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Auto merge of #85078 - RalfJung:const_fn_unsize, r=oli-obk

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stabilize const_fn_unsize

I will post a stabilization report and ask for FCP in https://github.com/rust-lang/rust/issues/64992.
This PR is for the implementation side of stabilization.

r? `@oli-obk`
Fixes https://github.com/rust-lang/rust/issues/64992
This commit is contained in:
bors 2021-05-22 17:38:15 +00:00
commit f98bd7eeca
14 changed files with 51 additions and 123 deletions
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2
compiler/rustc_ast/src/lib.rs
View File

@ -10,8 +10,8 @@
)]
#![feature(box_syntax)]
#![feature(box_patterns)]
// On bootstrap bump, this will likely have to become const_fn_unsize
#![cfg_attr(bootstrap, feature(const_fn))] // For the `transmute` in `P::new`
#![cfg_attr(not(bootstrap), feature(const_fn_unsize))] // For the `transmute` in `P::new`
#![feature(const_fn_transmute)]
#![feature(const_panic)]
#![feature(crate_visibility_modifier)]

2
compiler/rustc_feature/src/accepted.rs
View File

@ -283,6 +283,8 @@ macro_rules! declare_features {
(accepted, non_ascii_idents, "1.53.0", Some(55467), None),
/// Allows arbitrary expressions in key-value attributes at parse time.
(accepted, extended_key_value_attributes, "1.54.0", Some(78835), None),
/// Allows unsizing coercions in `const fn`.
(accepted, const_fn_unsize, "1.54.0", Some(64992), None),
// -------------------------------------------------------------------------
// feature-group-end: accepted features

3
compiler/rustc_feature/src/active.rs
View File

@ -644,9 +644,6 @@ pub fn set(&self, features: &mut Features, span: Span) {
/// Allows trait bounds in `const fn`.
(active, const_fn_trait_bound, "1.53.0", Some(57563), None),
/// Allows unsizing coercions in `const fn`.
(active, const_fn_unsize, "1.53.0", Some(64992), None),
/// Allows `async {}` expressions in const contexts.
(active, const_async_blocks, "1.53.0", Some(85368), None),

24
compiler/rustc_mir/src/transform/check_consts/ops.rs
View File

@ -541,30 +541,6 @@ fn build_error(&self, ccx: &ConstCx<'_, 'tcx>, span: Span) -> DiagnosticBuilder<
}
}
/// See [#64992].
///
/// [#64992]: https://github.com/rust-lang/rust/issues/64992
#[derive(Debug)]
pub struct UnsizingCast;
impl NonConstOp for UnsizingCast {
fn status_in_item(&self, ccx: &ConstCx<'_, '_>) -> Status {
if ccx.const_kind() != hir::ConstContext::ConstFn {
Status::Allowed
} else {
Status::Unstable(sym::const_fn_unsize)
}
}
fn build_error(&self, ccx: &ConstCx<'_, 'tcx>, span: Span) -> DiagnosticBuilder<'tcx> {
feature_err(
&ccx.tcx.sess.parse_sess,
sym::const_fn_unsize,
span,
"unsizing casts to types besides slices are not allowed in const fn",
)
}
}
// Types that cannot appear in the signature or locals of a `const fn`.
pub mod ty {
use super::*;

18
compiler/rustc_mir/src/transform/check_consts/validation.rs
View File

@ -10,9 +10,7 @@
use rustc_middle::mir::*;
use rustc_middle::ty::cast::CastTy;
use rustc_middle::ty::subst::GenericArgKind;
use rustc_middle::ty::{
self, adjustment::PointerCast, Instance, InstanceDef, Ty, TyCtxt, TypeAndMut,
};
use rustc_middle::ty::{self, adjustment::PointerCast, Instance, InstanceDef, Ty, TyCtxt};
use rustc_middle::ty::{Binder, TraitPredicate, TraitRef};
use rustc_span::{sym, Span, Symbol};
use rustc_trait_selection::traits::error_reporting::InferCtxtExt;
@ -636,17 +634,9 @@ fn visit_rvalue(&mut self, rvalue: &Rvalue<'tcx>, location: Location) {
_,
) => self.check_op(ops::FnPtrCast),
Rvalue::Cast(CastKind::Pointer(PointerCast::Unsize), _, cast_ty) => {
if let Some(TypeAndMut { ty, .. }) = cast_ty.builtin_deref(true) {
let unsized_ty = self.tcx.struct_tail_erasing_lifetimes(ty, self.param_env);
// Casting/coercing things to slices is fine.
if let ty::Slice(_) | ty::Str = unsized_ty.kind() {
return;
}
}
self.check_op(ops::UnsizingCast);
Rvalue::Cast(CastKind::Pointer(PointerCast::Unsize), _, _) => {
// Nothing to check here (`check_local_or_return_ty` ensures no trait objects occur
// in the type of any local, which also excludes casts).
}
Rvalue::Cast(CastKind::Misc, ref operand, cast_ty) => {

8
src/test/ui/consts/const_fn_unsize.gated.stderr
View File

@ -1,8 +0,0 @@
error: fatal error triggered by #[rustc_error]
--> $DIR/const_fn_unsize.rs:16:1
|
LL | fn main() {}
| ^^^^^^^^^
error: aborting due to previous error

23
src/test/ui/consts/const_fn_unsize.rs
View File

@ -1,16 +1,21 @@
// gate-test-const_fn_unsize
// revisions: stock gated
#![feature(rustc_attrs)]
#![cfg_attr(gated, feature(const_fn_unsize))]
// run-pass
#![feature(slice_ptr_len)]
use std::ptr::NonNull;
#[allow(unused)]
const fn test() {
let _x = NonNull::<[i32; 0]>::dangling() as NonNull<[i32]>;
//[stock]~^ unsizing cast
}
#[rustc_error]
fn main() {} //[gated]~ fatal error triggered by #[rustc_error]
// Regression test for #75118.
pub const fn dangling_slice<T>() -> NonNull<[T]> {
NonNull::<[T; 1]>::dangling()
}
const C: NonNull<[i32]> = dangling_slice();
fn main() {
assert_eq!(C.as_ptr(), NonNull::<[i32; 1]>::dangling().as_ptr() as *mut _);
assert_eq!(C.as_ptr().len(), 1);
}

12
src/test/ui/consts/const_fn_unsize.stock.stderr
View File

@ -1,12 +0,0 @@
error[E0658]: unsizing casts to types besides slices are not allowed in const fn
--> $DIR/const_fn_unsize.rs:11:14
|
LL | let _x = NonNull::<[i32; 0]>::dangling() as NonNull<[i32]>;
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
= note: see issue #64992 <https://github.com/rust-lang/rust/issues/64992> for more information
= help: add `#![feature(const_fn_unsize)]` to the crate attributes to enable
error: aborting due to previous error
For more information about this error, try `rustc --explain E0658`.

6
src/test/ui/consts/min_const_fn/min_const_fn.rs
View File

@ -133,13 +133,13 @@ const fn no_dyn_trait(_x: &dyn std::fmt::Debug) {}
//~^ ERROR trait bounds other than `Sized`
const fn no_dyn_trait_ret() -> &'static dyn std::fmt::Debug { &() }
//~^ ERROR trait bounds other than `Sized`
//~| ERROR unsizing cast
//~| ERROR unsizing cast
const fn no_unsafe() { unsafe {} }
const fn really_no_traits_i_mean_it() { (&() as &dyn std::fmt::Debug, ()).1 }
//~^ ERROR unsizing cast
//~^ ERROR trait bounds other than `Sized`
//~| ERROR trait bounds other than `Sized`
//~| ERROR trait bounds other than `Sized`
const fn no_fn_ptrs(_x: fn()) {}
//~^ ERROR function pointer

46
src/test/ui/consts/min_const_fn/min_const_fn.stderr
View File

@ -288,32 +288,32 @@ LL | const fn no_dyn_trait_ret() -> &'static dyn std::fmt::Debug { &() }
= note: see issue #57563 <https://github.com/rust-lang/rust/issues/57563> for more information
= help: add `#![feature(const_fn_trait_bound)]` to the crate attributes to enable
error[E0658]: unsizing casts to types besides slices are not allowed in const fn
--> $DIR/min_const_fn.rs:134:63
|
LL | const fn no_dyn_trait_ret() -> &'static dyn std::fmt::Debug { &() }
| ^^^
|
= note: see issue #64992 <https://github.com/rust-lang/rust/issues/64992> for more information
= help: add `#![feature(const_fn_unsize)]` to the crate attributes to enable
error[E0658]: unsizing casts to types besides slices are not allowed in const fn
--> $DIR/min_const_fn.rs:134:63
|
LL | const fn no_dyn_trait_ret() -> &'static dyn std::fmt::Debug { &() }
| ^^^
|
= note: see issue #64992 <https://github.com/rust-lang/rust/issues/64992> for more information
= help: add `#![feature(const_fn_unsize)]` to the crate attributes to enable
error[E0658]: unsizing casts to types besides slices are not allowed in const fn
--> $DIR/min_const_fn.rs:141:42
error[E0658]: trait bounds other than `Sized` on const fn parameters are unstable
--> $DIR/min_const_fn.rs:139:41
|
LL | const fn really_no_traits_i_mean_it() { (&() as &dyn std::fmt::Debug, ()).1 }
| ^^^
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
= note: see issue #64992 <https://github.com/rust-lang/rust/issues/64992> for more information
= help: add `#![feature(const_fn_unsize)]` to the crate attributes to enable
= note: see issue #57563 <https://github.com/rust-lang/rust/issues/57563> for more information
= help: add `#![feature(const_fn_trait_bound)]` to the crate attributes to enable
error[E0658]: trait bounds other than `Sized` on const fn parameters are unstable
--> $DIR/min_const_fn.rs:139:42
|
LL | const fn really_no_traits_i_mean_it() { (&() as &dyn std::fmt::Debug, ()).1 }
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
= note: see issue #57563 <https://github.com/rust-lang/rust/issues/57563> for more information
= help: add `#![feature(const_fn_trait_bound)]` to the crate attributes to enable
error[E0658]: trait bounds other than `Sized` on const fn parameters are unstable
--> $DIR/min_const_fn.rs:139:42
|
LL | const fn really_no_traits_i_mean_it() { (&() as &dyn std::fmt::Debug, ()).1 }
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
= note: see issue #57563 <https://github.com/rust-lang/rust/issues/57563> for more information
= help: add `#![feature(const_fn_trait_bound)]` to the crate attributes to enable
error[E0658]: function pointers cannot appear in constant functions
--> $DIR/min_const_fn.rs:144:21

2
src/test/ui/consts/min_const_fn/min_const_fn_dyn.rs
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@ -10,6 +10,6 @@ const fn no_inner_dyn_trait2(x: Hide) {
//~^ ERROR trait bounds other than `Sized`
}
const fn no_inner_dyn_trait_ret() -> Hide { Hide(HasDyn { field: &0 }) }
//~^ ERROR unsizing cast
//~^ ERROR trait bounds other than `Sized`
fn main() {}

6
src/test/ui/consts/min_const_fn/min_const_fn_dyn.stderr
View File

@ -7,14 +7,14 @@ LL | x.0.field;
= note: see issue #57563 <https://github.com/rust-lang/rust/issues/57563> for more information
= help: add `#![feature(const_fn_trait_bound)]` to the crate attributes to enable
error[E0658]: unsizing casts to types besides slices are not allowed in const fn
error[E0658]: trait bounds other than `Sized` on const fn parameters are unstable
--> $DIR/min_const_fn_dyn.rs:12:66
|
LL | const fn no_inner_dyn_trait_ret() -> Hide { Hide(HasDyn { field: &0 }) }
| ^^
|
= note: see issue #64992 <https://github.com/rust-lang/rust/issues/64992> for more information
= help: add `#![feature(const_fn_unsize)]` to the crate attributes to enable
= note: see issue #57563 <https://github.com/rust-lang/rust/issues/57563> for more information
= help: add `#![feature(const_fn_trait_bound)]` to the crate attributes to enable
error: aborting due to 2 previous errors

10
src/test/ui/consts/unsizing-cast-non-null.rs
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@ -1,10 +0,0 @@
// Regression test for #75118.
use std::ptr::NonNull;
pub const fn dangling_slice<T>() -> NonNull<[T]> {
NonNull::<[T; 0]>::dangling()
//~^ ERROR: unsizing casts to types besides slices
}
fn main() {}

12
src/test/ui/consts/unsizing-cast-non-null.stderr
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@ -1,12 +0,0 @@
error[E0658]: unsizing casts to types besides slices are not allowed in const fn
--> $DIR/unsizing-cast-non-null.rs:6:5
|
LL | NonNull::<[T; 0]>::dangling()
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
= note: see issue #64992 <https://github.com/rust-lang/rust/issues/64992> for more information
= help: add `#![feature(const_fn_unsize)]` to the crate attributes to enable
error: aborting due to previous error
For more information about this error, try `rustc --explain E0658`.