Record impl args in the InsepctCandiate rather than rematching during select

compiler/rustc_middle/src/traits/solve/inspect.rs

@@ -123,6 +123,8 @@ pub enum ProbeStep<'tcx> {
     /// used whenever there are multiple candidates to prove the
     /// current goalby .
     NestedProbe(Probe<'tcx>),
+    /// A trait goal was satisfied by an impl candidate.
+    RecordImplArgs { impl_args: CanonicalState<'tcx, ty::GenericArgsRef<'tcx>> },
     /// A call to `EvalCtxt::evaluate_added_goals_make_canonical_response` with
     /// `Certainty` was made. This is the certainty passed in, so it's not unified
     /// with the certainty of the `try_evaluate_added_goals` that is done within;

compiler/rustc_middle/src/traits/solve/inspect/format.rs

@@ -136,6 +136,9 @@ impl<'a, 'b> ProofTreeFormatter<'a, 'b> {
                     ProbeStep::MakeCanonicalResponse { shallow_certainty } => {
                         writeln!(this.f, "EVALUATE GOALS AND MAKE RESPONSE: {shallow_certainty:?}")?
                     }
+                    ProbeStep::RecordImplArgs { impl_args } => {
+                        writeln!(this.f, "RECORDED IMPL ARGS: {impl_args:?}")?
+                    }
                 }
             }
             Ok(())