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[macro-metavar-expr] Fix generated tokens hygiene #95188

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merged 1 commit into from
Mar 22, 2022
Merged

[macro-metavar-expr] Fix generated tokens hygiene #95188

merged 1 commit into from
Mar 22, 2022

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@c410-f3r c410-f3r commented Mar 21, 2022 •
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Only uses Marker on generated tokens -> #83527 (comment))

I really don't know how to test this PR

r? @petrochenkov

@rustbot rustbot added the T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. label Mar 21, 2022
@rust-highfive rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Mar 21, 2022
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@bors r+ rollup

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bors commented Mar 22, 2022

📌 Commit 74e7313 has been approved by petrochenkov

@bors bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Mar 22, 2022
@Dylan-DPC Dylan-DPC mentioned this pull request Mar 22, 2022
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bors added a commit to rust-lang-ci/rust that referenced this pull request Mar 22, 2022
@bors
Auto merge of rust-lang#95215 - Dylan-DPC:rollup-l9f9t7l, r=Dylan-DPC
5f37001 
Rollup of 5 pull requests

Successful merges:

 - rust-lang#95188 ([`macro-metavar-expr`] Fix generated tokens hygiene)
 - rust-lang#95196 (rename LocalState::Uninitialized to Unallocated)
 - rust-lang#95197 (Suggest constraining param for unary ops when missing trait impl)
 - rust-lang#95200 (Cancel a not emitted error after parsing const generic args)
 - rust-lang#95207 (update Termination trait docs)

Failed merges:

r? `@ghost`
`@rustbot` modify labels: rollup
@bors bors merged commit 7c38093 into rust-lang:master Mar 22, 2022
@rustbot rustbot added this to the 1.61.0 milestone Mar 22, 2022
@c410-f3r c410-f3r mentioned this pull request Apr 9, 2022
Merged
JohnTitor added a commit to JohnTitor/rust that referenced this pull request Jun 9, 2022
@JohnTitor
Rollup merge of rust-lang#95860 - c410-f3r:stabilize-meta, r=joshtrip…
41e40ec 
…lett

Stabilize `$$` in Rust 1.63.0

# Stabilization proposal

This PR proposes the stabilization of a subset of `#![feature(macro_metavar_expr)]` or more specifically, the stabilization of dollar-dollar (`$$`).

Tracking issue: rust-lang#83527
Version: 1.63 (2022-06-28 => beta, 2022-08-11 => stable).

## What is stabilized

```rust
macro_rules! foo {
    () => {
        macro_rules! bar {
            ( $$( $$any:tt )* ) => { $$( $$any )* };
        }
    };
}

fn main() {
    foo!();
}
```

## Motivation

For more examples, see the [RFC](https://github.com/markbt/rfcs/blob/macro_metavar_expr/text/0000-macro-metavar-expr.md).

Users must currently resort to a tricky and not so well-known hack to declare nested macros with repetitions.

```rust
macro_rules! foo {
    ($dollar:tt) => {
        macro_rules! bar {
            ( $dollar ( $any:tt )* ) => { $dollar ( $any )* };
        }
    };
}
fn main() {
    foo!($);
}
```

As seen above, such hack is fragile and makes work with declarative macros much more unpleasant. Dollar-dollar (`$$`), on the other hand, makes nested macros more intuitive.

## What isn't stabilized

`count`, `ignore`, `index` and `length` are not being stabilized due to the lack of consensus.

## History

* 2021-02-22, [RFC: Declarative macro metavariable expressions](rust-lang/rfcs#3086)
* 2021-03-26, [Tracking Issue for RFC 3086: macro metavariable expressions](rust-lang#83527)
* 2022-02-01, [Implement macro meta-variable expressions](rust-lang#93545)
* 2022-02-25, [[1/2] Implement macro meta-variable expressions](rust-lang#94368)
* 2022-03-11, [[2/2] Implement macro meta-variable expressions](rust-lang#94833)
* 2022-03-12, [Fix remaining meta-variable expression TODOs](rust-lang#94884)
* 2019-03-21, [[macro-metavar-expr] Fix generated tokens hygiene](rust-lang#95188)
* 2022-04-07, [Kickstart the inner usage of macro_metavar_expr](rust-lang#95761)
* 2022-04-07, [[macro_metavar_expr] Add tests to ensure the feature requirement](rust-lang#95764)

## Non-stabilized expressions

rust-lang#83527 lists several concerns about some characteristics of `count`, `index` and `length` that effectively make their stabilization unfeasible. `$$` and `ignore`, however, are not part of any discussion and thus are suitable for stabilization.

It is not in the scope of this PR to detail each concern or suggest any possible converging solution. Such thing should be restrained in this tracking issue.

## Tests

This list is a subset of https://github.com/rust-lang/rust/tree/master/src/test/ui/macros/rfc-3086-metavar-expr

* [Ensures that nested macros have correct behavior](https://github.com/rust-lang/rust/blob/master/src/test/ui/macros/rfc-3086-metavar-expr/dollar-dollar-has-correct-behavior.rs)

* [Compares produced tokens to assert expected outputs](https://github.com/rust-lang/rust/blob/master/src/test/ui/macros/rfc-3086-metavar-expr/feature-gate-macro_metavar_expr.rs)

* [Checks the declarations of the feature](https://github.com/rust-lang/rust/blob/master/src/test/ui/macros/rfc-3086-metavar-expr/required-feature.rs)

* [Verifies all possible errors that can occur due to incorrect user input](https://github.com/rust-lang/rust/blob/master/src/test/ui/macros/rfc-3086-metavar-expr/syntax-errors.rs)

## Possible future work

Once consensus is achieved, other nightly expressions can be stabilized.

Thanks `@markbt` for creating the RFC and thanks to `@petrochenkov` and `@mark-i-m` for reviewing the implementations.
JohnTitor added a commit to JohnTitor/rust that referenced this pull request Jun 9, 2022
@JohnTitor
Rollup merge of rust-lang#95860 - c410-f3r:stabilize-meta, r=joshtrip…
afa2edb 
…lett

Stabilize `$$` in Rust 1.63.0

# Stabilization proposal

This PR proposes the stabilization of a subset of `#![feature(macro_metavar_expr)]` or more specifically, the stabilization of dollar-dollar (`$$`).

Tracking issue: rust-lang#83527
Version: 1.63 (2022-06-28 => beta, 2022-08-11 => stable).

## What is stabilized

```rust
macro_rules! foo {
    () => {
        macro_rules! bar {
            ( $$( $$any:tt )* ) => { $$( $$any )* };
        }
    };
}

fn main() {
    foo!();
}
```

## Motivation

For more examples, see the [RFC](https://github.com/markbt/rfcs/blob/macro_metavar_expr/text/0000-macro-metavar-expr.md).

Users must currently resort to a tricky and not so well-known hack to declare nested macros with repetitions.

```rust
macro_rules! foo {
    ($dollar:tt) => {
        macro_rules! bar {
            ( $dollar ( $any:tt )* ) => { $dollar ( $any )* };
        }
    };
}
fn main() {
    foo!($);
}
```

As seen above, such hack is fragile and makes work with declarative macros much more unpleasant. Dollar-dollar (`$$`), on the other hand, makes nested macros more intuitive.

## What isn't stabilized

`count`, `ignore`, `index` and `length` are not being stabilized due to the lack of consensus.

## History

* 2021-02-22, [RFC: Declarative macro metavariable expressions](rust-lang/rfcs#3086)
* 2021-03-26, [Tracking Issue for RFC 3086: macro metavariable expressions](rust-lang#83527)
* 2022-02-01, [Implement macro meta-variable expressions](rust-lang#93545)
* 2022-02-25, [[1/2] Implement macro meta-variable expressions](rust-lang#94368)
* 2022-03-11, [[2/2] Implement macro meta-variable expressions](rust-lang#94833)
* 2022-03-12, [Fix remaining meta-variable expression TODOs](rust-lang#94884)
* 2019-03-21, [[macro-metavar-expr] Fix generated tokens hygiene](rust-lang#95188)
* 2022-04-07, [Kickstart the inner usage of macro_metavar_expr](rust-lang#95761)
* 2022-04-07, [[macro_metavar_expr] Add tests to ensure the feature requirement](rust-lang#95764)

## Non-stabilized expressions

rust-lang#83527 lists several concerns about some characteristics of `count`, `index` and `length` that effectively make their stabilization unfeasible. `$$` and `ignore`, however, are not part of any discussion and thus are suitable for stabilization.

It is not in the scope of this PR to detail each concern or suggest any possible converging solution. Such thing should be restrained in this tracking issue.

## Tests

This list is a subset of https://github.com/rust-lang/rust/tree/master/src/test/ui/macros/rfc-3086-metavar-expr

* [Ensures that nested macros have correct behavior](https://github.com/rust-lang/rust/blob/master/src/test/ui/macros/rfc-3086-metavar-expr/dollar-dollar-has-correct-behavior.rs)

* [Compares produced tokens to assert expected outputs](https://github.com/rust-lang/rust/blob/master/src/test/ui/macros/rfc-3086-metavar-expr/feature-gate-macro_metavar_expr.rs)

* [Checks the declarations of the feature](https://github.com/rust-lang/rust/blob/master/src/test/ui/macros/rfc-3086-metavar-expr/required-feature.rs)

* [Verifies all possible errors that can occur due to incorrect user input](https://github.com/rust-lang/rust/blob/master/src/test/ui/macros/rfc-3086-metavar-expr/syntax-errors.rs)

## Possible future work

Once consensus is achieved, other nightly expressions can be stabilized.

Thanks ``@markbt`` for creating the RFC and thanks to ``@petrochenkov`` and ``@mark-i-m`` for reviewing the implementations.
@c410-f3r c410-f3r mentioned this pull request Mar 21, 2024
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