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Mitigate `#[align]` name resolution ambiguity regression with a rename
Mitigates beta regression rust-lang/rust#143834 after a beta backport.
### Background on the beta regression
The name resolution regression arises due to rust-lang/rust#142507 adding a new feature-gated built-in attribute named `#[align]`. However, unfortunately even [introducing new feature-gated unstable built-in attributes can break user code](https://www.github.com/rust-lang/rust/issues/134963) such as
```rs
macro_rules! align {
() => {
/* .. */
};
}
pub(crate) use align; // `use` here becomes ambiguous
```
### Mitigation approach
This PR renames `#[align]` to `#[rustc_align]` to mitigate the beta regression by:
1. Undoing the introduction of a new built-in attribute with a common name, i.e. `#[align]`.
2. Renaming `#[align]` to `#[rustc_align]`. The renamed attribute being `rustc_align` will not introduce new stable breakages, as attributes beginning with `rustc` are reserved and perma-unstable. This does mean existing nightly code using `fn_align` feature will additionally need to specify `#![feature(rustc_attrs)]`.
This PR is very much a short-term mitigation to alleviate time pressure from having to fully fix the current limitation of inevitable name resolution regressions that would arise from adding any built-in attributes. Long-term solutions are discussed in [#t-lang > namespacing macro attrs to reduce conflicts with new adds](https://rust-lang.zulipchat.com/#narrow/channel/213817-t-lang/topic/namespacing.20macro.20attrs.20to.20reduce.20conflicts.20with.20new.20adds/with/529249622).
### Alternative mitigation options
[Various mitigation options were considered during the compiler triage meeting](https://github.com/rust-lang/rust/issues/143834#issuecomment-3084415277), and those consideration are partly reproduced here:
- Reverting the PR doesn't seem very minimal/trivial, and carries risks of its own.
- Rename to a less-common but aim-to-stabilization name is itself not safe nor convenient, because (1) that risks introducing new regressions (i.e. ambiguity against the new name), and (2) lang would have to FCP the new name hastily for the mitigation to land timely and have a chance to be backported. This also makes the path towards stabilization annoying.
- Rename the attribute to a rustc attribute, which will be perma-unstable and does not cause new ambiguities in stable code.
- This alleviates the time pressure to address *this* regression, or for lang to have to rush an FCP for some new name that can still break user code.
- This avoids backing out a whole implementation.
### Review advice
This PR is best reviewed commit-by-commit.
- Commit 1 adds a test `tests/ui/attributes/fn-align-nameres-ambiguity-143834.rs` which demonstrates the current name resolution regression re. `align`. This test fails against current master.
- Commit 2 carries out the renames and test reblesses. Notably, commit 2 will cause `tests/ui/attributes/fn-align-nameres-ambiguity-143834.rs` to change from fail (nameres regression) to pass.
This PR, if the approach still seems acceptable, will need a beta-backport to address the beta regression.
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From `#[align]` -> `#[rustc_align]`. Attributes starting with `rustc`
are always perma-unstable and feature-gated by `feature(rustc_attrs)`.
See regression RUST-143834.
For the underlying problem where even introducing new feature-gated
unstable built-in attributes can break user code such as
```rs
macro_rules! align {
() => {
/* .. */
};
}
pub(crate) use align; // `use` here becomes ambiguous
```
refer to RUST-134963.
Since the `#[align]` attribute is still feature-gated by
`feature(fn_align)`, we can rename it as a mitigation. Note that
`#[rustc_align]` will obviously mean that current unstable user code
using `feature(fn_aling)` will need additionally `feature(rustc_attrs)`,
but this is a short-term mitigation to buy time, and is expected to be
changed to a better name with less collision potential.
See
<https://rust-lang.zulipchat.com/#narrow/channel/238009-t-compiler.2Fmeetings/topic/.5Bweekly.5D.202025-07-17/near/529290371>
where mitigation options were considered.
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Split-up stability_index query
This PR aims to move deprecation and stability processing away from the monolithic `stability_index` query, and directly implement `lookup_{deprecation,stability,body_stability,const_stability}` queries.
The basic idea is to:
- move per-attribute sanity checks into `check_attr.rs`;
- move attribute compatibility checks into the `MissingStabilityAnnotations` visitor;
- progressively dismantle the `Annotator` visitor and the `stability_index` query.
The first commit contains functional change, and now warns when `#[automatically_derived]` is applied on a non-trait impl block. The other commits should not change visible behaviour.
Perf in https://github.com/rust-lang/rust/pull/143845#issuecomment-3066308630 shows small but consistent improvement, except for unused-warnings case. That case being a stress test, I'm leaning towards accepting the regression.
This PR changes `check_attr`, so has a high conflict rate on that file. This should not cause issues for review.
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Port `#[coverage]` to the new attribute system
r? ``````@jdonszelmann``````
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parse `const trait Trait`
r? oli-obk or anyone from project-const-traits
cc `@rust-lang/project-const-traits`
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Fix ice for feature-gated `cfg` attributes applied to the crate
This PR fixes two fixes:
1. When a feature gated option of the `cfg` attribute is applied to the crate, an ICE would occur because features are not yet available at that stage. This is fixed by ignoring the feature gate at that point, the attribute will later be re-checked (this was already done) when the feature gate is available. Fixes https://github.com/rust-lang/rust/issues/143977
2. Errors and lints on the `cfg` attribute applied to the crate would be produced twice, because of the re-checking. This is fixed by not producing any errors and lints during the first run.
The added regression test checks both problems.
r? ``@jdonszelmann``
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Implement unstable trait impl
This PR allows marking impls of stable trait with stable type as unstable.
## Approach
In std/core, an impl can be marked as unstable by annotating it with ``#[unstable_feature_bound(feat_name)]``. This will add a ``ClauseKind::Unstable_Feature(feat_name)`` to the list of predicates in ``predicates_of`` .
When an unstable impl's function is called, we will first iterate through all the goals in ``param_env`` to check if there is any ``ClauseKind::UnstableFeature(feat_name)`` in ``param_env``.
The existence of ``ClauseKind::Unstable_Feature(feat_name)`` in ``param_env`` means an``#[unstable_feature_bound(feat_name)]`` is present at the call site of the function, so we allow the check to succeed in this case.
If ``ClauseKind::UnstableFeature(feat_name)`` does not exist in ``param_env``, we will still allow the check to succeed for either of the cases below:
1. The feature is enabled through ``#[feature(feat_name)]`` outside of std / core.
2. We are in codegen because we may be monomorphizing a body from an upstream crate which had an unstable feature enabled that the downstream crate do not.
For the rest of the case, it will fail with ambiguity.
## Limitation
In this PR, we do not support:
1. using items that need ``#[unstable_feature_bound]`` within stable APIs
2. annotate main function with ``#[unstable_feature_bound]``
3. annotate ``#[unstable_feature_bound]`` on items other than free function and impl
## Acknowledgement
The design and mentoring are done by `@BoxyUwU`
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Signed-off-by: Jonathan Brouwer <jonathantbrouwer@gmail.com>
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item
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Rollup of 13 pull requests
Successful merges:
- rust-lang/rust#142301 (tests: Fix duplicated-path-in-error fail with musl)
- rust-lang/rust#143630 (Drop `./x suggest`)
- rust-lang/rust#143736 (Give all bytes of TypeId provenance)
- rust-lang/rust#143752 (Don't panic if WASI_SDK_PATH not set when detecting compiler)
- rust-lang/rust#143837 (Adjust `run_make_support::symbols` helpers)
- rust-lang/rust#143878 (Port `#[pointee]` to the new attribute parsing infrastructure)
- rust-lang/rust#143905 (Recover and suggest to use `;` to construct array type)
- rust-lang/rust#143907 (core: make `str::split_at_unchecked()` inline)
- rust-lang/rust#143910 (Add experimental `backtrace-trace-only` std feature)
- rust-lang/rust#143927 (Preserve constness in trait objects up to hir ty lowering)
- rust-lang/rust#143935 (rustc_type_ir/walk: move docstring to `TypeWalker` itself)
- rust-lang/rust#143938 (Update books)
- rust-lang/rust#143941 (update `cfg_select!` documentation)
Failed merges:
- rust-lang/rust#143926 (Remove deprecated fields in bootstrap)
r? `@ghost`
`@rustbot` modify labels: rollup
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Signed-off-by: Jonathan Brouwer <jonathantbrouwer@gmail.com>
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r=jdonszelmann
Port `#[omit_gdb_pretty_printer_section]` to the new attribute parsing
Ports `#[omit_gdb_pretty_printer_section]` to the new attribute parsing infrastructure for https://github.com/rust-lang/rust/issues/131229#issuecomment-2971351163
r? ```@jdonszelmann```
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Port #[link_ordinal] to the new attribute parsing infrastructure
Ports link_ordinal to the new attribute parsing infrastructure for https://github.com/rust-lang/rust/issues/131229#issuecomment-2971353197
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infrastructure
Signed-off-by: Jonathan Brouwer <jonathantbrouwer@gmail.com>
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Signed-off-by: Jonathan Brouwer <jonathantbrouwer@gmail.com>
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Port several trait/coherence-related attributes the new attribute system
Part of rust-lang/rust#131229
This ports:
- `#[const_trait]`
- `#[rustc_deny_explicit_impl]`
- `#[rustc_do_not_implement_via_object]`
- `#[rustc_coinductive]`
- `#[type_const]`
- `#[rustc_specialization_trait]`
- `#[rustc_unsafe_specialization_marker]`
- `#[marker]`
- `#[fundamental]`
- `#[rustc_paren_sugar]`
- `#[rustc_allow_incoherent_impl]`
- `#[rustc_coherence_is_core]`
This also changes `#[marker]` to error on duplicates instead of warning.
cc rust-lang/rust#142838, but I don't think it matters too much, since it's unstable.
r? ``@oli-obk``
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Clarify the meaning of `AttributeOrder::KeepFirst` and `AttributeOrder::KeepLast`
Clarify the meaning of `KeepLast` and `KeepFirst` for https://github.com/rust-lang/rust/issues/131229#issuecomment-2971353197
Just a minor clarification, but me and ``@JonathanBrouwer`` have confused these two a few times so I think it's warranted.
r? ``@oli-obk``
cc ``@JonathanBrouwer``
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Port #[rustc_dummy]
r? ``@jdonszelmann``
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`AttributeOrder::KeepLast`
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Signed-off-by: Jonathan Brouwer <jonathantbrouwer@gmail.com>
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Signed-off-by: Jonathan Brouwer <jonathantbrouwer@gmail.com>
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Signed-off-by: Jonathan Brouwer <jonathantbrouwer@gmail.com>
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Port `#[rustc_pass_by_value]` to the new attribute system
Part of rust-lang/rust#131229
r? `@oli-obk`
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