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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 https://github.com/rust-lang/rust/pull/137944#issuecomment-2912207485 Fixes rust-lang/rust#79409. r? `@ghost` (I'll discuss this with relevant teams to find a reviewer)
The run-make test suite
The run-make test suite contains tests which are the most flexible out of all the rust-lang/rust test suites. run-make tests can basically contain arbitrary code, and are supported by the run_make_support library.
Infrastructure
A run-make test is a test recipe source file rmake.rs accompanied by its parent directory (e.g. tests/run-make/foo/rmake.rs is the foo run-make test).
The implementation for collecting and building the rmake.rs recipes are in src/tools/compiletest/src/runtest.rs, in run_rmake_test.
The setup for the rmake.rs can be summarized as a 3-stage process:
-
First, we build the
run_make_supportlibrary in bootstrap as a tool lib. -
Then, we compile the
rmake.rs"recipe" linking the support library and its dependencies in, and provide a bunch of env vars. We setup a directory structure withinbuild/<target>/test/run-make/<test-name>/ rmake.exe # recipe binary rmake_out/ # sources from test sources copied overand copy non-
rmake.rsinput support files over tormake_out/. The support library is made available as an extern prelude. -
Finally, we run the recipe binary and set
rmake_out/as the working directory.