Stop using translate_args in the new solver

Author: compiler-errors

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

@@ -12,7 +12,6 @@ use rustc_middle::bug;
 use rustc_middle::traits::solve::{
     inspect, CanonicalInput, CanonicalResponse, Certainty, PredefinedOpaquesData, QueryResult,
 };
-use rustc_middle::traits::specialization_graph;
 use rustc_middle::ty::AliasRelationDirection;
 use rustc_middle::ty::TypeFolder;
 use rustc_middle::ty::{
@@ -900,16 +899,6 @@ impl<'tcx> EvalCtxt<'_, InferCtxt<'tcx>> {
         args
     }
 
-    pub(super) fn translate_args(
-        &self,
-        param_env: ty::ParamEnv<'tcx>,
-        source_impl: DefId,
-        source_args: ty::GenericArgsRef<'tcx>,
-        target_node: specialization_graph::Node,
-    ) -> ty::GenericArgsRef<'tcx> {
-        crate::traits::translate_args(self.infcx, param_env, source_impl, source_args, target_node)
-    }
-
     pub(super) fn register_ty_outlives(&self, ty: Ty<'tcx>, lt: ty::Region<'tcx>) {
         self.infcx.register_region_obligation_with_cause(ty, lt, &ObligationCause::dummy());
     }

compiler/rustc_trait_selection/src/solve/normalizes_to/mod.rs

@@ -1,4 +1,4 @@
-use crate::traits::specialization_graph;
+use crate::traits::specialization_graph::{self, LeafDef, Node};
 
 use super::assembly::structural_traits::AsyncCallableRelevantTypes;
 use super::assembly::{self, structural_traits, Candidate};
@@ -9,7 +9,6 @@ use rustc_infer::infer::InferCtxt;
 use rustc_infer::traits::query::NoSolution;
 use rustc_infer::traits::solve::inspect::ProbeKind;
 use rustc_infer::traits::solve::MaybeCause;
-use rustc_infer::traits::specialization_graph::LeafDef;
 use rustc_infer::traits::Reveal;
 use rustc_middle::traits::solve::{CandidateSource, Certainty, Goal, QueryResult};
 use rustc_middle::traits::BuiltinImplSource;
@@ -235,16 +234,10 @@ impl<'tcx> assembly::GoalKind<'tcx> for NormalizesTo<'tcx> {
             //
             // And then map these args to the args of the defining impl of `Assoc`, going
             // from `[u32, u64]` to `[u32, i32, u64]`.
-            let impl_args_with_gat =
-                goal.predicate.alias.args.rebase_onto(tcx, goal_trait_ref.def_id, impl_args);
-            let args = ecx.translate_args(
-                goal.param_env,
-                impl_def_id,
-                impl_args_with_gat,
-                assoc_def.defining_node,
-            );
+            let associated_item_args =
+                translate_args(ecx, &assoc_def, goal, impl_def_id, impl_args, impl_trait_ref)?;
 
-            if !tcx.check_args_compatible(assoc_def.item.def_id, args) {
+            if !tcx.check_args_compatible(assoc_def.item.def_id, associated_item_args) {
                 return error_response(
                     ecx,
                     "associated item has mismatched generic item arguments",
@@ -272,7 +265,7 @@ impl<'tcx> assembly::GoalKind<'tcx> for NormalizesTo<'tcx> {
                 ty::AssocKind::Fn => unreachable!("we should never project to a fn"),
             };
 
-            ecx.instantiate_normalizes_to_term(goal, term.instantiate(tcx, args));
+            ecx.instantiate_normalizes_to_term(goal, term.instantiate(tcx, associated_item_args));
             ecx.evaluate_added_goals_and_make_canonical_response(Certainty::Yes)
         })
     }
@@ -889,6 +882,43 @@ impl<'tcx> assembly::GoalKind<'tcx> for NormalizesTo<'tcx> {
     }
 }
 
+fn translate_args<'tcx>(
+    ecx: &mut EvalCtxt<'_, InferCtxt<'tcx>>,
+    assoc_def: &LeafDef,
+    goal: Goal<'tcx, ty::NormalizesTo<'tcx>>,
+    impl_def_id: DefId,
+    impl_args: ty::GenericArgsRef<'tcx>,
+    impl_trait_ref: rustc_type_ir::TraitRef<TyCtxt<'tcx>>,
+) -> Result<ty::GenericArgsRef<'tcx>, NoSolution> {
+    let tcx = ecx.interner();
+    Ok(match assoc_def.defining_node {
+        Node::Trait(_) => goal.predicate.alias.args,
+        Node::Impl(target_impl_def_id) => {
+            if target_impl_def_id == impl_def_id {
+                // Same impl, no need to fully translate, just a rebase from
+                // the trait is sufficient.
+                goal.predicate.alias.args.rebase_onto(tcx, impl_trait_ref.def_id, impl_args)
+            } else {
+                let target_args = ecx.fresh_args_for_item(target_impl_def_id);
+                let target_trait_ref =
+                    tcx.impl_trait_ref(target_impl_def_id).unwrap().instantiate(tcx, target_args);
+                // Relate source impl to target impl by equating trait refs.
+                ecx.eq(goal.param_env, impl_trait_ref, target_trait_ref)?;
+                // Also add predicates since they may be needed to constrain the
+                // target impl's params.
+                ecx.add_goals(
+                    GoalSource::Misc,
+                    tcx.predicates_of(target_impl_def_id)
+                        .instantiate(tcx, target_args)
+                        .into_iter()
+                        .map(|(pred, _)| goal.with(tcx, pred)),
+                );
+                goal.predicate.alias.args.rebase_onto(tcx, impl_trait_ref.def_id, target_args)
+            }
+        }
+    })
+}
+
 /// This behavior is also implemented in `rustc_ty_utils` and in the old `project` code.
 ///
 /// FIXME: We should merge these 3 implementations as it's likely that they otherwise

tests/ui/specialization/source-impl-requires-constraining-predicates-ambig.next.stderr

@@ -0,0 +1,12 @@
+warning: the feature `specialization` is incomplete and may not be safe to use and/or cause compiler crashes
+  --> $DIR/source-impl-requires-constraining-predicates-ambig.rs:14:12
+   |
+LL | #![feature(specialization)]
+   |            ^^^^^^^^^^^^^^
+   |
+   = note: see issue #31844 <https://github.com/rust-lang/rust/issues/31844> for more information
+   = help: consider using `min_specialization` instead, which is more stable and complete
+   = note: `#[warn(incomplete_features)]` on by default
+
+warning: 1 warning emitted
+

tests/ui/specialization/source-impl-requires-constraining-predicates-ambig.rs

@@ -0,0 +1,29 @@
+//@ revisions: current next
+//@ ignore-compare-mode-next-solver (explicit revisions)
+//@[next] compile-flags: -Znext-solver
+//@[next] check-pass
+//@[current] known-bug: unknown
+//@[current] failure-status: 101
+//@[current] dont-check-compiler-stderr
+
+// Tests that rebasing from the concrete impl to the default impl also processes the
+// `[u32; 0]: IntoIterator<Item = ?U>` predicate to constrain the `?U` impl arg.
+// This test also makes sure that we don't do anything weird when rebasing the args
+// is ambiguous.
+
+#![feature(specialization)]
+//[next]~^ WARN the feature `specialization` is incomplete
+
+trait Spec {
+    type Assoc;
+}
+
+default impl<T, U> Spec for T where T: IntoIterator<Item = U> {
+    type Assoc = U;
+}
+
+impl<T> Spec for [T; 0] {}
+
+fn main() {
+    let x: <[_; 0] as Spec>::Assoc = 1;
+}

tests/ui/specialization/source-impl-requires-constraining-predicates.current.stderr

@@ -0,0 +1,12 @@
+warning: the feature `specialization` is incomplete and may not be safe to use and/or cause compiler crashes
+  --> $DIR/source-impl-requires-constraining-predicates.rs:9:12
+   |
+LL | #![feature(specialization)]
+   |            ^^^^^^^^^^^^^^
+   |
+   = note: see issue #31844 <https://github.com/rust-lang/rust/issues/31844> for more information
+   = help: consider using `min_specialization` instead, which is more stable and complete
+   = note: `#[warn(incomplete_features)]` on by default
+
+warning: 1 warning emitted
+

tests/ui/specialization/source-impl-requires-constraining-predicates.next.stderr

@@ -0,0 +1,12 @@
+warning: the feature `specialization` is incomplete and may not be safe to use and/or cause compiler crashes
+  --> $DIR/source-impl-requires-constraining-predicates.rs:9:12
+   |
+LL | #![feature(specialization)]
+   |            ^^^^^^^^^^^^^^
+   |
+   = note: see issue #31844 <https://github.com/rust-lang/rust/issues/31844> for more information
+   = help: consider using `min_specialization` instead, which is more stable and complete
+   = note: `#[warn(incomplete_features)]` on by default
+
+warning: 1 warning emitted
+

tests/ui/specialization/source-impl-requires-constraining-predicates.rs

@@ -0,0 +1,24 @@
+//@ check-pass
+//@ revisions: current next
+//@ ignore-compare-mode-next-solver (explicit revisions)
+//@[next] compile-flags: -Znext-solver
+
+// Tests that rebasing from the concrete impl to the default impl also processes the
+// `[u32; 0]: IntoIterator<Item = ?U>` predicate to constrain the `?U` impl arg.
+
+#![feature(specialization)]
+//~^ WARN the feature `specialization` is incomplete
+
+trait Spec {
+    type Assoc;
+}
+
+default impl<T, U> Spec for T where T: IntoIterator<Item = U> {
+    type Assoc = U;
+}
+
+impl<T> Spec for [T; 0] {}
+
+fn main() {
+    let x: <[u32; 0] as Spec>::Assoc = 1;
+}