Deprecate the unstable `concat_idents!`#137653

tgross35 · 2025-02-26T04:48:24Z

concat_idents has been around unstably for a long time, but there is now a better (but still unstable) way to join identifiers using ${concat(...)} syntax with macro_metavar_expr_concat. This resolves a lot of the problems with concat_idents and is on a better track toward stabilization, so there is no need to keep both versions around. concat_idents! still has a lot of use in the ecosystem so deprecate it before removing, as discussed in 1.

Link: #124225

rustbot · 2025-02-26T04:48:28Z

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tgross35 · 2025-02-26T04:48:38Z

r? libs-api

tgross35 · 2025-03-06T08:23:40Z

I'd like to propose deprecating it now (1.87) and removing in the next version (1.88), nominating for libs-api. Cc @rust-lang/lang since this is tightly coupled.

traviscross · 2025-03-06T18:57:56Z

Let's just FCP it. That's maybe weird for an unstable thing, but no more weird than doing a deprecation cycle for it.

@rfcbot fcp merge

rfcbot · 2025-03-06T18:57:58Z

Team member @traviscross has proposed to merge this. The next step is review by the rest of the tagged team members:

No concerns currently listed.

Once a majority of reviewers approve (and at most 2 approvals are outstanding), this will enter its final comment period. If you spot a major issue that hasn't been raised at any point in this process, please speak up!

cc @rust-lang/lang-advisors: FCP proposed for lang, please feel free to register concerns.
See this document for info about what commands tagged team members can give me.

nikomatsakis · 2025-03-12T15:09:42Z

@rfcbot reviewed

joshtriplett · 2025-03-12T15:19:24Z

👍 for deprecating concat_idents!, in favor of concat from macro metavar expressions.

I saw that @tgross35 proposed rust-lang/rfcs#3649 to supersede the count and len mechanism. I want to make sure that RFC 3649 is only being proposed as an alternative to count and len, and that concat is still on track to continue.

tgross35 · 2025-03-12T18:33:10Z

I saw that @tgross35 proposed rust-lang/rfcs#3649 to supersede the count and len mechanism. I want to make sure that RFC 3649 is only being proposed as an alternative to count and len, and that concat is still on track to continue.

That's correct; I think concat can move forward at any point, RFC 3649 just handles the group- and index-related things 👍

traviscross · 2025-03-12T22:43:13Z

@rustbot labels -I-lang-nominated

We discussed this in the lang call today. Thanks @tgross35 for pushing this forward.

As above, the one question that came up was whether this was related to our open question:

Decide what we want about macro_metavar_expr #137581

But it's not, as macro_metavar_expr_concat is under a separate feature flag and isn't part of that proposed stabilization.

rfcbot · 2025-03-13T05:18:08Z

🔔 This is now entering its final comment period, as per the review above. 🔔

`concat_idents` has been around unstably for a long time, but there is now a better (but still unstable) way to join identifiers using `${concat(...)}` syntax with `macro_metavar_expr_concat`. This resolves a lot of the problems with `concat_idents` and is on a better track toward stabilization, so there is no need to keep both versions around. `concat_idents!` still has a lot of use in the ecosystem so deprecate it before removing, as discussed in [1]. Link: rust-lang#124225 [1]: https://rust-lang.zulipchat.com/#narrow/channel/219381-t-libs/topic/Removing.20.60concat_idents.60

tgross35 · 2025-04-24T22:15:52Z

@bors r=workingjubilee

bors · 2025-04-24T22:15:55Z

📌 Commit 75a9be6 has been approved by workingjubilee

It is now in the queue for this repository.

cuviper · 2025-04-24T22:30:21Z

It would be nice if deprecated supported RUSTC_CURRENT_VERSION

Hmm, I think that should work -- the tool simply calls str::replace:

rust/src/tools/replace-version-placeholder/src/main.rs

Line 24 in 3c877f6

let new_contents = contents.replace(VERSION_PLACEHOLDER, version_str);

(although the placeholder is CURRENT_RUSTC_VERSION)

tgross35 · 2025-04-24T22:36:31Z

I did try it before and IIRC it got rejected somewhere for not being a valid version. But maybe I just made the same typo at that time too :)

cuviper · 2025-04-24T22:40:37Z

Oh, I didn't think about attribute validation -- you're right, it doesn't work, and it should!

…iaskrgr Rollup of 8 pull requests Successful merges: - rust-lang#137653 (Deprecate the unstable `concat_idents!`) - rust-lang#138957 (Update the index of Option to make the summary more comprehensive) - rust-lang#140006 (ensure compiler existance of tools on the dist step) - rust-lang#140143 (Move `sys::pal::os::Env` into `sys::env`) - rust-lang#140202 (Make #![feature(let_chains)] bootstrap conditional in compiler/) - rust-lang#140236 (norm nested aliases before evaluating the parent goal) - rust-lang#140257 (Some drive-by housecleaning in `rustc_borrowck`) - rust-lang#140278 (Don't use item name to look up associated item from trait item) r? `@ghost` `@rustbot` modify labels: rollup

Rollup merge of rust-lang#137653 - tgross35:deprecate-concat_idents, r=workingjubilee Deprecate the unstable `concat_idents!` `concat_idents` has been around unstably for a long time, but there is now a better (but still unstable) way to join identifiers using `${concat(...)}` syntax with `macro_metavar_expr_concat`. This resolves a lot of the problems with `concat_idents` and is on a better track toward stabilization, so there is no need to keep both versions around. `concat_idents!` still has a lot of use in the ecosystem so deprecate it before removing, as discussed in [1]. Link: rust-lang#124225 [1]: https://rust-lang.zulipchat.com/#narrow/channel/219381-t-libs/topic/Removing.20.60concat_idents.60

…r=workingjubilee Deprecate the unstable `concat_idents!` `concat_idents` has been around unstably for a long time, but there is now a better (but still unstable) way to join identifiers using `${concat(...)}` syntax with `macro_metavar_expr_concat`. This resolves a lot of the problems with `concat_idents` and is on a better track toward stabilization, so there is no need to keep both versions around. `concat_idents!` still has a lot of use in the ecosystem so deprecate it before removing, as discussed in [1]. Link: rust-lang#124225 [1]: https://rust-lang.zulipchat.com/#narrow/channel/219381-t-libs/topic/Removing.20.60concat_idents.60

…iaskrgr Rollup of 8 pull requests Successful merges: - rust-lang#137653 (Deprecate the unstable `concat_idents!`) - rust-lang#138957 (Update the index of Option to make the summary more comprehensive) - rust-lang#140006 (ensure compiler existance of tools on the dist step) - rust-lang#140143 (Move `sys::pal::os::Env` into `sys::env`) - rust-lang#140202 (Make #![feature(let_chains)] bootstrap conditional in compiler/) - rust-lang#140236 (norm nested aliases before evaluating the parent goal) - rust-lang#140257 (Some drive-by housecleaning in `rustc_borrowck`) - rust-lang#140278 (Don't use item name to look up associated item from trait item) r? `@ghost` `@rustbot` modify labels: rollup

`concat_idents!` was deprecated in [1] and will be removed in the near future. Drop rust-analyzer's support for this macro here to avoid problems during the next sync. [1]: rust-lang/rust#137653

`concat_idents!` was deprecated in [1] and will be removed in the near future. rust-analyzer's support is independent of rustc's, so drop RA support now to make syncing easier. [1]: rust-lang/rust#137653

`concat_idents!` was deprecated in [1] and will be removed in the near future. rust-analyzer's support is independent of rustc's, so drop RA support now to make syncing easier. [1]: rust-lang#137653

In [rust-lang#137653], the lang and libs-API teams did a joint FCP to deprecate and eventually remove the long-unstable `concat_idents!` macro. The deprecation is landing in 1.88, so do the removal here (target version 1.90). This macro has been superseded by the more recent `${concat(...)}` metavariable expression language feature, which avoids some of the limitations of `concat_idents!`. The metavar expression is unstably available under the [`macro_metavar_expr_concat`] feature. History is mildly interesting here: `concat_idents!` goes back to 2011 when it was introduced with 513276e ("Add #concat_idents[] and #ident_to_str[]"). The syntax looks a bit different but it still works about the same: let asdf_fdsa = "<.<"; assert(#concat_idents[asd,f_f,dsa] == "<.<"); assert(#ident_to_str[use_mention_distinction] == "use_mention_distinction"); (That test existed from introduction until its removal here.) Closes: rust-lang#29599 [rust-lang#137653]: rust-lang#137653 [`macro_metavar_expr_concat`]: rust-lang#124225

tgross35 · 2025-06-19T07:03:09Z

Removal PR is up at #142704

Remove the deprecated `concat_idents!` macro In [#137653], the lang and libs-API teams did a joint FCP to deprecate and eventually remove the long-unstable `concat_idents!` macro. The deprecation is landing in 1.88, so do the removal here (target version 1.90). This macro has been superseded by the more recent `${concat(...)}` metavariable expression language feature, which avoids some of the limitations of `concat_idents!`. The metavar expression is unstably available under the [`macro_metavar_expr_concat`] feature. History is mildly interesting here: `concat_idents!` goes back to 2011 when it was introduced with 513276e ("Add #concat_idents[] and #ident_to_str[]"). The syntax looks a bit different but it still works about the same: let asdf_fdsa = "<.<"; assert(#concat_idents[asd,f_f,dsa] == "<.<"); assert(#ident_to_str[use_mention_distinction] == "use_mention_distinction"); (That test existed from introduction until its removal here.) Closes: #29599 [#137653]: #137653 [`macro_metavar_expr_concat`]: #124225

In [rust-lang#137653], the lang and libs-API teams did a joint FCP to deprecate and eventually remove the long-unstable `concat_idents!` macro. The deprecation is landing in 1.88, so do the removal here (target version 1.90). This macro has been superseded by the more recent `${concat(...)}` metavariable expression language feature, which avoids some of the limitations of `concat_idents!`. The metavar expression is unstably available under the [`macro_metavar_expr_concat`] feature. History is mildly interesting here: `concat_idents!` goes back to 2011 when it was introduced with 513276e ("Add #concat_idents[] and #ident_to_str[]"). The syntax looks a bit different but it still works about the same: let asdf_fdsa = "<.<"; assert(#concat_idents[asd,f_f,dsa] == "<.<"); assert(#ident_to_str[use_mention_distinction] == "use_mention_distinction"); (That test existed from introduction until its removal here.) Closes: rust-lang#29599 [rust-lang#137653]: rust-lang#137653 [`macro_metavar_expr_concat`]: rust-lang#124225

…ee1-dead Remove the deprecated unstable `concat_idents!` macro In [rust-lang#137653], the lang and libs-API teams did a joint FCP to deprecate and eventually remove the long-unstable `concat_idents!` macro. The deprecation is landing in 1.88, so do the removal here (target version 1.90). This macro has been superseded by the more recent `${concat(...)}` metavariable expression language feature, which avoids some of the limitations of `concat_idents!`. The metavar expression is unstably available under the [`macro_metavar_expr_concat`] feature. History is mildly interesting here: `concat_idents!` goes back to 2011 when it was introduced with 513276e ("Add #concat_idents[] and #ident_to_str[]"). The syntax looks a bit different but it still works about the same: let asdf_fdsa = "<.<"; assert(#concat_idents[asd,f_f,dsa] == "<.<"); assert(#ident_to_str[use_mention_distinction] == "use_mention_distinction"); (That test existed from introduction until its removal here.) Closes: rust-lang#29599 [rust-lang#137653]: rust-lang#137653 [`macro_metavar_expr_concat`]: rust-lang#124225

Rollup merge of #142704 - tgross35:remove-concat_idents, r=fee1-dead Remove the deprecated unstable `concat_idents!` macro In [#137653], the lang and libs-API teams did a joint FCP to deprecate and eventually remove the long-unstable `concat_idents!` macro. The deprecation is landing in 1.88, so do the removal here (target version 1.90). This macro has been superseded by the more recent `${concat(...)}` metavariable expression language feature, which avoids some of the limitations of `concat_idents!`. The metavar expression is unstably available under the [`macro_metavar_expr_concat`] feature. History is mildly interesting here: `concat_idents!` goes back to 2011 when it was introduced with 513276e ("Add #concat_idents[] and #ident_to_str[]"). The syntax looks a bit different but it still works about the same: let asdf_fdsa = "<.<"; assert(#concat_idents[asd,f_f,dsa] == "<.<"); assert(#ident_to_str[use_mention_distinction] == "use_mention_distinction"); (That test existed from introduction until its removal here.) Closes: #29599 [#137653]: #137653 [`macro_metavar_expr_concat`]: #124225

…ee1-dead Remove the deprecated unstable `concat_idents!` macro In [rust-lang#137653], the lang and libs-API teams did a joint FCP to deprecate and eventually remove the long-unstable `concat_idents!` macro. The deprecation is landing in 1.88, so do the removal here (target version 1.90). This macro has been superseded by the more recent `${concat(...)}` metavariable expression language feature, which avoids some of the limitations of `concat_idents!`. The metavar expression is unstably available under the [`macro_metavar_expr_concat`] feature. History is mildly interesting here: `concat_idents!` goes back to 2011 when it was introduced with 513276e ("Add #concat_idents[] and #ident_to_str[]"). The syntax looks a bit different but it still works about the same: let asdf_fdsa = "<.<"; assert(#concat_idents[asd,f_f,dsa] == "<.<"); assert(#ident_to_str[use_mention_distinction] == "use_mention_distinction"); (That test existed from introduction until its removal here.) Closes: rust-lang#29599 [rust-lang#137653]: rust-lang#137653 [`macro_metavar_expr_concat`]: rust-lang#124225

rustbot assigned nnethercote Feb 26, 2025

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. T-libs Relevant to the library team, which will review and decide on the PR/issue. labels Feb 26, 2025

tgross35 changed the title ~~Mark concat_idents! deprecated~~ Deprecate concat_idents! Feb 26, 2025

rustbot added the T-libs-api Relevant to the library API team, which will review and decide on the PR/issue. label Feb 26, 2025

rustbot assigned m-ou-se and unassigned nnethercote Feb 26, 2025

tgross35 changed the title ~~Deprecate concat_idents!~~ Deprecate the unstable concat_idents! Feb 26, 2025

tgross35 force-pushed the deprecate-concat_idents branch from ecac1cc to 4f7ea23 Compare February 26, 2025 04:49

tgross35 added the I-libs-api-nominated Nominated for discussion during a libs-api team meeting. label Mar 6, 2025

rfcbot added proposed-final-comment-period Proposed to merge/close by relevant subteam, see T-<team> label. Will enter FCP once signed off. disposition-merge This issue / PR is in PFCP or FCP with a disposition to merge it. labels Mar 6, 2025

traviscross added the I-lang-easy-decision Issue: The decision needed by the team is conjectured to be easy; this does not imply nomination label Mar 6, 2025

rustbot removed the I-lang-nominated Nominated for discussion during a lang team meeting. label Mar 12, 2025

rfcbot added the final-comment-period In the final comment period and will be merged soon unless new substantive objections are raised. label Mar 13, 2025

tgross35 force-pushed the deprecate-concat_idents branch from 3f7d833 to 75a9be6 Compare April 24, 2025 22:14

matthiaskrgr mentioned this pull request Apr 25, 2025

Rollup of 8 pull requests #140282

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bors merged commit 84a921d into rust-lang:master Apr 25, 2025
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rustbot added this to the 1.88.0 milestone Apr 25, 2025

tgross35 deleted the deprecate-concat_idents branch April 25, 2025 15:53

tgross35 mentioned this pull request May 28, 2025

chore: Remove support for concat_idents! rust-lang/rust-analyzer#19877

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tgross35 mentioned this pull request Jun 19, 2025

Remove the deprecated unstable concat_idents! macro #142704

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apiraino removed the to-announce Announce this issue on triage meeting label Jun 26, 2025

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