Skip to content
Permalink
Browse files

ignore higher-ranked WF requirements for trait objects

In the `issue-53548` test added in this commit, the `Box<dyn Trait>`
type is expanded to `Box<dyn Trait + 'static>`, but the generator
"witness" that results is `for<'r> { Box<dyn Trait + 'r> }`. The WF
code was encountering an ICE (when debug-assertions were enabled) and
an unexpected compilation error (without debug-asserions) when trying
to process this `'r` region bound. In particular, to be WF, the region
bound must meet the requirements of the trait, and hence we got
`for<'r> { 'r: 'static }`. This would ICE because the `Binder`
constructor we were using was assering that no higher-ranked regions
were involved (because the WF code is supposed to skip those). The
error (if debug-asserions were disabled) came because we obviously
cannot prove that `'r: 'static` for any region `'r`.  Pursuant with
our "lazy WF" strategy for higher-ranked regions, the fix is not to
require that `for<'r> { 'r: 'static }` holds (this is also analogous
to what we would do for higher-ranked regions appearing within the
trait in other positions).
  • Loading branch information...
nikomatsakis committed Mar 12, 2019
1 parent 4632e33 commit 261daf27c9e4b9332ac8d17fc4f9997fcd1ded3f
Showing with 60 additions and 2 deletions.
  1. +1 −2 src/librustc/ty/wf.rs
  2. +20 −0 src/test/ui/generator/issue-53548-1.rs
  3. +39 −0 src/test/ui/generator/issue-53548.rs
@@ -482,8 +482,7 @@ impl<'a, 'gcx, 'tcx> WfPredicates<'a, 'gcx, 'tcx> {
//
// Note: in fact we only permit builtin traits, not `Bar<'d>`, I
// am looking forward to the future here.

if !data.has_escaping_bound_vars() {
if !data.has_escaping_bound_vars() && !region.has_escaping_bound_vars() {
let implicit_bounds =
object_region_bounds(self.infcx.tcx, data);

@@ -0,0 +1,20 @@
// A variant of #53548 that does not actually require generators,
// but which encountered the same ICE/error. See `issue-53548.rs`
// for details.
//
// compile-pass

use std::cell::RefCell;
use std::rc::Rc;

trait Trait: 'static {}

struct Store<C> {
inner: Rc<RefCell<Option<C>>>,
}

fn main() {
let store = Store::<Box<for<'a> fn(&(dyn Trait + 'a))>> {
inner: Default::default(),
};
}
@@ -0,0 +1,39 @@
// Regression test for #53548. The `Box<dyn Trait>` type below is
// expanded to `Box<dyn Trait + 'static>`, but the generator "witness"
// that results is `for<'r> { Box<dyn Trait + 'r> }`. The WF code was
// encountering an ICE (when debug-assertions were enabled) and an
// unexpected compilation error (without debug-asserions) when trying
// to process this `'r` region bound. In particular, to be WF, the
// region bound must meet the requirements of the trait, and hence we
// got `for<'r> { 'r: 'static }`. This would ICE because the `Binder`
// constructor we were using was assering that no higher-ranked
// regions were involved (because the WF code is supposed to skip
// those). The error (if debug-asserions were disabled) came because
// we obviously cannot prove that `'r: 'static` for any region `'r`.
// Pursuant with our "lazy WF" strategy for higher-ranked regions, the
// fix is not to require that `for<'r> { 'r: 'static }` holds (this is
// also analogous to what we would do for higher-ranked regions
// appearing within the trait in other positions).
//
// compile-pass

#![feature(generators)]

use std::cell::RefCell;
use std::rc::Rc;

trait Trait: 'static {}

struct Store<C> {
inner: Rc<RefCell<Option<C>>>,
}

fn main() {
Box::new(static move || {
let store = Store::<Box<dyn Trait>> {
inner: Default::default(),
};
yield ();
});
}

0 comments on commit 261daf2

Please sign in to comment.
You can’t perform that action at this time.