support revealing uses in HIR typeck

lcnr · lcnr · commit 93ea83691e3e · 2025-05-05T03:32:04.000Z
diff --git a/compiler/rustc_hir_typeck/src/lib.rs b/compiler/rustc_hir_typeck/src/lib.rs
@@ -231,6 +231,10 @@ fn typeck_with_inspect<'tcx>(
 
     fcx.select_obligations_where_possible(|_| {});
 
+    if fcx.next_trait_solver() {
+        fcx.handle_opaque_type_uses_next();
+    }
+
     debug!(pending_obligations = ?fcx.fulfillment_cx.borrow().pending_obligations());
 
     // This must be the last thing before `report_ambiguity_errors`.
diff --git a/compiler/rustc_hir_typeck/src/opaque_types.rs b/compiler/rustc_hir_typeck/src/opaque_types.rs
@@ -1,5 +1,123 @@
-use super::FnCtxt;
-impl<'tcx> FnCtxt<'_, 'tcx> {
+use rustc_middle::ty::{
+    DefiningScopeKind, EarlyBinder, OpaqueHiddenType, OpaqueTypeKey, Ty, TypeVisitableExt,
+};
+use rustc_trait_selection::opaque_types::{
+    InvalidOpaqueTypeArgs, check_opaque_type_parameter_valid,
+};
+use tracing::{debug, instrument};
+
+use crate::FnCtxt;
+
+impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
+    #[instrument(level = "debug", skip(self))]
+    pub(super) fn handle_opaque_type_uses_next(&mut self) {
+        // We clone the opaques instead of stealing them here as they are still used for
+        // normalization in the next generation trait solver.
+        //
+        // FIXME(-Znext-solver): Opaque types defined after this would simply get dropped
+        // at the end of typeck. Ideally we can feed some query here to no longer define
+        // new opaque uses but instead always reveal by using the definitions inferred here.
+        let mut opaque_types: Vec<_> = self.infcx.clone_opaque_types();
+        let num_entries = self.inner.borrow_mut().opaque_types().num_entries();
+        let prev = self.checked_opaque_types_storage_entries.replace(Some(num_entries));
+        debug_assert_eq!(prev, None);
+        for entry in &mut opaque_types {
+            *entry = self.resolve_vars_if_possible(*entry);
+        }
+        debug!(?opaque_types);
+
+        self.collect_defining_uses(&opaque_types);
+        self.apply_defining_uses(&opaque_types);
+    }
+
+    fn collect_defining_uses(
+        &mut self,
+        opaque_types: &[(OpaqueTypeKey<'tcx>, OpaqueHiddenType<'tcx>)],
+    ) {
+        let tcx = self.tcx;
+        let typeck_results = &mut *self.typeck_results.borrow_mut();
+        for &(opaque_type_key, hidden_type) in opaque_types {
+            match check_opaque_type_parameter_valid(
+                &self,
+                opaque_type_key,
+                hidden_type.span,
+                DefiningScopeKind::HirTypeck,
+            ) {
+                Ok(()) => {}
+                Err(InvalidOpaqueTypeArgs::AlreadyReported(guar)) => {
+                    typeck_results
+                        .concrete_opaque_types
+                        .insert(opaque_type_key.def_id, OpaqueHiddenType::new_error(tcx, guar));
+                }
+                // Not a defining use, ignore and treat as revealing use instead.
+                Err(
+                    InvalidOpaqueTypeArgs::NotAParam { .. }
+                    | InvalidOpaqueTypeArgs::DuplicateParam { .. },
+                ) => continue,
+            }
+
+            // We ignore uses of the opaque if they have any inference variables
+            // as this can frequently happen with recursive calls.
+            //
+            // See `tests/ui/traits/next-solver/opaques/universal-args-non-defining.rs`.
+            if hidden_type.ty.has_non_region_infer() {
+                continue;
+            }
+
+            let hidden_type = hidden_type.remap_generic_params_to_declaration_params(
+                opaque_type_key,
+                tcx,
+                DefiningScopeKind::HirTypeck,
+            );
+
+            if let Some(prev) =
+                typeck_results.concrete_opaque_types.insert(opaque_type_key.def_id, hidden_type)
+            {
+                let entry =
+                    typeck_results.concrete_opaque_types.get_mut(&opaque_type_key.def_id).unwrap();
+                if prev.ty != hidden_type.ty {
+                    if let Some(guar) = typeck_results.tainted_by_errors {
+                        entry.ty = Ty::new_error(tcx, guar);
+                    } else {
+                        let (Ok(guar) | Err(guar)) =
+                            prev.build_mismatch_error(&hidden_type, tcx).map(|d| d.emit());
+                        entry.ty = Ty::new_error(tcx, guar);
+                    }
+                }
+
+                // Pick a better span if there is one.
+                // FIXME(oli-obk): collect multiple spans for better diagnostics down the road.
+                entry.span = prev.span.substitute_dummy(hidden_type.span);
+            }
+        }
+
+        // FIXME(-Znext-solver): Check that all opaques have been defined hre.
+    }
+
+    fn apply_defining_uses(
+        &mut self,
+        opaque_types: &[(OpaqueTypeKey<'tcx>, OpaqueHiddenType<'tcx>)],
+    ) {
+        let tcx = self.tcx;
+        for &(key, hidden_type) in opaque_types {
+            let Some(&expected) =
+                self.typeck_results.borrow_mut().concrete_opaque_types.get(&key.def_id)
+            else {
+                let guar =
+                    tcx.dcx().span_err(hidden_type.span, "non-defining use in the defining scope");
+                self.typeck_results
+                    .borrow_mut()
+                    .concrete_opaque_types
+                    .insert(key.def_id, OpaqueHiddenType::new_error(tcx, guar));
+                self.set_tainted_by_errors(guar);
+                continue;
+            };
+
+            let expected = EarlyBinder::bind(expected.ty).instantiate(tcx, key.args);
+            self.demand_eqtype(hidden_type.span, expected, hidden_type.ty);
+        }
+    }
+
     /// We may in theory add further uses of an opaque after cloning the opaque
     /// types storage during writeback when computing the defining uses.
     ///
diff --git a/compiler/rustc_hir_typeck/src/writeback.rs b/compiler/rustc_hir_typeck/src/writeback.rs
@@ -534,26 +534,34 @@ impl<'cx, 'tcx> WritebackCx<'cx, 'tcx> {
         }
     }
 
+    fn visit_opaque_types_next(&mut self) {
+        let fcx_typeck_results = self.fcx.typeck_results.borrow();
+        assert_eq!(fcx_typeck_results.hir_owner, self.typeck_results.hir_owner);
+        for (&def_id, &hidden_type) in &fcx_typeck_results.concrete_opaque_types {
+            assert!(!hidden_type.has_infer());
+            self.typeck_results.concrete_opaque_types.insert(def_id, hidden_type);
+        }
+    }
+
     #[instrument(skip(self), level = "debug")]
     fn visit_opaque_types(&mut self) {
+        if self.fcx.next_trait_solver() {
+            return self.visit_opaque_types_next();
+        }
+
         let tcx = self.tcx();
-        // We clone the opaques instead of stealing them here as they are still used for
-        // normalization in the next generation trait solver.
-        let opaque_types = self.fcx.infcx.clone_opaque_types();
+        let opaque_types = self.fcx.infcx.take_opaque_types();
         let num_entries = self.fcx.inner.borrow_mut().opaque_types().num_entries();
         let prev = self.fcx.checked_opaque_types_storage_entries.replace(Some(num_entries));
         debug_assert_eq!(prev, None);
         for (opaque_type_key, hidden_type) in opaque_types {
             let hidden_type = self.resolve(hidden_type, &hidden_type.span);
             let opaque_type_key = self.resolve(opaque_type_key, &hidden_type.span);
-
-            if !self.fcx.next_trait_solver() {
-                if let ty::Alias(ty::Opaque, alias_ty) = hidden_type.ty.kind()
-                    && alias_ty.def_id == opaque_type_key.def_id.to_def_id()
-                    && alias_ty.args == opaque_type_key.args
-                {
-                    continue;
-                }
+            if let ty::Alias(ty::Opaque, alias_ty) = hidden_type.ty.kind()
+                && alias_ty.def_id == opaque_type_key.def_id.to_def_id()
+                && alias_ty.args == opaque_type_key.args
+            {
+                continue;
             }
 
             if let Err(err) = check_opaque_type_parameter_valid(
diff --git a/compiler/rustc_next_trait_solver/src/solve/eval_ctxt/mod.rs b/compiler/rustc_next_trait_solver/src/solve/eval_ctxt/mod.rs
@@ -4,7 +4,6 @@ use std::ops::ControlFlow;
 #[cfg(feature = "nightly")]
 use rustc_macros::HashStable_NoContext;
 use rustc_type_ir::data_structures::{HashMap, HashSet, ensure_sufficient_stack};
-use rustc_type_ir::fast_reject::DeepRejectCtxt;
 use rustc_type_ir::inherent::*;
 use rustc_type_ir::relate::Relate;
 use rustc_type_ir::relate::solver_relating::RelateExt;
@@ -1067,25 +1066,6 @@ where
         self.add_goals(GoalSource::AliasWellFormed, goals);
     }
 
-    // Do something for each opaque/hidden pair defined with `def_id` in the
-    // current inference context.
-    pub(super) fn probe_existing_opaque_ty(
-        &mut self,
-        key: ty::OpaqueTypeKey<I>,
-    ) -> Option<(ty::OpaqueTypeKey<I>, I::Ty)> {
-        let mut matching = self.delegate.clone_opaque_types_lookup_table().into_iter().filter(
-            |(candidate_key, _)| {
-                candidate_key.def_id == key.def_id
-                    && DeepRejectCtxt::relate_rigid_rigid(self.cx())
-                        .args_may_unify(candidate_key.args, key.args)
-            },
-        );
-        let first = matching.next();
-        let second = matching.next();
-        assert_eq!(second, None);
-        first
-    }
-
     // Try to evaluate a const, or return `None` if the const is too generic.
     // This doesn't mean the const isn't evaluatable, though, and should be treated
     // as an ambiguity rather than no-solution.
diff --git a/compiler/rustc_next_trait_solver/src/solve/normalizes_to/opaque_types.rs b/compiler/rustc_next_trait_solver/src/solve/normalizes_to/opaque_types.rs
@@ -1,13 +1,12 @@
 //! Computes a normalizes-to (projection) goal for opaque types. This goal
 //! behaves differently depending on the current `TypingMode`.
 
-use rustc_index::bit_set::GrowableBitSet;
 use rustc_type_ir::inherent::*;
 use rustc_type_ir::solve::GoalSource;
-use rustc_type_ir::{self as ty, Interner, TypingMode, fold_regions};
+use rustc_type_ir::{self as ty, GenericArgKind, Interner, TypingMode, fold_regions};
 
 use crate::delegate::SolverDelegate;
-use crate::solve::{Certainty, EvalCtxt, Goal, NoSolution, QueryResult, inspect};
+use crate::solve::{Certainty, EvalCtxt, Goal, QueryResult};
 
 impl<D, I> EvalCtxt<'_, D>
 where
@@ -49,54 +48,29 @@ where
                     return self.evaluate_added_goals_and_make_canonical_response(Certainty::Yes);
                 };
 
-                // FIXME: This may have issues when the args contain aliases...
-                match uses_unique_placeholders_ignoring_regions(self.cx(), opaque_ty.args) {
-                    Err(NotUniqueParam::NotParam(param)) if param.is_non_region_infer() => {
-                        return self.evaluate_added_goals_and_make_canonical_response(
-                            Certainty::AMBIGUOUS,
-                        );
-                    }
-                    Err(_) => {
-                        return Err(NoSolution);
-                    }
-                    Ok(()) => {}
-                }
-                // Prefer opaques registered already.
-                let opaque_type_key = ty::OpaqueTypeKey { def_id, args: opaque_ty.args };
-                // FIXME: This also unifies the previous hidden type with the expected.
-                //
-                // If that fails, we insert `expected` as a new hidden type instead of
-                // eagerly emitting an error.
-                let existing = self.probe_existing_opaque_ty(opaque_type_key);
-                if let Some((candidate_key, candidate_ty)) = existing {
-                    return self
-                        .probe(|result| inspect::ProbeKind::OpaqueTypeStorageLookup {
-                            result: *result,
-                        })
-                        .enter(|ecx| {
-                            for (a, b) in std::iter::zip(
-                                candidate_key.args.iter(),
-                                opaque_type_key.args.iter(),
-                            ) {
-                                ecx.eq(goal.param_env, a, b)?;
-                            }
-                            ecx.eq(goal.param_env, candidate_ty, expected)?;
-                            ecx.add_item_bounds_for_hidden_type(
-                                def_id.into(),
-                                candidate_key.args,
-                                goal.param_env,
-                                candidate_ty,
-                            );
-                            ecx.evaluate_added_goals_and_make_canonical_response(Certainty::Yes)
-                        });
+                // We structurally normalize the args so that we're able to detect defining uses
+                // later on. It also reduces the amount of duplicate definitions in the
+                // `opaque_type_storage`.
+                let normalized_args =
+                    cx.mk_args_from_iter(opaque_ty.args.iter().map(|arg| match arg.kind() {
+                        GenericArgKind::Lifetime(lt) => Ok(lt.into()),
+                        GenericArgKind::Type(ty) => {
+                            self.structurally_normalize_ty(goal.param_env, ty).map(Into::into)
+                        }
+                        GenericArgKind::Const(ct) => {
+                            self.structurally_normalize_const(goal.param_env, ct).map(Into::into)
+                        }
+                    }))?;
+
+                let opaque_type_key = ty::OpaqueTypeKey { def_id, args: normalized_args };
+                if let Some(prev) = self.register_hidden_type_in_storage(opaque_type_key, expected)
+                {
+                    self.eq(goal.param_env, expected, prev)?;
                 }
 
-                // Otherwise, define a new opaque type
-                let prev = self.register_hidden_type_in_storage(opaque_type_key, expected);
-                assert_eq!(prev, None);
                 self.add_item_bounds_for_hidden_type(
                     def_id.into(),
-                    opaque_ty.args,
+                    normalized_args,
                     goal.param_env,
                     expected,
                 );
@@ -168,44 +142,3 @@ where
         }
     }
 }
-
-/// Checks whether each generic argument is simply a unique generic placeholder.
-///
-/// FIXME: Interner argument is needed to constrain the `I` parameter.
-fn uses_unique_placeholders_ignoring_regions<I: Interner>(
-    _cx: I,
-    args: I::GenericArgs,
-) -> Result<(), NotUniqueParam<I>> {
-    let mut seen = GrowableBitSet::default();
-    for arg in args.iter() {
-        match arg.kind() {
-            // Ignore regions, since we can't resolve those in a canonicalized
-            // query in the trait solver.
-            ty::GenericArgKind::Lifetime(_) => {}
-            ty::GenericArgKind::Type(t) => match t.kind() {
-                ty::Placeholder(p) => {
-                    if !seen.insert(p.var()) {
-                        return Err(NotUniqueParam::DuplicateParam(t.into()));
-                    }
-                }
-                _ => return Err(NotUniqueParam::NotParam(t.into())),
-            },
-            ty::GenericArgKind::Const(c) => match c.kind() {
-                ty::ConstKind::Placeholder(p) => {
-                    if !seen.insert(p.var()) {
-                        return Err(NotUniqueParam::DuplicateParam(c.into()));
-                    }
-                }
-                _ => return Err(NotUniqueParam::NotParam(c.into())),
-            },
-        }
-    }
-
-    Ok(())
-}
-
-// FIXME: This should check for dupes and non-params first, then infer vars.
-enum NotUniqueParam<I: Interner> {
-    DuplicateParam(I::GenericArg),
-    NotParam(I::GenericArg),
-}
diff --git a/tests/ui/traits/next-solver/opaques/revealing-use-in-nested-body.rs b/tests/ui/traits/next-solver/opaques/revealing-use-in-nested-body.rs
@@ -3,6 +3,9 @@
 // of the async block. This caused borrowck of the recursive
 // call to ICE.
 
+//@ revisions: current next
+//@ ignore-compare-mode-next-solver (explicit revisions)
+//@[next] compile-flags: -Znext-solver
 //@ edition: 2021
 //@ check-pass
 async fn test() {
diff --git a/tests/ui/traits/next-solver/opaques/universal-args-non-defining.rs b/tests/ui/traits/next-solver/opaques/universal-args-non-defining.rs
@@ -0,0 +1,16 @@
+//@ check-pass
+//@ revisions: current next
+//@ ignore-compare-mode-next-solver (explicit revisions)
+//@[next] compile-flags: -Znext-solver
+
+// The recursive call to `foo` results in the opaque type use `opaque<U, T> = ?unconstrained`.
+// This needs to be supported and treated as a revealing use.
+
+fn foo<T, U>(b: bool) -> impl Sized {
+    if b {
+        foo::<U, T>(b);
+    }
+    1u16
+}
+
+fn main() {}
