Pass ObligationCtxt from enter_canonical_trait_query and use ObligationCtxt API

Author: spastorino

Diff for: compiler/rustc_traits/src/implied_outlives_bounds.rs

@@ -5,16 +5,15 @@
 use rustc_hir as hir;
 use rustc_infer::infer::canonical::{self, Canonical};
 use rustc_infer::infer::outlives::components::{push_outlives_components, Component};
-use rustc_infer::infer::{InferCtxt, TyCtxtInferExt};
+use rustc_infer::infer::TyCtxtInferExt;
 use rustc_infer::traits::query::OutlivesBound;
-use rustc_infer::traits::TraitEngineExt as _;
 use rustc_middle::ty::query::Providers;
 use rustc_middle::ty::{self, Ty, TyCtxt, TypeVisitable};
 use rustc_span::source_map::DUMMY_SP;
 use rustc_trait_selection::infer::InferCtxtBuilderExt;
 use rustc_trait_selection::traits::query::{CanonicalTyGoal, Fallible, NoSolution};
 use rustc_trait_selection::traits::wf;
-use rustc_trait_selection::traits::{TraitEngine, TraitEngineExt};
+use rustc_trait_selection::traits::ObligationCtxt;
 use smallvec::{smallvec, SmallVec};
 
 pub(crate) fn provide(p: &mut Providers) {
@@ -30,16 +29,16 @@ fn implied_outlives_bounds<'tcx>(
 > {
     tcx.infer_ctxt().enter_canonical_trait_query(&goal, |ocx, key| {
         let (param_env, ty) = key.into_parts();
-        compute_implied_outlives_bounds(&ocx.infcx, param_env, ty)
+        compute_implied_outlives_bounds(ocx, param_env, ty)
     })
 }
 
 fn compute_implied_outlives_bounds<'tcx>(
-    infcx: &InferCtxt<'tcx>,
+    ocx: &ObligationCtxt<'_, 'tcx>,
     param_env: ty::ParamEnv<'tcx>,
     ty: Ty<'tcx>,
 ) -> Fallible<Vec<OutlivesBound<'tcx>>> {
-    let tcx = infcx.tcx;
+    let tcx = ocx.infcx.tcx;
 
     // Sometimes when we ask what it takes for T: WF, we get back that
     // U: WF is required; in that case, we push U onto this stack and
@@ -52,8 +51,6 @@ fn compute_implied_outlives_bounds<'tcx>(
     let mut outlives_bounds: Vec<ty::OutlivesPredicate<ty::GenericArg<'tcx>, ty::Region<'tcx>>> =
         vec![];
 
-    let mut fulfill_cx = <dyn TraitEngine<'tcx>>::new(tcx);
-
     while let Some(arg) = wf_args.pop() {
         if !checked_wf_args.insert(arg) {
             continue;
@@ -70,15 +67,15 @@ fn compute_implied_outlives_bounds<'tcx>(
         // FIXME(@lcnr): It's not really "always fine", having fewer implied
         // bounds can be backward incompatible, e.g. #101951 was caused by
         // us not dealing with inference vars in `TypeOutlives` predicates.
-        let obligations = wf::obligations(infcx, param_env, hir::CRATE_HIR_ID, 0, arg, DUMMY_SP)
-            .unwrap_or_default();
+        let obligations =
+            wf::obligations(ocx.infcx, param_env, hir::CRATE_HIR_ID, 0, arg, DUMMY_SP)
+                .unwrap_or_default();
 
         // While these predicates should all be implied by other parts of
         // the program, they are still relevant as they may constrain
         // inference variables, which is necessary to add the correct
         // implied bounds in some cases, mostly when dealing with projections.
-        fulfill_cx.register_predicate_obligations(
-            infcx,
+        ocx.register_obligations(
             obligations.iter().filter(|o| o.predicate.has_non_region_infer()).cloned(),
         );
 
@@ -116,9 +113,9 @@ fn compute_implied_outlives_bounds<'tcx>(
         }));
     }
 
-    // Ensure that those obligations that we had to solve
-    // get solved *here*.
-    match fulfill_cx.select_all_or_error(infcx).as_slice() {
+    // This call to `select_all_or_error` is necessary to constrain inference variables, which we
+    // use further down when computing the implied bounds.
+    match ocx.select_all_or_error().as_slice() {
         [] => (),
         _ => return Err(NoSolution),
     }
@@ -130,7 +127,7 @@ fn compute_implied_outlives_bounds<'tcx>(
         .flat_map(|ty::OutlivesPredicate(a, r_b)| match a.unpack() {
             ty::GenericArgKind::Lifetime(r_a) => vec![OutlivesBound::RegionSubRegion(r_b, r_a)],
             ty::GenericArgKind::Type(ty_a) => {
-                let ty_a = infcx.resolve_vars_if_possible(ty_a);
+                let ty_a = ocx.infcx.resolve_vars_if_possible(ty_a);
                 let mut components = smallvec![];
                 push_outlives_components(tcx, ty_a, &mut components);
                 implied_bounds_from_components(r_b, components)