/
autoderef.rs
210 lines (178 loc) · 6.82 KB
/
autoderef.rs
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// Copyright 2016 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.
use astconv::AstConv;
use super::FnCtxt;
use rustc::traits;
use rustc::ty::{self, Ty, TraitRef};
use rustc::ty::{ToPredicate, TypeFoldable};
use rustc::ty::{MethodCall, MethodCallee};
use rustc::ty::subst::Substs;
use rustc::ty::{LvaluePreference, NoPreference, PreferMutLvalue};
use rustc::hir;
use syntax::codemap::Span;
use syntax::parse::token;
#[derive(Copy, Clone, Debug)]
enum AutoderefKind {
Builtin,
Overloaded
}
pub struct Autoderef<'a, 'gcx: 'tcx, 'tcx: 'a> {
fcx: &'a FnCtxt<'a, 'gcx, 'tcx>,
steps: Vec<(Ty<'tcx>, AutoderefKind)>,
cur_ty: Ty<'tcx>,
obligations: Vec<traits::PredicateObligation<'tcx>>,
at_start: bool,
span: Span
}
impl<'a, 'gcx, 'tcx> Iterator for Autoderef<'a, 'gcx, 'tcx> {
type Item = (Ty<'tcx>, usize);
fn next(&mut self) -> Option<Self::Item> {
let tcx = self.fcx.tcx;
debug!("autoderef: steps={:?}, cur_ty={:?}",
self.steps, self.cur_ty);
if self.at_start {
self.at_start = false;
debug!("autoderef stage #0 is {:?}", self.cur_ty);
return Some((self.cur_ty, 0));
}
if self.steps.len() == tcx.sess.recursion_limit.get() {
// We've reached the recursion limit, error gracefully.
span_err!(tcx.sess, self.span, E0055,
"reached the recursion limit while auto-dereferencing {:?}",
self.cur_ty);
return None;
}
if self.cur_ty.is_ty_var() {
return None;
}
// Otherwise, deref if type is derefable:
let (kind, new_ty) = if let Some(mt) = self.cur_ty.builtin_deref(false, NoPreference) {
(AutoderefKind::Builtin, mt.ty)
} else {
match self.overloaded_deref_ty(self.cur_ty) {
Some(ty) => (AutoderefKind::Overloaded, ty),
_ => return None
}
};
if new_ty.references_error() {
return None;
}
self.steps.push((self.cur_ty, kind));
debug!("autoderef stage #{:?} is {:?} from {:?}", self.steps.len(),
new_ty, (self.cur_ty, kind));
self.cur_ty = new_ty;
Some((self.cur_ty, self.steps.len()))
}
}
impl<'a, 'gcx, 'tcx> Autoderef<'a, 'gcx, 'tcx> {
fn overloaded_deref_ty(&mut self, ty: Ty<'tcx>) -> Option<Ty<'tcx>> {
debug!("overloaded_deref_ty({:?})", ty);
let tcx = self.fcx.tcx();
// <cur_ty as Deref>
let trait_ref = TraitRef {
def_id: match tcx.lang_items.deref_trait() {
Some(f) => f,
None => return None
},
substs: tcx.mk_substs(Substs::new_trait(vec![], vec![], self.cur_ty))
};
let cause = traits::ObligationCause::misc(self.span, self.fcx.body_id);
let mut selcx = traits::SelectionContext::new(self.fcx);
let obligation = traits::Obligation::new(cause.clone(), trait_ref.to_predicate());
if !selcx.evaluate_obligation(&obligation) {
debug!("overloaded_deref_ty: cannot match obligation");
return None;
}
let normalized = traits::normalize_projection_type(
&mut selcx,
ty::ProjectionTy {
trait_ref: trait_ref,
item_name: token::intern("Target")
},
cause,
0
);
debug!("overloaded_deref_ty({:?}) = {:?}", ty, normalized);
self.obligations.extend(normalized.obligations);
Some(self.fcx.resolve_type_vars_if_possible(&normalized.value))
}
pub fn unambiguous_final_ty(&self) -> Ty<'tcx> {
self.fcx.structurally_resolved_type(self.span, self.cur_ty)
}
pub fn finalize<'b, I>(self, pref: LvaluePreference, exprs: I)
where I: IntoIterator<Item=&'b hir::Expr>
{
let methods : Vec<_> = self.steps.iter().map(|&(ty, kind)| {
if let AutoderefKind::Overloaded = kind {
self.fcx.try_overloaded_deref(self.span, None, ty, pref)
} else {
None
}
}).collect();
debug!("finalize({:?}) - {:?},{:?}", pref, methods, self.obligations);
for expr in exprs {
debug!("finalize - finalizing #{} - {:?}", expr.id, expr);
for (n, method) in methods.iter().enumerate() {
if let &Some(method) = method {
let method_call = MethodCall::autoderef(expr.id, n as u32);
self.fcx.tables.borrow_mut().method_map.insert(method_call, method);
}
}
}
for obligation in self.obligations {
self.fcx.register_predicate(obligation);
}
}
}
impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
pub fn autoderef(&'a self,
span: Span,
base_ty: Ty<'tcx>)
-> Autoderef<'a, 'gcx, 'tcx>
{
Autoderef {
fcx: self,
steps: vec![],
cur_ty: self.resolve_type_vars_if_possible(&base_ty),
obligations: vec![],
at_start: true,
span: span
}
}
pub fn try_overloaded_deref(&self,
span: Span,
base_expr: Option<&hir::Expr>,
base_ty: Ty<'tcx>,
lvalue_pref: LvaluePreference)
-> Option<MethodCallee<'tcx>>
{
debug!("try_overloaded_deref({:?},{:?},{:?},{:?})",
span, base_expr, base_ty, lvalue_pref);
// Try DerefMut first, if preferred.
let method = match (lvalue_pref, self.tcx.lang_items.deref_mut_trait()) {
(PreferMutLvalue, Some(trait_did)) => {
self.lookup_method_in_trait(span, base_expr,
token::intern("deref_mut"), trait_did,
base_ty, None)
}
_ => None
};
// Otherwise, fall back to Deref.
let method = match (method, self.tcx.lang_items.deref_trait()) {
(None, Some(trait_did)) => {
self.lookup_method_in_trait(span, base_expr,
token::intern("deref"), trait_did,
base_ty, None)
}
(method, _) => method
};
method
}
}