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Rollup merge of #85564 - pnkfelix:issue-85435-readd-capture-disjoint-fields-gate, r=nikomatsakis

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readd capture disjoint fields gate

This readds a feature gate guard that was added in PR #83521. (Basically, there were unintended consequences to the code exposed by removing the feature gate guard.)

The root bug still remains to be resolved, as discussed in issue #85561. This is just a band-aid suitable for a beta backport.

Cc issue #85435

Note that the latter issue is unfixed until we backport this (or another fix) to 1.53 beta
This commit is contained in:
Dylan DPC 2021-05-27 03:02:08 +02:00 • committed by GitHub
commit 9d4a6449db
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2 changed files with 46 additions and 14 deletions
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33
compiler/rustc_mir_build/src/build/expr/as_rvalue.rs
View file

@ -185,21 +185,26 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
// match x { _ => () } // fake read of `x`
// };
// ```
for (thir_place, cause, hir_id) in fake_reads.into_iter() {
let place_builder =
unpack!(block = this.as_place_builder(block, &this.thir[*thir_place]));
//
// FIXME(RFC2229, rust#85435): Remove feature gate once diagnostics are
// improved and unsafe checking works properly in closure bodies again.
if this.tcx.features().capture_disjoint_fields {
for (thir_place, cause, hir_id) in fake_reads.into_iter() {
let place_builder =
unpack!(block = this.as_place_builder(block, &this.thir[*thir_place]));
if let Ok(place_builder_resolved) =
place_builder.try_upvars_resolved(this.tcx, this.typeck_results)
{
let mir_place =
place_builder_resolved.into_place(this.tcx, this.typeck_results);
this.cfg.push_fake_read(
block,
this.source_info(this.tcx.hir().span(*hir_id)),
*cause,
mir_place,
);
if let Ok(place_builder_resolved) =
place_builder.try_upvars_resolved(this.tcx, this.typeck_results)
{
let mir_place =
place_builder_resolved.into_place(this.tcx, this.typeck_results);
this.cfg.push_fake_read(
block,
this.source_info(this.tcx.hir().span(*hir_id)),
*cause,
mir_place,
);
}
}
}

27
src/test/ui/unsafe/issue-85435-unsafe-op-in-let-under-unsafe-under-closure.rs Normal file
View file

@ -0,0 +1,27 @@
// check-pass
// revisions: mir thir
// [thir]compile-flags: -Z thir-unsafeck
// This is issue #85435. But the real story is reflected in issue #85561, where
// a bug in the implementation of feature(capture_disjoint_fields) () was
// exposed to non-feature-gated code by a diagnostic changing PR that removed
// the gating in one case.
// This test is double-checking that the case of interest continues to work as
// expected in the *absence* of that feature gate. At the time of this writing,
// enabling the feature gate will cause this test to fail. We obviously cannot
// stabilize that feature until it can correctly handle this test.
fn main() {
let val: u8 = 5;
let u8_ptr: *const u8 = &val;
let _closure = || {
unsafe {
let tmp = *u8_ptr;
tmp
// Just dereferencing and returning directly compiles fine:
// *u8_ptr
}
};
}