Implement syntax for `impl Trait` to specify its captures explicitly (`feature(precise_capturing)`)
Implements `impl use<'a, 'b, T, U> Sized` syntax that allows users to explicitly list the captured parameters for an opaque, rather than inferring it from the opaque's bounds (or capturing *all* lifetimes under 2024-edition capture rules). This allows us to exclude some implicit captures, so this syntax may be used as a migration strategy for changes due to #117587.
We represent this list of captured params as `PreciseCapturingArg` in AST and HIR, resolving them between `rustc_resolve` and `resolve_bound_vars`. Later on, we validate that the opaques only capture the parameters in this list.
We artificially limit the feature to *require* mentioning all type and const parameters, since we don't currently have support for non-lifetime bivariant generics. This can be relaxed in the future.
We also may need to limit this to require naming *all* lifetime parameters for RPITIT, since GATs have no variance. I have to investigate this. This can also be relaxed in the future.
r? `@oli-obk`
Tracking issue:
- https://github.com/rust-lang/rust/issues/123432
Cleanup: Rename `ModSep` to `PathSep`
`::` is usually referred to as the *path separator* (citation needed).
The existing name `ModSep` for *module separator* is a bit misleading since it in fact separates the segments of arbitrary path segments, not only ones resolving to modules. Let me just give a shout-out to associated items (`T::Assoc`, `<Ty as Trait>::function`) and enum variants (`Option::None`).
Motivation: Reduce friction for new contributors, prevent potential confusion.
cc `@petrochenkov`
r? nnethercote or compiler
Add asm goto support to `asm!`
Tracking issue: #119364
This PR implements asm-goto support, using the syntax described in "future possibilities" section of [RFC2873](https://rust-lang.github.io/rfcs/2873-inline-asm.html#asm-goto).
Currently I have only implemented the `label` part, not the `fallthrough` part (i.e. fallthrough is implicit). This doesn't reduce the expressive though, since you can use label-break to get arbitrary control flow or simply set a value and rely on jump threading optimisation to get the desired control flow. I can add that later if deemed necessary.
r? ``@Amanieu``
cc ``@ojeda``
Add an ErrorGuaranteed to ast::TyKind::Err (attempt 2)
This makes it more like `hir::TyKind::Err`, and avoids a `has_errors` assertion in `LoweringContext::lower_ty_direct`.
r? ```@oli-obk```
This mostly works well, and eliminates a couple of delayed bugs.
One annoying thing is that we should really also add an
`ErrorGuaranteed` to `proc_macro::bridge::LitKind::Err`. But that's
difficult because `proc_macro` doesn't have access to `ErrorGuaranteed`,
so we have to fake it.
This makes it more like `hir::TyKind::Err`, and avoids a
`span_delayed_bug` call in `LoweringContext::lower_ty_direct`.
It also requires adding `ast::TyKind::Dummy`, now that
`ast::TyKind::Err` can't be used for that purpose in the absence of an
error emission.
There are a couple of cases that aren't as neat as I would have liked,
marked with `FIXME` comments.
There are a number of cases where we erroneously omit the space between
two tokens, all involving an exception to a more general case. The
affected tokens are `$`, `!`, `.`, `,`, and `let` followed by a
parenthesis.
This fixes a lot of FIXME comments.
Fix parenthesization of subexprs containing statement boundary
This PR fixes a multitude of false negatives and false positives in the AST pretty printer's parenthesis insertion related to statement boundaries — statements which terminate unexpectedly early if there aren't parentheses.
Without this fix, the AST pretty printer (including both `stringify!` and `rustc -Zunpretty=expanded`) is prone to producing output which is not syntactically valid Rust. Invalid output is problematic because it means Rustfmt is unable to parse the output of `cargo expand`, for example, causing friction by forcing someone trying to debug a macro into reading poorly formatted code.
I believe the set of bugs fixed in this PR account for the most prevalent reason that `cargo expand` produces invalid output in real-world usage.
Fixes#98790.
## False negatives
The following is a correct program — `cargo check` succeeds.
```rust
macro_rules! m {
($e:expr) => {
match () { _ => $e }
};
}
fn main() {
m!({ 1 } - 1);
}
```
But `rustc -Zunpretty=expanded main.rs` produces output that is invalid Rust syntax, because parenthesization is needed and not being done by the pretty printer.
```rust
fn main() { match () { _ => { 1 } - 1, }; }
```
Piping this expanded code to rustfmt, it fails to parse.
```console
error: unexpected `,` in pattern
--> <stdin>:1:38
|
1 | fn main() { match () { _ => { 1 } - 1, }; }
| ^
|
help: try adding parentheses to match on a tuple...
|
1 | fn main() { match () { _ => { 1 } (- 1,) }; }
| + +
help: ...or a vertical bar to match on multiple alternatives
|
1 | fn main() { match () { _ => { 1 } - 1 | }; }
| ~~~~~
```
Fixed output after this PR:
```rust
fn main() { match () { _ => ({ 1 }) - 1, }; }
```
## False positives
Less problematic, but worth fixing (just like #118726).
```rust
fn main() {
let _ = match () { _ => 1 } - 1;
}
```
Output of `rustc -Zunpretty=expanded lib.rs` before this PR. There is no reason parentheses would need to be inserted there.
```rust
fn main() { let _ = (match () { _ => 1, }) - 1; }
```
After this PR:
```rust
fn main() { let _ = match () { _ => 1, } - 1; }
```
## Alternatives considered
In this PR I opted to parenthesize only the leading subexpression causing the statement boundary, rather than the entire statement. Example:
```rust
macro_rules! m {
($e:expr) => {
$e
};
}
fn main() {
m!(loop { break [1]; }[0] - 1);
}
```
This PR produces the following pretty-printed contents for fn main:
```rust
(loop { break [1]; })[0] - 1;
```
A different equally correct output would be:
```rust
(loop { break [1]; }[0] - 1);
```
I chose the one I did because it is the *only* approach used by handwritten code in the standard library and compiler. There are 4 places where parenthesization is being used to prevent a statement boundary, and in all 4, the developer has chosen to parenthesize the smallest subexpression rather than the whole statement:
b37d43efd9/compiler/rustc_codegen_cranelift/example/alloc_system.rs (L102)b37d43efd9/compiler/rustc_parse/src/errors.rs (L1021-L1029)b37d43efd9/library/core/src/future/poll_fn.rs (L151)b37d43efd9/library/core/src/ops/range.rs (L824-L828)
Clairify `ast::PatKind::Struct` presese of `..` by using an enum instead of a bool
The bool is mainly used for when a `..` is present, but it is also set on recovery to avoid errors. The doc comment not describes both of these cases.
See cee794ee98/compiler/rustc_parse/src/parser/pat.rs (L890-L897) for the only place this is constructed.
r? ``@compiler-errors``
Do not parenthesize exterior struct lit inside match guards
Before this PR, the AST pretty-printer injects parentheses around expressions any time parens _could_ be needed depending on what else is in the code that surrounds that expression. But the pretty-printer did not pass around enough context to understand whether parentheses really _are_ needed on any particular expression. As a consequence, there are false positives where unneeded parentheses are being inserted.
Example:
```rust
#![feature(if_let_guard)]
macro_rules! pp {
($e:expr) => {
stringify!($e)
};
}
fn main() {
println!("{}", pp!(match () { () if let _ = Struct {} => {} }));
}
```
**Before:**
```console
match () { () if let _ = (Struct {}) => {} }
```
**After:**
```console
match () { () if let _ = Struct {} => {} }
```
This PR introduces a bit of state that is passed across various expression printing methods to help understand accurately whether particular situations require parentheses injected by the pretty printer, and it fixes one such false positive involving match guards as shown above.
There are other parenthesization false positive cases not fixed by this PR. I intend to address these in follow-up PRs. For example here is one: the expression `{ let _ = match x {} + 1; }` is pretty-printed as `{ let _ = (match x {}) + 1; }` despite there being no reason for parentheses to appear there.
This is an extension of the previous commit. It means the output of
something like this:
```
stringify!(let a: Vec<u32> = vec![];)
```
goes from this:
```
let a: Vec<u32> = vec![] ;
```
With this PR, it now produces this string:
```
let a: Vec<u32> = vec![];
```
`tokenstream::Spacing` appears on all `TokenTree::Token` instances,
both punct and non-punct. Its current usage:
- `Joint` means "can join with the next token *and* that token is a
punct".
- `Alone` means "cannot join with the next token *or* can join with the
next token but that token is not a punct".
The fact that `Alone` is used for two different cases is awkward.
This commit augments `tokenstream::Spacing` with a new variant
`JointHidden`, resulting in:
- `Joint` means "can join with the next token *and* that token is a
punct".
- `JointHidden` means "can join with the next token *and* that token is a
not a punct".
- `Alone` means "cannot join with the next token".
This *drastically* improves the output of `print_tts`. For example,
this:
```
stringify!(let a: Vec<u32> = vec![];)
```
currently produces this string:
```
let a : Vec < u32 > = vec! [] ;
```
With this PR, it now produces this string:
```
let a: Vec<u32> = vec![] ;
```
(The space after the `]` is because `TokenTree::Delimited` currently
doesn't have spacing information. The subsequent commit fixes this.)
The new `print_tts` doesn't replicate original code perfectly. E.g.
multiple space characters will be condensed into a single space
character. But it's much improved.
`print_tts` still produces the old, uglier output for code produced by
proc macros. Because we have to translate the generated code from
`proc_macro::Spacing` to the more expressive `token::Spacing`, which
results in too much `proc_macro::Along` usage and no
`proc_macro::JointHidden` usage. So `space_between` still exists and
is used by `print_tts` in conjunction with the `Spacing` field.
This change will also help with the removal of `Token::Interpolated`.
Currently interpolated tokens are pretty-printed nicely via AST pretty
printing. `Token::Interpolated` removal will mean they get printed with
`print_tts`. Without this change, that would result in much uglier
output for code produced by decl macro expansions. With this change, AST
pretty printing and `print_tts` produce similar results.
The commit also tweaks the comments on `proc_macro::Spacing`. In
particular, it refers to "compound tokens" rather than "multi-char
operators" because lifetimes aren't operators.
tidy error: /git/rust/compiler/rustc_ast_pretty/src/pprust/state.rs:1165: unexplained "```ignore" doctest; try one:
* make the test actually pass, by adding necessary imports and declarations, or
* use "```text", if the code is not Rust code, or
* use "```compile_fail,Ennnn", if the code is expected to fail at compile time, or
* use "```should_panic", if the code is expected to fail at run time, or
* use "```no_run", if the code should type-check but not necessary linkable/runnable, or
* explain it like "```ignore (cannot-test-this-because-xxxx)", if the annotation cannot be avoided.
tidy error: /git/rust/compiler/rustc_ast_pretty/src/pprust/state.rs:1176: unexplained "```ignore" doctest; try one:
* make the test actually pass, by adding necessary imports and declarations, or
* use "```text", if the code is not Rust code, or
* use "```compile_fail,Ennnn", if the code is expected to fail at compile time, or
* use "```should_panic", if the code is expected to fail at run time, or
* use "```no_run", if the code should type-check but not necessary linkable/runnable, or
* explain it like "```ignore (cannot-test-this-because-xxxx)", if the annotation cannot be avoided.
In all four of Break, Closure, Ret, Yeet, the needs_par_as_let_scrutinee
is guaranteed to return true because the .precedence().order() of those
expr kinds is <= AssocOp::LAnd.precedence().
The relevant functions in rustc_ast::util::parser are:
fn needs_par_as_let_scrutinee(order: i8) -> bool {
order <= prec_let_scrutinee_needs_par() as i8
}
fn prec_let_scrutinee_needs_par() -> usize {
AssocOp::LAnd.precedence()
}
The .precedence().order() of Closure is PREC_CLOSURE (-40) and of Break,
Ret, Yeet is PREC_JUMP (-30).
The value of AssocOp::LAnd.precedence() is 6.
So this commit causes no change in behavior, only potentially
performance by doing a redundant call to contains_exterior_struct_lit in
those four cases. This is fine because Break, Closure, Ret, Yeet should
be exceedingly rare in the position of a let scrutinee.
Add `never_patterns` feature gate
This PR adds the feature gate and most basic parsing for the experimental `never_patterns` feature. See the tracking issue (https://github.com/rust-lang/rust/issues/118155) for details on the experiment.
`@scottmcm` has agreed to be my lang-team liaison for this experiment.
The AST and HIR versions of `State::print_ident` are textually
identical, but the types differ slightly. This commit factors out the
common code they both have by replacing `print_ident` with `ann_post`,
which is a smaller function that still captures the type difference.
