`#[naked]`: report incompatible attributes
tracking issue: https://github.com/rust-lang/rust/issues/90957
this is a re-implementation of https://github.com/rust-lang/rust/pull/93809 by ``@bstrie`` which was closed 2 years ago due to inactivity.
This PR takes some of the final comments into account, specifically providing a little more context in error messages, and using an allow list to determine which attributes are compatible with `#[naked]`.
Notable attributes that are incompatible with `#[naked]` are:
* `#[inline]`
* `#[track_caller]`
* ~~`#[target_feature]`~~ (this is now allowed, see PR discussion)
* `#[test]`, `#[ignore]`, `#[should_panic]`
These attributes just directly conflict with what `#[naked]` should do.
Naked functions are still important for systems programming, embedded, and operating systems, so I'd like to move them forward.
Disable jump threading of float equality
Jump threading stores values as `u128` (`ScalarInt`) and does its comparisons for equality as integer comparisons.
This works great for integers. Sadly, not everything is an integer.
Floats famously have wonky equality semantcs, with `NaN!=NaN` and `0.0 == -0.0`. This does not match our beautiful integer bitpattern equality and therefore causes things to go horribly wrong.
While jump threading could be extended to support floats by remembering that they're floats in the value state and handling them properly, it's signficantly easier to just disable it for now.
fixes#128243
Remove logic to suggest clone of function output
I can't exactly tell, but I believe that this suggestion is operating off of a heuristic that the lifetime of a function's input is correlated with the lifetime of a function's output in such a way that cloning would fix an error. I don't think that actually manages to hit the bar of "actually provides useful suggestions" most of the time.
Specifically, I've hit false-positives due to this suggestion *twice* when fixing ICEs in the compiler, so I don't think it's worthwhile having this logic around. Neither of the two affected UI tests are actually fixed by the suggestion.
improve error message when `global_asm!` uses `asm!` options
specifically, what was
error: expected one of `)`, `att_syntax`, or `raw`, found `preserves_flags`
--> $DIR/bad-options.rs:45:25
|
LL | global_asm!("", options(preserves_flags));
| ^^^^^^^^^^^^^^^ expected one of `)`, `att_syntax`, or `raw`
is now
error: the `preserves_flags` option cannot be used with `global_asm!`
--> $DIR/bad-options.rs:45:25
|
LL | global_asm!("", options(preserves_flags));
| ^^^^^^^^^^^^^^^ the `preserves_flags` option is not meaningful for global-scoped inline assembly
mirroring the phrasing of the [reference](https://doc.rust-lang.org/reference/inline-assembly.html#options).
This is also a bit of a refactor for a future `naked_asm!` macro (for use in `#[naked]` functions). Currently this sort of error can come up when switching from inline to global asm, or when a user just isn't that experienced with assembly. With `naked_asm!` added to the mix hitting this error is more likely.
Jump threading stores values as `u128` (`ScalarInt`) and does its
comparisons for equality as integer comparisons.
This works great for integers. Sadly, not everything is an integer.
Floats famously have wonky equality semantcs, with `NaN!=NaN` and
`0.0 == -0.0`. This does not match our beautiful integer bitpattern
equality and therefore causes things to go horribly wrong.
While jump threading could be extended to support floats by remembering
that they're floats in the value state and handling them properly,
it's signficantly easier to just disable it for now.
Make `missing_fragment_specifier` an error in edition 2024
`missing_fragment_specifier` has been a future compatibility warning since 2017. Uplifting it to an unconditional hard error was attempted in 2020, but eventually reverted due to fallout.
Make it an error only in edition >= 2024, leaving the lint for older editions. This change will make it easier to support more macro syntax that relies on usage of `$`.
Fixes <https://github.com/rust-lang/rust/issues/40107>
---
It is rather late for the edition but since this change is relatively small, it seems worth at least bringing up. This follows a brief [Zulip discussion](https://rust-lang.zulipchat.com/#narrow/stream/268952-edition/topic/.60.20DBD.20-.3E.20hard.20error) (cc `@tmandry).`
Making this an edition-dependent lint has come up before but there was not a strong motivation. I am proposing it at this time because this would simplify the [named macro capture groups](https://github.com/rust-lang/rfcs/pull/3649) RFC, which has had mildly positive response, and makes use of new `$` syntax in the matcher. The proposed syntax currently parses as metavariables without a fragment specifier; this warning is raised, but there are no errors.
It is obviously not known that this specific RFC will eventually be accepted, but forbidding `missing_fragment_specifier` should make it easier to support any new syntax in the future that makes use of `$` in different ways. The syntax conflict is also not impossible to overcome, but making it clear that unnamed metavariables are rejected makes things more straightforward and should allow for better diagnostics.
`@Mark-Simulacrum` suggested making this forbid-by-default instead of an error at https://github.com/rust-lang/rust/issues/40107#issuecomment-761727885, but I don't think this would allow the same level of syntax flexibility.
It is also possible to reconsider making this an unconditional error since four years have elapsed since the previous attempt, but this seems likely to hit the same pitfalls. (Possibly worth a crater run?)
Tracking:
- https://github.com/rust-lang/rust/issues/128143
- merge error codes
- use attribute name that is incompatible in error message
- add test for conditional incompatible attribute
- add `linkage` to the allowlist
`missing_fragment_specifier` has been a future compatibility warning
since 2017. Uplifting it to an unconditional hard error was attempted in
2020, but eventually reverted due to fallout.
Make it an error only in edition >= 2024, leaving the lint for older
editions. This change will make it easier to support more macro syntax
that relies on usage of `$`.
Fixes <https://github.com/rust-lang/rust/issues/40107>
Improve `extern "<abi>" unsafe fn()` error message
These errors were already reported in #87217, and fixed by #87235 but missed the case of an explicit ABI.
This PR does not cover multiple keywords like `extern "C" pub const unsafe fn()`, but I don't know what a good way to cover this would be. It also seems rarer than `extern "C" unsafe` which I saw happen a few times in workshops.
Remove unnecessary range replacements
This PR removes an unnecessary range replacement in `collect_tokens_trailing_token`, and does a couple of other small cleanups.
r? ````@petrochenkov````
Implement `Copy`/`Clone` for async closures
We can do so in the same cases that regular closures do.
For the purposes of cloning, coroutine-closures are actually precisely the same as regular closures, specifically in the aspect that `Clone` impls care about which is the upvars. The only difference b/w coroutine-closures and regular closures is the type that they *return*, but this type has not been *created* yet, so we don't really have a problem.
IDK why I didn't add this impl initially -- I went back and forth a bit on the internal representation for coroutine-closures before settling on a design which largely models regular closures. Previous (not published) iterations of coroutine-closures used to be represented as a special (read: cursed) kind of coroutine, which would probably suffer from the pitfalls that coroutines have that oli mentioned below in https://github.com/rust-lang/rust/pull/128201#issuecomment-2251230274.
r? oli-obk
Support ?Trait bounds in supertraits and dyn Trait under a feature gate
This patch allows `maybe` polarity bounds under a feature gate. The only language change here is that corresponding hard errors are replaced by feature gates. Example:
```rust
#![feature(allow_maybe_polarity)]
...
trait Trait1 : ?Trait { ... } // ok
fn foo(_: Box<(dyn Trait2 + ?Trait)>) {} // ok
fn bar<T: ?Sized + ?Trait>(_: &T) {} // ok
```
Maybe bounds still don't do anything (except for `Sized` trait), however this patch will allow us to [experiment with default auto traits](https://github.com/rust-lang/rust/pull/120706#issuecomment-1934006762).
This is a part of the [MCP: Low level components for async drop](https://github.com/rust-lang/compiler-team/issues/727)
Let InstCombine remove Clone shims inside Clone shims
The Clone shims that we generate tend to recurse into other Clone shims, which gets very silly very quickly. Here's our current state: https://godbolt.org/z/E69YeY8eq
So I've added InstSimplify to the shims optimization passes, and improved `is_trivially_pure_clone_copy` so that it can delete those calls inside the shim. This makes the shim way smaller because most of its size is the required ceremony for unwinding.
This change also completely breaks the UI test added for https://github.com/rust-lang/rust/issues/104870. With this PR, that program ICEs in MIR type checking because `is_trivially_pure_clone_copy` and the trait solver disagree on whether `*mut u8` is `Copy`. And adding the requisite `Copy` impl to make them agree makes the test not generate any diagnostics. Considering that I spent most of my time on this PR fixing `#![no_core]` tests, I would prefer to just delete this one. The maintenance burden of `#![no_core]` is uniquely high because when they break they tend to break in very confusing ways.
try-job: x86_64-mingw
exhaustiveness: Explain why a given pattern is considered unreachable
This PR tells the user why a given pattern is considered unreachable. I reused the intersection information we were already computing; even though it's incomplete I convinced myself that it is sufficient to always get a set of patterns that cover the unreachable one.
I'm not a fan of the diagnostic messages I came up with, I'm open to suggestions.
Fixes https://github.com/rust-lang/rust/issues/127870. This is also the other one of the two diagnostic improvements I wanted to do before https://github.com/rust-lang/rust/pull/122792.
Note: the first commit is an unrelated drive-by tweak.
r? `@compiler-errors`
A fully imperative style is easier to read than a half-iterator,
half-imperative style. Also, rename `inner_attr` as `attr` because it
might be an outer attribute.
Imagine you have replace ranges (2..20,X) and (5..15,Y), and these tokens:
```
a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p,q,r,s,t,u,v,w,x
```
If we replace (5..15,Y) first, then (2..20,X) we get this sequence
```
a,b,c,d,e,Y,_,_,_,_,_,_,_,_,_,p,q,r,s,t,u,v,w,x
a,b,X,_,_,_,_,_,_,_,_,_,_,_,_,_,_,_,_,_,u,v,w,x
```
which is what we want.
If we do it in the other order, we get this:
```
a,b,X,_,_,_,_,_,_,_,_,_,_,_,_,p,q,r,s,t,u,v,w,x
a,b,X,_,_,Y,_,_,_,_,_,_,_,_,_,_,_,_,_,_,u,v,w,x
```
which is wrong. So it's true that we need the `.rev()` but the comment
is wrong about why.
Make Clone::clone a lang item
I want to absorb all the logic for picking whether an Instance is LocalCopy or GloballyShared into one place. As part of this, I wanted to identify Clone shims inside `cross_crate_inlinable` and found that rather tricky. `@compiler-errors` suggested that I add a lang item for `Clone::clone` because that would produce other cleanups in the compiler.
That sounds good to me, but I have looked and I've only been able to find one.
r? compiler-errors
Extend rules of dead code analysis for impls for adts to impls for types refer to adts
The rules of dead code analysis for impl blocks can be extended to self types which refer to adts.
So that we can lint the following unused struct and trait:
```rust
struct Foo; //~ ERROR struct `Foo` is never constructed
trait Trait { //~ ERROR trait `Trait` is never used
fn foo(&self) {}
}
impl Trait for &Foo {}
```
r? `@pnkfelix`
Make it crystal clear what lint `type_alias_bounds` actually signifies
This is part of my work on https://github.com/rust-lang/rust/labels/F-lazy_type_alias ([tracking issue](#112792)).
---
To recap, the lint `type_alias_bounds` detects bounds on generic parameters and where clauses on (eager) type aliases. These bounds should've never been allowed because they are currently neither enforced[^1] at usage sites of type aliases nor thoroughly checked for correctness at definition sites due to the way type aliases are represented in the compiler. Allowing them was an oversight.
Explicitly label this as a known limitation of the type checker/system and establish the experimental feature `lazy_type_alias` as its eventual proper solution.
Where this becomes a bit tricky (for me as a rustc dev) are the "secondary effects" of these bounds whose existence I sadly can't deny. As a matter of fact, type alias bounds do play some small roles during type checking. However, after a lot of thinking over the last two weeks I've come to the conclusion (not without second-guessing myself though) that these use cases should not trump the fact that these bounds are currently *inherently broken*. Therefore the lint `type_alias_bounds` should and will continue to flag bounds that may have subordinate uses.
The two *known* secondary effects are:
1. They may enable the use of "shorthand" associated type paths `T::Assoc` (as opposed to fully qualified paths `<T as Trait>::Assoc`) where `T` is a type param bounded by some trait `Trait` which defines that assoc ty.
2. They may affect the default lifetime of trait object types passed as a type argument to the type alias. That concept is called (trait) object lifetime default.
The second one is negligible, no question asked. The first one however is actually "kinda nice" (for writability) and comes up in practice from time to time.
So why don't I just special-case trait bounds that "define" shorthand assoc type paths as originally planned in #125709?
1. Starting to permit even a tiny subset of bounds would already be enough to send a signal to users that bounds in type aliases have been legitimized and that they can expect to see type alias bounds in the wild from now on (proliferation). This would be actively misleading and dangerous because those bounds don't behave at all like one would expect, they are *not real*[^2]!
1. Let's take `type A<T: Trait> = T::Proj;` for example. Everywhere else in the language `T: Trait` means `T: Trait + Sized`. For type aliases, that's not the case though: `T: Trait` and `T: Trait + ?Sized` for that matter do neither mean `T: Trait + Sized` nor `T: Trait + ?Sized` (for both!). Instead, whether `T` requires `Sized` or not entirely depends on the definition of `Trait`[^2]. Namely, whether or not it is bounded by `Sized`.
2. Given `type A<T: Trait<AssocA = ()>> = T::AssocB;`, while `X: Trait` gets checked given `A<X>` (by virtue of projection wfchecking post alias expansion[^2]), the associated type constraint `AssocA = ()` gets dropped entirely! While we could choose to warn on such cases, it would inevitably lead to a huge pile of special cases.
3. While it's common knowledge that the body / aliased type / RHS of an (eager) type alias does not get checked for well-formedness, I'm not sure if people would realize that that extends to bounds as well. Namely, `type A<T: Trait<[u8]>> = T::Proj;` compiles even if `Trait`'s generic parameter requires `Sized`. Of course, at usage sites `[u8]: Sized` would still end up getting checked[^2], so it's not a huge problem if you have full control over `A`. However, imagine that `A` was actually part of a public API and was never used inside the defining crate (not unreasonable). In such a scenario, downstream users would be presented with an impossible to use type alias! Remember, bounds may grow arbitrarily complex and nuanced in practice.
4. Even if we allowed trait bounds that "define" shorthand assoc type paths, we would still need to continue to warn in cases where the assoc ty comes from a supertrait despite the fact that the shorthand syntax can be used: `type A<T: Sub> = T::Assoc;` does compile given `trait Sub: Super {}` and `trait Super { type Assoc; }`. However, `A<X>` does not enforce `X: Sub`, only `X: Super`[^2]. All that to say, type alias bounds are simply not real and we shouldn't pretend they are!
5. Summarizing the points above, we would be legitimizing bounds that are completely broken!
2. It's infeasible to implement: Due to the lack of `TypeckResults` in `ItemCtxt` (and a way to propagate it to other parts of the compiler), the resolution of type-dependent paths in non-`Body` items (most notably type aliases) is not recoverable from the HIR alone which would be necessary because the information of whether an associated type path (projection) is a shorthand is only present pre&in-HIR and doesn't survive HIR ty lowering. Of course, I could rerun parts of HIR ty lowering inside the lint `type_alias_bounds` (namely, `probe_single_ty_param_bound_for_assoc_ty` which would need to be exposed or alternatively a stripped-down version of it). This likely has a performance impact and introduces complexity. In short, the "benefits" are not worth the costs.
---
* 3rd commit: Update a diagnostic to avoid suggesting type alias bounds
* 4th commit: Flag type alias bounds even if the RHS contains inherent associated types.
* I started to allow them at some point in the past which was not correct (see commit for details)
* 5th commit: Allow type alias bounds if the RHS contains const projections and GCEs are enabled
* (and add a `FIXME(generic_const_exprs)` to be revisited before (M)GCE's stabilization)
* As a matter of fact type alias bounds are enforced in this case because the contained AnonConsts do get checked for well-formedness and crucially they inherit the generics and predicates of their parent item (here: the type alias)
* Remaining commits: Improve the lint `type_alias_bounds` itself
---
Fixes#125789 (sugg diag fix).
Fixes#125709 (wontfix, acknowledgement, sugg diag applic fix).
Fixes#104918 (sugg diag applic fix).
Fixes#100270 (wontfix, acknowledgement, sugg diag applic fix).
Fixes#94398 (true fix).
r? `@compiler-errors` `@oli-obk`
[^1]: From the perspective of the trait solver.
[^2]: Given `type A<T: Trait> = T::Proj;`, the reason why the trait bound "`T: Trait`" gets *seemingly* enforced at usage sites of the type alias `A` is simply because `A<X>` gets expanded to "`<X as Trait>::Proj`" very early on and it's the *expansion* that gets checked for well-formedness, not the type alias reference.
The current code is this:
```
self.capture_state.replace_ranges.push((start_pos..end_pos, Some(target)));
self.capture_state.replace_ranges.extend(inner_attr_replace_ranges);
```
What's not obvious is that every range in `inner_attr_replace_ranges`
must be a strict sub-range of `start_pos..end_pos`. Which means, in
`LazyAttrTokenStreamImpl::to_attr_token_stream`, they will be done
first, and then the `start_pos..end_pos` replacement will just overwrite
them. So they aren't needed.
This has been bugging me for a while. I find complex "if any of these
are true" conditions easier to think about than complex "if all of these
are true" conditions, because you can stop as soon as one is true.
