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Fix overflow when performing drop check calculations in NLL #47920

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Feb 5, 2018
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115 changes: 78 additions & 37 deletions src/librustc_mir/borrow_check/nll/type_check/liveness.rs
Original file line number Diff line number Diff line change
Expand Up @@ -15,7 +15,10 @@ use dataflow::move_paths::{HasMoveData, MoveData};
use rustc::mir::{BasicBlock, Location, Mir};
use rustc::mir::Local;
use rustc::ty::{self, Ty, TyCtxt, TypeFoldable};
use rustc::traits;
use rustc::infer::InferOk;
use rustc::util::common::ErrorReported;
use borrow_check::nll::type_check::AtLocation;
use rustc_data_structures::fx::FxHashSet;
use syntax::codemap::DUMMY_SP;
use util::liveness::LivenessResults;
Expand Down Expand Up @@ -184,48 +187,86 @@ impl<'gen, 'typeck, 'flow, 'gcx, 'tcx> TypeLivenessGenerator<'gen, 'typeck, 'flo
location
);

let tcx = self.cx.infcx.tcx;
let mut types = vec![(dropped_ty, 0)];
let mut known = FxHashSet();
while let Some((ty, depth)) = types.pop() {
let span = DUMMY_SP; // FIXME
let result = match tcx.dtorck_constraint_for_ty(span, dropped_ty, depth, ty) {
Ok(result) => result,
Err(ErrorReported) => {
continue;
}
};

let ty::DtorckConstraint {
outlives,
dtorck_types,
} = result;

// All things in the `outlives` array may be touched by
// the destructor and must be live at this point.
for outlive in outlives {
let cause = Cause::DropVar(dropped_local, location);
self.push_type_live_constraint(outlive, location, cause);
}
// If we end visiting the same type twice (usually due to a cycle involving
// associated types), we need to ensure that its region types match up with the type
// we added to the 'known' map the first time around. For this reason, we need
// our infcx to hold onto its calculated region constraints after each call
// to dtorck_constraint_for_ty. Otherwise, normalizing the corresponding associated
// type will end up instantiating the type with a new set of inference variables
// Since this new type will never be in 'known', we end up looping forever.
//
// For this reason, we avoid calling TypeChecker.normalize, instead doing all normalization
// ourselves in one large 'fully_perform_op' callback.
let (type_constraints, kind_constraints) = self.cx.fully_perform_op(location.at_self(),
|cx| {

let tcx = cx.infcx.tcx;
let mut selcx = traits::SelectionContext::new(cx.infcx);
let cause = cx.misc(cx.last_span);

let mut types = vec![(dropped_ty, 0)];
let mut final_obligations = Vec::new();
let mut type_constraints = Vec::new();
let mut kind_constraints = Vec::new();

// However, there may also be some types that
// `dtorck_constraint_for_ty` could not resolve (e.g.,
// associated types and parameters). We need to normalize
// associated types here and possibly recursively process.
for ty in dtorck_types {
let ty = self.cx.normalize(&ty, location);
let ty = self.cx.infcx.resolve_type_and_region_vars_if_possible(&ty);
match ty.sty {
ty::TyParam(..) | ty::TyProjection(..) | ty::TyAnon(..) => {
let cause = Cause::DropVar(dropped_local, location);
self.push_type_live_constraint(ty, location, cause);
let mut known = FxHashSet();

while let Some((ty, depth)) = types.pop() {
let span = DUMMY_SP; // FIXME
let result = match tcx.dtorck_constraint_for_ty(span, dropped_ty, depth, ty) {
Ok(result) => result,
Err(ErrorReported) => {
continue;
}
};

let ty::DtorckConstraint {
outlives,
dtorck_types,
} = result;

// All things in the `outlives` array may be touched by
// the destructor and must be live at this point.
for outlive in outlives {
let cause = Cause::DropVar(dropped_local, location);
kind_constraints.push((outlive, location, cause));
}

_ => if known.insert(ty) {
types.push((ty, depth + 1));
},
// However, there may also be some types that
// `dtorck_constraint_for_ty` could not resolve (e.g.,
// associated types and parameters). We need to normalize
// associated types here and possibly recursively process.
for ty in dtorck_types {
let traits::Normalized { value: ty, obligations } =
traits::normalize(&mut selcx, cx.param_env, cause.clone(), &ty);

final_obligations.extend(obligations);

let ty = cx.infcx.resolve_type_and_region_vars_if_possible(&ty);
match ty.sty {
ty::TyParam(..) | ty::TyProjection(..) | ty::TyAnon(..) => {
let cause = Cause::DropVar(dropped_local, location);
type_constraints.push((ty, location, cause));
}

_ => if known.insert(ty) {
types.push((ty, depth + 1));
},
}
}
}

Ok(InferOk {
value: (type_constraints, kind_constraints), obligations: final_obligations
})
}).unwrap();

for (ty, location, cause) in type_constraints {
self.push_type_live_constraint(ty, location, cause);
}

for (kind, location, cause) in kind_constraints {
self.push_type_live_constraint(kind, location, cause);
}
}
}
33 changes: 33 additions & 0 deletions src/test/run-pass/nll/issue-47589.rs
Original file line number Diff line number Diff line change
@@ -0,0 +1,33 @@
// Copyright 2018 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.

#![feature(nll)]

pub struct DescriptorSet<'a> {
pub slots: Vec<AttachInfo<'a, Resources>>
}

pub trait ResourcesTrait<'r>: Sized {
type DescriptorSet: 'r;
}

pub struct Resources;

impl<'a> ResourcesTrait<'a> for Resources {
type DescriptorSet = DescriptorSet<'a>;
}

pub enum AttachInfo<'a, R: ResourcesTrait<'a>> {
NextDescriptorSet(Box<R::DescriptorSet>)
}

fn main() {
let _x = DescriptorSet {slots: Vec::new()};
}