Shrink `Nonterminal`
These commits shrink `Nonterminal` from 240 bytes to 40 bytes. When building `serde_derive` they reduce the number of `memcpy` calls from 9.6M to 7.4M, and it's a tiny win on a few other benchmarks.
r? @petrochenkov
This commit reduces the size of `Nonterminal` from a whopping 240 bytes
to 72 bytes (on x86-64), which gets it below the `memcpy` threshold.
It also removes some impedance mismatches with `Annotatable`, which
already uses `P` for these variants.
Implement `?const` opt-out for trait bounds
For now, such bounds are treated exactly the same as unprefixed ones in all contexts. [RFC 2632](https://github.com/rust-lang/rfcs/pull/2632) does not specify whether such bounds are forbidden outside of `const` contexts, so they are allowed at the moment.
Prior to this PR, the constness of a trait bound/impl was stored in `TraitRef`. Now, the constness of an `impl` is stored in `ast::ItemKind::Impl` and the constness of a bound in `ast::TraitBoundModifer`. Additionally, constness of trait bounds is now stored in an additional field of `ty::Predicate::Trait`, and the combination of the constness of the item along with any `TraitBoundModifier` determines the constness of the bound in accordance with the RFC. Encoding the constness of impls at the `ty` level is left for a later PR.
After a discussion in \#wg-grammar on Discord, it was decided that the grammar should not encode the mutual exclusivity of trait bound modifiers. The grammar for trait bound modifiers remains `[?const] [?]`. To encode this, I add a dummy variant to `ast::TraitBoundModifier` that is used when the syntax `?const ?` appears. This variant causes an error in AST validation and disappears during HIR lowering.
cc #67794
r? @oli-obk
Clean up some diagnostics by making them more consistent
In general:
- Diagnostic should start with a lowercase letter.
- Diagnostics should not end with a full stop.
- Ellipses contain three dots.
- Backticks should encode Rust code.
I also reworded a couple of messages to make them read more clearly.
It might be sensible to create a style guide for diagnostics, so these informal conventions are written down somewhere, after which we could audit the existing diagnostics.
r? @Centril
Add suggestions when encountering chained comparisons
Ideally, we'd also prevent the type error, which is just extra noise, but that will require moving the error from the parser, and I think the suggestion makes things clear enough for now.
Fixes https://github.com/rust-lang/rust/issues/65659.
Extend support of `_` in type parameters
- Account for `impl Trait<_>`.
- Provide a reasonable `Span` for empty `Generics` in `impl`s.
- Account for `fn foo<_>(_: _) {}` to suggest `fn foo<T>(_: T) {}`.
- Fix#67995. Follow up to #67597.
- Account for `impl Trait<_>`.
- Provide a reasonable `Span` for empty `Generics` in `impl`s.
- Account for `fn foo<_>(_: _) {}` to suggest `fn foo<T>(_: T) {}`.
- Fix#67995.
tweak wording of mismatched delimiter errors
This PR improves the wording of the "incorrect delimiter" error messages. Here's a quick rationale:
- *"un-closed" -> "unclosed"*: "unclosed" is valid English, so there's no need to hyphenate the prefix. This should be pretty uncontroversial, I think.
- *"close delimiter" -> "closing delimiter"*: In my anecdotal experience, I've always heard "closing delimiter" or "closing parenthesis". In addition, the codebase already uses this terminology in comments and function names more than "close delimiter", which could indicate that it's more intuitive.
- "incorrect delimiter" -> "mismatched delimiter": "Incorrect delimiter" is vague; why is it incorrect? "mismatched" clearly indicates why the delimiter is causing the error.
r? @estebank
Nix reexports from `rustc_span` in `syntax`
Remove reexports `syntax::{source_map, symbol, edition}` and use `rustc_span` paths directly.
r? @petrochenkov
