Sized Hierarchy: Part I #137944
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Sized Hierarchy: Part I #137944
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cc @rust-lang/lang |
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Does this perhaps fix #127336 by rejecting it? |
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It doesn't currently. |
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Undrafting now that CI passes |
`nominal_obligations` calls `predicates_of` on a `Sized` obligation, effectively elaborating the trait and making the well-formedness checking machinery do a bunch of extra work checking a `MetaSized` obligation is well-formed, but given that both `Sized` and `MetaSized` are built-ins, if `Sized` is otherwise well-formed, so `MetaSized` will be.
These should never be shown to users at the moment.
Some rustdoc tests are `no_core` and need to have `MetaSized` and `PointeeSized` added to them.
As before, updating types using extern types to use `PointeeSized` bounds.
Unexpected Clippy lint triggering is fixed in upcoming commits but is necessary for `cfg(bootstrap)`.
Existing lints that had special-casing for `Sized` predicates ought to have these same special cases applied to `MetaSized` predicates.
One clippy test is `no_core` and needs to have `MetaSized` and `PointeeSized` added to it.
As in many previous commits, adding the new traits to minicore, but this time for cranelift and gcc.
It isn't clear why the `Deref` impl isn't found for this in a stage two build, but presumably relates to `rustc_middle::ty::RawList` containing an extern type and `Deref` not yet being relaxed to `PointeeSized` (this is technically a breaking change but unlikely to be one and will be tested in a follow-up).
These error messages include lines of the standard library which have changed and so need updated.
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The final comment period, with a disposition to merge, as per the review above, is now complete. As the automated representative of the governance process, I would like to thank the author for their work and everyone else who contributed. This will be merged soon. |
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@bors r+ p=5 Let's not let this bit rot any more |
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Sized Hierarchy: Part I This patch implements the non-const parts of rust-lang/rfcs#3729. It introduces two new traits to the standard library, `MetaSized` and `PointeeSized`. See the RFC for the rationale behind these traits and to discuss whether this change makes sense in the abstract. These traits are unstable (as is their constness), so users cannot refer to them without opting-in to `feature(sized_hierarchy)`. These traits are not behind `cfg`s as this would make implementation unfeasible, there would simply be too many `cfg`s required to add the necessary bounds everywhere. So, like `Sized`, these traits are automatically implemented by the compiler. RFC 3729 describes changes which are necessary to preserve backwards compatibility given the introduction of these traits, which are implemented and as follows: - `?Sized` is rewritten as `MetaSized` - `MetaSized` is added as a default supertrait for all traits w/out an explicit sizedness supertrait already. There are no edition migrations implemented in this, as these are primarily required for the constness parts of the RFC and prior to stabilisation of this (and so will come in follow-up PRs alongside the const parts). All diagnostic output should remain the same (showing `?Sized` even if the compiler sees `MetaSized`) unless the `sized_hierarchy` feature is enabled. Due to the use of unstable extern types in the standard library and rustc, some bounds in both projects have had to be relaxed already - this is unfortunate but unavoidable so that these extern types can continue to be used where they were before. Performing these relaxations in the standard library and rustc are desirable longer-term anyway, but some bounds are not as relaxed as they ideally would be due to the inability to relax `Deref::Target` (this will be investigated separately). It is hoped that this is implemented such that it could be merged and these traits could exist "under the hood" without that being observable to the user (other than in any performance impact this has on the compiler, etc). Some details might leak through due to the standard library relaxations, but this has not been observed in test output. **Notes:** - Any commits starting with "upstream:" can be ignored, as these correspond to other upstream PRs that this is based on which have yet to be merged. - This best reviewed commit-by-commit. I've attempted to make the implementation easy to follow and keep similar changes and test output updates together. - Each commit has a short description describing its purpose. - This patch is large but it's primarily in the test suite. - I've worked on the performance of this patch and a few optimisations are implemented so that the performance impact is neutral-to-minor. - `PointeeSized` is a different name from the RFC just to make it more obvious that it is different from `std::ptr::Pointee` but all the names are yet to be bikeshed anyway. - `@nikomatsakis` has confirmed [that this can proceed as an experiment from the t-lang side](https://rust-lang.zulipchat.com/#narrow/channel/435869-project-goals/topic/SVE.20and.20SME.20on.20AArch64.20.28goals.23270.29/near/506196491) - FCP in #137944 (comment) Fixes #79409. r? `@ghost` (I'll discuss this with relevant teams to find a reviewer)
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The job Click to see the possible cause of the failure (guessed by this bot) |
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💔 Test failed - checks-actions |
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Handwritten minicores. |
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☔ The latest upstream changes (presumably #142483) made this pull request unmergeable. Please resolve the merge conflicts. |
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572b452 is in so this should be good to go after rebase. |
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This patch implements the non-const parts of rust-lang/rfcs#3729. It introduces two new traits to the standard library,
MetaSizedandPointeeSized. See the RFC for the rationale behind these traits and to discuss whether this change makes sense in the abstract.These traits are unstable (as is their constness), so users cannot refer to them without opting-in to
feature(sized_hierarchy). These traits are not behindcfgs as this would make implementation unfeasible, there would simply be too manycfgs required to add the necessary bounds everywhere. So, likeSized, these traits are automatically implemented by the compiler.RFC 3729 describes changes which are necessary to preserve backwards compatibility given the introduction of these traits, which are implemented and as follows:
?Sizedis rewritten asMetaSizedMetaSizedis added as a default supertrait for all traits w/out an explicit sizedness supertrait already.There are no edition migrations implemented in this, as these are primarily required for the constness parts of the RFC and prior to stabilisation of this (and so will come in follow-up PRs alongside the const parts). All diagnostic output should remain the same (showing
?Sizedeven if the compiler seesMetaSized) unless thesized_hierarchyfeature is enabled.Due to the use of unstable extern types in the standard library and rustc, some bounds in both projects have had to be relaxed already - this is unfortunate but unavoidable so that these extern types can continue to be used where they were before. Performing these relaxations in the standard library and rustc are desirable longer-term anyway, but some bounds are not as relaxed as they ideally would be due to the inability to relax
Deref::Target(this will be investigated separately).It is hoped that this is implemented such that it could be merged and these traits could exist "under the hood" without that being observable to the user (other than in any performance impact this has on the compiler, etc). Some details might leak through due to the standard library relaxations, but this has not been observed in test output.
Notes:
PointeeSizedis a different name from the RFC just to make it more obvious that it is different fromstd::ptr::Pointeebut all the names are yet to be bikeshed anyway.Fixes #79409.
r? @ghost (I'll discuss this with relevant teams to find a reviewer)