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Guarantee result nonzero for FFI #110968

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Guarantee result nonzero for FFI #110968

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zacklukem
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Implements the required comipler changes for result_ffi_guarantees (rust-lang/rfcs#3391)

Allows Result<T, E> to be used in extern "C" functions where one of (T, E) is a non-zero type and one of (T, E) is a zero sized type. e.g. Result<NonZeroI32, ()>

Adds test cases to ensure that the abi for Result and Option types with nonzero representation remains consistent

tracking issue: #110503

@zacklukem
Guarantee result nonzero for FFI
949e166 
Implements the required comipler changes for result_ffi_guarantees
(rust-lang#3391)

Allows `Result<T, E>` to be used in extern "C" functions where one of
(T, E) is a non-zero type and one of (T, E) is a zero sized type.
e.g. `Result<NonZeroI32, ()>`

Adds test cases to ensure that the abi for Result and Option types
with nonzero representation remains consistent
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rustbot commented Apr 28, 2023

r? @jackh726

(rustbot has picked a reviewer for you, use r? to override)

@rustbot rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Apr 28, 2023
@apiraino
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r? compiler

@rustbot rustbot assigned WaffleLapkin and unassigned jackh726 May 17, 2023
WaffleLapkin
WaffleLapkin reviewed May 18, 2023
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compiler/rustc_lint/src/types.rs
Comment on lines +781 to +787
let is_zst = |field: &FieldDef, variant: &VariantDef| {
let param_env = cx.tcx.param_env(variant.def_id);
let field_ty = field.ty(cx.tcx, substs);
cx.tcx
.layout_of(param_env.and(field_ty))
.map_or(false, |layout| layout.is_zst())
};
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@WaffleLapkin WaffleLapkin May 18, 2023 •
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This is not sufficient, see the RFC:

Result<T, E> where either T or E meet all of the following conditions:

  • Is a zero-sized type with alignment 1 (a "1-ZST").
  • Has no fields.
  • Does not have the #[non_exhaustive] attribute.

(emph. mine)

compiler/rustc_lint/src/types.rs
@@ -770,8 +773,26 @@ pub(crate) fn repr_nullable_ptr<'tcx>(
debug!("is_repr_nullable_ptr(cx, ty = {:?})", ty);
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Please also update the documentation comment on this function.

compiler/rustc_lint/src/types.rs
) -> FfiResult<'tcx> {
let field_ty = field.ty(self.cx.tcx, substs);
if field_ty.has_opaque_types() {
if field_ty.is_unit() && allow_unit_type {
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This only checks for unit, shouldn't it be the same check as above? (ZST + no fields + exhaustive)

compiler/rustc_lint/src/types.rs
@@ -770,8 +773,26 @@ pub(crate) fn repr_nullable_ptr<'tcx>(
debug!("is_repr_nullable_ptr(cx, ty = {:?})", ty);
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Also, the doc comment seems to suggest we have similar code in codegen, but I don't see it changed in this PR.

@WaffleLapkin WaffleLapkin added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels May 18, 2023
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cc @Lokathor

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bors commented Jul 14, 2023

☔ The latest upstream changes (presumably #113591) made this pull request unmergeable. Please resolve the merge conflicts.

@JohnCSimon
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@zacklukem
ping from triage - can you post your status on this PR? There hasn't been an update in a few months. Thanks!

FYI: when a PR is ready for review, send a message containing
@rustbot ready to switch to S-waiting-on-review so the PR is in the reviewer's backlog.

RalfJung
RalfJung reviewed Aug 31, 2023
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compiler/rustc_lint/src/types.rs
([], [field]) | ([field], []) => field.ty(cx.tcx, substs),
// If one variant has a ZST and the other has a single field (e.g. Result<T, ()> or Result<(), T>)
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All of these uses of "ZST" here should become "1-ZST" -- it is quite important that we exclude ZST with alignment requirements. There now is a layout.is_1zst method that can and should be used here.

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Closing this as inactive. Feel free to reöpen this pr or create a new pr if you get the time to work on this. Thanks

@Dylan-DPC Dylan-DPC closed this Oct 24, 2023
@Dylan-DPC Dylan-DPC added S-inactive Status: Inactive and waiting on the author. This is often applied to closed PRs. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Oct 24, 2023
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@zacklukem @rustbot @apiraino @WaffleLapkin @bors @JohnCSimon @Dylan-DPC @RalfJung @jackh726