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use crate::errors::AutoDerefReachedRecursionLimit;
use crate::traits::query::evaluate_obligation::InferCtxtExt;
use crate::traits::{self, TraitEngine};
use rustc_hir as hir;
use rustc_infer::infer::InferCtxt;
use rustc_middle::ty::{self, TraitRef, Ty, TyCtxt};
use rustc_middle::ty::{ToPredicate, TypeVisitable};
use rustc_session::Limit;
use rustc_span::def_id::LOCAL_CRATE;
use rustc_span::Span;
#[derive(Copy, Clone, Debug)]
pub enum AutoderefKind {
Builtin,
Overloaded,
}
struct AutoderefSnapshot<'tcx> {
at_start: bool,
reached_recursion_limit: bool,
steps: Vec<(Ty<'tcx>, AutoderefKind)>,
cur_ty: Ty<'tcx>,
obligations: Vec<traits::PredicateObligation<'tcx>>,
}
pub struct Autoderef<'a, 'tcx> {
// Meta infos:
infcx: &'a InferCtxt<'a, 'tcx>,
span: Span,
overloaded_span: Span,
body_id: hir::HirId,
param_env: ty::ParamEnv<'tcx>,
// Current state:
state: AutoderefSnapshot<'tcx>,
// Configurations:
include_raw_pointers: bool,
silence_errors: bool,
}
impl<'a, 'tcx> Iterator for Autoderef<'a, 'tcx> {
type Item = (Ty<'tcx>, usize);
fn next(&mut self) -> Option<Self::Item> {
let tcx = self.infcx.tcx;
debug!("autoderef: steps={:?}, cur_ty={:?}", self.state.steps, self.state.cur_ty);
if self.state.at_start {
self.state.at_start = false;
debug!("autoderef stage #0 is {:?}", self.state.cur_ty);
return Some((self.state.cur_ty, 0));
}
// If we have reached the recursion limit, error gracefully.
if !tcx.recursion_limit().value_within_limit(self.state.steps.len()) {
if !self.silence_errors {
report_autoderef_recursion_limit_error(tcx, self.span, self.state.cur_ty);
}
self.state.reached_recursion_limit = true;
return None;
}
if self.state.cur_ty.is_ty_var() {
return None;
}
// Otherwise, deref if type is derefable:
let (kind, new_ty) =
if let Some(mt) = self.state.cur_ty.builtin_deref(self.include_raw_pointers) {
(AutoderefKind::Builtin, mt.ty)
} else if let Some(ty) = self.overloaded_deref_ty(self.state.cur_ty) {
(AutoderefKind::Overloaded, ty)
} else {
return None;
};
if new_ty.references_error() {
return None;
}
self.state.steps.push((self.state.cur_ty, kind));
debug!(
"autoderef stage #{:?} is {:?} from {:?}",
self.step_count(),
new_ty,
(self.state.cur_ty, kind)
);
self.state.cur_ty = new_ty;
Some((self.state.cur_ty, self.step_count()))
}
}
impl<'a, 'tcx> Autoderef<'a, 'tcx> {
pub fn new(
infcx: &'a InferCtxt<'a, 'tcx>,
param_env: ty::ParamEnv<'tcx>,
body_id: hir::HirId,
span: Span,
base_ty: Ty<'tcx>,
overloaded_span: Span,
) -> Autoderef<'a, 'tcx> {
Autoderef {
infcx,
span,
overloaded_span,
body_id,
param_env,
state: AutoderefSnapshot {
steps: vec![],
cur_ty: infcx.resolve_vars_if_possible(base_ty),
obligations: vec![],
at_start: true,
reached_recursion_limit: false,
},
include_raw_pointers: false,
silence_errors: false,
}
}
fn overloaded_deref_ty(&mut self, ty: Ty<'tcx>) -> Option<Ty<'tcx>> {
debug!("overloaded_deref_ty({:?})", ty);
let tcx = self.infcx.tcx;
// <ty as Deref>
let trait_ref = TraitRef {
def_id: tcx.lang_items().deref_trait()?,
substs: tcx.mk_substs_trait(ty, &[]),
};
let cause = traits::ObligationCause::misc(self.span, self.body_id);
let obligation = traits::Obligation::new(
cause.clone(),
self.param_env,
ty::Binder::dummy(trait_ref).without_const().to_predicate(tcx),
);
if !self.infcx.predicate_may_hold(&obligation) {
debug!("overloaded_deref_ty: cannot match obligation");
return None;
}
let mut fulfillcx = traits::FulfillmentContext::new_in_snapshot();
let normalized_ty = fulfillcx.normalize_projection_type(
&self.infcx,
self.param_env,
ty::ProjectionTy {
item_def_id: tcx.lang_items().deref_target()?,
substs: trait_ref.substs,
},
cause,
);
let errors = fulfillcx.select_where_possible(&self.infcx);
if !errors.is_empty() {
// This shouldn't happen, except for evaluate/fulfill mismatches,
// but that's not a reason for an ICE (`predicate_may_hold` is conservative
// by design).
debug!("overloaded_deref_ty: encountered errors {:?} while fulfilling", errors);
return None;
}
let obligations = fulfillcx.pending_obligations();
debug!("overloaded_deref_ty({:?}) = ({:?}, {:?})", ty, normalized_ty, obligations);
self.state.obligations.extend(obligations);
Some(self.infcx.resolve_vars_if_possible(normalized_ty))
}
/// Returns the final type we ended up with, which may be an inference
/// variable (we will resolve it first, if we want).
pub fn final_ty(&self, resolve: bool) -> Ty<'tcx> {
if resolve {
self.infcx.resolve_vars_if_possible(self.state.cur_ty)
} else {
self.state.cur_ty
}
}
pub fn step_count(&self) -> usize {
self.state.steps.len()
}
pub fn into_obligations(self) -> Vec<traits::PredicateObligation<'tcx>> {
self.state.obligations
}
pub fn steps(&self) -> &[(Ty<'tcx>, AutoderefKind)] {
&self.state.steps
}
pub fn span(&self) -> Span {
self.span
}
pub fn overloaded_span(&self) -> Span {
self.overloaded_span
}
pub fn reached_recursion_limit(&self) -> bool {
self.state.reached_recursion_limit
}
/// also dereference through raw pointer types
/// e.g., assuming ptr_to_Foo is the type `*const Foo`
/// fcx.autoderef(span, ptr_to_Foo) => [*const Foo]
/// fcx.autoderef(span, ptr_to_Foo).include_raw_ptrs() => [*const Foo, Foo]
pub fn include_raw_pointers(mut self) -> Self {
self.include_raw_pointers = true;
self
}
pub fn silence_errors(mut self) -> Self {
self.silence_errors = true;
self
}
}
pub fn report_autoderef_recursion_limit_error<'tcx>(tcx: TyCtxt<'tcx>, span: Span, ty: Ty<'tcx>) {
// We've reached the recursion limit, error gracefully.
let suggested_limit = match tcx.recursion_limit() {
Limit(0) => Limit(2),
limit => limit * 2,
};
tcx.sess.emit_err(AutoDerefReachedRecursionLimit {
span,
ty,
suggested_limit,
crate_name: tcx.crate_name(LOCAL_CRATE),
});
}
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