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).
`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.
As a performance optimization, skip elaborating the supertraits of
`Sized`, and if a `MetaSized` obligation is being checked, then look for
a `Sized` predicate in the parameter environment. This makes the
`ParamEnv` smaller which should improve compiler performance as it avoids
all the iteration over the larger `ParamEnv`.
These tests just need blessing, they don't have any interesting behaviour
changes.
Some of these tests have new errors because `LegacyReceiver` cannot be
proven to be implemented now that it is also testing for `MetaSized` -
but this is just a consequence of the other errors in the test.
This test case is a reduction from the `hwc` crate on GitHub, following a
crater run. It passes with the next solver but fails on the current
solver due to a known limitation of the current solver. It starts fails
on the current solver with the `sized_hierarchy` changes because `?Sized`
is now a proper bound.
It seems like generics from `non_lifetime_binders` don't have any default
bounds like normal generics, so all of the `?Sized` relaxations need
to be further relaxed with `PointeeSized` for this test to be the
equivalent of before.
These tests necessarily need to change now that `?Sized` is not
sufficient to accept extern types and `PointeeSized` is now necessary. In
addition, the `size_of_val`/`align_of_val` test can now be changed to
expect an error.
When printing impl headers in a diagnostic, the compiler has to account
for `?Sized` implying `MetaSized` and new `MetaSized` and `PointeeSized`
bounds.
Like `Sized` diagnostics, sorting `MetaSized` and `PointeeSized`
diagnostics last prevents earlier more useful diagnostics from being
skipped because there has already been error tainting.
Given the necessary additions of bounds to these traits and their impls
in the standard library, it is necessary to add `MetaSized` bounds to
the obligation which is proven as part of checking for dyn
dispatchability.
With `MetaSized` bounds replacing `?Sized` and being added as a
supertrait, the same relaxations applied to the standard library must be
applied to minicore.
Opting-out of `Sized` with `?Sized` is now equivalent to adding a
`MetaSized` bound, and adding a `MetaSized` or `PointeeSized` bound
is equivalent to removing the default `Sized` bound - this commit
implements this change in `rustc_hir_analysis::hir_ty_lowering`.
`MetaSized` is also added as a supertrait of all traits, as this is
necessary to preserve backwards compatibility.
Unfortunately, non-global where clauses being preferred over item bounds
(where `PointeeSized` bounds would be proven) - which can result in
errors when a `PointeeSized` supertrait/bound/predicate is added to some
items. Rather than `PointeeSized` being a bound on everything, it can
be the absence of a bound on everything, as `?Sized` was.
As core uses an extern type (`ptr::VTable`), the default `?Sized` to
`MetaSized` migration isn't sufficient, and some code that previously
accepted `VTable` needs relaxed to continue to accept extern types.
Similarly, the compiler uses many extern types in `rustc_codegen_llvm`
and in the `rustc_middle::ty::List` implementation (`OpaqueListContents`)
some bounds must be relaxed to continue to accept these types.
Unfortunately, due to the current inability to relax `Deref::Target`,
some of the bounds in the standard library are forced to be stricter than
they ideally would be.
In a PR to emit warnings on misuse of `--print native-static-libs`,
we did not consider the matter of composing parts of build systems.
If you are not directly invoking rustc, it can be difficult to know
when you will in fact compile a staticlib, so making sure everyone
uses `--print native-static-lib` correctly can be just a nuisance.
This reverts the following commits:
- f66787a08d
- 72a9219e82
- 98bb597c05
- c59b70841c
Next cycle we can reland a slightly more narrowly focused variant or one
that focuses on `--emit` instead of `--print native-static-libs`.
But in its current state, I am not sure the warning is very useful.
