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Rollup merge of #95179 - b-naber:eval-in-try-unify, r=lcnr

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Try to evaluate in try unify and postpone resolution of constants that contain inference variables

We want code like that in [`ui/const-generics/generic_const_exprs/eval-try-unify.rs`](https://github.com/rust-lang/rust/compare/master...b-naber:eval-in-try-unify?expand=1#diff-8027038201cf07a6c96abf3cbf0b0f4fdd8a64ce6292435f01c8ed995b87fe9b) to compile. To do that we need to try to evaluate constants in `try_unify_abstract_consts`, this requires us to be more careful about what constants we try to resolve, specifically we cannot try to resolve constants that still contain inference variables.

r? `@lcnr`
This commit is contained in:
Dylan DPC 2022-03-25 01:34:30 +01:00 • committed by GitHub
commit 1fcb8fc3e0
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13 changed files with 283 additions and 287 deletions
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28
compiler/rustc_infer/src/infer/mod.rs
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@ -20,8 +20,7 @@ use rustc_hir::def_id::{DefId, LocalDefId};
use rustc_middle::infer::canonical::{Canonical, CanonicalVarValues};
use rustc_middle::infer::unify_key::{ConstVarValue, ConstVariableValue};
use rustc_middle::infer::unify_key::{ConstVariableOrigin, ConstVariableOriginKind, ToType};
use rustc_middle::mir::interpret::ErrorHandled;
use rustc_middle::mir::interpret::EvalToConstValueResult;
use rustc_middle::mir::interpret::{ErrorHandled, EvalToConstValueResult};
use rustc_middle::traits::select;
use rustc_middle::ty::error::{ExpectedFound, TypeError};
use rustc_middle::ty::fold::{TypeFoldable, TypeFolder};
@ -71,7 +70,6 @@ mod sub;
pub mod type_variable;
mod undo_log;
use crate::infer::canonical::OriginalQueryValues;
pub use rustc_middle::infer::unify_key;
#[must_use]
@ -687,15 +685,28 @@ pub struct CombinedSnapshot<'a, 'tcx> {
impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
/// calls `tcx.try_unify_abstract_consts` after
/// canonicalizing the consts.
#[instrument(skip(self), level = "debug")]
pub fn try_unify_abstract_consts(
&self,
a: ty::Unevaluated<'tcx, ()>,
b: ty::Unevaluated<'tcx, ()>,
param_env: ty::ParamEnv<'tcx>,
) -> bool {
let canonical = self.canonicalize_query((a, b), &mut OriginalQueryValues::default());
debug!("canonical consts: {:?}", &canonical.value);
// Reject any attempt to unify two unevaluated constants that contain inference
// variables, since inference variables in queries lead to ICEs.
if a.substs.has_infer_types_or_consts()
|| b.substs.has_infer_types_or_consts()
|| param_env.has_infer_types_or_consts()
{
debug!("a or b or param_env contain infer vars in its substs -> cannot unify");
return false;
}
self.tcx.try_unify_abstract_consts(canonical.value)
let param_env_and = param_env.and((a, b));
let erased = self.tcx.erase_regions(param_env_and);
debug!("after erase_regions: {:?}", erased);
self.tcx.try_unify_abstract_consts(erased)
}
pub fn is_in_snapshot(&self) -> bool {
@ -1598,6 +1609,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
///
/// This handles inferences variables within both `param_env` and `substs` by
/// performing the operation on their respective canonical forms.
#[instrument(skip(self), level = "debug")]
pub fn const_eval_resolve(
&self,
param_env: ty::ParamEnv<'tcx>,
@ -1605,15 +1617,19 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
span: Option<Span>,
) -> EvalToConstValueResult<'tcx> {
let substs = self.resolve_vars_if_possible(unevaluated.substs);
debug!(?substs);
// Postpone the evaluation of constants whose substs depend on inference
// variables
if substs.has_infer_types_or_consts() {
debug!("substs have infer types or consts: {:?}", substs);
return Err(ErrorHandled::TooGeneric);
}
let param_env_erased = self.tcx.erase_regions(param_env);
let substs_erased = self.tcx.erase_regions(substs);
debug!(?param_env_erased);
debug!(?substs_erased);
let unevaluated = ty::Unevaluated {
def: unevaluated.def,