rustc_trait_selection/infer.rs
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use std::fmt::Debug;
use rustc_hir::def_id::DefId;
use rustc_hir::lang_items::LangItem;
pub use rustc_infer::infer::*;
use rustc_macros::extension;
use rustc_middle::arena::ArenaAllocatable;
use rustc_middle::infer::canonical::{
Canonical, CanonicalQueryInput, CanonicalQueryResponse, QueryResponse,
};
use rustc_middle::traits::query::NoSolution;
use rustc_middle::ty::{self, GenericArg, Ty, TyCtxt, TypeFoldable, TypeVisitableExt, Upcast};
use rustc_span::DUMMY_SP;
use tracing::instrument;
use crate::infer::at::ToTrace;
use crate::traits::query::evaluate_obligation::InferCtxtExt as _;
use crate::traits::{self, Obligation, ObligationCause, ObligationCtxt, SelectionContext};
#[extension(pub trait InferCtxtExt<'tcx>)]
impl<'tcx> InferCtxt<'tcx> {
fn can_eq<T: ToTrace<'tcx>>(&self, param_env: ty::ParamEnv<'tcx>, a: T, b: T) -> bool {
self.probe(|_| {
let ocx = ObligationCtxt::new(self);
let Ok(()) = ocx.eq(&ObligationCause::dummy(), param_env, a, b) else {
return false;
};
ocx.select_where_possible().is_empty()
})
}
fn type_is_copy_modulo_regions(&self, param_env: ty::ParamEnv<'tcx>, ty: Ty<'tcx>) -> bool {
let ty = self.resolve_vars_if_possible(ty);
if !(param_env, ty).has_infer() {
return ty.is_copy_modulo_regions(self.tcx, param_env);
}
let copy_def_id = self.tcx.require_lang_item(LangItem::Copy, None);
// This can get called from typeck (by euv), and `moves_by_default`
// rightly refuses to work with inference variables, but
// moves_by_default has a cache, which we want to use in other
// cases.
traits::type_known_to_meet_bound_modulo_regions(self, param_env, ty, copy_def_id)
}
fn type_is_sized_modulo_regions(&self, param_env: ty::ParamEnv<'tcx>, ty: Ty<'tcx>) -> bool {
let lang_item = self.tcx.require_lang_item(LangItem::Sized, None);
traits::type_known_to_meet_bound_modulo_regions(self, param_env, ty, lang_item)
}
/// Check whether a `ty` implements given trait(trait_def_id) without side-effects.
///
/// The inputs are:
///
/// - the def-id of the trait
/// - the type parameters of the trait, including the self-type
/// - the parameter environment
///
/// Invokes `evaluate_obligation`, so in the event that evaluating
/// `Ty: Trait` causes overflow, EvaluatedToAmbigStackDependent will be returned.
///
/// `type_implements_trait` is a convenience function for simple cases like
///
/// ```ignore (illustrative)
/// let copy_trait = infcx.tcx.require_lang_item(LangItem::Copy, span);
/// let implements_copy = infcx.type_implements_trait(copy_trait, [ty], param_env)
/// .must_apply_modulo_regions();
/// ```
///
/// In most cases you should instead create an [Obligation] and check whether
/// it holds via [`evaluate_obligation`] or one of its helper functions like
/// [`predicate_must_hold_modulo_regions`], because it properly handles higher ranked traits
/// and it is more convenient and safer when your `params` are inside a [`Binder`].
///
/// [Obligation]: traits::Obligation
/// [`evaluate_obligation`]: crate::traits::query::evaluate_obligation::InferCtxtExt::evaluate_obligation
/// [`predicate_must_hold_modulo_regions`]: crate::traits::query::evaluate_obligation::InferCtxtExt::predicate_must_hold_modulo_regions
/// [`Binder`]: ty::Binder
#[instrument(level = "debug", skip(self, params), ret)]
fn type_implements_trait(
&self,
trait_def_id: DefId,
params: impl IntoIterator<Item: Into<GenericArg<'tcx>>>,
param_env: ty::ParamEnv<'tcx>,
) -> traits::EvaluationResult {
let trait_ref = ty::TraitRef::new(self.tcx, trait_def_id, params);
let obligation = traits::Obligation {
cause: traits::ObligationCause::dummy(),
param_env,
recursion_depth: 0,
predicate: trait_ref.upcast(self.tcx),
};
self.evaluate_obligation(&obligation).unwrap_or(traits::EvaluationResult::EvaluatedToErr)
}
/// Returns `Some` if a type implements a trait shallowly, without side-effects,
/// along with any errors that would have been reported upon further obligation
/// processing.
///
/// - If this returns `Some([])`, then the trait holds modulo regions.
/// - If this returns `Some([errors..])`, then the trait has an impl for
/// the self type, but some nested obligations do not hold.
/// - If this returns `None`, no implementation that applies could be found.
///
/// FIXME(-Znext-solver): Due to the recursive nature of the new solver,
/// this will probably only ever return `Some([])` or `None`.
fn type_implements_trait_shallow(
&self,
trait_def_id: DefId,
ty: Ty<'tcx>,
param_env: ty::ParamEnv<'tcx>,
) -> Option<Vec<traits::FulfillmentError<'tcx>>> {
self.probe(|_snapshot| {
let mut selcx = SelectionContext::new(self);
match selcx.select(&Obligation::new(
self.tcx,
ObligationCause::dummy(),
param_env,
ty::TraitRef::new(self.tcx, trait_def_id, [ty]),
)) {
Ok(Some(selection)) => {
let ocx = ObligationCtxt::new_with_diagnostics(self);
ocx.register_obligations(selection.nested_obligations());
Some(ocx.select_all_or_error())
}
Ok(None) | Err(_) => None,
}
})
}
}
#[extension(pub trait InferCtxtBuilderExt<'tcx>)]
impl<'tcx> InferCtxtBuilder<'tcx> {
/// The "main method" for a canonicalized trait query. Given the
/// canonical key `canonical_key`, this method will create a new
/// inference context, instantiate the key, and run your operation
/// `op`. The operation should yield up a result (of type `R`) as
/// well as a set of trait obligations that must be fully
/// satisfied. These obligations will be processed and the
/// canonical result created.
///
/// Returns `NoSolution` in the event of any error.
///
/// (It might be mildly nicer to implement this on `TyCtxt`, and
/// not `InferCtxtBuilder`, but that is a bit tricky right now.
/// In part because we would need a `for<'tcx>` sort of
/// bound for the closure and in part because it is convenient to
/// have `'tcx` be free on this function so that we can talk about
/// `K: TypeFoldable<TyCtxt<'tcx>>`.)
fn enter_canonical_trait_query<K, R>(
self,
canonical_key: &CanonicalQueryInput<'tcx, K>,
operation: impl FnOnce(&ObligationCtxt<'_, 'tcx>, K) -> Result<R, NoSolution>,
) -> Result<CanonicalQueryResponse<'tcx, R>, NoSolution>
where
K: TypeFoldable<TyCtxt<'tcx>>,
R: Debug + TypeFoldable<TyCtxt<'tcx>>,
Canonical<'tcx, QueryResponse<'tcx, R>>: ArenaAllocatable<'tcx>,
{
let (infcx, key, canonical_inference_vars) =
self.build_with_canonical(DUMMY_SP, canonical_key);
let ocx = ObligationCtxt::new(&infcx);
let value = operation(&ocx, key)?;
ocx.make_canonicalized_query_response(canonical_inference_vars, value)
}
}