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use crate::infer::canonical::OriginalQueryValues;
use crate::infer::InferCtxt;
use crate::traits::{
EvaluationResult, OverflowError, PredicateObligation, SelectionContext, TraitQueryMode,
};
pub trait InferCtxtExt<'tcx> {
fn predicate_may_hold(&self, obligation: &PredicateObligation<'tcx>) -> bool;
fn predicate_must_hold_considering_regions(
&self,
obligation: &PredicateObligation<'tcx>,
) -> bool;
fn predicate_must_hold_modulo_regions(&self, obligation: &PredicateObligation<'tcx>) -> bool;
fn evaluate_obligation(
&self,
obligation: &PredicateObligation<'tcx>,
) -> Result<EvaluationResult, OverflowError>;
// Helper function that canonicalizes and runs the query. If an
// overflow results, we re-run it in the local context so we can
// report a nice error.
/*crate*/
fn evaluate_obligation_no_overflow(
&self,
obligation: &PredicateObligation<'tcx>,
) -> EvaluationResult;
}
impl<'cx, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'cx, 'tcx> {
/// Evaluates whether the predicate can be satisfied (by any means)
/// in the given `ParamEnv`.
fn predicate_may_hold(&self, obligation: &PredicateObligation<'tcx>) -> bool {
self.evaluate_obligation_no_overflow(obligation).may_apply()
}
/// Evaluates whether the predicate can be satisfied in the given
/// `ParamEnv`, and returns `false` if not certain. However, this is
/// not entirely accurate if inference variables are involved.
///
/// This version may conservatively fail when outlives obligations
/// are required.
fn predicate_must_hold_considering_regions(
&self,
obligation: &PredicateObligation<'tcx>,
) -> bool {
self.evaluate_obligation_no_overflow(obligation).must_apply_considering_regions()
}
/// Evaluates whether the predicate can be satisfied in the given
/// `ParamEnv`, and returns `false` if not certain. However, this is
/// not entirely accurate if inference variables are involved.
///
/// This version ignores all outlives constraints.
fn predicate_must_hold_modulo_regions(&self, obligation: &PredicateObligation<'tcx>) -> bool {
self.evaluate_obligation_no_overflow(obligation).must_apply_modulo_regions()
}
/// Evaluate a given predicate, capturing overflow and propagating it back.
fn evaluate_obligation(
&self,
obligation: &PredicateObligation<'tcx>,
) -> Result<EvaluationResult, OverflowError> {
let mut _orig_values = OriginalQueryValues::default();
let c_pred = self
.canonicalize_query(&obligation.param_env.and(obligation.predicate), &mut _orig_values);
// Run canonical query. If overflow occurs, rerun from scratch but this time
// in standard trait query mode so that overflow is handled appropriately
// within `SelectionContext`.
self.tcx.evaluate_obligation(c_pred)
}
// Helper function that canonicalizes and runs the query. If an
// overflow results, we re-run it in the local context so we can
// report a nice error.
fn evaluate_obligation_no_overflow(
&self,
obligation: &PredicateObligation<'tcx>,
) -> EvaluationResult {
match self.evaluate_obligation(obligation) {
Ok(result) => result,
Err(OverflowError) => {
let mut selcx = SelectionContext::with_query_mode(&self, TraitQueryMode::Standard);
selcx.evaluate_root_obligation(obligation).unwrap_or_else(|r| {
span_bug!(
obligation.cause.span,
"Overflow should be caught earlier in standard query mode: {:?}, {:?}",
obligation,
r,
)
})
}
}
}
}
|
