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Auto merge of #99943 - compiler-errors:tuple-trait, r=jackh726

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Implement `std::marker::Tuple`, use it in `extern "rust-call"` and `Fn`-family traits

Implements rust-lang/compiler-team#537

I made a few opinionated decisions in this implementation, specifically:
1. Enforcing `extern "rust-call"` on fn items during wfcheck,
2. Enforcing this for all functions (not just ones that have bodies),
3. Gating this `Tuple` marker trait behind its own feature, instead of grouping it into (e.g.) `unboxed_closures`.

Still needing to be done:
1. Enforce that `extern "rust-call"` `fn`-ptrs are well-formed only if they have 1/2 args and the second one implements `Tuple`. (Doing this would fix ICE in #66696.)
2. Deny all explicit/user `impl`s of the `Tuple` trait, kinda like `Sized`.
3. Fixing `Tuple` trait built-in impl for chalk, so that chalkification tests are un-broken.

Open questions:
1. Does this need t-lang or t-libs signoff?

Fixes #99820
This commit is contained in:
bors 2022-11-06 17:48:33 +00:00
commit 7eef946fc0
53 changed files with 843 additions and 244 deletions
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28
compiler/rustc_hir_analysis/src/check/wfcheck.rs
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@ -21,6 +21,7 @@ use rustc_middle::ty::{GenericArgKind, InternalSubsts};
use rustc_session::parse::feature_err;
use rustc_span::symbol::{sym, Ident, Symbol};
use rustc_span::{Span, DUMMY_SP};
use rustc_target::spec::abi::Abi;
use rustc_trait_selection::autoderef::Autoderef;
use rustc_trait_selection::traits::error_reporting::TypeErrCtxtExt;
use rustc_trait_selection::traits::outlives_bounds::InferCtxtExt as _;
@ -1542,6 +1543,33 @@ fn check_fn_or_method<'tcx>(
sig.output(),
hir_decl.output.span(),
);
if sig.abi == Abi::RustCall {
let span = tcx.def_span(def_id);
let has_implicit_self = hir_decl.implicit_self != hir::ImplicitSelfKind::None;
let mut inputs = sig.inputs().iter().skip(if has_implicit_self { 1 } else { 0 });
// Check that the argument is a tuple
if let Some(ty) = inputs.next() {
wfcx.register_bound(
ObligationCause::new(span, wfcx.body_id, ObligationCauseCode::RustCall),
wfcx.param_env,
*ty,
tcx.require_lang_item(hir::LangItem::Tuple, Some(span)),
);
} else {
tcx.sess.span_err(
hir_decl.inputs.last().map_or(span, |input| input.span),
"functions with the \"rust-call\" ABI must take a single non-self tuple argument",
);
}
// No more inputs other than the `self` type and the tuple type
if inputs.next().is_some() {
tcx.sess.span_err(
hir_decl.inputs.last().map_or(span, |input| input.span),
"functions with the \"rust-call\" ABI must take a single non-self tuple argument",
);
}
}
}
/// Basically `check_associated_type_bounds`, but separated for now and should be