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Rollup merge of #92037 - fee1-dead:fix_env_dmbic, r=oli-obk

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Use a const ParamEnv when in default_method_body_is_const

r? `@oli-obk`

This PR fixes the param_env function to return `constness: Const` correctly for trait methods marked with `#[default_method_body_is_const]`. The snippet below is erroneously accepted by the compiler and has been fixed by this change. ([Playground](https://play.rust-lang.org/?version=nightly&mode=debug&edition=2021&gist=12dc6681b2eeee5f604203d96259eeb4))

```rust
#![feature(const_fn_trait_bound)]
#![feature(const_trait_impl)]

trait Tr {}
impl Tr for () {}

const fn foo<T>() where T: ~const Tr {}

pub trait Foo {
    #[default_method_body_is_const]
    fn foo() {
        foo::<()>();
    }
}
```
This commit is contained in:
Matthias Krüger 2021-12-18 14:49:42 +01:00 • committed by GitHub
commit cc043aa75f
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3 changed files with 43 additions and 1 deletions
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8
compiler/rustc_ty_utils/src/ty.rs
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@ -3,7 +3,7 @@ use rustc_hir as hir;
use rustc_hir::def_id::{DefId, LocalDefId};
use rustc_middle::ty::subst::Subst;
use rustc_middle::ty::{self, Binder, Predicate, PredicateKind, ToPredicate, Ty, TyCtxt};
use rustc_span::Span;
use rustc_span::{sym, Span};
use rustc_trait_selection::traits;
fn sized_constraint_for_ty<'tcx>(
@ -285,6 +285,12 @@ fn param_env(tcx: TyCtxt<'_>, def_id: DefId) -> ty::ParamEnv<'_> {
let constness = match hir_id {
Some(hir_id) => match tcx.hir().get(hir_id) {
hir::Node::TraitItem(hir::TraitItem { kind: hir::TraitItemKind::Fn(..), .. })
if tcx.has_attr(def_id, sym::default_method_body_is_const) =>
{
hir::Constness::Const
}
hir::Node::Item(hir::Item { kind: hir::ItemKind::Const(..), .. })
| hir::Node::Item(hir::Item { kind: hir::ItemKind::Static(..), .. })
| hir::Node::TraitItem(hir::TraitItem {