/
project.rs
928 lines (828 loc) · 34.4 KB
/
project.rs
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// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
//! Code for projecting associated types out of trait references.
use super::elaborate_predicates;
use super::report_overflow_error;
use super::Obligation;
use super::ObligationCause;
use super::PredicateObligation;
use super::SelectionContext;
use super::SelectionError;
use super::VtableImplData;
use super::util;
use middle::infer;
use middle::subst::{Subst, Substs};
use middle::ty::{self, AsPredicate, ReferencesError, RegionEscape,
HasProjectionTypes, ToPolyTraitRef, Ty};
use middle::ty_fold::{self, TypeFoldable, TypeFolder};
use std::rc::Rc;
use syntax::ast;
use syntax::parse::token;
use util::common::FN_OUTPUT_NAME;
use util::ppaux::Repr;
pub type PolyProjectionObligation<'tcx> =
Obligation<'tcx, ty::PolyProjectionPredicate<'tcx>>;
pub type ProjectionObligation<'tcx> =
Obligation<'tcx, ty::ProjectionPredicate<'tcx>>;
pub type ProjectionTyObligation<'tcx> =
Obligation<'tcx, ty::ProjectionTy<'tcx>>;
/// When attempting to resolve `<T as TraitRef>::Name` ...
pub enum ProjectionTyError<'tcx> {
/// ...we found multiple sources of information and couldn't resolve the ambiguity.
TooManyCandidates,
/// ...an error occurred matching `T : TraitRef`
TraitSelectionError(SelectionError<'tcx>),
}
#[derive(Clone)]
pub struct MismatchedProjectionTypes<'tcx> {
pub err: ty::type_err<'tcx>
}
#[derive(PartialEq, Eq)]
enum ProjectionTyCandidate<'tcx> {
ParamEnv(ty::PolyProjectionPredicate<'tcx>),
Impl(VtableImplData<'tcx, PredicateObligation<'tcx>>),
Closure(ast::DefId, Substs<'tcx>),
FnPointer(Ty<'tcx>),
}
struct ProjectionTyCandidateSet<'tcx> {
vec: Vec<ProjectionTyCandidate<'tcx>>,
ambiguous: bool
}
/// Evaluates constraints of the form:
///
/// for<...> <T as Trait>::U == V
///
/// If successful, this may result in additional obligations.
pub fn poly_project_and_unify_type<'cx,'tcx>(
selcx: &mut SelectionContext<'cx,'tcx>,
obligation: &PolyProjectionObligation<'tcx>)
-> Result<Option<Vec<PredicateObligation<'tcx>>>, MismatchedProjectionTypes<'tcx>>
{
debug!("poly_project_and_unify_type(obligation={})",
obligation.repr(selcx.tcx()));
let infcx = selcx.infcx();
infcx.try(|snapshot| {
let (skol_predicate, skol_map) =
infcx.skolemize_late_bound_regions(&obligation.predicate, snapshot);
let skol_obligation = obligation.with(skol_predicate);
match project_and_unify_type(selcx, &skol_obligation) {
Ok(result) => {
match infcx.leak_check(&skol_map, snapshot) {
Ok(()) => Ok(infcx.plug_leaks(skol_map, snapshot, &result)),
Err(e) => Err(MismatchedProjectionTypes { err: e }),
}
}
Err(e) => {
Err(e)
}
}
})
}
/// Evaluates constraints of the form:
///
/// <T as Trait>::U == V
///
/// If successful, this may result in additional obligations.
fn project_and_unify_type<'cx,'tcx>(
selcx: &mut SelectionContext<'cx,'tcx>,
obligation: &ProjectionObligation<'tcx>)
-> Result<Option<Vec<PredicateObligation<'tcx>>>, MismatchedProjectionTypes<'tcx>>
{
debug!("project_and_unify_type(obligation={})",
obligation.repr(selcx.tcx()));
let Normalized { value: normalized_ty, obligations } =
match opt_normalize_projection_type(selcx,
obligation.predicate.projection_ty.clone(),
obligation.cause.clone(),
obligation.recursion_depth) {
Some(n) => n,
None => {
consider_unification_despite_ambiguity(selcx, obligation);
return Ok(None);
}
};
debug!("project_and_unify_type: normalized_ty={} obligations={}",
normalized_ty.repr(selcx.tcx()),
obligations.repr(selcx.tcx()));
let infcx = selcx.infcx();
let origin = infer::RelateOutputImplTypes(obligation.cause.span);
match infer::mk_eqty(infcx, true, origin, normalized_ty, obligation.predicate.ty) {
Ok(()) => Ok(Some(obligations)),
Err(err) => Err(MismatchedProjectionTypes { err: err }),
}
}
fn consider_unification_despite_ambiguity<'cx,'tcx>(selcx: &mut SelectionContext<'cx,'tcx>,
obligation: &ProjectionObligation<'tcx>) {
debug!("consider_unification_despite_ambiguity(obligation={})",
obligation.repr(selcx.tcx()));
let def_id = obligation.predicate.projection_ty.trait_ref.def_id;
match selcx.tcx().lang_items.fn_trait_kind(def_id) {
Some(_) => { }
None => { return; }
}
let infcx = selcx.infcx();
let self_ty = obligation.predicate.projection_ty.trait_ref.self_ty();
let self_ty = infcx.shallow_resolve(self_ty);
debug!("consider_unification_despite_ambiguity: self_ty.sty={:?}",
self_ty.sty);
match self_ty.sty {
ty::ty_closure(closure_def_id, substs) => {
let closure_typer = selcx.closure_typer();
let closure_type = closure_typer.closure_type(closure_def_id, substs);
let ty::Binder((_, ret_type)) =
util::closure_trait_ref_and_return_type(infcx.tcx,
def_id,
self_ty,
&closure_type.sig,
util::TupleArgumentsFlag::No);
let (ret_type, _) =
infcx.replace_late_bound_regions_with_fresh_var(
obligation.cause.span,
infer::AssocTypeProjection(obligation.predicate.projection_ty.item_name),
&ty::Binder(ret_type));
debug!("consider_unification_despite_ambiguity: ret_type={:?}",
ret_type.repr(selcx.tcx()));
let origin = infer::RelateOutputImplTypes(obligation.cause.span);
let obligation_ty = obligation.predicate.ty;
match infer::mk_eqty(infcx, true, origin, obligation_ty, ret_type) {
Ok(()) => { }
Err(_) => { /* ignore errors */ }
}
}
_ => { }
}
}
/// Normalizes any associated type projections in `value`, replacing
/// them with a fully resolved type where possible. The return value
/// combines the normalized result and any additional obligations that
/// were incurred as result.
pub fn normalize<'a,'b,'tcx,T>(selcx: &'a mut SelectionContext<'b,'tcx>,
cause: ObligationCause<'tcx>,
value: &T)
-> Normalized<'tcx, T>
where T : TypeFoldable<'tcx> + HasProjectionTypes + Clone + Repr<'tcx>
{
normalize_with_depth(selcx, cause, 0, value)
}
/// As `normalize`, but with a custom depth.
pub fn normalize_with_depth<'a,'b,'tcx,T>(selcx: &'a mut SelectionContext<'b,'tcx>,
cause: ObligationCause<'tcx>,
depth: uint,
value: &T)
-> Normalized<'tcx, T>
where T : TypeFoldable<'tcx> + HasProjectionTypes + Clone + Repr<'tcx>
{
let mut normalizer = AssociatedTypeNormalizer::new(selcx, cause, depth);
let result = normalizer.fold(value);
Normalized {
value: result,
obligations: normalizer.obligations,
}
}
struct AssociatedTypeNormalizer<'a,'b:'a,'tcx:'b> {
selcx: &'a mut SelectionContext<'b,'tcx>,
cause: ObligationCause<'tcx>,
obligations: Vec<PredicateObligation<'tcx>>,
depth: uint,
}
impl<'a,'b,'tcx> AssociatedTypeNormalizer<'a,'b,'tcx> {
fn new(selcx: &'a mut SelectionContext<'b,'tcx>,
cause: ObligationCause<'tcx>,
depth: uint)
-> AssociatedTypeNormalizer<'a,'b,'tcx>
{
AssociatedTypeNormalizer {
selcx: selcx,
cause: cause,
obligations: vec!(),
depth: depth,
}
}
fn fold<T:TypeFoldable<'tcx> + HasProjectionTypes + Clone>(&mut self, value: &T) -> T {
let value = self.selcx.infcx().resolve_type_vars_if_possible(value);
if !value.has_projection_types() {
value.clone()
} else {
value.fold_with(self)
}
}
}
impl<'a,'b,'tcx> TypeFolder<'tcx> for AssociatedTypeNormalizer<'a,'b,'tcx> {
fn tcx(&self) -> &ty::ctxt<'tcx> {
self.selcx.tcx()
}
fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
// We don't want to normalize associated types that occur inside of region
// binders, because they may contain bound regions, and we can't cope with that.
//
// Example:
//
// for<'a> fn(<T as Foo<&'a>>::A)
//
// Instead of normalizing `<T as Foo<&'a>>::A` here, we'll
// normalize it when we instantiate those bound regions (which
// should occur eventually).
let ty = ty_fold::super_fold_ty(self, ty);
match ty.sty {
ty::ty_projection(ref data) if !data.has_escaping_regions() => { // (*)
// (*) This is kind of hacky -- we need to be able to
// handle normalization within binders because
// otherwise we wind up a need to normalize when doing
// trait matching (since you can have a trait
// obligation like `for<'a> T::B : Fn(&'a int)`), but
// we can't normalize with bound regions in scope. So
// far now we just ignore binders but only normalize
// if all bound regions are gone (and then we still
// have to renormalize whenever we instantiate a
// binder). It would be better to normalize in a
// binding-aware fashion.
let Normalized { value: ty, obligations } =
normalize_projection_type(self.selcx,
data.clone(),
self.cause.clone(),
self.depth);
self.obligations.extend(obligations.into_iter());
ty
}
_ => {
ty
}
}
}
}
pub struct Normalized<'tcx,T> {
pub value: T,
pub obligations: Vec<PredicateObligation<'tcx>>,
}
pub type NormalizedTy<'tcx> = Normalized<'tcx, Ty<'tcx>>;
impl<'tcx,T> Normalized<'tcx,T> {
pub fn with<U>(self, value: U) -> Normalized<'tcx,U> {
Normalized { value: value, obligations: self.obligations }
}
}
/// The guts of `normalize`: normalize a specific projection like `<T
/// as Trait>::Item`. The result is always a type (and possibly
/// additional obligations). If ambiguity arises, which implies that
/// there are unresolved type variables in the projection, we will
/// substitute a fresh type variable `$X` and generate a new
/// obligation `<T as Trait>::Item == $X` for later.
pub fn normalize_projection_type<'a,'b,'tcx>(
selcx: &'a mut SelectionContext<'b,'tcx>,
projection_ty: ty::ProjectionTy<'tcx>,
cause: ObligationCause<'tcx>,
depth: uint)
-> NormalizedTy<'tcx>
{
opt_normalize_projection_type(selcx, projection_ty.clone(), cause.clone(), depth)
.unwrap_or_else(move || {
// if we bottom out in ambiguity, create a type variable
// and a deferred predicate to resolve this when more type
// information is available.
let ty_var = selcx.infcx().next_ty_var();
let projection = ty::Binder(ty::ProjectionPredicate {
projection_ty: projection_ty,
ty: ty_var
});
let obligation = Obligation::with_depth(cause, depth+1, projection.as_predicate());
Normalized {
value: ty_var,
obligations: vec!(obligation)
}
})
}
/// The guts of `normalize`: normalize a specific projection like `<T
/// as Trait>::Item`. The result is always a type (and possibly
/// additional obligations). Returns `None` in the case of ambiguity,
/// which indicates that there are unbound type variables.
fn opt_normalize_projection_type<'a,'b,'tcx>(
selcx: &'a mut SelectionContext<'b,'tcx>,
projection_ty: ty::ProjectionTy<'tcx>,
cause: ObligationCause<'tcx>,
depth: uint)
-> Option<NormalizedTy<'tcx>>
{
debug!("normalize_projection_type(\
projection_ty={}, \
depth={})",
projection_ty.repr(selcx.tcx()),
depth);
let obligation = Obligation::with_depth(cause.clone(), depth, projection_ty.clone());
match project_type(selcx, &obligation) {
Ok(ProjectedTy::Progress(projected_ty, mut obligations)) => {
// if projection succeeded, then what we get out of this
// is also non-normalized (consider: it was derived from
// an impl, where-clause etc) and hence we must
// re-normalize it
debug!("normalize_projection_type: projected_ty={} depth={} obligations={}",
projected_ty.repr(selcx.tcx()),
depth,
obligations.repr(selcx.tcx()));
if ty::type_has_projection(projected_ty) {
let tcx = selcx.tcx();
let mut normalizer = AssociatedTypeNormalizer::new(selcx, cause, depth);
let normalized_ty = normalizer.fold(&projected_ty);
debug!("normalize_projection_type: normalized_ty={} depth={}",
normalized_ty.repr(tcx),
depth);
obligations.extend(normalizer.obligations.into_iter());
Some(Normalized {
value: normalized_ty,
obligations: obligations,
})
} else {
Some(Normalized {
value: projected_ty,
obligations: obligations,
})
}
}
Ok(ProjectedTy::NoProgress(projected_ty)) => {
Some(Normalized {
value: projected_ty,
obligations: vec!()
})
}
Err(ProjectionTyError::TooManyCandidates) => {
None
}
Err(ProjectionTyError::TraitSelectionError(_)) => {
// if we got an error processing the `T as Trait` part,
// just return `ty::err` but add the obligation `T :
// Trait`, which when processed will cause the error to be
// reported later
Some(normalize_to_error(selcx, projection_ty, cause, depth))
}
}
}
/// in various error cases, we just set ty_err and return an obligation
/// that, when fulfilled, will lead to an error
fn normalize_to_error<'a,'tcx>(selcx: &mut SelectionContext<'a,'tcx>,
projection_ty: ty::ProjectionTy<'tcx>,
cause: ObligationCause<'tcx>,
depth: uint)
-> NormalizedTy<'tcx>
{
let trait_ref = projection_ty.trait_ref.to_poly_trait_ref();
let trait_obligation = Obligation { cause: cause,
recursion_depth: depth,
predicate: trait_ref.as_predicate() };
Normalized {
value: selcx.tcx().types.err,
obligations: vec!(trait_obligation)
}
}
enum ProjectedTy<'tcx> {
Progress(Ty<'tcx>, Vec<PredicateObligation<'tcx>>),
NoProgress(Ty<'tcx>),
}
/// Compute the result of a projection type (if we can).
fn project_type<'cx,'tcx>(
selcx: &mut SelectionContext<'cx,'tcx>,
obligation: &ProjectionTyObligation<'tcx>)
-> Result<ProjectedTy<'tcx>, ProjectionTyError<'tcx>>
{
debug!("project(obligation={})",
obligation.repr(selcx.tcx()));
let recursion_limit = selcx.tcx().sess.recursion_limit.get();
if obligation.recursion_depth >= recursion_limit {
debug!("project: overflow!");
report_overflow_error(selcx.infcx(), &obligation);
}
let obligation_trait_ref =
selcx.infcx().resolve_type_vars_if_possible(&obligation.predicate.trait_ref);
debug!("project: obligation_trait_ref={}", obligation_trait_ref.repr(selcx.tcx()));
if obligation_trait_ref.references_error() {
return Ok(ProjectedTy::Progress(selcx.tcx().types.err, vec!()));
}
let mut candidates = ProjectionTyCandidateSet {
vec: Vec::new(),
ambiguous: false,
};
assemble_candidates_from_param_env(selcx,
obligation,
&obligation_trait_ref,
&mut candidates);
assemble_candidates_from_trait_def(selcx,
obligation,
&obligation_trait_ref,
&mut candidates);
if let Err(e) = assemble_candidates_from_impls(selcx,
obligation,
&obligation_trait_ref,
&mut candidates) {
return Err(ProjectionTyError::TraitSelectionError(e));
}
debug!("{} candidates, ambiguous={}",
candidates.vec.len(),
candidates.ambiguous);
// We probably need some winnowing logic similar to select here.
// Drop duplicates.
//
// Note: `candidates.vec` seems to be on the critical path of the
// compiler. Replacing it with an hash set was also tried, which would
// render the following dedup unnecessary. It led to cleaner code but
// prolonged compiling time of `librustc` from 5m30s to 6m in one test, or
// ~9% performance lost.
if candidates.vec.len() > 1 {
let mut i = 0;
while i < candidates.vec.len() {
let has_dup = (0..i).any(|j| candidates.vec[i] == candidates.vec[j]);
if has_dup {
candidates.vec.swap_remove(i);
} else {
i += 1;
}
}
}
if candidates.ambiguous || candidates.vec.len() > 1 {
return Err(ProjectionTyError::TooManyCandidates);
}
match candidates.vec.pop() {
Some(candidate) => {
let (ty, obligations) = confirm_candidate(selcx, obligation, candidate);
Ok(ProjectedTy::Progress(ty, obligations))
}
None => {
Ok(ProjectedTy::NoProgress(ty::mk_projection(selcx.tcx(),
obligation.predicate.trait_ref.clone(),
obligation.predicate.item_name)))
}
}
}
/// The first thing we have to do is scan through the parameter
/// environment to see whether there are any projection predicates
/// there that can answer this question.
fn assemble_candidates_from_param_env<'cx,'tcx>(
selcx: &mut SelectionContext<'cx,'tcx>,
obligation: &ProjectionTyObligation<'tcx>,
obligation_trait_ref: &Rc<ty::TraitRef<'tcx>>,
candidate_set: &mut ProjectionTyCandidateSet<'tcx>)
{
let env_predicates = selcx.param_env().caller_bounds.clone();
assemble_candidates_from_predicates(selcx, obligation, obligation_trait_ref,
candidate_set, env_predicates);
}
/// In the case of a nested projection like <<A as Foo>::FooT as Bar>::BarT, we may find
/// that the definition of `Foo` has some clues:
///
/// ```
/// trait Foo {
/// type FooT : Bar<BarT=i32>
/// }
/// ```
///
/// Here, for example, we could conclude that the result is `i32`.
fn assemble_candidates_from_trait_def<'cx,'tcx>(
selcx: &mut SelectionContext<'cx,'tcx>,
obligation: &ProjectionTyObligation<'tcx>,
obligation_trait_ref: &Rc<ty::TraitRef<'tcx>>,
candidate_set: &mut ProjectionTyCandidateSet<'tcx>)
{
// Check whether the self-type is itself a projection.
let trait_ref = match obligation_trait_ref.self_ty().sty {
ty::ty_projection(ref data) => data.trait_ref.clone(),
ty::ty_infer(ty::TyVar(_)) => {
// If the self-type is an inference variable, then it MAY wind up
// being a projected type, so induce an ambiguity.
candidate_set.ambiguous = true;
return;
}
_ => { return; }
};
// If so, extract what we know from the trait and try to come up with a good answer.
let trait_predicates = ty::lookup_predicates(selcx.tcx(), trait_ref.def_id);
let bounds = trait_predicates.instantiate(selcx.tcx(), trait_ref.substs);
assemble_candidates_from_predicates(selcx, obligation, obligation_trait_ref,
candidate_set, bounds.predicates.into_vec());
}
fn assemble_candidates_from_predicates<'cx,'tcx>(
selcx: &mut SelectionContext<'cx,'tcx>,
obligation: &ProjectionTyObligation<'tcx>,
obligation_trait_ref: &Rc<ty::TraitRef<'tcx>>,
candidate_set: &mut ProjectionTyCandidateSet<'tcx>,
env_predicates: Vec<ty::Predicate<'tcx>>)
{
debug!("assemble_candidates_from_predicates(obligation={}, env_predicates={})",
obligation.repr(selcx.tcx()),
env_predicates.repr(selcx.tcx()));
let infcx = selcx.infcx();
for predicate in elaborate_predicates(selcx.tcx(), env_predicates) {
match predicate {
ty::Predicate::Projection(ref data) => {
let same_name = data.item_name() == obligation.predicate.item_name;
let is_match = same_name && infcx.probe(|_| {
let origin = infer::Misc(obligation.cause.span);
let data_poly_trait_ref =
data.to_poly_trait_ref();
let obligation_poly_trait_ref =
obligation_trait_ref.to_poly_trait_ref();
infcx.sub_poly_trait_refs(false,
origin,
data_poly_trait_ref,
obligation_poly_trait_ref).is_ok()
});
debug!("assemble_candidates_from_predicates: candidate {} is_match {} same_name {}",
data.repr(selcx.tcx()),
is_match,
same_name);
if is_match {
candidate_set.vec.push(
ProjectionTyCandidate::ParamEnv(data.clone()));
}
}
_ => { }
}
}
}
fn assemble_candidates_from_object_type<'cx,'tcx>(
selcx: &mut SelectionContext<'cx,'tcx>,
obligation: &ProjectionTyObligation<'tcx>,
obligation_trait_ref: &Rc<ty::TraitRef<'tcx>>,
candidate_set: &mut ProjectionTyCandidateSet<'tcx>,
object_ty: Ty<'tcx>)
{
let infcx = selcx.infcx();
debug!("assemble_candidates_from_object_type(object_ty={})",
object_ty.repr(infcx.tcx));
let data = match object_ty.sty {
ty::ty_trait(ref data) => data,
_ => {
selcx.tcx().sess.span_bug(
obligation.cause.span,
&format!("assemble_candidates_from_object_type called with non-object: {}",
object_ty.repr(selcx.tcx())));
}
};
let projection_bounds = data.projection_bounds_with_self_ty(selcx.tcx(), object_ty);
let env_predicates = projection_bounds.iter()
.map(|p| p.as_predicate())
.collect();
assemble_candidates_from_predicates(selcx, obligation, obligation_trait_ref,
candidate_set, env_predicates)
}
fn assemble_candidates_from_impls<'cx,'tcx>(
selcx: &mut SelectionContext<'cx,'tcx>,
obligation: &ProjectionTyObligation<'tcx>,
obligation_trait_ref: &Rc<ty::TraitRef<'tcx>>,
candidate_set: &mut ProjectionTyCandidateSet<'tcx>)
-> Result<(), SelectionError<'tcx>>
{
// If we are resolving `<T as TraitRef<...>>::Item == Type`,
// start out by selecting the predicate `T as TraitRef<...>`:
let poly_trait_ref = obligation_trait_ref.to_poly_trait_ref();
let trait_obligation = obligation.with(poly_trait_ref.to_poly_trait_predicate());
let vtable = match selcx.select(&trait_obligation) {
Ok(Some(vtable)) => vtable,
Ok(None) => {
candidate_set.ambiguous = true;
return Ok(());
}
Err(e) => {
debug!("assemble_candidates_from_impls: selection error {}",
e.repr(selcx.tcx()));
return Err(e);
}
};
match vtable {
super::VtableImpl(data) => {
debug!("assemble_candidates_from_impls: impl candidate {}",
data.repr(selcx.tcx()));
candidate_set.vec.push(
ProjectionTyCandidate::Impl(data));
}
super::VtableObject(data) => {
assemble_candidates_from_object_type(
selcx, obligation, obligation_trait_ref, candidate_set,
data.object_ty);
}
super::VtableClosure(closure_def_id, substs) => {
candidate_set.vec.push(
ProjectionTyCandidate::Closure(closure_def_id, substs));
}
super::VtableFnPointer(fn_type) => {
candidate_set.vec.push(
ProjectionTyCandidate::FnPointer(fn_type));
}
super::VtableParam(..) => {
// This case tell us nothing about the value of an
// associated type. Consider:
//
// ```
// trait SomeTrait { type Foo; }
// fn foo<T:SomeTrait>(...) { }
// ```
//
// If the user writes `<T as SomeTrait>::Foo`, then the `T
// : SomeTrait` binding does not help us decide what the
// type `Foo` is (at least, not more specifically than
// what we already knew).
//
// But wait, you say! What about an example like this:
//
// ```
// fn bar<T:SomeTrait<Foo=uint>>(...) { ... }
// ```
//
// Doesn't the `T : Sometrait<Foo=uint>` predicate help
// resolve `T::Foo`? And of course it does, but in fact
// that single predicate is desugared into two predicates
// in the compiler: a trait predicate (`T : SomeTrait`) and a
// projection. And the projection where clause is handled
// in `assemble_candidates_from_param_env`.
}
super::VtableDefaultImpl(..) |
super::VtableBuiltin(..) => {
// These traits have no associated types.
selcx.tcx().sess.span_bug(
obligation.cause.span,
&format!("Cannot project an associated type from `{}`",
vtable.repr(selcx.tcx())));
}
}
Ok(())
}
fn confirm_candidate<'cx,'tcx>(
selcx: &mut SelectionContext<'cx,'tcx>,
obligation: &ProjectionTyObligation<'tcx>,
candidate: ProjectionTyCandidate<'tcx>)
-> (Ty<'tcx>, Vec<PredicateObligation<'tcx>>)
{
let infcx = selcx.infcx();
debug!("confirm_candidate(candidate={}, obligation={})",
candidate.repr(infcx.tcx),
obligation.repr(infcx.tcx));
match candidate {
ProjectionTyCandidate::ParamEnv(poly_projection) => {
confirm_param_env_candidate(selcx, obligation, poly_projection)
}
ProjectionTyCandidate::Impl(impl_vtable) => {
confirm_impl_candidate(selcx, obligation, impl_vtable)
}
ProjectionTyCandidate::Closure(def_id, substs) => {
confirm_closure_candidate(selcx, obligation, def_id, &substs)
}
ProjectionTyCandidate::FnPointer(fn_type) => {
confirm_fn_pointer_candidate(selcx, obligation, fn_type)
}
}
}
fn confirm_fn_pointer_candidate<'cx,'tcx>(
selcx: &mut SelectionContext<'cx,'tcx>,
obligation: &ProjectionTyObligation<'tcx>,
fn_type: Ty<'tcx>)
-> (Ty<'tcx>, Vec<PredicateObligation<'tcx>>)
{
let fn_type = selcx.infcx().shallow_resolve(fn_type);
let sig = ty::ty_fn_sig(fn_type);
confirm_callable_candidate(selcx, obligation, sig, util::TupleArgumentsFlag::Yes)
}
fn confirm_closure_candidate<'cx,'tcx>(
selcx: &mut SelectionContext<'cx,'tcx>,
obligation: &ProjectionTyObligation<'tcx>,
closure_def_id: ast::DefId,
substs: &Substs<'tcx>)
-> (Ty<'tcx>, Vec<PredicateObligation<'tcx>>)
{
let closure_typer = selcx.closure_typer();
let closure_type = closure_typer.closure_type(closure_def_id, substs);
confirm_callable_candidate(selcx, obligation, &closure_type.sig, util::TupleArgumentsFlag::No)
}
fn confirm_callable_candidate<'cx,'tcx>(
selcx: &mut SelectionContext<'cx,'tcx>,
obligation: &ProjectionTyObligation<'tcx>,
fn_sig: &ty::PolyFnSig<'tcx>,
flag: util::TupleArgumentsFlag)
-> (Ty<'tcx>, Vec<PredicateObligation<'tcx>>)
{
let tcx = selcx.tcx();
debug!("confirm_closure_candidate({},{})",
obligation.repr(tcx),
fn_sig.repr(tcx));
// Note: we unwrap the binder here but re-create it below (1)
let ty::Binder((trait_ref, ret_type)) =
util::closure_trait_ref_and_return_type(tcx,
obligation.predicate.trait_ref.def_id,
obligation.predicate.trait_ref.self_ty(),
fn_sig,
flag);
let predicate = ty::Binder(ty::ProjectionPredicate { // (1) recreate binder here
projection_ty: ty::ProjectionTy {
trait_ref: trait_ref,
item_name: token::intern(FN_OUTPUT_NAME),
},
ty: ret_type
});
confirm_param_env_candidate(selcx, obligation, predicate)
}
fn confirm_param_env_candidate<'cx,'tcx>(
selcx: &mut SelectionContext<'cx,'tcx>,
obligation: &ProjectionTyObligation<'tcx>,
poly_projection: ty::PolyProjectionPredicate<'tcx>)
-> (Ty<'tcx>, Vec<PredicateObligation<'tcx>>)
{
let infcx = selcx.infcx();
let projection =
infcx.replace_late_bound_regions_with_fresh_var(
obligation.cause.span,
infer::LateBoundRegionConversionTime::HigherRankedType,
&poly_projection).0;
assert_eq!(projection.projection_ty.item_name,
obligation.predicate.item_name);
let origin = infer::RelateOutputImplTypes(obligation.cause.span);
match infcx.sub_trait_refs(false,
origin,
obligation.predicate.trait_ref.clone(),
projection.projection_ty.trait_ref.clone()) {
Ok(()) => { }
Err(e) => {
selcx.tcx().sess.span_bug(
obligation.cause.span,
&format!("Failed to unify `{}` and `{}` in projection: {}",
obligation.repr(selcx.tcx()),
projection.repr(selcx.tcx()),
ty::type_err_to_str(selcx.tcx(), &e)));
}
}
(projection.ty, vec!())
}
fn confirm_impl_candidate<'cx,'tcx>(
selcx: &mut SelectionContext<'cx,'tcx>,
obligation: &ProjectionTyObligation<'tcx>,
impl_vtable: VtableImplData<'tcx, PredicateObligation<'tcx>>)
-> (Ty<'tcx>, Vec<PredicateObligation<'tcx>>)
{
// there don't seem to be nicer accessors to these:
let impl_items_map = selcx.tcx().impl_items.borrow();
let impl_or_trait_items_map = selcx.tcx().impl_or_trait_items.borrow();
let impl_items = &impl_items_map[impl_vtable.impl_def_id];
let mut impl_ty = None;
for impl_item in impl_items {
let assoc_type = match impl_or_trait_items_map[impl_item.def_id()] {
ty::TypeTraitItem(ref assoc_type) => assoc_type.clone(),
ty::MethodTraitItem(..) => { continue; }
};
if assoc_type.name != obligation.predicate.item_name {
continue;
}
let impl_poly_ty = ty::lookup_item_type(selcx.tcx(), assoc_type.def_id);
impl_ty = Some(impl_poly_ty.ty.subst(selcx.tcx(), &impl_vtable.substs));
break;
}
match impl_ty {
Some(ty) => (ty, impl_vtable.nested.into_vec()),
None => {
// This means that the impl is missing a
// definition for the associated type. This error
// ought to be reported by the type checker method
// `check_impl_items_against_trait`, so here we
// just return ty_err.
(selcx.tcx().types.err, vec!())
}
}
}
impl<'tcx> Repr<'tcx> for ProjectionTyError<'tcx> {
fn repr(&self, tcx: &ty::ctxt<'tcx>) -> String {
match *self {
ProjectionTyError::TooManyCandidates =>
format!("NoCandidate"),
ProjectionTyError::TraitSelectionError(ref e) =>
format!("TraitSelectionError({})", e.repr(tcx)),
}
}
}
impl<'tcx> Repr<'tcx> for ProjectionTyCandidate<'tcx> {
fn repr(&self, tcx: &ty::ctxt<'tcx>) -> String {
match *self {
ProjectionTyCandidate::ParamEnv(ref data) =>
format!("ParamEnv({})", data.repr(tcx)),
ProjectionTyCandidate::Impl(ref data) =>
format!("Impl({})", data.repr(tcx)),
ProjectionTyCandidate::Closure(ref a, ref b) =>
format!("Closure(({},{}))", a.repr(tcx), b.repr(tcx)),
ProjectionTyCandidate::FnPointer(a) =>
format!("FnPointer(({}))", a.repr(tcx)),
}
}
}
impl<'tcx, T: TypeFoldable<'tcx>> TypeFoldable<'tcx> for Normalized<'tcx, T> {
fn fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> Normalized<'tcx, T> {
Normalized {
value: self.value.fold_with(folder),
obligations: self.obligations.fold_with(folder),
}
}
}
impl<'tcx, T:Repr<'tcx>> Repr<'tcx> for Normalized<'tcx, T> {
fn repr(&self, tcx: &ty::ctxt<'tcx>) -> String {
format!("Normalized({},{})",
self.value.repr(tcx),
self.obligations.repr(tcx))
}
}