Rollup merge of #109956 - compiler-errors:tweak-debug-outputs, r=oli-obk

Tweak debug outputs to make debugging new solver easier

1. Move the fields that are "most important" (I know this is subjective) to the beginning of the structs.

For goals, I typically care more about the predicate than the param-env (which is significantly longer in debug output).
For canonicalized things, I typically care more about what is *being* canonicalized.
For a canonical response, I typically care about the response -- or at least, it's typically useful to put it first since it's short and affects the whether the solver recurses or not...

2. Add some more debug and instrument calls to functions to add more structure to tracing lines.

r? `@oli-obk` or `@BoxyUwU` (since I think `@lcnr` is on holiday)

compiler/rustc_middle/src/infer/canonical.rs

@@ -35,9 +35,9 @@ use std::ops::Index;
 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, TyDecodable, TyEncodable)]
 #[derive(HashStable, TypeFoldable, TypeVisitable, Lift)]
 pub struct Canonical<'tcx, V> {
+    pub value: V,
     pub max_universe: ty::UniverseIndex,
     pub variables: CanonicalVarInfos<'tcx>,
-    pub value: V,
 }
 
 pub type CanonicalVarInfos<'tcx> = &'tcx List<CanonicalVarInfo<'tcx>>;

compiler/rustc_middle/src/traits/solve.rs

@@ -20,8 +20,8 @@ pub type EvaluationCache<'tcx> = Cache<CanonicalGoal<'tcx>, QueryResult<'tcx>>;
 /// we're currently typechecking while the `predicate` is some trait bound.
 #[derive(Debug, PartialEq, Eq, Clone, Copy, Hash, TypeFoldable, TypeVisitable)]
 pub struct Goal<'tcx, P> {
-    pub param_env: ty::ParamEnv<'tcx>,
     pub predicate: P,
+    pub param_env: ty::ParamEnv<'tcx>,
 }
 
 impl<'tcx, P> Goal<'tcx, P> {
@@ -41,10 +41,10 @@ impl<'tcx, P> Goal<'tcx, P> {
 
 #[derive(Debug, PartialEq, Eq, Clone, Copy, Hash, TypeFoldable, TypeVisitable)]
 pub struct Response<'tcx> {
+    pub certainty: Certainty,
     pub var_values: CanonicalVarValues<'tcx>,
     /// Additional constraints returned by this query.
     pub external_constraints: ExternalConstraints<'tcx>,
-    pub certainty: Certainty,
 }
 
 #[derive(Debug, PartialEq, Eq, Clone, Copy, Hash, TypeFoldable, TypeVisitable)]