Forbid `$$crate` #99193

c410-f3r · 2022-07-12T22:29:56Z

Fixes #99035 by simply denying the usage of $$crate. Future decisions about how $$crate should behave (if it should) won't be a breaking change and I am out of a better idea.

cc @rust-lang/lang (Responsible team)
cc @petrochenkov (Reviewed most of the implementation)
cc @CAD97 (Created the issue)
cc @Mark-Simulacrum (Nominated the issue)

rust-highfive · 2022-07-12T22:29:59Z

r? @cjgillot

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CAD97 · 2022-07-12T22:35:31Z

Can we add a test that this is forbidden even through macro indirection? E.g. smth like

macro dollar_dollar_crate($d:tt) {
    $d $d crate
}

macro use_it() {
    use dollar_dollar_crate!($$);
}

use_it!()

Edit: also the same, but putting crate behind a tt/ident metavar

compiler/rustc_expand/src/mbe/quoted.rs

src/test/ui/macros/rfc-3086-metavar-expr/syntax-errors.stderr

CAD97 · 2022-07-13T00:08:22Z

src/test/ui/macros/rfc-3086-metavar-expr/syntax-errors.rs

+macro_rules! dollar_dollar_crate {
+    ($d:tt) => {
+        const _: usize = $d$d crate::IDX;
+        //~^ ERROR expected expression, found `$`
+    };
+}
+dollar_dollar_crate!($);


This isn't quite the test I had in mind. Instead,

Suggested change

macro_rules! dollar_dollar_crate {

($d:tt) => {

const _: usize = $d$d crate::IDX;

//~^ ERROR expected expression, found `$`

};

}

dollar_dollar_crate!($);

macro_rules! dollar_dollar_crate {

($d:tt) => {

const _: usize = $d$d crate::IDX;

//~^ ERROR expected expression, found `$`

};

}

macro_rules! dollar_dollar_use {

($d:tt) => {

dollar_dollar_crate!($d);

}

}

dollar_dollar_use!($);

The fact that the current error message is "expected expression, found $" and not "$$crate is not allowed" makes me worried that this actually will work i.e. $$crate is insufficiently gated.

Changed as requested

Is this resolved? There is still no error on the indirect $$crate.

apiraino · 2022-07-13T09:50:44Z

I think this PR is meant to reach stable, right? (i.e. the alternate implementation of $$crate will take longer than 1.63 milestone). If yes I hope it's correct to label this revert to be mentioned in the release notes.

@rustbot label relnotes T-lang

c410-f3r · 2022-07-13T10:49:34Z

I think this PR is meant to reach stable, right? (i.e. the alternate implementation of $$crate will take longer than 1.63 milestone). If yes I hope it's correct to label this revert to be mentioned in the release notes.

@rustbot label relnotes T-lang

Everything is a best effort to solve a problem. It is not clear if the feature will be removed from 1.63 or if this PR can be back-ported .

EDIT: The feature will actually be reverted as described in #99035 (comment)

c410-f3r · 2022-07-18T19:01:25Z

Is the lang-team going to merge this PR? Perhaps some other strategy will be used? Perhaps try another compiler reviewer?

Its been 6 days and it would be a shame to miss 1.64 for whatever reason.

Mark-Simulacrum · 2022-07-18T19:07:47Z

beta-nominating -- partially to get eyes on this from T-compiler (who should do the code review), and partially because we do need to beta backport either this PR or a full revert of the original PR. (Either is fine, but if it's the latter someone needs to do the legwork).

CAD97 · 2022-07-18T19:47:00Z

Mechanical revert available at #99435

…=Mark-Simulacrum Revert "Stabilize $$ in Rust 1.63.0" This mechanically reverts commit 9edaa76, the one commit from rust-lang#95860. rust-lang#99035; the behavior of `$$crate` is potentially unexpected and not ready to be stabilized. rust-lang#99193 attempts to forbid `$$crate` without also destabilizing `$$` more generally. `@rustbot` modify labels +T-compiler +T-lang +P-medium +beta-nominated +relnotes (applying the labels I think are accurate from the issue and alternative partial revert) cc `@Mark-Simulacrum`

cjgillot · 2022-07-18T19:55:23Z

compiler/rustc_expand/src/mbe/quoted.rs

+                            token.span,
+                            &format!("unexpected token: {}", pprust::token_to_string(token))
+                        );
+                        sess.span_diagnostic.note_without_error("`$$crate` is not allowed in any context");


Why not directly span_err on this message? Should we point to the two $ tokens too?

cjgillot · 2022-07-18T20:02:24Z

src/test/ui/macros/rfc-3086-metavar-expr/syntax-errors.rs

+macro_rules! dollar_dollar_crate {
+    ($d:tt) => {
+        const _: usize = $d$d crate::IDX;
+        //~^ ERROR expected expression, found `$`
+    };
+}
+dollar_dollar_crate!($);


Is this resolved? There is still no error on the indirect $$crate.

c410-f3r · 2022-07-25T11:56:38Z

Sorry, all the obstacles imposed by different actors in different fronts made me lost the motivation/energy to keep coding this PR. Closing.

rust-highfive assigned cjgillot Jul 12, 2022

rustbot added the T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. label Jul 12, 2022

rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Jul 12, 2022

c410-f3r commented Jul 12, 2022

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c410-f3r force-pushed the yet-yet-yet-yet-another-macro branch from 9e9b542 to e2995e6 Compare July 12, 2022 22:57

CAD97 reviewed Jul 13, 2022

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rustbot added relnotes Marks issues that should be documented in the release notes of the next release. T-lang Relevant to the language team, which will review and decide on the PR/issue. labels Jul 13, 2022

steffahn mentioned this pull request Jul 13, 2022

$$crate unexpectedly fails to defer which crate $crate refers to #99035

Open

Forbid $$crate

f4f3913

c410-f3r force-pushed the yet-yet-yet-yet-another-macro branch from e2995e6 to f4f3913 Compare July 18, 2022 18:58

Mark-Simulacrum added the beta-nominated Nominated for backporting to the compiler in the beta channel. label Jul 18, 2022

CAD97 mentioned this pull request Jul 18, 2022

Revert "Stabilize $$ in Rust 1.63.0" #99435

Merged

Mark-Simulacrum removed the beta-nominated Nominated for backporting to the compiler in the beta channel. label Jul 18, 2022

cjgillot reviewed Jul 24, 2022

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cjgillot added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Jul 24, 2022

c410-f3r closed this Jul 25, 2022

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Forbid `$$crate` #99193

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Forbid $$crate #99193

Forbid $$crate #99193

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c410-f3r commented Jul 25, 2022

Forbid `$$crate` #99193

Forbid `$$crate` #99193

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