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Auto merge of #117278 - lcnr:try-normalize-ty, r=compiler-errors

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new solver normalization improvements

cool beans

At the core of this PR is a `try_normalize_ty` which stops for rigid aliases by using `commit_if_ok`.

Reworks alias-relate to fully normalize both the lhs and rhs and then equate the resulting rigid (or inference) types. This fixes https://github.com/rust-lang/trait-system-refactor-initiative/issues/68 by avoiding the exponential blowup. Also supersedes #116369 by only defining opaque types if the hidden type is rigid.

I removed the stability check in `EvalCtxt::evaluate_goal` due to https://github.com/rust-lang/trait-system-refactor-initiative/issues/75. While I personally have opinions on how to fix it, that still requires further t-types/`@nikomatsakis` buy-in, so I removed that for now. Once we've decided on our approach there, we can revert this commit.

r? `@compiler-errors`
This commit is contained in:
bors 2023-11-17 10:16:41 +00:00
commit 78efca8845
30 changed files with 411 additions and 317 deletions
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17
compiler/rustc_trait_selection/src/solve/assembly/mod.rs
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@ -352,7 +352,7 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
let &ty::Alias(_, projection_ty) = goal.predicate.self_ty().kind() else { return };
candidates.extend(self.probe(|_| ProbeKind::NormalizedSelfTyAssembly).enter(|ecx| {
if num_steps < ecx.local_overflow_limit() {
if tcx.recursion_limit().value_within_limit(num_steps) {
let normalized_ty = ecx.next_ty_infer();
let normalizes_to_goal = goal.with(
tcx,
@ -864,23 +864,18 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
let result = self.probe_misc_candidate("coherence unknowable").enter(|ecx| {
let trait_ref = goal.predicate.trait_ref(tcx);
#[derive(Debug)]
enum FailureKind {
Overflow,
NoSolution(NoSolution),
}
struct Overflow;
let lazily_normalize_ty = |ty| match ecx.try_normalize_ty(goal.param_env, ty) {
Ok(Some(ty)) => Ok(ty),
Ok(None) => Err(FailureKind::Overflow),
Err(e) => Err(FailureKind::NoSolution(e)),
Some(ty) => Ok(ty),
None => Err(Overflow),
};
match coherence::trait_ref_is_knowable(tcx, trait_ref, lazily_normalize_ty) {
Err(FailureKind::Overflow) => {
Err(Overflow) => {
ecx.evaluate_added_goals_and_make_canonical_response(Certainty::OVERFLOW)
}
Err(FailureKind::NoSolution(NoSolution)) | Ok(Ok(())) => Err(NoSolution),
Ok(Ok(())) => Err(NoSolution),
Ok(Err(_)) => {
ecx.evaluate_added_goals_and_make_canonical_response(Certainty::AMBIGUOUS)
}