrete_ty = tcx
                         .mir_borrowck(owner)
                         .concrete_opaque_types
-                        .get_value_matching(|(key, _)| key.def_id == def_id.to_def_id())
+                        .get(&def_id.to_def_id())
                         .copied()
                         .map(|concrete| concrete.ty)
                         .unwrap_or_else(|| {
@@ -591,13 +591,13 @@ fn find_opaque_ty_constraints(tcx: TyCtxt<'_>, def_id: LocalDefId) -> Ty<'_> {
             // Use borrowck to get the type with unerased regions.
             let concrete_opaque_types = &self.tcx.mir_borrowck(def_id).concrete_opaque_types;
             debug!(?concrete_opaque_types);
-            for &(opaque_type_key, concrete_type) in concrete_opaque_types {
-                if opaque_type_key.def_id != self.def_id {
+            for &(def_id, concrete_type) in concrete_opaque_types {
+                if def_id != self.def_id {
                     // Ignore constraints for other opaque types.
                     continue;
                 }
 
-                debug!(?concrete_type, ?opaque_type_key.substs, "found constraint");
+                debug!(?concrete_type, "found constraint");
 
                 if let Some(prev) = self.found {
                     if concrete_type.ty != prev.ty && !(concrete_type, prev).references_error() {