Rollup merge of #109511 - compiler-errors:eval-ctxt-infcx-private, r=lcnr

Make `EvalCtxt`'s `infcx` private

To better protect against people doing bad things with the inner `InferCtxt`

r? `@lcnr`

5 files changed, 84 insertions, 50 deletions

diff --git a/compiler/rustc_trait_selection/src/solve/canonical/canonicalize.rs b/compiler/rustc_trait_selection/src/solve/canonicalize.rs
index 7ee4f332306..7ee4f332306 100644
--- a/compiler/rustc_trait_selection/src/solve/canonical/canonicalize.rs
+++ b/compiler/rustc_trait_selection/src/solve/canonicalize.rs
diff --git a/compiler/rustc_trait_selection/src/solve/eval_ctxt.rs b/compiler/rustc_trait_selection/src/solve/eval_ctxt.rs
index e47b5ae21b5..e64b4a7656f 100644
--- a/compiler/rustc_trait_selection/src/solve/eval_ctxt.rs
+++ b/compiler/rustc_trait_selection/src/solve/eval_ctxt.rs
@@ -6,9 +6,9 @@ use rustc_infer::infer::{
     DefineOpaqueTypes, InferCtxt, InferOk, LateBoundRegionConversionTime, TyCtxtInferExt,
 };
 use rustc_infer::traits::query::NoSolution;
-use rustc_infer::traits::solve::{CanonicalGoal, Certainty, MaybeCause, QueryResult};
 use rustc_infer::traits::ObligationCause;
 use rustc_middle::infer::unify_key::{ConstVariableOrigin, ConstVariableOriginKind};
+use rustc_middle::traits::solve::{CanonicalGoal, Certainty, MaybeCause, QueryResult};
 use rustc_middle::ty::{
     self, Ty, TyCtxt, TypeFoldable, TypeSuperVisitable, TypeVisitable, TypeVisitableExt,
     TypeVisitor,
@@ -16,13 +16,32 @@ use rustc_middle::ty::{
 use rustc_span::DUMMY_SP;
 use std::ops::ControlFlow;
 
+use crate::traits::specialization_graph;
+
 use super::search_graph::{self, OverflowHandler};
 use super::SolverMode;
 use super::{search_graph::SearchGraph, Goal};
 
+mod canonical;
+
 pub struct EvalCtxt<'a, 'tcx> {
-    // FIXME: should be private.
-    pub(super) infcx: &'a InferCtxt<'tcx>,
+    /// The inference context that backs (mostly) inference and placeholder terms
+    /// instantiated while solving goals.
+    ///
+    /// NOTE: The `InferCtxt` that backs the `EvalCtxt` is intentionally private,
+    /// because the `InferCtxt` is much more general than `EvalCtxt`. Methods such
+    /// as  `take_registered_region_obligations` can mess up query responses,
+    /// using `At::normalize` is totally wrong, calling `evaluate_root_goal` can
+    /// cause coinductive unsoundness, etc.
+    ///
+    /// Methods that are generally of use for trait solving are *intentionally*
+    /// re-declared through the `EvalCtxt` below, often with cleaner signatures
+    /// since we don't care about things like `ObligationCause`s and `Span`s here.
+    /// If some `InferCtxt` method is missing, please first think defensively about
+    /// the method's compatibility with this solver, or if an existing one does
+    /// the job already.
+    infcx: &'a InferCtxt<'tcx>,
+
     pub(super) var_values: CanonicalVarValues<'tcx>,
     /// The highest universe index nameable by the caller.
     ///
@@ -393,7 +412,7 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
                 if let &ty::Infer(ty::TyVar(vid)) = ty.kind() {
                     match self.infcx.probe_ty_var(vid) {
                         Ok(value) => bug!("resolved var in query: {goal:?} {value:?}"),
-                        Err(universe) => universe == self.universe(),
+                        Err(universe) => universe == self.infcx.universe(),
                     }
                 } else {
                     false
@@ -403,7 +422,7 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
                 if let ty::ConstKind::Infer(ty::InferConst::Var(vid)) = ct.kind() {
                     match self.infcx.probe_const_var(vid) {
                         Ok(value) => bug!("resolved var in query: {goal:?} {value:?}"),
-                        Err(universe) => universe == self.universe(),
+                        Err(universe) => universe == self.infcx.universe(),
                     }
                 } else {
                     false
@@ -545,7 +564,43 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
         self.infcx.fresh_substs_for_item(DUMMY_SP, def_id)
     }
 
-    pub(super) fn universe(&self) -> ty::UniverseIndex {
-        self.infcx.universe()
+    pub(super) fn translate_substs(
+        &self,
+        param_env: ty::ParamEnv<'tcx>,
+        source_impl: DefId,
+        source_substs: ty::SubstsRef<'tcx>,
+        target_node: specialization_graph::Node,
+    ) -> ty::SubstsRef<'tcx> {
+        crate::traits::translate_substs(
+            self.infcx,
+            param_env,
+            source_impl,
+            source_substs,
+            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());
+    }
+
+    pub(super) fn register_region_outlives(&self, a: ty::Region<'tcx>, b: ty::Region<'tcx>) {
+        // `b : a` ==> `a <= b`
+        // (inlined from `InferCtxt::region_outlives_predicate`)
+        self.infcx.sub_regions(
+            rustc_infer::infer::SubregionOrigin::RelateRegionParamBound(DUMMY_SP),
+            b,
+            a,
+        );
+    }
+
+    /// Computes the list of goals required for `arg` to be well-formed
+    pub(super) fn well_formed_goals(
+        &self,
+        param_env: ty::ParamEnv<'tcx>,
+        arg: ty::GenericArg<'tcx>,
+    ) -> Option<impl Iterator<Item = Goal<'tcx, ty::Predicate<'tcx>>>> {
+        crate::traits::wf::unnormalized_obligations(self.infcx, param_env, arg)
+            .map(|obligations| obligations.into_iter().map(|obligation| obligation.into()))
     }
 }
diff --git a/compiler/rustc_trait_selection/src/solve/canonical/mod.rs b/compiler/rustc_trait_selection/src/solve/eval_ctxt/canonical.rs
index efecaf33ef9..ee90488730a 100644
--- a/compiler/rustc_trait_selection/src/solve/canonical/mod.rs
+++ b/compiler/rustc_trait_selection/src/solve/eval_ctxt/canonical.rs
@@ -8,22 +8,19 @@
 /// section of the [rustc-dev-guide][c].
 ///
 /// [c]: https://rustc-dev-guide.rust-lang.org/solve/canonicalization.html
-use self::canonicalize::{CanonicalizeMode, Canonicalizer};
 use super::{CanonicalGoal, Certainty, EvalCtxt, Goal};
-use super::{CanonicalResponse, ExternalConstraints, QueryResult, Response};
+use crate::solve::canonicalize::{CanonicalizeMode, Canonicalizer};
+use crate::solve::{CanonicalResponse, QueryResult, Response};
 use rustc_infer::infer::canonical::query_response::make_query_region_constraints;
 use rustc_infer::infer::canonical::CanonicalVarValues;
 use rustc_infer::infer::canonical::{CanonicalExt, QueryRegionConstraints};
-use rustc_infer::traits::query::NoSolution;
-use rustc_infer::traits::solve::ExternalConstraintsData;
-use rustc_infer::traits::ObligationCause;
+use rustc_middle::traits::query::NoSolution;
+use rustc_middle::traits::solve::{ExternalConstraints, ExternalConstraintsData};
 use rustc_middle::ty::{self, GenericArgKind};
 use rustc_span::DUMMY_SP;
 use std::iter;
 use std::ops::Deref;
 
-mod canonicalize;
-
 impl<'tcx> EvalCtxt<'_, 'tcx> {
     /// Canonicalizes the goal remembering the original values
     /// for each bound variable.
@@ -48,7 +45,7 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
     /// - `external_constraints`: additional constraints which aren't expressable
     ///   using simple unification of inference variables.
     #[instrument(level = "debug", skip(self))]
-    pub(super) fn evaluate_added_goals_and_make_canonical_response(
+    pub(in crate::solve) fn evaluate_added_goals_and_make_canonical_response(
         &mut self,
         certainty: Certainty,
     ) -> QueryResult<'tcx> {
@@ -219,15 +216,8 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
     fn register_region_constraints(&mut self, region_constraints: &QueryRegionConstraints<'tcx>) {
         for &(ty::OutlivesPredicate(lhs, rhs), _) in &region_constraints.outlives {
             match lhs.unpack() {
-                GenericArgKind::Lifetime(lhs) => self.infcx.region_outlives_predicate(
-                    &ObligationCause::dummy(),
-                    ty::Binder::dummy(ty::OutlivesPredicate(lhs, rhs)),
-                ),
-                GenericArgKind::Type(lhs) => self.infcx.register_region_obligation_with_cause(
-                    lhs,
-                    rhs,
-                    &ObligationCause::dummy(),
-                ),
+                GenericArgKind::Lifetime(lhs) => self.register_region_outlives(lhs, rhs),
+                GenericArgKind::Type(lhs) => self.register_ty_outlives(lhs, rhs),
                 GenericArgKind::Const(_) => bug!("const outlives: {lhs:?}: {rhs:?}"),
             }
         }
diff --git a/compiler/rustc_trait_selection/src/solve/mod.rs b/compiler/rustc_trait_selection/src/solve/mod.rs
index 65e7bcb7f01..a96ec2c60f0 100644
--- a/compiler/rustc_trait_selection/src/solve/mod.rs
+++ b/compiler/rustc_trait_selection/src/solve/mod.rs
@@ -13,18 +13,15 @@ use rustc_hir::def_id::DefId;
 use rustc_infer::infer::canonical::{Canonical, CanonicalVarValues};
 use rustc_infer::traits::query::NoSolution;
 use rustc_middle::traits::solve::{
-    CanonicalGoal, CanonicalResponse, Certainty, ExternalConstraints, ExternalConstraintsData,
-    Goal, QueryResult, Response,
+    CanonicalResponse, Certainty, ExternalConstraintsData, Goal, QueryResult, Response,
 };
 use rustc_middle::ty::{self, Ty, TyCtxt};
 use rustc_middle::ty::{
     CoercePredicate, RegionOutlivesPredicate, SubtypePredicate, TypeOutlivesPredicate,
 };
 
-use crate::traits::ObligationCause;
-
 mod assembly;
-mod canonical;
+mod canonicalize;
 mod eval_ctxt;
 mod fulfill;
 mod project_goals;
@@ -66,7 +63,7 @@ impl<'a, 'tcx> EvalCtxt<'a, 'tcx> {
         goal: Goal<'tcx, TypeOutlivesPredicate<'tcx>>,
     ) -> QueryResult<'tcx> {
         let ty::OutlivesPredicate(ty, lt) = goal.predicate;
-        self.infcx.register_region_obligation_with_cause(ty, lt, &ObligationCause::dummy());
+        self.register_ty_outlives(ty, lt);
         self.evaluate_added_goals_and_make_canonical_response(Certainty::Yes)
     }
 
@@ -75,10 +72,8 @@ impl<'a, 'tcx> EvalCtxt<'a, 'tcx> {
         &mut self,
         goal: Goal<'tcx, RegionOutlivesPredicate<'tcx>>,
     ) -> QueryResult<'tcx> {
-        self.infcx.region_outlives_predicate(
-            &ObligationCause::dummy(),
-            ty::Binder::dummy(goal.predicate),
-        );
+        let ty::OutlivesPredicate(a, b) = goal.predicate;
+        self.register_region_outlives(a, b);
         self.evaluate_added_goals_and_make_canonical_response(Certainty::Yes)
     }
 
@@ -142,13 +137,9 @@ impl<'a, 'tcx> EvalCtxt<'a, 'tcx> {
         &mut self,
         goal: Goal<'tcx, ty::GenericArg<'tcx>>,
     ) -> QueryResult<'tcx> {
-        match crate::traits::wf::unnormalized_obligations(
-            self.infcx,
-            goal.param_env,
-            goal.predicate,
-        ) {
-            Some(obligations) => {
-                self.add_goals(obligations.into_iter().map(|o| o.into()));
+        match self.well_formed_goals(goal.param_env, goal.predicate) {
+            Some(goals) => {
+                self.add_goals(goals);
                 self.evaluate_added_goals_and_make_canonical_response(Certainty::Yes)
             }
             None => self.evaluate_added_goals_and_make_canonical_response(Certainty::AMBIGUOUS),
diff --git a/compiler/rustc_trait_selection/src/solve/project_goals.rs b/compiler/rustc_trait_selection/src/solve/project_goals.rs
index 91b56fe3522..48f7d3e3e40 100644
--- a/compiler/rustc_trait_selection/src/solve/project_goals.rs
+++ b/compiler/rustc_trait_selection/src/solve/project_goals.rs
@@ -1,4 +1,4 @@
-use crate::traits::{specialization_graph, translate_substs};
+use crate::traits::specialization_graph;
 
 use super::assembly;
 use super::trait_goals::structural_traits;
@@ -7,7 +7,6 @@ use rustc_errors::ErrorGuaranteed;
 use rustc_hir::def::DefKind;
 use rustc_hir::def_id::DefId;
 use rustc_hir::LangItem;
-use rustc_infer::infer::InferCtxt;
 use rustc_infer::traits::query::NoSolution;
 use rustc_infer::traits::specialization_graph::LeafDef;
 use rustc_infer::traits::Reveal;
@@ -165,7 +164,7 @@ impl<'tcx> assembly::GoalKind<'tcx> for ProjectionPredicate<'tcx> {
             // return ambiguity this would otherwise be incomplete, resulting in
             // unsoundness during coherence (#105782).
             let Some(assoc_def) = fetch_eligible_assoc_item_def(
-                ecx.infcx,
+                ecx,
                 goal.param_env,
                 goal_trait_ref,
                 goal.predicate.def_id(),
@@ -196,8 +195,7 @@ impl<'tcx> assembly::GoalKind<'tcx> for ProjectionPredicate<'tcx> {
                 goal_trait_ref.def_id,
                 impl_substs,
             );
-            let substs = translate_substs(
-                ecx.infcx,
+            let substs = ecx.translate_substs(
                 goal.param_env,
                 impl_def_id,
                 impl_substs_with_gat,
@@ -504,15 +502,15 @@ impl<'tcx> assembly::GoalKind<'tcx> for ProjectionPredicate<'tcx> {
 ///
 /// FIXME: We should merge these 3 implementations as it's likely that they otherwise
 /// diverge.
-#[instrument(level = "debug", skip(infcx, param_env), ret)]
+#[instrument(level = "debug", skip(ecx, param_env), ret)]
 fn fetch_eligible_assoc_item_def<'tcx>(
-    infcx: &InferCtxt<'tcx>,
+    ecx: &EvalCtxt<'_, 'tcx>,
     param_env: ty::ParamEnv<'tcx>,
     goal_trait_ref: ty::TraitRef<'tcx>,
     trait_assoc_def_id: DefId,
     impl_def_id: DefId,
 ) -> Result<Option<LeafDef>, NoSolution> {
-    let node_item = specialization_graph::assoc_def(infcx.tcx, impl_def_id, trait_assoc_def_id)
+    let node_item = specialization_graph::assoc_def(ecx.tcx(), impl_def_id, trait_assoc_def_id)
         .map_err(|ErrorGuaranteed { .. }| NoSolution)?;
 
     let eligible = if node_item.is_final() {
@@ -524,7 +522,7 @@ fn fetch_eligible_assoc_item_def<'tcx>(
         // transmute checking and polymorphic MIR optimizations could
         // get a result which isn't correct for all monomorphizations.
         if param_env.reveal() == Reveal::All {
-            let poly_trait_ref = infcx.resolve_vars_if_possible(goal_trait_ref);
+            let poly_trait_ref = ecx.resolve_vars_if_possible(goal_trait_ref);
             !poly_trait_ref.still_further_specializable()
         } else {
             debug!(?node_item.item.def_id, "not eligible due to default");