Auto merge of #145951 - lcnr:proof-tree-as-query, r=compiler-errors

cleanup and cache proof tree building

There's some cruft left over from when we had deep proof trees. We never encounter overflow when evaluating proof trees. Even if the recursion limit is `0`, we still only hit the overflow limit when evaluating nested goals of the root. The root goal simply inherits the `root_depth` of the `SearchGraph`.

Split `evaluate_root_goal_for_proof_tree` from the rest of the trait solver. This enables us to simplify the implementation of `evaluate_goal_raw` and the `ProofTreeBuilder` as we no longer need to manually track the state of the builder and can instead use separate types for that. It does require making a few internal methods into associated functions taking a `delegate` and a `span` instead of the `EvalCtxt` itself.

I've also split `SearchGraph::evaluate_goal` and `SearchGraph::evaluate_root_goal_for_proof_tree` for the same reason. Both functions don't actually share too much code, so by splitting them each version gets significantly easier to read.

Add a `query evaluate_root_goal_for_proof_tree_raw` to cache proof tree building. This requires arena allocating `inspect::Probe`. I've added a new type alias `I::ProbeRef` for this. We may need to adapt this for rust-analyzer? It would definitely be easy to remove the `Copy` bound here :thinking:

1 files changed, 2 insertions, 1 deletions

diff --git a/compiler/rustc_interface/src/passes.rs b/compiler/rustc_interface/src/passes.rs
index bc5ef04079e..ca8c10311fb 100644
--- a/compiler/rustc_interface/src/passes.rs
+++ b/compiler/rustc_interface/src/passes.rs
@@ -41,7 +41,7 @@ use rustc_span::{
     Symbol, sym,
 };
 use rustc_target::spec::PanicStrategy;
-use rustc_trait_selection::traits;
+use rustc_trait_selection::{solve, traits};
 use tracing::{info, instrument};
 
 use crate::interface::Compiler;
@@ -895,6 +895,7 @@ pub static DEFAULT_QUERY_PROVIDERS: LazyLock<Providers> = LazyLock::new(|| {
     rustc_hir_typeck::provide(providers);
     ty::provide(providers);
     traits::provide(providers);
+    solve::provide(providers);
     rustc_passes::provide(providers);
     rustc_traits::provide(providers);
     rustc_ty_utils::provide(providers);