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Rollup merge of #129664 - adetaylor:arbitrary-self-types-pointers-feature-gate, r=wesleywiser

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Arbitrary self types v2: pointers feature gate.

The main `arbitrary_self_types` feature gate will shortly be reused for a new version of arbitrary self types which we are amending per [this RFC](https://github.com/rust-lang/rfcs/blob/master/text/3519-arbitrary-self-types-v2.md). The main amendments are:

* _do_ support `self` types which can't safely implement `Deref`
* do _not_ support generic `self` types
* do _not_ support raw pointers as `self` types.

This PR relates to the last of those bullet points: this strips pointer support from the current `arbitrary_self_types` feature. We expect this to cause some amount of breakage for crates using this unstable feature to allow raw pointer self types. If that's the case, we want to know about it, and we want crate authors to know of the upcoming changes.

For now, this can be resolved by adding the new
`arbitrary_self_types_pointers` feature to such crates. If we determine that use of raw pointers as self types is common, then we may maintain that as an unstable feature even if we come to stabilize the rest of the `arbitrary_self_types` support in future. If we don't hear that this PR is causing breakage, then perhaps we don't need it at all, even behind an unstable feature gate.

[Tracking issue](https://github.com/rust-lang/rust/issues/44874)

This is [step 4 of the plan outlined here](https://github.com/rust-lang/rust/issues/44874#issuecomment-2122179688)
This commit is contained in:
Matthias Krüger 2024-09-05 03:47:42 +02:00 • committed by GitHub
commit 08187c32c7
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14 changed files with 132 additions and 34 deletions
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82
compiler/rustc_hir_analysis/src/check/wfcheck.rs
View file

@ -1652,6 +1652,13 @@ fn check_fn_or_method<'tcx>(
}
}
/// The `arbitrary_self_types_pointers` feature implies `arbitrary_self_types`.
#[derive(Clone, Copy, PartialEq)]
enum ArbitrarySelfTypesLevel {
Basic, // just arbitrary_self_types
WithPointers, // both arbitrary_self_types and arbitrary_self_types_pointers
}
#[instrument(level = "debug", skip(wfcx))]
fn check_method_receiver<'tcx>(
wfcx: &WfCheckingCtxt<'_, 'tcx>,
@ -1684,14 +1691,27 @@ fn check_method_receiver<'tcx>(
return Ok(());
}
if tcx.features().arbitrary_self_types {
if !receiver_is_valid(wfcx, span, receiver_ty, self_ty, true) {
// Report error; `arbitrary_self_types` was enabled.
return Err(tcx.dcx().emit_err(errors::InvalidReceiverTy { span, receiver_ty }));
}
let arbitrary_self_types_level = if tcx.features().arbitrary_self_types_pointers {
Some(ArbitrarySelfTypesLevel::WithPointers)
} else if tcx.features().arbitrary_self_types {
Some(ArbitrarySelfTypesLevel::Basic)
} else {
if !receiver_is_valid(wfcx, span, receiver_ty, self_ty, false) {
return Err(if receiver_is_valid(wfcx, span, receiver_ty, self_ty, true) {
None
};
if !receiver_is_valid(wfcx, span, receiver_ty, self_ty, arbitrary_self_types_level) {
return Err(match arbitrary_self_types_level {
// Wherever possible, emit a message advising folks that the features
// `arbitrary_self_types` or `arbitrary_self_types_pointers` might
// have helped.
None if receiver_is_valid(
wfcx,
span,
receiver_ty,
self_ty,
Some(ArbitrarySelfTypesLevel::Basic),
) =>
{
// Report error; would have worked with `arbitrary_self_types`.
feature_err(
&tcx.sess,
@ -1699,25 +1719,49 @@ fn check_method_receiver<'tcx>(
span,
format!(
"`{receiver_ty}` cannot be used as the type of `self` without \
the `arbitrary_self_types` feature",
the `arbitrary_self_types` feature",
),
)
.with_help(fluent::hir_analysis_invalid_receiver_ty_help)
.emit()
} else {
// Report error; would not have worked with `arbitrary_self_types`.
}
None | Some(ArbitrarySelfTypesLevel::Basic)
if receiver_is_valid(
wfcx,
span,
receiver_ty,
self_ty,
Some(ArbitrarySelfTypesLevel::WithPointers),
) =>
{
// Report error; would have worked with `arbitrary_self_types_pointers`.
feature_err(
&tcx.sess,
sym::arbitrary_self_types_pointers,
span,
format!(
"`{receiver_ty}` cannot be used as the type of `self` without \
the `arbitrary_self_types_pointers` feature",
),
)
.with_help(fluent::hir_analysis_invalid_receiver_ty_help)
.emit()
}
_ =>
// Report error; would not have worked with `arbitrary_self_types[_pointers]`.
{
tcx.dcx().emit_err(errors::InvalidReceiverTy { span, receiver_ty })
});
}
}
});
}
Ok(())
}
/// Returns whether `receiver_ty` would be considered a valid receiver type for `self_ty`. If
/// `arbitrary_self_types` is enabled, `receiver_ty` must transitively deref to `self_ty`, possibly
/// through a `*const/mut T` raw pointer. If the feature is not enabled, the requirements are more
/// strict: `receiver_ty` must implement `Receiver` and directly implement
/// `Deref<Target = self_ty>`.
/// through a `*const/mut T` raw pointer if `arbitrary_self_types_pointers` is also enabled.
/// If neither feature is enabled, the requirements are more strict: `receiver_ty` must implement
/// `Receiver` and directly implement `Deref<Target = self_ty>`.
///
/// N.B., there are cases this function returns `true` but causes an error to be emitted,
/// particularly when `receiver_ty` derefs to a type that is the same as `self_ty` but has the
@ -1727,7 +1771,7 @@ fn receiver_is_valid<'tcx>(
span: Span,
receiver_ty: Ty<'tcx>,
self_ty: Ty<'tcx>,
arbitrary_self_types_enabled: bool,
arbitrary_self_types_enabled: Option<ArbitrarySelfTypesLevel>,
) -> bool {
let infcx = wfcx.infcx;
let tcx = wfcx.tcx();
@ -1745,8 +1789,8 @@ fn receiver_is_valid<'tcx>(
let mut autoderef = Autoderef::new(infcx, wfcx.param_env, wfcx.body_def_id, span, receiver_ty);
// The `arbitrary_self_types` feature allows raw pointer receivers like `self: *const Self`.
if arbitrary_self_types_enabled {
// The `arbitrary_self_types_pointers` feature allows raw pointer receivers like `self: *const Self`.
if arbitrary_self_types_enabled == Some(ArbitrarySelfTypesLevel::WithPointers) {
autoderef = autoderef.include_raw_pointers();
}
@ -1772,7 +1816,7 @@ fn receiver_is_valid<'tcx>(
// Without `feature(arbitrary_self_types)`, we require that each step in the
// deref chain implement `receiver`.
if !arbitrary_self_types_enabled {
if arbitrary_self_types_enabled.is_none() {
if !receiver_is_implemented(
wfcx,
receiver_trait_def_id,