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Rollup merge of #112443 - compiler-errors:next-solver-opportunistically-resolve-regions, r=lcnr

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Opportunistically resolve regions in new solver

Use `opportunistic_resolve_var` during canonicalization to collapse some regions.

We have to start using `CanonicalVarValues::is_identity_modulo_regions`. We also have to modify that function to consider responses like `['static, ^0, '^1, ^2]` to be an "identity" response, since because we opportunistically resolve regions, there's no longer a 1:1 mapping between canonical var values and bound var indices in the response...

There's one nasty side-effect -- one test (`tests/ui/dyn-star/param-env-infer.rs`) starts to ICE because the certainty goes from `Yes` to `Maybe(Overflow)`... Not exactly sure why, though? Putting this up for discussion/investigation.

r? ```@lcnr```
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Dylan DPC 2023-06-16 14:46:15 +05:30 • committed by GitHub
commit 64f6c00772
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4 changed files with 75 additions and 11 deletions
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41
compiler/rustc_middle/src/infer/canonical.rs
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@ -82,15 +82,40 @@ impl CanonicalVarValues<'_> {
}
pub fn is_identity_modulo_regions(&self) -> bool {
self.var_values.iter().enumerate().all(|(bv, arg)| match arg.unpack() {
ty::GenericArgKind::Lifetime(_) => true,
ty::GenericArgKind::Type(ty) => {
matches!(*ty.kind(), ty::Bound(ty::INNERMOST, bt) if bt.var.as_usize() == bv)
let mut var = ty::BoundVar::from_u32(0);
for arg in self.var_values {
match arg.unpack() {
ty::GenericArgKind::Lifetime(r) => {
if let ty::ReLateBound(ty::INNERMOST, br) = *r
&& var == br.var
{
var = var + 1;
} else {
// It's ok if this region var isn't unique
}
},
ty::GenericArgKind::Type(ty) => {
if let ty::Bound(ty::INNERMOST, bt) = *ty.kind()
&& var == bt.var
{
var = var + 1;
} else {
return false;
}
}
ty::GenericArgKind::Const(ct) => {
if let ty::ConstKind::Bound(ty::INNERMOST, bc) = ct.kind()
&& var == bc
{
var = var + 1;
} else {
return false;
}
}
}
ty::GenericArgKind::Const(ct) => {
matches!(ct.kind(), ty::ConstKind::Bound(ty::INNERMOST, bc) if bc.as_usize() == bv)
}
})
}
true
}
}