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Rollup merge of #136107 - dingxiangfei2009:coerce-pointee-wellformed, r=compiler-errors

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Introduce CoercePointeeWellformed for coherence checks at typeck stage

Fix #135206

This is the first PR to introduce the "wellformedness" check for `derive(CoercePointee)`.

This patch introduces a new error code to cover all the prerequisites of the said macro. The checks that is enforced with this patch is whether the data is indeed `struct` and whether the layout is set to `repr(transparent)`.

A following series of patch will arrive later to address the following concern.
1. #135217 so that we would only admit one single coercion on one type parameter, and leave the rest for future consideration in tandem of development of other coercion rules.
1. Enforcement of data field requirements.

**An open question** is whether there is a good schema to encode the `#[pointee]` as well, so that we could also check if the `#[pointee]` type parameter is indeed `?Sized`.

``@rustbot`` label F-derive_coerce_pointee
This commit is contained in:
Matthias Krüger 2025-02-11 02:53:42 +01:00 • committed by GitHub
commit af3c51d849
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15 changed files with 385 additions and 54 deletions
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6
compiler/rustc_hir/src/lang_items.rs
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@ -370,6 +370,8 @@ language_item_table! {
PointerLike, sym::pointer_like, pointer_like, Target::Trait, GenericRequirement::Exact(0);
CoercePointeeValidated, sym::coerce_pointee_validated, coerce_pointee_validated_trait, Target::Trait, GenericRequirement::Exact(0);
ConstParamTy, sym::const_param_ty, const_param_ty_trait, Target::Trait, GenericRequirement::Exact(0);
UnsizedConstParamTy, sym::unsized_const_param_ty, unsized_const_param_ty_trait, Target::Trait, GenericRequirement::Exact(0);
@ -429,9 +431,13 @@ language_item_table! {
ContractCheckRequires, sym::contract_check_requires, contract_check_requires_fn, Target::Fn, GenericRequirement::None;
}
/// The requirement imposed on the generics of a lang item
pub enum GenericRequirement {
/// No restriction on the generics
None,
/// A minimum number of generics that is demanded on a lang item
Minimum(usize),
/// The number of generics must match precisely as stipulated
Exact(usize),
}