Transition unsupported naked functions future incompatibility lint into
an error:
* Naked functions must contain a single inline assembly block.
Introduced as future incompatibility lint in 1.50 #79653.
Change into an error fixes a soundness issue described in #32489.
* Naked functions must not use any forms of inline attribute.
Introduced as future incompatibility lint in 1.56 #87652.
Introduce drop range tracking to generator interior analysis
This PR addresses cases such as this one from #57478:
```rust
struct Foo;
impl !Send for Foo {}
let _: impl Send = || {
let guard = Foo;
drop(guard);
yield;
};
```
Previously, the `generator_interior` pass would unnecessarily include the type `Foo` in the generator because it was not aware of the behavior of `drop`. We fix this issue by introducing a drop range analysis that finds portions of the code where a value is guaranteed to be dropped. If a value is dropped at all suspend points, then it is no longer included in the generator type. Note that we are using "dropped" in a generic sense to include any case in which a value has been moved. That is, we do not only look at calls to the `drop` function.
There are several phases to the drop tracking algorithm, and we'll go into more detail below.
1. Use `ExprUseVisitor` to find values that are consumed and borrowed.
2. `DropRangeVisitor` uses consume and borrow information to gather drop and reinitialization events, as well as build a control flow graph.
3. We then propagate drop and reinitialization information through the CFG until we reach a fix point (see `DropRanges::propagate_to_fixpoint`).
4. When recording a type (see `InteriorVisitor::record`), we check the computed drop ranges to see if that value is definitely dropped at the suspend point. If so, we skip including it in the type.
## 1. Use `ExprUseVisitor` to find values that are consumed and borrowed.
We use `ExprUseVisitor` to identify the places where values are consumed. We track both the `hir_id` of the value, and the `hir_id` of the expression that consumes it. For example, in the expression `[Foo]`, the `Foo` is consumed by the array expression, so after the array expression we can consider the `Foo` temporary to be dropped.
In this process, we also collect values that are borrowed. The reason is that the MIR transform for generators conservatively assumes anything borrowed is live across a suspend point (see `rustc_mir_transform::generator::locals_live_across_suspend_points`). We match this behavior here as well.
## 2. Gather drop events, reinitialization events, and control flow graph
After finding the values of interest, we perform a post-order traversal over the HIR tree to find the points where these values are dropped or reinitialized. We use the post-order index of each event because this is how the existing generator interior analysis refers to the position of suspend points and the scopes of variables.
During this traversal, we also record branching and merging information to handle control flow constructs such as `if`, `match`, and `loop`. This is necessary because values may be dropped along some control flow paths but not others.
## 3. Iterate to fixed point
The previous pass found the interesting events and locations, but now we need to find the actual ranges where things are dropped. Upon entry, we have a list of nodes ordered by their position in the post-order traversal. Each node has a set of successors. For each node we additionally keep a bitfield with one bit per potentially consumed value. The bit is set if we the value is dropped along all paths entering this node.
To compute the drop information, we first reverse the successor edges to find each node's predecessors. Then we iterate through each node, and for each node we set its dropped value bitfield to the intersection of all incoming dropped value bitfields.
If any bitfield for any node changes, we re-run the propagation loop again.
## 4. Ignore dropped values across suspend points
At this point we have a data structure where we can ask whether a value is guaranteed to be dropped at any post order index for the HIR tree. We use this information in `InteriorVisitor` to check whether a value in question is dropped at a particular suspend point. If it is, we do not include that value's type in the generator type.
Note that we had to augment the region scope tree to include all yields in scope, rather than just the last one as we did before.
r? `@nikomatsakis`
This change adds the basic infrastructure for tracking drop ranges in
generator interior analysis, which allows us to exclude dropped types
from the generator type.
Not yet complete, but many of the async/await and generator tests pass.
The main missing piece is tracking branching control flow (e.g. around
an `if` expression). The patch does include support, however, for
multiple yields in th e same block.
Issue #57478
Avoid unnecessary monomorphization of inline asm related functions
This should reduce build time for codegen backends by avoiding duplicated monomorphization of certain inline asm related functions for each passed in closure type.
Add some more attribute validation
This adds some more validation for the position of attributes:
* `link` is only valid on an `extern` block
* `windows_subsystem` and `no_builtins` are only valid at the crate level
Replace `NestedVisitorMap` with generic `NestedFilter`
This is an attempt to make the `intravisit::Visitor` API simpler and "more const" with regard to nested visiting.
With this change, `intravisit::Visitor` does not visit nested things by default, unless you specify `type NestedFilter = nested_filter::OnlyBodies` (or `All`). `nested_visit_map` returns `Self::Map` instead of `NestedVisitorMap<Self::Map>`. It panics by default (unreachable if `type NestedFilter` is omitted).
One somewhat trixty thing here is that `nested_filter::{OnlyBodies, All}` live in `rustc_middle` so that they may have `type Map = map::Map` and so that `impl Visitor`s never need to specify `type Map` - it has a default of `Self::NestedFilter::Map`.
Remove deprecated LLVM-style inline assembly
The `llvm_asm!` was deprecated back in #87590 1.56.0, with intention to remove
it once `asm!` was stabilized, which already happened in #91728 1.59.0. Now it
is time to remove `llvm_asm!` to avoid continued maintenance cost.
Closes#70173.
Closes#92794.
Closes#87612.
Closes#82065.
cc `@rust-lang/wg-inline-asm`
r? `@Amanieu`
expand: Pick `cfg`s and `cfg_attrs` one by one, like other attributes
This is a rebase of https://github.com/rust-lang/rust/pull/83354, but without any language-changing parts ~(except for https://github.com/rust-lang/rust/pull/84110)~, i.e. the attribute expansion order is the same.
This is a pre-requisite for any other changes making cfg attributes closer to regular macro attributes
- Possibly changing their expansion order (https://github.com/rust-lang/rust/issues/83331)
- Keeping macro backtraces for cfg attributes, or otherwise making them visible after expansion without keeping them in place literally (https://github.com/rust-lang/rust/pull/84110).
Two exceptions to the "one by one" behavior are:
- cfgs eagerly expanded by `derive` and `cfg_eval`, they are still expanded in a batch, that's by design.
- cfgs at the crate root, they are currently expanded not during the main expansion pass, but before that, during `#![feature]` collection. I'll try to disentangle that logic later in a separate PR.
r? `@Aaron1011`
Closure capture cleanup & refactor
Follow up of #89648
Each commit is self-contained and the rationale/changes are documented in the commit message, so it's advisable to review commit by commit.
The code is significantly cleaner (at least IMO), but that could have some perf implication, so I'd suggest a perf run.
r? `@wesleywiser`
cc `@arora-aman`
Remove `SymbolStr`
This was originally proposed in https://github.com/rust-lang/rust/pull/74554#discussion_r466203544. As well as removing the icky `SymbolStr` type, it allows the removal of a lot of `&` and `*` occurrences.
Best reviewed one commit at a time.
r? `@oli-obk`
Implement let-else type annotations natively
Tracking issue: #87335Fixes#89688, fixes#89807, edit: fixes #89960 as well
As explained in https://github.com/rust-lang/rust/issues/89688#issuecomment-940405082, the previous desugaring moved the let-else scrutinee into a dummy variable, which meant if you wanted to refer to it again in the else block, it had moved.
This introduces a new hir type, ~~`hir::LetExpr`~~ `hir::Let`, which takes over all the fields of `hir::ExprKind::Let(...)` and adds an optional type annotation. The `hir::Let` is then treated like a `hir::Local` when type checking a function body, specifically:
* `GatherLocalsVisitor` overrides a new `Visitor::visit_let_expr` and does pretty much exactly what it does for `visit_local`, assigning a local type to the `hir::Let` ~~(they could be deduplicated but they are right next to each other, so at least we know they're the same)~~
* It reuses the code in `check_decl_local` to typecheck the `hir::Let`, simply returning 'bool' for the expression type after doing that.
* ~~`FnCtxt::check_expr_let` passes this local type in to `demand_scrutinee_type`, and then imitates check_decl_local's pattern checking~~
* ~~`demand_scrutinee_type` (the blindest change for me, please give this extra scrutiny) uses this local type instead of of creating a new one~~
* ~~Just realised the `check_expr_with_needs` was passing NoExpectation further down, need to pass the type there too. And apparently this Expectation API already exists.~~
Some other misc notes:
* ~~Is the clippy code supposed to be autoformatted? I tried not to give huge diffs but maybe some rustfmt changes simply haven't hit it yet.~~
* in `rustc_ast_lowering/src/block.rs`, I noticed some existing `self.alias_attrs()` calls in `LoweringContext::lower_stmts` seem to be copying attributes from the lowered locals/etc to the statements. Is that right? I'm new at this, I don't know.
Stabilize `iter::zip`
Hello all!
As the tracking issue (#83574) for `iter::zip` completed the final commenting period without any concerns being raised, I hereby submit this stabilization PR on the issue.
As the pull request that introduced the feature (#82917) states, the `iter::zip` function is a shorter way to zip two iterators. As it's generally a quality-of-life/ergonomic improvement, it has been integrated into the codebase without any trouble, and has been
used in many places across the rust compiler and standard library since March without any issues.
For more details, I would refer to `@cuviper's` original PR, or the [function's documentation](https://doc.rust-lang.org/std/iter/fn.zip.html).
Tweak errors coming from `for`-loop, `?` and `.await` desugaring
* Suggest removal of `.await` on non-`Future` expression
* Keep track of obligations introduced by desugaring
* Remove span pointing at method for obligation errors coming from desugaring
* Point at called local sync `fn` and suggest making it `async`
```
error[E0277]: `()` is not a future
--> $DIR/unnecessary-await.rs:9:10
|
LL | boo().await;
| -----^^^^^^ `()` is not a future
| |
| this call returns `()`
|
= help: the trait `Future` is not implemented for `()`
help: do not `.await` the expression
|
LL - boo().await;
LL + boo();
|
help: alternatively, consider making `fn boo` asynchronous
|
LL | async fn boo () {}
| +++++
```
Fix#66731.
tidy run
update invalid crate attributes, improve error
update test outputs
de-capitalise error
update tests
Update invalid crate attributes, add help message
Update - generate span without using BytePos
Add correct dependancies
Update - generate suggestion without BytePos
Tidy run
update tests
Generate Suggestion without BytePos
Add all builtin attributes
add err builtin inner attr at top of crate
fix tests
add err builtin inner attr at top of crate
tidy fix
add err builtin inner attr at top of crate
Take a LocalDefId in expect_*item.
Items and item-likes are always HIR owners.
When trying to find such nodes, there is no ambiguity, the `LocalDefId` and the `HirId::owner` always match.
In such cases, `local_def_id_to_hir_id` does not carry any meaningful information, so we can just skip calling it altogether.
Various fixes for const_trait_impl
A few problems I found while making `Iterator` easier to const-implement.
1. More generous `~const Drop` check.
We check for nested fields with caller bounds.
For example, an ADT type with fields of types `A`, `B`, `C`, check if all of them are either:
- Bounded (`A: ~const Drop`, `B: Copy`)
- Known to be able to destruct at compile time (`C = i32`, `struct C(i32)`, `C = some_fn`)
2. Don't treat trait functions marked with `#[default_method_body_is_const]` as stable const fns when checking `const_for` and `const_try` feature gates.
I think anyone can review this, so no r? this time.
warn on must_use use on async fn's
As referenced in #78149
This only works on `async` fn's for now, I can also look into if I can get `Box<dyn Future>` and `impl Future` working at this level (hir)
Type inference for inline consts
Fixes#78132Fixes#78174Fixes#81857Fixes#89964
Perform type checking/inference of inline consts in the same context as the outer def, similar to what is currently done to closure.
Doing so would require `closure_base_def_id` of the inline const to return the outer def, and since `closure_base_def_id` can be called on non-local crate (and thus have no HIR available), a new `DefKind` is created for inline consts.
The type of the generated anon const can capture lifetime of outer def, so we couldn't just use the typeck result as the type of the inline const's def. Closure has a similar issue, and it uses extra type params `CK, CS, U` to capture closure kind, input/output signature and upvars. I use a similar approach for inline consts, letting it have an extra type param `R`, and then `typeof(InlineConst<[paremt generics], R>)` would just be `R`. In borrowck region requirements are also propagated to the outer MIR body just like it's currently done for closure.
With this PR, inline consts in expression position are quitely usable now; however the usage in pattern position is still incomplete -- since those does not remain in the MIR borrowck couldn't verify the lifetime there. I have left an ignored test as a FIXME.
Some disucssions can be found on [this Zulip thread](https://rust-lang.zulipchat.com/#narrow/stream/260443-project-const-generics/topic/inline.20consts.20typeck).
cc `````@spastorino````` `````@lcnr`````
r? `````@nikomatsakis`````
`````@rustbot````` label A-inference F-inline_const T-compiler
Unify titles in rustdoc book doc attributes chapter
As discussed in https://github.com/rust-lang/rust/pull/90339.
I wasn't able to find out where the link to the titles was used so let's see if the CI fails. :)
r? ``@camelid``
Rollup of 7 pull requests
Successful merges:
- #89298 (Issue 89193 - Fix ICE when using `usize` and `isize` with SIMD gathers )
- #89461 (Add `deref_into_dyn_supertrait` lint.)
- #89477 (Move items related to computing diffs to a separate file)
- #89559 (RustWrapper: adapt for LLVM API change)
- #89585 (Emit item no type error even if type inference fails)
- #89596 (Make cfg imply doc(cfg))
- #89615 (Add InferCtxt::with_opaque_type_inference to get_body_with_borrowck_facts)
Failed merges:
r? `@ghost`
`@rustbot` modify labels: rollup
Make cfg imply doc(cfg)
This is a reopening of #79341, rebased and modified a bit (we made a lot of refactoring in rustdoc's types so they needed to be reflected in this PR as well):
* `hidden_cfg` is now in the `Cache` instead of `DocContext` because `cfg` information isn't stored anymore on `clean::Attributes` type but instead computed on-demand, so we need this information in later parts of rustdoc.
* I removed the `bool_to_options` feature (which makes the code a bit simpler to read for `SingleExt` trait implementation.
* I updated the version for the feature.
There is only one thing I couldn't figure out: [this comment](https://github.com/rust-lang/rust/pull/79341#discussion_r561855624)
> I think I'll likely scrap the whole `SingleExt` extension trait as the diagnostics for 0 and >1 items should be different.
How/why should they differ?
EDIT: this part has been solved, the current code was fine, just needed a little simplification.
cc `@Nemo157`
r? `@jyn514`
Original PR description:
This is only active when the `doc_cfg` feature is active.
The implicit cfg can be overridden via `#[doc(cfg(...))]`, so e.g. to hide a `#[cfg]` you can use something like:
```rust
#[cfg(unix)]
#[doc(cfg(all()))]
pub struct Unix;
```
By adding `#![doc(cfg_hide(foobar))]` to the crate attributes the cfg `#[cfg(foobar)]` (and _only_ that _exact_ cfg) will not be implicitly treated as a `doc(cfg)` to render a message in the documentation.
Introduce `tcx.get_diagnostic_name`
Introduces a "reverse lookup" for diagnostic items. This is mainly intended for `@rust-lang/clippy` which often does a long series of `is_diagnostic_item` calls for the same `DefId`.
r? `@oli-obk`
perf: only check for `rustc_trivial_field_reads` attribute on traits, not items, impls, etc.
The checks that are removed in this PR (originally added in #85200) caused a small perf regression: https://github.com/rust-lang/rust/pull/88824#issuecomment-932664761
Since the attribute is currently only applied to traits, I don't think it's worth keeping the additional checks for now.
If/when we decide to apply the attribute somewhere else, we can (partially) revert this and reevaluate the perf impact.
r? `@nikomatsakis` cc `@FabianWolff`
The checks removed here caused a small perf regression:
https://github.com/rust-lang/rust/pull/88824#issuecomment-932664761
Since the attribute is currently only applied to traits, I don't think
it's worth keeping the additional checks for now.
If/when we decide to apply the attribute somewhere else, we can
(partially) revert this and evaluate if the perf impact is acceptable.
Implement `#[must_not_suspend]`
implements #83310
Some notes on the impl:
1. The code that searches for the attribute on the ADT is basically copied from the `must_use` lint. It's not shared, as the logic did diverge
2. The RFC does specify that the attribute can be placed on fn's (and fn-like objects), like `must_use`. I think this is a direct copy from the `must_use` reference definition. This implementation does NOT support this, as I felt that ADT's (+ `impl Trait` + `dyn Trait`) cover the usecase's people actually want on the RFC, and adding an imp for the fn call case would be significantly harder. The `must_use` impl can do a single check at fn call stmt time, but `must_not_suspend` would need to answer the question: "for some value X with type T, find any fn call that COULD have produced this value". That would require significant changes to `generator_interior.rs`, and I would need mentorship on that. `@eholk` and I are discussing it.
3. `@estebank` do you know a way I can make the user-provided `reason` note pop out? right now it seems quite hidden
Also, I am not sure if we should run perf on this
r? `@nikomatsakis`
Migrate in-tree crates to 2021
This replaces #89075 (cherry picking some of the commits from there), and closes#88637 and fixes#89074.
It excludes a migration of the library crates for now (see tidy diff) because we have some pending bugs around macro spans to fix there.
I instrumented bootstrap during the migration to make sure all crates moved from 2018 to 2021 had the compatibility warnings applied first.
Originally, the intent was to support cargo fix --edition within bootstrap, but this proved fairly difficult to pull off. We'd need to architect the check functionality to support running cargo check and cargo fix within the same x.py invocation, and only resetting sysroots on check. Further, it was found that cargo fix doesn't behave too well with "not quite workspaces", such as Clippy which has several crates. Bootstrap runs with --manifest-path ... for all the tools, and this makes cargo fix only attempt migration for that crate. We can't use e.g. --workspace due to needing to maintain sysroots for different phases of compilation appropriately.
It is recommended to skip the mass migration of Cargo.toml's to 2021 for review purposes; you can also use `git diff d6cd2c6c87 -I'^edition = .20...$'` to ignore the edition = 2018/21 lines in the diff.
Gather module items after lowering.
This avoids having a non-local analysis inside lowering.
By implementing `hir_module_items` using a visitor, we make sure that iterations and visitors are consistent.
If #![feature] is used outside the nightly channel for only lib
features, the check will be delayed to the stability pass after
parsing. This is done so that appropriate help messages can be shown if
the #![feature] has been used needlessly
Avoid invoking the hir_crate query to traverse the HIR
Walking the HIR tree is done using the `hir_crate` query. However, this is unnecessary, since `hir_owner(CRATE_DEF_ID)` provides the same information. Since depending on `hir_crate` forces dependents to always be executed, this leads to unnecessary work.
By splitting HIR and attributes visits, we can avoid an edge to `hir_crate` when trying to visit the HIR tree.
Provide `layout_of` automatically (given tcx + param_env + error handling).
After #88337, there's no longer any uses of `LayoutOf` within `rustc_target` itself, so I realized I could move the trait to `rustc_middle::ty::layout` and redesign it a bit.
This is similar to #88338 (and supersedes it), but at no ergonomic loss, since there's no funky `C: LayoutOf<Ty = Ty>` -> `Ty: TyAbiInterface<C>` generic `impl` chain, and each `LayoutOf` still corresponds to one `impl` (of `LayoutOfHelpers`) for the specific context.
After this PR, this is what's needed to get `trait LayoutOf` (with the `layout_of` method) implemented on some context type:
* `TyCtxt`, via `HasTyCtxt`
* `ParamEnv`, via `HasParamEnv`
* a way to transform `LayoutError`s into the desired error type
* an error type of `!` can be paired with having `cx.layout_of(...)` return `TyAndLayout` *without* `Result<...>` around it, such as used by codegen
* this is done through a new `LayoutOfHelpers` trait (and so is specifying the type of `cx.layout_of(...)`)
When going through this path (and not bypassing it with a manual `impl` of `LayoutOf`), the end result is that only the error case can be customized, the query itself and the success paths are guaranteed to be uniform.
(**EDIT**: just noticed that because of the supertrait relationship, you cannot actually implement `LayoutOf` yourself, the blanket `impl` fully covers all possible context types that could ever implement it)
Part of the motivation for this shape of API is that I've been working on querifying `FnAbi::of_*`, and what I want/need to introduce for that looks a lot like the setup in this PR - in particular, it's harder to express the `FnAbi` methods in `rustc_target`, since they're much more tied to `rustc` concepts.
r? `@nagisa` cc `@oli-obk` `@bjorn3`
MIR lowering for `if let` expressions is now more complicated now that
`if let` exists in HIR. This PR adds a scope for the variables bound in
an `if let` expression and then uses an approach similar to how we
handle loops to ensure that we reliably drop the correct variables.
Emit specific warning to clarify that `#[no_mangle]` should not be applied on foreign statics or functions
Foreign statics and foreign functions should not have `#[no_mangle]` applied, as it does nothing to the name and has some extra hidden behavior that is normally unwanted. There was an existing warning for this, but it says the attribute is only allowed on "statics or functions", which to the user can be confusing.
This PR adds a specific version of the unused `#[no_mangle]` warning that explains that the target is a *foreign* static or function and that they do not need the attribute.
Fixes#78989
rustc_target: `TyAndLayout::field` should never error.
This refactor (making `TyAndLayout::field` return `TyAndLayout` without any `Result` around it) is based on a simple observation, regarding `TyAndLayout::field`:
If `cx.layout_of(ty)` succeeds (for some `cx` and `ty`), then `.field(cx, i)` on the resulting `TyAndLayout` should *always* succeed in computing `cx.layout_of(field_ty)` (where `field_ty` is the type of the `i`th field of `ty`).
The reason for this is that no matter which field is chosen, `cx.layout_of(field_ty)` *will have already been computed*, as part of computing `cx.layout_of(ty)`, as we cannot determine the layout of *any* type without considering the layouts of *all* of its fields.
And so it should be fine to turn any errors into ICEs, since they likely indicate a `cx` mismatch, or some other edge case that is due to a compiler bug (as opposed to ever being an user-facing error).
<hr/>
Each commit should probably be reviewed separately, though note that there's some `where` clauses (in `rustc_target::abi::call::*`) that change in most commits.
cc `@nagisa` `@oli-obk`
Improve detection of generics on lang items
Adds detection for the required generics for all lang items. Many lang items require an exact or minimum amount of generic arguments and if they don't exist, the compiler will ICE. This does not add any additional validation about bounds on generics or any other lang item restrictions.
Fixes one of the ICEs in #87573
cc `@FabianWolff`
Improve liveness analysis for generators
Liveness analysis for generators assumes that execution always continues
normally after a yield point, not accounting for the fact that generator
could be dropped before completion.
If generators captures any variables by reference, those variables could
be used within a generator, or when the generator completes, but also
after each yield point in the case the generator is dropped.
Account for the case when generator is dropped after yielding, but
before running to the completion. This effectively considers all
variables captured by reference to be used after a yield point.
Fixes#84292.
Liveness analysis for generators assumes that execution always continues
normally after a yield point, not accounting for the fact that generator
could be dropped before completion.
If generators captures any variables by reference, those variables could
be used within a generator, or when the generator completes, but also
after each yield point in the case the generator is dropped.
Account for the case when generator is dropped after yielding, but
before running to the completion. This effectively considers all
variables captured by reference to be used after a yield point.
Remove `Session.used_attrs` and move logic to `CheckAttrVisitor`
Instead of updating global state to mark attributes as used,
we now explicitly emit a warning when an attribute is used in
an unsupported position. As a side effect, we are to emit more
detailed warning messages (instead of just a generic "unused" message).
`Session.check_name` is removed, since its only purpose was to mark
the attribute as used. All of the callers are modified to use
`Attribute.has_name`
Additionally, `AttributeType::AssumedUsed` is removed - an 'assumed
used' attribute is implemented by simply not performing any checks
in `CheckAttrVisitor` for a particular attribute.
We no longer emit unused attribute warnings for the `#[rustc_dummy]`
attribute - it's an internal attribute used for tests, so it doesn't
mark sense to treat it as 'unused'.
With this commit, a large source of global untracked state is removed.
Warn about unreachable code following an expression with an uninhabited type
This pull request fixes#85071. The issue is that liveness analysis currently is "smarter" than reachability analysis when it comes to detecting uninhabited types: Unreachable code is detected during type checking, where full type information is not yet available. Therefore, the check for type inhabitedness is quite crude:
fc81ad22c4/compiler/rustc_typeck/src/check/expr.rs (L202-L205)
i.e. it only checks for `!`, but not other, non-trivially uninhabited types, such as empty enums, structs containing an uninhabited type, etc. By contrast, liveness analysis, which runs after type checking, can benefit from the more sophisticated `tcx.is_ty_uninhabited_from()`:
fc81ad22c4/compiler/rustc_passes/src/liveness.rs (L981)fc81ad22c4/compiler/rustc_passes/src/liveness.rs (L996)
This can lead to confusing warnings when a variable is reported as unused, but the use of the variable is not reported as unreachable. For instance:
```rust
enum Foo {}
fn f() -> Foo {todo!()}
fn main() {
let x = f();
let _ = x;
}
```
currently leads to
```
warning: unused variable: `x`
--> t1.rs:5:9
|
5 | let x = f();
| ^ help: if this is intentional, prefix it with an underscore: `_x`
|
= note: `#[warn(unused_variables)]` on by default
warning: 1 warning emitted
```
which is confusing, because `x` _appears_ to be used in line 6. With my changes, I get:
```
warning: unreachable expression
--> t1.rs:6:13
|
5 | let x = f();
| --- any code following this expression is unreachable
6 | let _ = x;
| ^ unreachable expression
|
= note: `#[warn(unreachable_code)]` on by default
note: this expression has type `Foo`, which is uninhabited
--> t1.rs:5:13
|
5 | let x = f();
| ^^^
warning: unused variable: `x`
--> t1.rs:5:9
|
5 | let x = f();
| ^ help: if this is intentional, prefix it with an underscore: `_x`
|
= note: `#[warn(unused_variables)]` on by default
warning: 2 warnings emitted
```
My implementation is slightly inelegant because unreachable code warnings can now be issued in two different places (during type checking and during liveness analysis), but I think it is the solution with the least amount of unnecessary code duplication, given that the new warning integrates nicely with liveness analysis, where unreachable code is already implicitly detected for the purpose of finding unused variables.
Instead of updating global state to mark attributes as used,
we now explicitly emit a warning when an attribute is used in
an unsupported position. As a side effect, we are to emit more
detailed warning messages (instead of just a generic "unused" message).
`Session.check_name` is removed, since its only purpose was to mark
the attribute as used. All of the callers are modified to use
`Attribute.has_name`
Additionally, `AttributeType::AssumedUsed` is removed - an 'assumed
used' attribute is implemented by simply not performing any checks
in `CheckAttrVisitor` for a particular attribute.
We no longer emit unused attribute warnings for the `#[rustc_dummy]`
attribute - it's an internal attribute used for tests, so it doesn't
mark sense to treat it as 'unused'.
With this commit, a large source of global untracked state is removed.
Add future-incompat lint for `doc(primitive)`
## What is `doc(primitive)`?
`doc(primitive)` is an attribute recognized by rustdoc which adds documentation for the built-in primitive types, such as `usize` and `()`. It has been stable since Rust 1.0.
## Why change anything?
`doc(primitive)` is useless for anyone outside the standard library. Since rustdoc provides no way to combine the documentation on two different primitive items, you can only replace the docs, and since the standard library already provides extensive documentation there is no reason to do so.
While fixing rustdoc's handling of primitive items (https://github.com/rust-lang/rust/pull/87073) I discovered that even rustdoc's existing handling of primitive items was broken if you had more than two crates using it (it would pick randomly between them). That meant both:
- Keeping rustdoc's existing treatment was nigh-impossible, because it was random.
- doc(primitive) was even more useless than it would otherwise be.
The only use-case for this outside the standard library is for no-std libraries which want to link to primitives (https://github.com/rust-lang/rust/issues/73423) which is being fixed in https://github.com/rust-lang/rust/pull/87073.
https://github.com/rust-lang/rust/pull/87073 makes various breaking changes to `doc(primitive)` (breaking in the sense that they change the semantics, not in that they cause code to fail to compile). It's not possible to avoid these and still fix rustdoc's issues.
## What can we do about it?
As shown by the crater run (https://github.com/rust-lang/rust/pull/87050#issuecomment-886166706), no one is actually using doc(primitive), there wasn't a single true regression in the whole run. We can either:
1. Feature gate it completely, breaking anyone who crater missed. They can easily fix the breakage just by removing the attribute.
2. add it to the `INVALID_DOC_ATTRIBUTES` future-incompat lint, and at the same time make it a no-op unless you add a feature gate. That would mean rustdoc has to look at the features of dependent crates, because it needs to know where primitives are defined in order to link to them.
3. add it to `INVALID_DOC_ATTRIBUTES`, but still use it to determine where primitives come from
4. do nothing; the behavior will silently change in https://github.com/rust-lang/rust/pull/87073.
My preference is for 2, but I would also be happy with 1 or 3. I don't think we should silently change the behavior.
This PR currently implements 3.
Move naked function ABI check to its own lint
This check was previously categorized under the lint named
`UNSUPPORTED_NAKED_FUNCTIONS`. That lint is future incompatible and will
be turned into an error in a future release. However, as defined in the
Constrained Naked Functions RFC, this check should only be a warning.
This is because it is possible for a naked function to be implemented in
such a way that it does not break even the undefined ABI. For example, a
`jmp` to a `const`.
Therefore, this patch defines a new lint named
`UNDEFINED_NAKED_FUNCTION_ABI` which contains just this single check.
Unlike `UNSUPPORTED_NAKED_FUNCTIONS`, `UNDEFINED_NAKED_FUNCTION_ABI`
will not be converted to an error in the future.
rust-lang/rfcs#2774rust-lang/rfcs#2972
In most calling conventions, accessing function parameters may require
stack access. However, naked functions have no assembly prelude to set
up stack access. This is why naked functions may only contain a single
`asm!()` block. All parameter access is done inside the `asm!()` block,
so we cannot validate the liveness of the input parameters. Therefore,
we should disable the lint for naked functions.
rust-lang/rfcs#2774rust-lang/rfcs#2972
This check was previously categorized under the lint named
`UNSUPPORTED_NAKED_FUNCTIONS`. That lint is future incompatible and will
be turned into an error in a future release. However, as defined in the
Constrained Naked Functions RFC, this check should only be a warning.
This is because it is possible for a naked function to be implemented in
such a way that it does not break even the undefined ABI. For example, a
`jmp` to a `const`.
Therefore, this patch defines a new lint named
`UNDEFINED_NAKED_FUNCTION_ABI` which contains just this single check.
Unlike `UNSUPPORTED_NAKED_FUNCTIONS`, `UNDEFINED_NAKED_FUNCTION_ABI`
will not be converted to an error in the future.
rust-lang/rfcs#2774rust-lang/rfcs#2972
rustc: Replace `HirId`s with `LocalDefId`s in `AccessLevels` tables
and passes using those tables - primarily privacy checking, stability checking and dead code checking.
All these passes work with definitions rather than with arbitrary HIR nodes.
r? `@cjgillot`
cc `@lambinoo` (#87487)
