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use crate::infer::canonical::query_response;
use crate::infer::{InferCtxt, InferOk};
use crate::traits::query::type_op::TypeOpOutput;
use crate::traits::query::Fallible;
use crate::traits::ObligationCtxt;
use rustc_infer::infer::region_constraints::RegionConstraintData;
use rustc_span::source_map::DUMMY_SP;
use std::fmt;
pub struct CustomTypeOp<F, G> {
closure: F,
description: G,
}
impl<F, G> CustomTypeOp<F, G> {
pub fn new<'tcx, R>(closure: F, description: G) -> Self
where
F: FnOnce(&InferCtxt<'tcx>) -> Fallible<InferOk<'tcx, R>>,
G: Fn() -> String,
{
CustomTypeOp { closure, description }
}
}
impl<'tcx, F, R: fmt::Debug, G> super::TypeOp<'tcx> for CustomTypeOp<F, G>
where
F: for<'a, 'cx> FnOnce(&'a InferCtxt<'tcx>) -> Fallible<InferOk<'tcx, R>>,
G: Fn() -> String,
{
type Output = R;
/// We can't do any custom error reporting for `CustomTypeOp`, so
/// we can use `!` to enforce that the implementation never provides it.
type ErrorInfo = !;
/// Processes the operation and all resulting obligations,
/// returning the final result along with any region constraints
/// (they will be given over to the NLL region solver).
fn fully_perform(self, infcx: &InferCtxt<'tcx>) -> Fallible<TypeOpOutput<'tcx, Self>> {
if cfg!(debug_assertions) {
info!("fully_perform({:?})", self);
}
Ok(scrape_region_constraints(infcx, || (self.closure)(infcx))?.0)
}
}
impl<F, G> fmt::Debug for CustomTypeOp<F, G>
where
G: Fn() -> String,
{
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
write!(f, "{}", (self.description)())
}
}
/// Executes `op` and then scrapes out all the "old style" region
/// constraints that result, creating query-region-constraints.
pub fn scrape_region_constraints<'tcx, Op: super::TypeOp<'tcx, Output = R>, R>(
infcx: &InferCtxt<'tcx>,
op: impl FnOnce() -> Fallible<InferOk<'tcx, R>>,
) -> Fallible<(TypeOpOutput<'tcx, Op>, RegionConstraintData<'tcx>)> {
// During NLL, we expect that nobody will register region
// obligations **except** as part of a custom type op (and, at the
// end of each custom type op, we scrape out the region
// obligations that resulted). So this vector should be empty on
// entry.
let pre_obligations = infcx.take_registered_region_obligations();
assert!(
pre_obligations.is_empty(),
"scrape_region_constraints: incoming region obligations = {:#?}",
pre_obligations,
);
let InferOk { value, obligations } = infcx.commit_if_ok(|_| op())?;
let ocx = ObligationCtxt::new(infcx);
ocx.register_obligations(obligations);
let errors = ocx.select_all_or_error();
if !errors.is_empty() {
infcx.tcx.sess.diagnostic().delay_span_bug(
DUMMY_SP,
&format!("errors selecting obligation during MIR typeck: {:?}", errors),
);
}
let region_obligations = infcx.take_registered_region_obligations();
let region_constraint_data = infcx.take_and_reset_region_constraints();
let region_constraints = query_response::make_query_region_constraints(
infcx.tcx,
region_obligations
.iter()
.map(|r_o| (r_o.sup_type, r_o.sub_region, r_o.origin.to_constraint_category()))
.map(|(ty, r, cc)| (infcx.resolve_vars_if_possible(ty), r, cc)),
®ion_constraint_data,
);
if region_constraints.is_empty() {
Ok((
TypeOpOutput { output: value, constraints: None, error_info: None },
region_constraint_data,
))
} else {
Ok((
TypeOpOutput {
output: value,
constraints: Some(infcx.tcx.arena.alloc(region_constraints)),
error_info: None,
},
region_constraint_data,
))
}
}
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