Previously, `Tree::from_enum`'s implementation branched into three disjoint
cases:
1. enums that uninhabited
2. enums for which all but one variant is uninhabited
3. enums with multiple inhabited variants
This branching (incorrectly) did not differentiate between variantful and
variantless uninhabited enums. In both cases, we assumed (and asserted) that
uninhabited enums are zero-sized types. This assumption is false for enums like:
enum Uninhabited { A(!, u128) }
...which, currently, has the same size as `u128`. This faulty assumption
manifested as the ICE reported in #126460.
In this PR, we revise the first case of `Tree::from_enum` to consider only the
narrow category of "enums that are uninhabited ZSTs". These enums, whose layouts
are described with `Variants::Single { index }`, are special in their layouts
otherwise resemble the `!` type and cannot be descended into like typical enums.
This first case captures uninhabited enums like:
enum Uninhabited { A(!, !), B(!) }
The second case is revised to consider the broader category of "enums that defer
their layout to one of their variants"; i.e., enums whose layouts are described
with `Variants::Single { index }` and that do have a variant at `index`. This
second case captures uninhabited enums that are not ZSTs, like:
enum Uninhabited { A(!, u128) }
...which represent their variants with `Variants::Single`.
Finally, the third case is revised to cover the broader category of "enums with
multiple variants", which captures uninhabited, non-ZST enums like:
enum Uninhabited { A(u8, !), B(!, u32) }
...which represent their variants with `Variants::Multiple`.
This PR also adds a comment requested by RalfJung in his review of #126358 to
`compiler/rustc_const_eval/src/interpret/discriminant.rs`.
Fixes#126460
These changes bring it closer to other standard library documentation
and, in particular, `std::fs::canonicalize`, which it will often be
compared with.
* Add `# Platform-specific behavior` section, with content moved from
Examples section.
* Create `# Errors` section.
* Phrase error description to allow future platforms to have new
syntactic errors, rather than only emptiness.
* Add missing commas.
* Indent example code 4 spaces.
I didn't find `crt-static` at first (for `x86_64-unknown-linux-gnu`),
because it was put at the bottom the large and otherwise sorted list.
Fully sort the list before we print it.
Note that `llvm_target_features` starts out sorted and does not need to
be sorted an extra time.
Add a new concat metavar expr
Revival of #111930
Giving it another try now that #117050 was merged.
With the new rules, meta-variable expressions must be referenced with a dollar sign (`$`) and this can cause misunderstands with `$concat`.
```rust
macro_rules! foo {
( $bar:ident ) => {
const ${concat(VAR, bar)}: i32 = 1;
};
}
// Will produce `VARbar` instead of `VAR_123`
foo!(_123);
```
In other words, forgetting the dollar symbol can produce undesired outputs.
cc #29599
cc https://github.com/rust-lang/rust/issues/124225
Rollup of 7 pull requests
Successful merges:
- #123769 (Improve escaping of byte, byte str, and c str proc-macro literals)
- #126054 (`E0229`: Suggest Moving Type Constraints to Type Parameter Declaration)
- #126135 (add HermitOS support for vectored read/write operations)
- #126266 (Unify guarantees about the default allocator)
- #126285 (`UniqueRc`: support allocators and `T: ?Sized`.)
- #126399 (extend the check for LLVM build)
- #126426 (const validation: fix ICE on dangling ZST reference)
r? `@ghost`
`@rustbot` modify labels: rollup
const validation: fix ICE on dangling ZST reference
Fixes https://github.com/rust-lang/rust/issues/126393
I'm not super happy with this fix but I can't think of a better one.
r? `@oli-obk`
`UniqueRc`: support allocators and `T: ?Sized`.
Added the following (all unstable):
* Defaulted type pararameter `A: Allocator`.
* `UniqueRc::new_in()`.
* `T: ?Sized` where possible.
* `impl CoerceUnsized for UniqueRc`.
These changes are motivated by supporting the implementation of unsized `Rc::make_mut()` (PR #116113), but are also intended to be obvious generalizations of `UniqueRc` to support the things `Rc` does.
r? ``````@the8472``````
Unify guarantees about the default allocator
`std::alloc` said that the default allocator is unspecified for all crrate types except `cdylib` and `staticlib`. Adjust `std::alloc::System` documentation to say the same.
Fixes#125870.
add HermitOS support for vectored read/write operations
In general, the I/O interface of hermit-abi is revised and now a more POSIX-like interface. Consequently, platform abstraction layer for HermitOS has slightly adjusted and some inaccuracies remove.
Hermit is a tier 3 platform and this PR changes only files, wich are related to the tier 3 platform.
`E0229`: Suggest Moving Type Constraints to Type Parameter Declaration
Fixes#113073
This PR suggests `impl<T: Bound> Trait<T> for Foo` when finding `impl Trait<T: Bound> for Foo`. Tangentially, it also improves a handful of other error messages.
It accomplishes this in two steps:
1. Check if constrained arguments and parameter names appear in the same order and delay emitting "incorrect number of generic arguments" error because it can be confusing for the programmer to see `0 generic arguments provided` when there are `n` constrained generic arguments.
2. Inside `E0229`, suggest declaring the type parameter right after the `impl` keyword by finding the relevant impl block's span for type parameter declaration. This also handles lifetime declarations correctly.
Also, the multi part suggestion doesn't use the fluent error mechanism because translating all the errors to fluent style feels outside the scope of this PR. I will handle it in a separate PR if this gets approved.
Improve escaping of byte, byte str, and c str proc-macro literals
This PR changes the behavior of `proc_macro::Literal::byte_character` (https://github.com/rust-lang/rust/issues/115268), `byte_string`, and `c_string` (https://github.com/rust-lang/rust/issues/119750) to improve their choice of escape sequences. 3 categories of changes are made:
1. Never use `\x00`. Always prefer `\0`, which is supported in all the same places.
2. Never escape `\'` inside double quotes and `\"` inside single quotes.
3. Never use `\x` for valid UTF-8 in literals that permit `\u`.
The second commit adds tests covering these cases, asserting the **old** behavior.
The third commit implements the behavior change and simultaneously updates the tests to assert the **new** behavior.
