allow method calls on opaques

Author: lcnr

compiler/rustc_hir_typeck/src/method/probe.rs

@@ -85,11 +85,32 @@ impl<'tcx> InferCtxt<'tcx> {
     where
         T: Debug + TypeFoldable<TyCtxt<'tcx>>,
     {
+        // While we ignore region constraints and pending obligations,
+        // we do return constrained opaque types to avoid unconstrained
+        // inference variables in the response. This is still slightly
+        // insufficient as ambiguous `Projection` obligations have the
+        // same issue.
+        //
+        // FIXME(-Znext-solver): We could alternatively extend the `var_values`
+        // each time we call `make_query_response_ignoring_pending_obligations`
+        // and equate inference variables created inside of the query this way.
+        // This is what we do for `CanonicalState` and is probably a bit nicer.
+        let opaque_types = if self.next_trait_solver() {
+            self.inner
+                .borrow_mut()
+                .opaque_type_storage
+                .iter_opaque_types()
+                .map(|(k, v)| (k, v.ty))
+                .collect()
+        } else {
+            vec![]
+        };
+
         self.canonicalize_response(QueryResponse {
             var_values: inference_vars,
             region_constraints: QueryRegionConstraints::default(),
             certainty: Certainty::Proven, // Ambiguities are OK!
-            opaque_types: vec![],
+            opaque_types,
             value: answer,
         })
     }

compiler/rustc_infer/src/infer/canonical/query_response.rs

@@ -154,6 +154,7 @@ impl<'tcx> FromIterator<DropckConstraint<'tcx>> for DropckConstraint<'tcx> {
 #[derive(Debug, HashStable)]
 pub struct CandidateStep<'tcx> {
     pub self_ty: Canonical<'tcx, QueryResponse<'tcx, Ty<'tcx>>>,
+    pub self_ty_is_opaque: bool,
     pub autoderefs: usize,
     /// `true` if the type results from a dereference of a raw pointer.
     /// when assembling candidates, we include these steps, but not when

compiler/rustc_middle/src/traits/query.rs

@@ -194,7 +194,7 @@ where
     D: SolverDelegate<Interner = I>,
     I: Interner,
 {
-    #[instrument(level = "debug", skip(self))]
+    #[instrument(level = "debug", skip(self), ret)]
     fn evaluate_root_goal(
         &self,
         goal: Goal<I, I::Predicate>,
@@ -206,6 +206,7 @@ where
         })
     }
 
+    #[instrument(level = "debug", skip(self), ret)]
     fn root_goal_may_hold_opaque_types_jank(
         &self,
         goal: Goal<Self::Interner, <Self::Interner as Interner>::Predicate>,

compiler/rustc_next_trait_solver/src/solve/eval_ctxt/mod.rs

@@ -381,6 +381,7 @@ where
 }
 
 /// The result of evaluating a goal.
+#[derive_where(Debug; I: Interner)]
 pub struct GoalEvaluation<I: Interner> {
     /// The goal we've evaluated. This is the input goal, but potentially with its
     /// inference variables resolved. This never applies any inference constraints

compiler/rustc_next_trait_solver/src/solve/mod.rs

@@ -1,6 +1,6 @@
 use rustc_infer::traits::solve::Goal;
 use rustc_macros::extension;
-use rustc_middle::span_bug;
+use rustc_middle::{span_bug, ty};
 use rustc_next_trait_solver::solve::SolverDelegateEvalExt;
 
 use crate::infer::InferCtxt;
@@ -22,7 +22,7 @@ impl<'tcx> InferCtxt<'tcx> {
     /// for more details.
     fn predicate_may_hold_opaque_types_jank(&self, obligation: &PredicateObligation<'tcx>) -> bool {
         if self.next_trait_solver() {
-            <&SolverDelegate<'tcx>>::from(self).root_goal_may_hold_opaque_types_jank(Goal::new(
+            self.goal_may_hold_opaque_types_jank(Goal::new(
                 self.tcx,
                 obligation.param_env,
                 obligation.predicate,
@@ -32,6 +32,13 @@ impl<'tcx> InferCtxt<'tcx> {
         }
     }
 
+    /// See the comment on [OpaqueTypesJank](crate::solve::OpaqueTypesJank)
+    /// for more details.
+    fn goal_may_hold_opaque_types_jank(&self, goal: Goal<'tcx, ty::Predicate<'tcx>>) -> bool {
+        assert!(self.next_trait_solver());
+        <&SolverDelegate<'tcx>>::from(self).root_goal_may_hold_opaque_types_jank(goal)
+    }
+
     /// Evaluates whether the predicate can be satisfied in the given
     /// `ParamEnv`, and returns `false` if not certain. However, this is
     /// not entirely accurate if inference variables are involved.

compiler/rustc_trait_selection/src/traits/query/evaluate_obligation.rs

@@ -1,17 +1,12 @@
-error[E0282]: type annotations needed
+warning: variable does not need to be mutable
   --> $DIR/call_method_ambiguous.rs:26:13
    |
 LL |         let mut iter = foo(n - 1, m);
-   |             ^^^^^^^^
-LL |
-LL |         assert_eq!(iter.get(), 1);
-   |                         --- type must be known at this point
+   |             ----^^^^
+   |             |
+   |             help: remove this `mut`
    |
-help: consider giving `iter` an explicit type
-   |
-LL |         let mut iter: /* Type */ = foo(n - 1, m);
-   |                     ++++++++++++
+   = note: `#[warn(unused_mut)]` (part of `#[warn(unused)]`) on by default
 
-error: aborting due to 1 previous error
+warning: 1 warning emitted
 
-For more information about this error, try `rustc --explain E0282`.

tests/ui/impl-trait/call_method_ambiguous.next.stderr

@@ -1,6 +1,6 @@
 //@ revisions: current next
 //@[next] compile-flags: -Znext-solver
-//@[current] run-pass
+//@ run-pass
 
 trait Get {
     fn get(&mut self) -> u32;
@@ -24,7 +24,6 @@ where
 fn foo(n: usize, m: &mut ()) -> impl Get + use<'_> {
     if n > 0 {
         let mut iter = foo(n - 1, m);
-        //[next]~^ ERROR type annotations needed
         assert_eq!(iter.get(), 1);
     }
     m

tests/ui/impl-trait/call_method_ambiguous.rs

@@ -1,6 +1,6 @@
 //@ revisions: current next
 //@[next] compile-flags: -Znext-solver
-//@[current] check-pass
+//@ check-pass
 
 trait MyDebug {
     fn my_debug(&self);
@@ -16,7 +16,6 @@ where
 fn my_foo() -> impl std::fmt::Debug {
     if false {
         let x = my_foo();
-        //[next]~^ ERROR type annotations needed
         x.my_debug();
     }
     ()