Collect item bounds for RPITITs from trait where clauses just like associated types
We collect item bounds from trait where clauses for *associated types*, i.e. this:
```rust
trait Foo
where
Self::Assoc: Send
{
type Assoc;
}
```
Becomes this:
```rust
trait Foo {
type Assoc: Send;
}
```
Today, with RPITITs/AFIT and return-type notation, we don't do that, i.e.:
```rust
trait Foo where Self::method(..): Send {
fn method() -> impl Sized;
}
fn is_send(_: impl Send) {}
fn test<T: Foo>() {
is_send(T::method());
}
```
...which fails on nightly today.
Turns out it's super easy to fix this, and we just need to use the `associated_type_bounds` lowering function in `explicit_item_bounds_with_filter`, which has that logic baked in.
Hack out effects support for old solver
Opening this for vibes ✨
Turns out that a basic, somewhat incomplete implementation of host effects is achievable in the old trait solver pretty easily. This should be sufficient for us to use in the standard library itself.
Regarding incompleteness, maybe we should always treat host predicates as ambiguous in intercrate mode (at least in the old solver) to avoid any worries about accidental impl overlap or something.
r? ```@lcnr``` cc ```@fee1-dead```
It's conditioned on `only-x86_64` because it doesn't reliably fail on
other platforms, it's optimization dependent and failed to ICE post-PGO
in
<https://github.com/rust-lang/rust/pull/132300#issuecomment-2443279042>.
Remove this test for now without prejudice against relanding the test in
a more reliable form.
Lint against getting pointers from immediately dropped temporaries
Fixes#123613
## Changes:
1. New lint: `dangling_pointers_from_temporaries`. Is a generalization of `temporary_cstring_as_ptr` for more types and more ways to get a temporary.
2. `temporary_cstring_as_ptr` is removed and marked as renamed to `dangling_pointers_from_temporaries`.
3. `clippy::temporary_cstring_as_ptr` is marked as renamed to `dangling_pointers_from_temporaries`.
4. Fixed a false positive[^fp] for when the pointer is not actually dangling because of lifetime extension for function/method call arguments.
5. `core::cell::Cell` is now `rustc_diagnostic_item = "Cell"`
## Questions:
- [ ] Instead of manually checking for a list of known methods and diagnostic items, maybe add some sort of annotation to those methods in library and check for the presence of that annotation? https://github.com/rust-lang/rust/pull/128985#issuecomment-2318714312
## Known limitations:
### False negatives[^fn]:
See the comments in `compiler/rustc_lint/src/dangling.rs`
1. Method calls that are not checked for:
- `temporary_unsafe_cell.get()`
- `temporary_sync_unsafe_cell.get()`
2. Ways to get a temporary that are not recognized:
- `owning_temporary.field`
- `owning_temporary[index]`
3. No checks for ref-to-ptr conversions:
- `&raw [mut] temporary`
- `&temporary as *(const|mut) _`
- `ptr::from_ref(&temporary)` and friends
[^fn]: lint **should** be emitted, but **is not**
[^fp]: lint **should not** be emitted, but **is**
Lower AST node id only once
Fixes#96346.
I basically followed the given instructions except the inline part.
`lower_jump_destination` can't reuse local existing `HirId` due to unknown name resolution result so I created an additional mapping for labels.
r? ```@cjgillot```
Rollup of 4 pull requests
Successful merges:
- #131391 (Stabilize `isqrt` feature)
- #132248 (rustc_transmute: Directly use types from rustc_abi)
- #132252 (compiler: rename LayoutS to LayoutData)
- #132253 (Known-bug test for `keyword_idents` lint not propagating to other files)
r? `@ghost`
`@rustbot` modify labels: rollup
Known-bug test for `keyword_idents` lint not propagating to other files
Known-bug test for `keyword_idents` lint not propagating to other files when configured via attribute (#132218).
fix various linker warnings
separated out from https://github.com/rust-lang/rust/pull/119286; this doesn't have anything user-facing, i just want to land these changes so i can stop rebasing them.
r? `@bjorn3`
Remove `ObligationCause::span()` method
I think it's an incredibly confusing footgun to expose both `obligation_cause.span` and `obligation_cause.span()`. Especially because `ObligationCause::span()` (the method) seems to just be hacking around a single quirk in the way we set up obligation causes for match arms.
First commit removes the need for that hack, with only one diagnostic span changing (but IMO not really getting worse -- I'd argue that it was already confusing).
Much like the previous commit.
I think the removal of "the token" in each message is fine here. There
are many more error messages that mention tokens without saying "the
token" than those that do say it.
By using `token_descr`, as is done for many other errors, we can get
slightly better descriptions in error messages, e.g.
"macro expansion ignores token `let` and any following" becomes
"macro expansion ignores keyword `let` and any tokens following".
This will be more important once invisible delimiters start being
mentioned in error messages -- without this commit, that leads to error
messages such as "error at ``" because invisible delimiters are
pretty printed as an empty string.
this makes it much easier to understand test failures.
before:
```
diff of stderr:
1 error: linking with `LINKER` failed: exit status: 1
2 |
- ld: Undefined symbols:
4 _CFRunLoopGetTypeID, referenced from:
5 clang: error: linker command failed with exit code 1 (use -v to see invocation)
```
after:
```
=== HAYSTACK ===
error: linking with `cc` failed: exit status: 1
|
= note: use `--verbose` to show all linker arguments
= note: Undefined symbols for architecture arm64:
"_CFRunLoopGetTypeID", referenced from:
main::main::hbb553f5dda62d3ea in main.main.d17f5fbe6225cf88-cgu.0.rcgu.o
ld: symbol(s) not found for architecture arm64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
error: aborting due to 1 previous error
=== NEEDLE ===
_CFRunLoopGetTypeID\.?, referenced from:
thread 'main' panicked at /Users/jyn/git/rust-lang/rust/tests/run-make/linkage-attr-framework/rmake.rs:22:10:
needle was not found in haystack
```
this also fixes a failure related to missing whitespace; we don't actually care about whitespace in this test.
Cleanup: Move an impl-Trait check from AST validation to AST lowering
Namely the one that rejects `impl Trait` in qself types and non-final path segments.
There's no good reason to perform this during AST validation.
We have better infrastructure in place in the AST lowerer (`ImplTraitContext`).
This shaves off a lot of code.
We now lower `impl Trait` in bad positions to `{type error}` which allows us to
remove a special case from HIR ty lowering.
Coincidentally fixes#126725. Well, it only *masks* it by passing `{type error}` to HIR analysis instead of a "bad" opaque. I was able to find a new reproducer for it. See the issue.
Rename macro `SmartPointer` to `CoercePointee`
As per resolution #129104 we will rename the macro to better reflect the technical specification of the feature and clarify the communication.
- `SmartPointer` is renamed to `CoerceReferent`
- `#[pointee]` attribute is renamed to `#[referent]`
- `#![feature(derive_smart_pointer)]` gate is renamed to `#![feature(derive_coerce_referent)]`.
- Any mention of `SmartPointer` in the file names are renamed accordingly.
r? `@compiler-errors`
cc `@nikomatsakis` `@Darksonn`
Rollup of 4 pull requests
Successful merges:
- #132123 (allow type-based search on foreign functions)
- #132183 (Fix code HTML items making big blocks if too long)
- #132192 (expand: Stop using artificial `ast::Item` for macros loaded from metadata)
- #132205 (docs: Correctly link riscv32e from platform-support.md)
r? `@ghost`
`@rustbot` modify labels: rollup
allow type-based search on foreign functions
fixes https://github.com/rust-lang/rust/issues/131804
preferably will be merged after #129708, but that may take a while to be approved due to being a new feature, whereas this is definitely a bug, and should be fixed.
Replace some LLVMRust wrappers with calls to the LLVM C API
This PR removes the LLVMRust wrapper functions for getting/setting linkage and visibility, and replaces them with direct calls to the corresponding functions in LLVM's C API.
To make this convenient and sound, two pieces of supporting code have also been added:
- A simple proc-macro that derives `TryFrom<u32>` for fieldless enums
- A wrapper type for C enum values returned by LLVM functions, to ensure soundness if LLVM returns an enum value we don't know about
In a few places, the use of safe wrapper functions means that an `unsafe` block is no longer needed, so the affected code has changed its indentation level.
Fixes#132203
This is a compatibility hack, because I think the new behavior is better.
When an A `include_str!` B, and B `include_str!` C, the path to C should
be resolved relative to B, not A. That's how `include!` itself works,
so that's how `include_str!` with should work.
rustc_target: Add pauth-lr aarch64 target feature
Add the pauth-lr target feature, corresponding to aarch64 FEAT_PAuth_LR. This feature has been added in LLVM 19.
It is currently not supported by the Linux hwcap and so we cannot add runtime feature detection for it at this time.
r? `@Amanieu`
(Big performance change) Do not run lints that cannot emit
Before this change, adding a lint was a difficult matter because it always had some overhead involved. This was because all lints would run, no matter their default level, or if the user had `#![allow]`ed them. This PR changes that. This change would improve both the Rust lint infrastructure and Clippy, but Clippy will see the most benefit, as it has about 900 registered lints (and growing!)
So yeah, with this little patch we filter all lints pre-linting, and remove any lint that is either:
- Manually `#![allow]`ed in the whole crate,
- Allowed in the command line, or
- Not manually enabled with `#[warn]` or similar, and its default level is `Allow`
As some lints **need** to run, this PR also adds **loadbearing lints**. On a lint declaration, you can use the ``@eval_always` = true` marker to label it as loadbearing. A loadbearing lint will never be filtered (it will always run)
Fixes#106983
Deny calls to non-`#[const_trait]` methods in MIR constck
This is a (potentially temporary) fix that closes off the mismatch in assumptions between MIR constck and typeck which does the const traits checking. Before this PR, MIR constck assumed that typeck correctly handled all calls to trait methods in const contexts if effects is enabled. That is not true because typeck only correctly handles callees that are const. For non-const callees (such as methods in a non-const_trait), typeck had never created an error.
45089ec19e/compiler/rustc_hir_typeck/src/callee.rs (L876-L877)
I called this potentially temporary because the const checks could be moved to HIR entirely. Alongside the recent refactor in const stability checks where that component could be placed would need more discussion. (cc ```@compiler-errors``` ```@RalfJung)```
Tests are updated, mainly due to traits not being const in core, so tests that call them correctly error.
This fixes https://github.com/rust-lang/project-const-traits/issues/12.
Const stability checks v2
The const stability system has served us well ever since `const fn` were first stabilized. It's main feature is that it enforces *recursive* validity -- a stable const fn cannot internally make use of unstable const features without an explicit marker in the form of `#[rustc_allow_const_fn_unstable]`. This is done to make sure that we don't accidentally expose unstable const features on stable in a way that would be hard to take back. As part of this, it is enforced that a `#[rustc_const_stable]` can only call `#[rustc_const_stable]` functions. However, some problems have been coming up with increased usage:
- It is baffling that we have to mark private or even unstable functions as `#[rustc_const_stable]` when they are used as helpers in regular stable `const fn`, and often people will rather add `#[rustc_allow_const_fn_unstable]` instead which was not our intention.
- The system has several gaping holes: a private `const fn` without stability attributes whose inherited stability (walking up parent modules) is `#[stable]` is allowed to call *arbitrary* unstable const operations, but can itself be called from stable `const fn`. Similarly, `#[allow_internal_unstable]` on a macro completely bypasses the recursive nature of the check.
Fundamentally, the problem is that we have *three* disjoint categories of functions, and not enough attributes to distinguish them:
1. const-stable functions
2. private/unstable functions that are meant to be callable from const-stable functions
3. functions that can make use of unstable const features
Functions in the first two categories cannot use unstable const features and they can only call functions from the first two categories.
This PR implements the following system:
- `#[rustc_const_stable]` puts functions in the first category. It may only be applied to `#[stable]` functions.
- `#[rustc_const_unstable]` by default puts functions in the third category. The new attribute `#[rustc_const_stable_indirect]` can be added to such a function to move it into the second category.
- `const fn` without a const stability marker are in the second category if they are still unstable. They automatically inherit the feature gate for regular calls, it can now also be used for const-calls.
Also, all the holes mentioned above have been closed. There's still one potential hole that is hard to avoid, which is when MIR building automatically inserts calls to a particular function in stable functions -- which happens in the panic machinery. Those need to be manually marked `#[rustc_const_stable_indirect]` to be sure they follow recursive const stability. But that's a fairly rare and special case so IMO it's fine.
The net effect of this is that a `#[unstable]` or unmarked function can be constified simply by marking it as `const fn`, and it will then be const-callable from stable `const fn` and subject to recursive const stability requirements. If it is publicly reachable (which implies it cannot be unmarked), it will be const-unstable under the same feature gate. Only if the function ever becomes `#[stable]` does it need a `#[rustc_const_unstable]` or `#[rustc_const_stable]` marker to decide if this should also imply const-stability.
Adding `#[rustc_const_unstable]` is only needed for (a) functions that need to use unstable const lang features (including intrinsics), or (b) `#[stable]` functions that are not yet intended to be const-stable. Adding `#[rustc_const_stable]` is only needed for functions that are actually meant to be directly callable from stable const code. `#[rustc_const_stable_indirect]` is used to mark intrinsics as const-callable and for `#[rustc_const_unstable]` functions that are actually called from other, exposed-on-stable `const fn`. No other attributes are required.
Also see the updated dev-guide at https://github.com/rust-lang/rustc-dev-guide/pull/2098.
I think in the future we may want to tweak this further, so that in the hopefully common case where a public function's const-stability just exactly mirrors its regular stability, we never have to add any attribute. But right now, once the function is stable this requires `#[rustc_const_stable]`.
### Open question
There is one point I could see we might want to do differently, and that is putting `#[rustc_const_unstable]` functions (but not intrinsics) in category 2 by default, and requiring an extra attribute for `#[rustc_const_not_exposed_on_stable]` or so. This would require a bunch of extra annotations, but would have the advantage that turning a `#[rustc_const_unstable]` into `#[rustc_const_stable]` will never change the way the function is const-checked. Currently, we often discover in the const stabilization PR that a function needs some other unstable const things, and then we rush to quickly deal with that. In this alternative universe, we'd work towards getting rid of the `rustc_const_not_exposed_on_stable` before stabilization, and once that is done stabilization becomes a trivial matter. `#[rustc_const_stable_indirect]` would then only be used for intrinsics.
I think I like this idea, but might want to do it in a follow-up PR, as it will need a whole bunch of annotations in the standard library. Also, we probably want to convert all const intrinsics to the "new" form (`#[rustc_intrinsic]` instead of an `extern` block) before doing this to avoid having to deal with two different ways of declaring intrinsics.
Cc `@rust-lang/wg-const-eval` `@rust-lang/libs-api`
Part of https://github.com/rust-lang/rust/issues/129815 (but not finished since this is not yet sufficient to safely let us expose `const fn` from hashbrown)
Fixes https://github.com/rust-lang/rust/issues/131073 by making it so that const-stable functions are always stable
try-job: test-various
Run the full stage 2 `run-make` test suite in `x86_64-gnu-debug`
Run the full `run-make` test suite in the `x86_64-gnu-debug` CI job. This is currently the *only* CI job where `//@ needs-force-clang-based-test` will be satisfied, so some `run-make` tests will literally never be run otherwise. Before this PR, the CI job only ran `run-make` tests which contains the substring `clang` in its test name, which is both (1) a footgun because it's very easy to forget and (2) it masks tests that would otherwise fail (even failing to compile) because the test is skipped if doesn't have a `clang` in its test name.
With the environment of `x86_64-gnu-debug`, two `run-make` tests failed before this PR:
1. `tests/run-make/issue-84395-lto-embed-bitcode/rmake.rs`: this was broken for a long time because `objcopy` in llvm bin tools was renamed to `llvm-objcopy`. This test was converted into a rmake.rs test, rather straight forward.
2. `tests/run-make/cross-lang-lto-riscv-abi/rmake.rs`: this was broken for a long time and never worked. The old version inspected human-readable output of `llvm-readobj --file-header` looking for substring `EF_RISCV_FLOAT_ABI_DOUBLE`, but the human-readable output will only contain something like `Flags: 0x5, RVC, double-float ABI`, hence it will never match. This test was fixed by instead using the `object` crate to actually decode the ELF headers looking for the specific `e_flags` based on reading the RISCV ELF psABI docs.
This PR is best reviewed commit-by-commit, two commits setup the support library for functionality and two commits are for each of the failing `run-make` tests.
I had to bump the `x86_64-gnu-debug` job to be ran with a runner with larger disk space.
Part of #132034.
try-job: x86_64-gnu-debug
Fundamentally, we have *three* disjoint categories of functions:
1. const-stable functions
2. private/unstable functions that are meant to be callable from const-stable functions
3. functions that can make use of unstable const features
This PR implements the following system:
- `#[rustc_const_stable]` puts functions in the first category. It may only be applied to `#[stable]` functions.
- `#[rustc_const_unstable]` by default puts functions in the third category. The new attribute `#[rustc_const_stable_indirect]` can be added to such a function to move it into the second category.
- `const fn` without a const stability marker are in the second category if they are still unstable. They automatically inherit the feature gate for regular calls, it can now also be used for const-calls.
Also, several holes in recursive const stability checking are being closed.
There's still one potential hole that is hard to avoid, which is when MIR
building automatically inserts calls to a particular function in stable
functions -- which happens in the panic machinery. Those need to *not* be
`rustc_const_unstable` (or manually get a `rustc_const_stable_indirect`) to be
sure they follow recursive const stability. But that's a fairly rare and special
case so IMO it's fine.
The net effect of this is that a `#[unstable]` or unmarked function can be
constified simply by marking it as `const fn`, and it will then be
const-callable from stable `const fn` and subject to recursive const stability
requirements. If it is publicly reachable (which implies it cannot be unmarked),
it will be const-unstable under the same feature gate. Only if the function ever
becomes `#[stable]` does it need a `#[rustc_const_unstable]` or
`#[rustc_const_stable]` marker to decide if this should also imply
const-stability.
Adding `#[rustc_const_unstable]` is only needed for (a) functions that need to
use unstable const lang features (including intrinsics), or (b) `#[stable]`
functions that are not yet intended to be const-stable. Adding
`#[rustc_const_stable]` is only needed for functions that are actually meant to
be directly callable from stable const code. `#[rustc_const_stable_indirect]` is
used to mark intrinsics as const-callable and for `#[rustc_const_unstable]`
functions that are actually called from other, exposed-on-stable `const fn`. No
other attributes are required.
When printing
```
= help: the trait `chumsky::private::ParserSealed<'_, &'a str, ((), ()), chumsky::extra::Full<EmptyErr, (), ()>>` is implemented for `Then<Ignored<chumsky::combinator::Filter<chumsky::primitive::Any<&str, chumsky::extra::Full<EmptyErr, (), ()>>, {closure@src/main.rs:9:17: 9:27}>, char>, chumsky::combinator::Map<impl CSTParser<'a, O>, O, {closure@src/main.rs:11:24: 11:27}>, (), (), chumsky::extra::Full<EmptyErr, (), ()>>`
= help: for that trait implementation, expected `((), ())`, found `()`
```
Highlight only the `expected` and `found` types, instead of the full type in the first `help`.
Emit future-incompatibility lint when calling/declaring functions with vectors that require missing target feature
On some architectures, vector types may have a different ABI depending on whether the relevant target features are enabled. (The ABI when the feature is disabled is often not specified, but LLVM implements some de-facto ABI.)
As discussed in https://github.com/rust-lang/lang-team/issues/235, this turns out to very easily lead to unsound code.
This commit makes it a post-monomorphization error to declare or call functions using those vector types in a context in which the corresponding target features are disabled, if using an ABI for which the difference is relevant. This ensures that these functions are always called with a consistent ABI.
See the [nomination comment](https://github.com/rust-lang/rust/pull/127731#issuecomment-2288558187) for more discussion.
r? RalfJung
Part of https://github.com/rust-lang/rust/issues/116558
ci: aarch64-gnu-debug job
- Adds a new CI job which checks that the compiler builds with `--enable-debug` and tests that `needs-force-clang-based-tests` pass (where cross-language LTO is tested).
- Add a test confirming that `-Zbranch-protection=pac-ret` and cross-language LTO work together.
r? `@Mark-Simulacrum`
try-job: aarch64-gnu-debug
On some architectures, vector types may have a different ABI when
relevant target features are enabled.
As discussed in https://github.com/rust-lang/lang-team/issues/235, this
turns out to very easily lead to unsound code.
This commit makes it an error to declare or call functions using those
vector types in a context in which the corresponding target features are
disabled, if using an ABI for which the difference is relevant.
Add support for `~const` item bounds
Supports the only missing capability of `~const` associated types that I can think of now (this is obviously excluding `~const` opaques, which I see as an extension to this; I'll probably do that next).
r? ``@lcnr`` mostly b/c it changes candidate assembly, or reassign
cc ``@fee1-dead``
[rustdoc] Do not consider nested functions as main function even if named `main` in doctests
Fixes#131893.
If a nested function is called `main`, it is not considered as the entry point of the program. Therefore, doctests should not consider such functions as such either.
r? `@notriddle`
Rollup of 6 pull requests
Successful merges:
- #131851 ([musl] use posix_spawn if a directory change was requested)
- #132048 (AIX: use /dev/urandom for random implementation )
- #132093 (compiletest: suppress Windows Error Reporting (WER) for `run-make` tests)
- #132101 (Avoid using imports in thread_local_inner! in static)
- #132113 (Provide a default impl for Pattern::as_utf8_pattern)
- #132115 (rustdoc: Extend fake_variadic to "wrapped" tuples)
r? `@ghost`
`@rustbot` modify labels: rollup
Stabilize shorter-tail-lifetimes
Close#131445
Tracked by #123739
We found a test case `tests/ui/drop/drop_order.rs` that had not been covered by the change. The test fixture is fixed now with the correct expectation.
Represent trait constness as a distinct predicate
cc `@rust-lang/project-const-traits`
r? `@ghost` for now
Also mirrored everything that is written below on this hackmd here: https://hackmd.io/`@compiler-errors/r12zoixg1l`
# Tl;dr:
* This PR removes the bulk of the old effect desugaring.
* This PR reimplements most of the effect desugaring as a new predicate and set of a couple queries. I believe it majorly simplifies the implementation and allows us to move forward more easily on its implementation.
I'm putting this up both as a request for comments and a vibe-check, but also as a legitimate implementation that I'd like to see land (though no rush of course on that last part).
## Background
### Early days
Once upon a time, we represented trait constness in the param-env and in `TraitPredicate`. This was very difficult to implement correctly; it had bugs and was also incomplete; I don't think this was anyone's fault though, it was just the limit of experimental knowledge we had at that point.
Dealing with `~const` within predicates themselves meant dealing with constness all throughout the trait solver. This was difficult to keep track of, and afaict was not handled well with all the corners of candidate assembly.
Specifically, we had to (in various places) remap constness according to the param-env constness:
574b64a97f/compiler/rustc_trait_selection/src/traits/select/mod.rs (L1498)
This was annoying and manual and also error prone.
### Beginning of the effects desugaring
Later on, #113210 reimplemented a new desugaring for const traits via a `<const HOST: bool>` predicate. This essentially "reified" the const checking and separated it from any of the remapping or separate tracking in param-envs. For example, if I was in a const-if-const environment, but I wanted to call a trait that was non-const, this reification would turn the constness mismatch into a simple *type* mismatch of the effect parameter.
While this was a monumental step towards straightening out const trait checking in the trait system, it had its own issues, since that meant that the constness of a trait (or any item within it, like an associated type) was *early-bound*. This essentially meant that `<T as Trait>::Assoc` was *distinct* from `<T as ~const Trait>::Assoc`, which was bad.
### Associated-type bound based effects desugaring
After this, #120639 implemented a new effects desugaring. This used an associated type to more clearly represent the fact that the constness is not an input parameter of a trait, but a property that could be computed of a impl. The write-up linked in that PR explains it better than I could.
However, I feel like it really reached the limits of what can comfortably be expressed in terms of associated type and trait calculus. Also, `<const HOST: bool>` remains a synthetic const parameter, which is observable in nested items like RPITs and closures, and comes with tons of its own hacks in the astconv and middle layer.
For example, there are pieces of unintuitive code that are needed to represent semantics like elaboration, and eventually will be needed to make error reporting intuitive, and hopefully in the future assist us in implementing built-in traits (eventually we'll want something like `~const Fn` trait bounds!).
elaboration hack: 8069f8d17a/compiler/rustc_type_ir/src/elaborate.rs (L133-L195)
trait bound remapping hack for diagnostics: 8069f8d17a/compiler/rustc_trait_selection/src/error_reporting/traits/fulfillment_errors.rs (L2370-L2413)
I want to be clear that I don't think this is a issue of implementation quality or anything like that; I think it's simply a very clear sign that we're using types and traits in a way that they're not fundamentally supposed to be used, especially given that constness deserves to be represented as a first-class concept.
### What now?
This PR implements a new desugaring for const traits. Specifically, it introduces a `HostEffect` predicate to represent the obligation an impl is const, rather than using associated type bounds and the compat trait that exists for effects today.
### `HostEffect` predicate
A `HostEffect` clause has two parts -- the `TraitRef` we're trying to prove, and a `HostPolarity::{Maybe, Const}`.
`HostPolarity::Const` corresponds to `T: const Trait` bounds, which must *always* be proven as const, and which can be written in any context. These are lowered directly into the predicates of an item, since they're not "context-specific".
On the other hand, `HostPolarity::Maybe` corresponds to `T: ~const Trait` bounds which must only exist in a conditionally-const context like a method in a `#[const_trait]`, or a `const fn` free function. We do not lower these immediately into the predicates of an item; instead, we collect them into a new query called the **`const_conditions`**. These are the set of trait refs that we need to prove have const implementations for an item to be const.
Notably, they're represented as bare (poly) trait refs because they are meant to be paired back together with a `HostPolarity` when they're being registered in typeck (see next section).
For example, given:
```rust
const fn foo<T: ~const A + const B>() {}
```
`foo`'s const conditions would contain `T: A`, but not `T: B`. On the flip side, foo's predicates (`predicates_of`) query would contain `HostEffect(T: B, HostPolarity::Const)` but not `HostEffect(T: A, HostPolarity::Maybe)` since we don't need to prove that predicate in a non-const environment (and it's not even the right predicate to prove in an unconditionally const environment).
### Type checking const bodies
When type checking bodies in HIR, when we encounter a call expression, we additionally register the callee item's const conditions with the `HostPolarity` from the body we're typechecking (`Const` for unconditionally const things like `const`/`static` items, and `Maybe` for conditionally const things like const fns; and we don't register `HostPolarity` predicates for non-const bodies).
When type-checking a conditionally const body, we augment its param-env with `HostEffect(..., Maybe)` predicates.
### Checking that const impls are WF
We extend the logic in `compare_method_predicate_entailment` to also check the const-conditions of the impl method, to make sure that we error for:
```rust
#[const_trait] Bar {}
#[const_trait] trait Foo {
fn method<T: Bar>();
}
impl Foo for () {
fn method<T: ~const Bar>() {} // stronger assumption!
}
```
We also extend the WF check for impls to register the const conditions of the trait that is being implemented. This is to make sure we error for:
```rust
#[const_trait] trait Bar {}
#[const_trait] trait Foo<T> where T: ~const Bar {}
impl<T> const Foo<T> for () {}
//~^ `T: ~const Bar` is missing!
```
### Proving a `HostEffect` predicate
We have several ways of proving a `HostEffect` predicate:
1. Matching a `HostEffect` predicate from the param-env
2. From an impl - we do impl selection very similar to confirming a trait goal, except we filter for only const impls, and we additionally register the impl's const conditions (i.e. the impl's `~const` where clauses).
Later I expect that we will add more built-in implementations for things like `Fn`.
## What next?
After this PR, I'd like to split out the work more so it can proceed in parallel and probably amongst others that are not me.
* Register `HostEffect` goal for places in HIR typeck that correspond to call terminators, like autoderef.
* Make traits in libstd const again.
* Probably need to impl host effect preds in old solver.
* Implement built-in `HostEffect` rules for traits like `Fn`.
* Rip out const checking from MIR altogether.
## So what?
This ends up being super convenient basically everywhere in the compiler. Due to the design of the new trait solver, we end up having an almost parallel structure to the existing trait and projection predicates for assembling `HostEffect` predicates; adding new candidates and especially new built-in implementations is now basically trivial, and it's quite straightforward to understand the confirmation logic for these predicates.
Same with diagnostics reporting; since we have predicates which represent the obligation to prove an impl is const, we can simplify and make these diagnostics richer without having to write a ton of logic to intercept and rewrite the existing `Compat` trait errors.
Finally, it gives us a much more straightforward path for supporting the const effect on the old trait solver. I'm personally quite passionate about getting const trait support into the hands of users without having to wait until the new solver lands[^1], so I think after this PR lands we can begin to gauge how difficult it would be to implement constness in the old trait solver too. This PR will not do this yet.
[^1]: Though this is not a prerequisite or by any means the only justification for this PR.
Adds a new CI job which checks that the compiler builds with
`--enable-debug` and tests that `needs-force-clang-based-tests` pass
(where cross-language LTO is tested).
Remove the `Arc` rt::init allocation for thread info
Removes an allocation pre-main by just not storing anything in std:🧵:Thread for the main thread.
- The thread name can just be a hard coded literal, as was done in #123433.
- Storing ThreadId and Parker in a static that is initialized once at startup. This uses SyncUnsafeCell and MaybeUninit as this is quite performance critical and we don't need synchronization or to store a tag value and possibly leave in a panic.
Consider param-env candidates even if they have errors
I added this logic in https://github.com/rust-lang/rust/pull/106309, but frankly I don't know why -- the logic was a very large hammer. It seems like recent changes to error tainting has made that no longer necessary.
Ideally we'd rework the way we handle error reporting in all of candidate assembly to be a bit more responsible; we're just suppressing candidates all willy-nilly and it leads to mysterious *other* errors cropping up, like the one that #132082 originally wanted to fix.
**N.B.** This has the side-effect of turning a failed resolution like `where Missing: Sized` into a trivial where clause that matches all types, but also I don't think it really matters?
I'm putting this up as an alternative to #132082, since that PR doesn't address the case when one desugars the APIT into a regular type param.
r? lcnr vibeck
Taking a raw ref (`&raw (const|mut)`) of a deref of pointer (`*ptr`) is always safe
T-opsem decided in https://github.com/rust-lang/reference/pull/1387 that `*ptr` is only unsafe if the place is accessed. This means that taking a raw ref of a deref expr is always safe, since it doesn't constitute a read.
This also relaxes the `DEREF_NULLPTR` lint to stop warning in the case of raw ref of a deref'd nullptr, and updates its docs to reflect that change in the UB specification.
This does not change the behavior of `addr_of!((*ptr).field)`, since field projections still require the projection is in-bounds.
I'm on the fence whether this requires an FCP, since it's something that is guaranteed by the reference you could ostensibly call this a bugfix since we were counting truly safe operations as unsafe. Perhaps someone on opsem has a strong opinion? cc `@rust-lang/opsem`
Don't allow test revisions that conflict with built in cfgs
Fixes#128964
Sorry `@heysujal` I started working on this about 1 minute before your comment by complete coincidence 😅
minor `*dyn` cast cleanup
Small follow-up to https://github.com/rust-lang/rust/pull/130234 to remove a redundant check and clean up comments. No functional changes.
Also, explain why casts cannot drop the principal even though coercions can, and add a test because apparently we didn't have one already.
r? `@WaffleLapkin` or `@compiler-errors`
Deeply normalize `TypeTrace` when reporting type error in new solver
Normalize the values that come from the `TypeTrace` for various type mismatches.
Side-note: We can't normalize the `TypeError` itself bc it may come from instantiated binders, so it may reference values from within the probe...
r? lcnr
Rename Receiver -> LegacyReceiver
As part of the "arbitrary self types v2" project, we are going to replace the current `Receiver` trait with a new mechanism based on a new, different `Receiver` trait.
This PR renames the old trait to get it out the way. Naming is hard. Options considered included:
* HardCodedReceiver (because it should only be used for things in the standard library, and hence is sort-of hard coded)
* LegacyReceiver
* TargetLessReceiver
* OldReceiver
These are all bad names, but fortunately this will be temporary. Assuming the new mechanism proceeds to stabilization as intended, the legacy trait will be removed altogether.
Although we expect this trait to be used only in the standard library, we suspect it may be in use elsehwere, so we're landing this change separately to identify any surprising breakages.
It's known that this trait is used within the Rust for Linux project; a patch is in progress to remove their dependency.
This is a part of the arbitrary self types v2 project,
https://github.com/rust-lang/rfcs/pull/3519https://github.com/rust-lang/rust/issues/44874
r? `@wesleywiser`
Rollup of 9 pull requests
Successful merges:
- #130991 (Vectorized SliceContains)
- #131928 (rustdoc: Document `markdown` module.)
- #131955 (Set `signext` or `zeroext` for integer arguments on RISC-V and LoongArch64)
- #131979 (Minor tweaks to `compare_impl_item.rs`)
- #132036 (Add a test case for #131164)
- #132039 (Specialize `read_exact` and `read_buf_exact` for `VecDeque`)
- #132060 ("innermost", "outermost", "leftmost", and "rightmost" don't need hyphens)
- #132065 (Clarify documentation of `ptr::dangling()` function)
- #132066 (Fix a typo in documentation of `pointer::sub_ptr()`)
r? `@ghost`
`@rustbot` modify labels: rollup
"innermost", "outermost", "leftmost", and "rightmost" don't need hyphens
These are all standard dictionary words and don't require hyphenation.
-----
Encountered an instance of this in error messages and it bugged me, so I
figured I'd fix it across the entire codebase.
Add a test case for #131164
The upstream has already been fixed, but it won't be backported to LLVM 19.
r? jieyouxu or compiler
try-job: x86_64-gnu-stable
Set `signext` or `zeroext` for integer arguments on RISC-V and LoongArch64
This PR contains 3 commits:
- the first one introduces a new function `adjust_for_rust_abi` in `rustc_target`, and moves the x86 specific adjustment code into it;
- the second one adds RISC-V specific adjustment code into it, which sets `signext` or `zeroext` attribute for integer arguments.
- **UPDATE**: added the 3rd commit to apply the same adjustment for LoongArch64.
