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auto merge of #19466 : nikomatsakis/rust/recursion-limit, r=eddyb

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This is particularly important for deeply nested types, which generate deeply nested impls. This is a fix for #19318. It's possible we could also improve this particular case not to increment the recursion count, but it's worth being able to adjust the recursion limit anyhow.

cc @jdm 
r? @pcwalton
This commit is contained in:
bors 2014-12-09 14:02:45 +00:00
commit ef4982f0f8
8 changed files with 126 additions and 294 deletions
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1
src/librustc/lib.rs
View file

@ -88,6 +88,7 @@ pub mod middle {
pub mod privacy;
pub mod reachable;
pub mod region;
pub mod recursion_limit;
pub mod resolve;
pub mod resolve_lifetime;
pub mod stability;

39
src/librustc/middle/recursion_limit.rs Normal file
View file

@ -0,0 +1,39 @@
// Copyright 2012 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.
// Recursion limit.
//
// There are various parts of the compiler that must impose arbitrary limits
// on how deeply they recurse to prevent stack overflow. Users can override
// this via an attribute on the crate like `#![recursion_limit(22)]`. This pass
// just peeks and looks for that attribute.
use session::Session;
use syntax::ast;
use syntax::attr::AttrMetaMethods;
use std::str::FromStr;
pub fn update_recursion_limit(sess: &Session, krate: &ast::Crate) {
for attr in krate.attrs.iter() {
if !attr.check_name("recursion_limit") {
continue;
}
if let Some(s) = attr.value_str() {
if let Some(n) = FromStr::from_str(s.get()) {
sess.recursion_limit.set(n);
return;
}
}
sess.span_err(attr.span, "malformed recursion limit attribute, \
expected #![recursion_limit(\"N\")]");
}
}

312
src/librustc/middle/traits/select.rs
View file

@ -158,10 +158,10 @@ enum BuiltinBoundConditions<'tcx> {
}
#[deriving(Show)]
enum EvaluationResult {
enum EvaluationResult<'tcx> {
EvaluatedToOk,
EvaluatedToErr,
EvaluatedToAmbig,
EvaluatedToErr(SelectionError<'tcx>),
}
impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
@ -275,7 +275,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
bound: ty::BuiltinBound,
previous_stack: &ObligationStack<'o, 'tcx>,
ty: Ty<'tcx>)
-> EvaluationResult
-> EvaluationResult<'tcx>
{
let obligation =
util::obligation_for_builtin_bound(
@ -298,7 +298,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
fn evaluate_obligation_recursively<'o>(&mut self,
previous_stack: Option<&ObligationStack<'o, 'tcx>>,
obligation: &Obligation<'tcx>)
-> EvaluationResult
-> EvaluationResult<'tcx>
{
debug!("evaluate_obligation_recursively({})",
obligation.repr(self.tcx()));
@ -313,7 +313,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
fn evaluate_stack<'o>(&mut self,
stack: &ObligationStack<'o, 'tcx>)
-> EvaluationResult
-> EvaluationResult<'tcx>
{
// In intercrate mode, whenever any of the types are unbound,
// there can always be an impl. Even if there are no impls in
@ -384,7 +384,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
match self.candidate_from_obligation(stack) {
Ok(Some(c)) => self.winnow_candidate(stack, &c),
Ok(None) => EvaluatedToAmbig,
Err(_) => EvaluatedToErr,
Err(e) => EvaluatedToErr(e),
}
}
@ -415,285 +415,6 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
})
}
///////////////////////////////////////////////////////////////////////////
// METHOD MATCHING
//
// Method matching is a variation on the normal select/evaluation
// situation. In this scenario, rather than having a full trait
// reference to select from, we start with an expression like
// `receiver.method(...)`. This means that we have `rcvr_ty`, the
// type of the receiver, and we have a possible trait that
// supplies `method`. We must determine whether the receiver is
// applicable, taking into account the transformed self type
// declared on `method`. We also must consider the possibility
// that `receiver` can be *coerced* into a suitable type (for
// example, a receiver type like `&(Any+Send)` might be coerced
// into a receiver like `&Any` to allow for method dispatch). See
// the body of `evaluate_method_obligation()` for more details on
// the algorithm.
/// Determine whether a trait-method is applicable to a receiver of
/// type `rcvr_ty`. *Does not affect the inference state.*
///
/// - `rcvr_ty` -- type of the receiver
/// - `xform_self_ty` -- transformed self type declared on the method, with `Self`
/// to a fresh type variable
/// - `obligation` -- a reference to the trait where the method is declared, with
/// the input types on the trait replaced with fresh type variables
pub fn evaluate_method_obligation(&mut self,
rcvr_ty: Ty<'tcx>,
xform_self_ty: Ty<'tcx>,
obligation: &Obligation<'tcx>)
-> MethodMatchResult
{
// Here is the situation. We have a trait method declared (say) like so:
//
// trait TheTrait {
// fn the_method(self: Rc<Self>, ...) { ... }
// }
//
// And then we have a call looking (say) like this:
//
// let x: Rc<Foo> = ...;
// x.the_method()
//
// Now we want to decide if `TheTrait` is applicable. As a
// human, we can see that `TheTrait` is applicable if there is
// an impl for the type `Foo`. But how does the compiler know
// what impl to look for, given that our receiver has type
// `Rc<Foo>`? We need to take the method's self type into
// account.
//
// On entry to this function, we have the following inputs:
//
// - `rcvr_ty = Rc<Foo>`
// - `xform_self_ty = Rc<$0>`
// - `obligation = $0 as TheTrait`
//
// We do the match in two phases. The first is a *precise
// match*, which means that no coercion is required. This is
// the preferred way to match. It works by first making
// `rcvr_ty` a subtype of `xform_self_ty`. This unifies `$0`
// and `Foo`. We can then evaluate (roughly as normal) the
// trait reference `Foo as TheTrait`.
//
// If this fails, we fallback to a coercive match, described below.
match self.infcx.probe(|| self.match_method_precise(rcvr_ty, xform_self_ty, obligation)) {
Ok(()) => { return MethodMatched(PreciseMethodMatch); }
Err(_) => { }
}
// Coercive matches work slightly differently and cannot
// completely reuse the normal trait matching machinery
// (though they employ many of the same bits and pieces). To
// see how it works, let's continue with our previous example,
// but with the following declarations:
//
// ```
// trait Foo : Bar { .. }
// trait Bar : Baz { ... }
// trait Baz { ... }
// impl TheTrait for Bar {
// fn the_method(self: Rc<Bar>, ...) { ... }
// }
// ```
//
// Now we see that the receiver type `Rc<Foo>` is actually an
// object type. And in fact the impl we want is an impl on the
// supertrait `Rc<Bar>`. The precise matching procedure won't
// find it, however, because `Rc<Foo>` is not a subtype of
// `Rc<Bar>` -- it is *coercible* to `Rc<Bar>` (actually, such
// coercions are not yet implemented, but let's leave that
// aside for now).
//
// To handle this case, we employ a different procedure. Recall
// that our initial state is as follows:
//
// - `rcvr_ty = Rc<Foo>`
// - `xform_self_ty = Rc<$0>`
// - `obligation = $0 as TheTrait`
//
// We now go through each impl and instantiate all of its type
// variables, yielding the trait reference that the impl
// provides. In our example, the impl would provide `Bar as
// TheTrait`. Next we (try to) unify the trait reference that
// the impl provides with the input obligation. This would
// unify `$0` and `Bar`. Now we can see whether the receiver
// type (`Rc<Foo>`) is *coercible to* the transformed self
// type (`Rc<$0> == Rc<Bar>`). In this case, the answer is
// yes, so the impl is considered a candidate.
//
// Note that there is the possibility of ambiguity here, even
// when all types are known. In our example, this might occur
// if there was *also* an impl of `TheTrait` for `Baz`. In
// this case, `Rc<Foo>` would be coercible to both `Rc<Bar>`
// and `Rc<Baz>`. (Note that it is not a *coherence violation*
// to have impls for both `Bar` and `Baz`, despite this
// ambiguity). In this case, we report an error, listing all
// the applicable impls. The user can explicitly "up-coerce"
// to the type they want.
//
// Note that this coercion step only considers actual impls
// found in the source. This is because all the
// compiler-provided impls (such as those for unboxed
// closures) do not have relevant coercions. This simplifies
// life immensely.
let mut impls =
self.assemble_method_candidates_from_impls(rcvr_ty, xform_self_ty, obligation);
if impls.len() > 1 {
impls.retain(|&c| self.winnow_method_impl(c, rcvr_ty, xform_self_ty, obligation));
}
if impls.len() > 1 {
return MethodAmbiguous(impls);
}
match impls.pop() {
Some(def_id) => MethodMatched(CoerciveMethodMatch(def_id)),
None => MethodDidNotMatch
}
}
/// Given the successful result of a method match, this function "confirms" the result, which
/// basically repeats the various matching operations, but outside of any snapshot so that
/// their effects are committed into the inference state.
pub fn confirm_method_match(&mut self,
rcvr_ty: Ty<'tcx>,
xform_self_ty: Ty<'tcx>,
obligation: &Obligation<'tcx>,
data: MethodMatchedData)
{
let is_ok = match data {
PreciseMethodMatch => {
self.match_method_precise(rcvr_ty, xform_self_ty, obligation).is_ok()
}
CoerciveMethodMatch(impl_def_id) => {
self.match_method_coerce(impl_def_id, rcvr_ty, xform_self_ty, obligation).is_ok()
}
};
if !is_ok {
self.tcx().sess.span_bug(
obligation.cause.span,
format!("match not repeatable: {}, {}, {}, {}",
rcvr_ty.repr(self.tcx()),
xform_self_ty.repr(self.tcx()),
obligation.repr(self.tcx()),
data)[]);
}
}
/// Implements the *precise method match* procedure described in
/// `evaluate_method_obligation()`.
fn match_method_precise(&mut self,
rcvr_ty: Ty<'tcx>,
xform_self_ty: Ty<'tcx>,
obligation: &Obligation<'tcx>)
-> Result<(),()>
{
self.infcx.commit_if_ok(|| {
match self.infcx.sub_types(false, infer::RelateSelfType(obligation.cause.span),
rcvr_ty, xform_self_ty) {
Ok(()) => { }
Err(_) => { return Err(()); }
}
if self.evaluate_obligation(obligation) {
Ok(())
} else {
Err(())
}
})
}
/// Assembles a list of potentially applicable impls using the *coercive match* procedure
/// described in `evaluate_method_obligation()`.
fn assemble_method_candidates_from_impls(&mut self,
rcvr_ty: Ty<'tcx>,
xform_self_ty: Ty<'tcx>,
obligation: &Obligation<'tcx>)
-> Vec<ast::DefId>
{
let mut candidates = Vec::new();
let all_impls = self.all_impls(obligation.trait_ref.def_id);
for &impl_def_id in all_impls.iter() {
self.infcx.probe(|| {
match self.match_method_coerce(impl_def_id, rcvr_ty, xform_self_ty, obligation) {
Ok(_) => { candidates.push(impl_def_id); }
Err(_) => { }
}
});
}
candidates
}
/// Applies the *coercive match* procedure described in `evaluate_method_obligation()` to a
/// particular impl.
fn match_method_coerce(&mut self,
impl_def_id: ast::DefId,
rcvr_ty: Ty<'tcx>,
xform_self_ty: Ty<'tcx>,
obligation: &Obligation<'tcx>)
-> Result<Substs<'tcx>, ()>
{
// This is almost always expected to succeed. It
// causes the impl's self-type etc to be unified with
// the type variable that is shared between
// obligation/xform_self_ty. In our example, after
// this is done, the type of `xform_self_ty` would
// change from `Rc<$0>` to `Rc<Foo>` (because $0 is
// unified with `Foo`).
let substs = try!(self.match_impl(impl_def_id, obligation));
// Next, check whether we can coerce. For now we require
// that the coercion be a no-op.
let origin = infer::Misc(obligation.cause.span);
match infer::mk_coercety(self.infcx, true, origin,
rcvr_ty, xform_self_ty) {
Ok(None) => { /* Fallthrough */ }
Ok(Some(_)) | Err(_) => { return Err(()); }
}
Ok(substs)
}
/// A version of `winnow_impl` applicable to coerice method matching. This is basically the
/// same as `winnow_impl` but it uses the method matching procedure and is specific to impls.
fn winnow_method_impl(&mut self,
impl_def_id: ast::DefId,
rcvr_ty: Ty<'tcx>,
xform_self_ty: Ty<'tcx>,
obligation: &Obligation<'tcx>)
-> bool
{
debug!("winnow_method_impl: impl_def_id={} rcvr_ty={} xform_self_ty={} obligation={}",
impl_def_id.repr(self.tcx()),
rcvr_ty.repr(self.tcx()),
xform_self_ty.repr(self.tcx()),
obligation.repr(self.tcx()));
self.infcx.probe(|| {
match self.match_method_coerce(impl_def_id, rcvr_ty, xform_self_ty, obligation) {
Ok(substs) => {
let vtable_impl = self.vtable_impl(impl_def_id,
substs,
obligation.cause,
obligation.recursion_depth + 1);
self.winnow_selection(None, VtableImpl(vtable_impl)).may_apply()
}
Err(()) => {
false
}
}
})
}
///////////////////////////////////////////////////////////////////////////
// CANDIDATE ASSEMBLY
//
@ -1112,14 +833,14 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
fn winnow_candidate<'o>(&mut self,
stack: &ObligationStack<'o, 'tcx>,
candidate: &Candidate<'tcx>)
-> EvaluationResult
-> EvaluationResult<'tcx>
{
debug!("winnow_candidate: candidate={}", candidate.repr(self.tcx()));
self.infcx.probe(|| {
let candidate = (*candidate).clone();
match self.confirm_candidate(stack.obligation, candidate) {
Ok(selection) => self.winnow_selection(Some(stack), selection),
Err(_) => EvaluatedToErr,
Err(error) => EvaluatedToErr(error),
}
})
}
@ -1127,12 +848,12 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
fn winnow_selection<'o>(&mut self,
stack: Option<&ObligationStack<'o, 'tcx>>,
selection: Selection<'tcx>)
-> EvaluationResult
-> EvaluationResult<'tcx>
{
let mut result = EvaluatedToOk;
for obligation in selection.iter_nested() {
match self.evaluate_obligation_recursively(stack, obligation) {
EvaluatedToErr => { return EvaluatedToErr; }
EvaluatedToErr(e) => { return EvaluatedToErr(e); }
EvaluatedToAmbig => { result = EvaluatedToAmbig; }
EvaluatedToOk => { }
}
@ -2146,11 +1867,18 @@ impl<'o, 'tcx> Repr<'tcx> for ObligationStack<'o, 'tcx> {
}
}
impl EvaluationResult {
impl<'tcx> EvaluationResult<'tcx> {
fn may_apply(&self) -> bool {
match *self {
EvaluatedToOk | EvaluatedToAmbig => true,
EvaluatedToErr => false,
EvaluatedToOk |
EvaluatedToAmbig |
EvaluatedToErr(Overflow) |
EvaluatedToErr(OutputTypeParameterMismatch(..)) => {
true
}
EvaluatedToErr(Unimplemented) => {
false
}
}
}
}

4
src/librustc_driver/driver.rs
View file

@ -180,6 +180,10 @@ pub fn phase_2_configure_and_expand(sess: &Session,
*sess.features.borrow_mut() = features;
});
time(time_passes, "recursion limit", (), |_| {
middle::recursion_limit::update_recursion_limit(sess, &krate);
});
// strip before expansion to allow macros to depend on
// configuration variables e.g/ in
//

9
src/librustc_typeck/check/vtable.rs
View file

@ -366,6 +366,15 @@ pub fn report_selection_error<'a, 'tcx>(fcx: &FnCtxt<'a, 'tcx>,
"overflow evaluating the trait `{}` for the type `{}`",
trait_ref.user_string(fcx.tcx()),
self_ty.user_string(fcx.tcx())).as_slice());
let current_limit = fcx.tcx().sess.recursion_limit.get();
let suggested_limit = current_limit * 2;
fcx.tcx().sess.span_note(
obligation.cause.span,
format!(
"consider adding a `#![recursion_limit=\"{}\"]` attribute to your crate",
suggested_limit)[]);
note_obligation_cause(fcx, obligation);
}
Unimplemented => {

51
src/test/compile-fail/recursion_limit.rs Normal file
View file

@ -0,0 +1,51 @@
// 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.
// Test that the recursion limit can be changed. In this case, we have
// deeply nested types that will fail the `Send` check by overflow
// when the recursion limit is set very low.
#![feature(macro_rules)]
#![allow(dead_code)]
#![recursion_limit="10"]
macro_rules! link {
($id:ident, $t:ty) => {
enum $id { $id($t) }
}
}
link!(A,B)
link!(B,C)
link!(C,D)
link!(D,E)
link!(E,F)
link!(F,G)
link!(G,H)
link!(H,I)
link!(I,J)
link!(J,K)
link!(K,L)
link!(L,M)
link!(M,N)
enum N { N(uint) }
fn is_send<T:Send>() { }
fn main() {
is_send::<A>();
//~^ ERROR overflow evaluating
//~^^ NOTE consider adding a `#![recursion_limit="20"]` attribute to your crate
//~^^^ NOTE must be implemented
//~^^^^ ERROR overflow evaluating
//~^^^^^ NOTE consider adding a `#![recursion_limit="20"]` attribute to your crate
//~^^^^^^ NOTE must be implemented
}

2
src/test/compile-fail/unboxed-closures-type-mismatch.rs
View file

@ -14,6 +14,6 @@ use std::ops::FnMut;
pub fn main() {
let mut f = |&mut: x: int, y: int| -> int { x + y };
let z = f.call_mut((1u, 2)); //~ ERROR not implemented
let z = f.call_mut((1u, 2)); //~ ERROR type mismatch
println!("{}", z);
}

2
src/test/compile-fail/unboxed-closures-vtable-mismatch.rs
View file

@ -18,7 +18,7 @@ fn call_it<F:FnMut<(int,int),int>>(y: int, mut f: F) -> int {
pub fn main() {
let f = |&mut: x: uint, y: int| -> int { (x as int) + y };
let z = call_it(3, f); //~ ERROR not implemented
let z = call_it(3, f); //~ ERROR type mismatch
println!("{}", z);
}