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Auto merge of #49943 - pnkfelix:fix-issue-49918, r=nikomatsakis

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Treat generators as if they have an arbitrary destructor

Conservatively assume dropping a generator touches its upvars, via locals' destructors.

Fix #49918
This commit is contained in:
bors 2018-05-02 12:20:31 +00:00
commit d40a0b3dc1
7 changed files with 106 additions and 40 deletions
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40
src/librustc_traits/dropck_outlives.rs
View file

@ -193,14 +193,38 @@ fn dtorck_constraint_for_ty<'a, 'gcx, 'tcx>(
.map(|ty| dtorck_constraint_for_ty(tcx, span, for_ty, depth + 1, ty))
.collect(),
ty::TyGenerator(def_id, substs, _) => {
// Note that the interior types are ignored here.
// Any type reachable inside the interior must also be reachable
// through the upvars.
substs
.upvar_tys(def_id, tcx)
.map(|ty| dtorck_constraint_for_ty(tcx, span, for_ty, depth + 1, ty))
.collect()
ty::TyGenerator(def_id, substs, _interior) => {
// rust-lang/rust#49918: types can be constructed, stored
// in the interior, and sit idle when generator yields
// (and is subsequently dropped).
//
// It would be nice to descend into interior of a
// generator to determine what effects dropping it might
// have (by looking at any drop effects associated with
// its interior).
//
// However, the interior's representation uses things like
// TyGeneratorWitness that explicitly assume they are not
// traversed in such a manner. So instead, we will
// simplify things for now by treating all generators as
// if they were like trait objects, where its upvars must
// all be alive for the generator's (potential)
// destructor.
//
// In particular, skipping over `_interior` is safe
// because any side-effects from dropping `_interior` can
// only take place through references with lifetimes
// derived from lifetimes attached to the upvars, and we
// *do* incorporate the upvars here.
let constraint = DtorckConstraint {
outlives: substs.upvar_tys(def_id, tcx).map(|t| t.into()).collect(),
dtorck_types: vec![],
overflows: vec![],
};
debug!("dtorck_constraint: generator {:?} => {:?}", def_id, constraint);
Ok(constraint)
}
ty::TyAdt(def, substs) => {

36
src/test/ui/generator/borrowing.nll.stderr
View file

@ -1,14 +1,30 @@
error: compilation successful
--> $DIR/borrowing.rs:15:1
error[E0597]: `a` does not live long enough
--> $DIR/borrowing.rs:18:18
|
LL | / fn main() { #![rustc_error] // rust-lang/rust#49855
LL | | let _b = {
LL | | let a = 3;
LL | | unsafe { (|| yield &a).resume() }
... |
LL | | };
LL | unsafe { (|| yield &a).resume() }
| ^^^^^^^^^^^^^
| |
| borrowed value does not live long enough
| borrow may end up in a temporary, created here
LL | //~^ ERROR: `a` does not live long enough
LL | };
| -- temporary later dropped here, potentially using the reference
| |
| borrowed value only lives until here
error[E0597]: `a` does not live long enough
--> $DIR/borrowing.rs:24:9
|
LL | / || {
LL | | yield &a
LL | | //~^ ERROR: `a` does not live long enough
LL | | }
| |_^
| |_________^ borrowed value does not live long enough
LL | };
| - borrowed value only lives until here
LL | }
| - borrow later used here, when `_b` is dropped
error: aborting due to previous error
error: aborting due to 2 previous errors
For more information about this error, try `rustc --explain E0597`.

4
src/test/ui/generator/borrowing.rs
View file

@ -8,11 +8,11 @@
// option. This file may not be copied, modified, or distributed
// except according to those terms.
#![feature(generators, generator_trait, rustc_attrs)]
#![feature(generators, generator_trait)]
use std::ops::Generator;
fn main() { #![rustc_error] // rust-lang/rust#49855
fn main() {
let _b = {
let a = 3;
unsafe { (|| yield &a).resume() }

26
src/test/ui/generator/dropck.nll.stderr
View file

@ -1,14 +1,20 @@
error: compilation successful
--> $DIR/dropck.rs:16:1
error[E0597]: `ref_` does not live long enough
--> $DIR/dropck.rs:22:11
|
LL | / fn main() { #![rustc_error] // rust-lang/rust#49855
LL | | let (cell, mut gen);
LL | | cell = Box::new(RefCell::new(0));
LL | | let ref_ = Box::leak(Box::new(Some(cell.borrow_mut())));
... |
LL | | // drops the RefCell and then the Ref, leading to use-after-free
LL | | }
| |_^
LL | gen = || {
| ___________^
LL | | // but the generator can use it to drop a `Ref<'a, i32>`.
LL | | let _d = ref_.take(); //~ ERROR `ref_` does not live long enough
LL | | yield;
LL | | };
| |_____^ borrowed value does not live long enough
...
LL | }
| -
| |
| borrowed value only lives until here
| borrow later used here, when `gen` is dropped
error: aborting due to previous error
For more information about this error, try `rustc --explain E0597`.

5
src/test/ui/generator/dropck.rs
View file

@ -8,15 +8,16 @@
// option. This file may not be copied, modified, or distributed
// except according to those terms.
#![feature(generators, generator_trait, box_leak, rustc_attrs)]
#![feature(generators, generator_trait, box_leak)]
use std::cell::RefCell;
use std::ops::Generator;
fn main() { #![rustc_error] // rust-lang/rust#49855
fn main() {
let (cell, mut gen);
cell = Box::new(RefCell::new(0));
let ref_ = Box::leak(Box::new(Some(cell.borrow_mut())));
//~^ ERROR `*cell` does not live long enough [E0597]
// the upvar is the non-dropck `&mut Option<Ref<'a, i32>>`.
gen = || {
// but the generator can use it to drop a `Ref<'a, i32>`.

15
src/test/ui/generator/dropck.stderr
View file

@ -1,5 +1,16 @@
error[E0597]: `*cell` does not live long enough
--> $DIR/dropck.rs:19:40
|
LL | let ref_ = Box::leak(Box::new(Some(cell.borrow_mut())));
| ^^^^ borrowed value does not live long enough
...
LL | }
| - `*cell` dropped here while still borrowed
|
= note: values in a scope are dropped in the opposite order they are created
error[E0597]: `ref_` does not live long enough
--> $DIR/dropck.rs:23:18
--> $DIR/dropck.rs:24:18
|
LL | gen = || {
| -- capture occurs here
@ -12,6 +23,6 @@ LL | }
|
= note: values in a scope are dropped in the opposite order they are created
error: aborting due to previous error
error: aborting due to 2 previous errors
For more information about this error, try `rustc --explain E0597`.

18
src/test/ui/generator/ref-escapes-but-not-over-yield.nll.stderr
View file

@ -1,11 +1,19 @@
error[E0597]: `b` does not live long enough
--> $DIR/ref-escapes-but-not-over-yield.rs:24:13
|
LL | a = &b;
| ^^ borrowed value does not live long enough
LL | //~^ ERROR `b` does not live long enough
LL | };
| - borrowed value only lives until here
LL | let mut b = move || {
| _________________-
LL | | yield();
LL | | let b = 5;
LL | | a = &b;
| | ^^ borrowed value does not live long enough
LL | | //~^ ERROR `b` does not live long enough
LL | | };
| | -
| | |
| | borrowed value only lives until here
| |_____temporary later dropped here, potentially using the reference
| borrow may end up in a temporary, created here
error: aborting due to previous error