regression: error[E0658]: use of unstable library feature proc_macro_totokens

[cuviper]

Two logs failed to compile sqlx-models-proc-macro:

1. https://crater-reports.s3.amazonaws.com/beta-1.84.0-4-retry2/beta-2024-12-08/reg/sql_from_models-proc-macro-0.1.2/log.txt
2. https://crater-reports.s3.amazonaws.com/beta-1.84.0-4-retry2/beta-2024-12-08/reg/sqlx-models-proc-macro-0.0.3/log.txt

[INFO] [stdout] warning: `ToTokens` is ambiguous
[INFO] [stdout]   --> src/model/mod.rs:59:6
[INFO] [stdout]    |
[INFO] [stdout] 59 | impl ToTokens for Model {
[INFO] [stdout]    |      ^^^^^^^^ ambiguous name
[INFO] [stdout]    |
[INFO] [stdout]    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
[INFO] [stdout]    = note: for more information, see issue #114095 <https://github.com/rust-lang/rust/issues/114095>
[INFO] [stdout]    = note: ambiguous because of multiple glob imports of a name in the same module
[INFO] [stdout] note: `ToTokens` could refer to the trait imported here
[INFO] [stdout]   --> src/prelude.rs:2:35
[INFO] [stdout]    |
[INFO] [stdout] 2  | pub use proc_macro::{TokenStream, *};
[INFO] [stdout]    |                                   ^
[INFO] [stdout]    = help: consider adding an explicit import of `ToTokens` to disambiguate
[INFO] [stdout] note: `ToTokens` could also refer to the trait imported here
[INFO] [stdout]   --> src/prelude.rs:4:24
[INFO] [stdout]    |
[INFO] [stdout] 4  | pub use quote::{quote, *};
[INFO] [stdout]    |                        ^
[INFO] [stdout]    = help: consider adding an explicit import of `ToTokens` to disambiguate
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stdout] error[E0658]: use of unstable library feature `proc_macro_totokens`
[INFO] [stdout]   --> src/model/mod.rs:60:5
[INFO] [stdout]    |
[INFO] [stdout] 60 | /     fn to_tokens(&self, tokens: &mut TokenStream2) {
[INFO] [stdout] 61 | |         let name = &self.name;
[INFO] [stdout] 62 | |         let name_lowercase = &self.name_lowercase;
[INFO] [stdout] 63 | |         let columns = &self.get_columns();
[INFO] [stdout] ...  |
[INFO] [stdout] 75 | |         tokens.extend(template);
[INFO] [stdout] 76 | |     }
[INFO] [stdout]    | |_____^
[INFO] [stdout]    |
[INFO] [stdout]    = note: see issue #130977 <https://github.com/rust-lang/rust/issues/130977> for more information

So it appears to be globbing the unstable proc_macro::ToTokens before the desired quote::ToTokens.

Version it worked on

It most recently worked on: 1.83.0

Version with regression

Using rustc 1.84.0-beta.4 in crater #134138.

@rustbot modify labels: +regression-from-stable-to-beta -regression-untriaged

[compiler-errors]

This was introduced by #131441. I'm not sure if it's avoidable in general given this pattern of glob imports, seems like the code was just waiting to have a glob import ambiguity :'(

[cuviper]

Also related: https://crater-reports.s3.amazonaws.com/beta-1.84.0-4-retry2/beta-2024-12-08/reg/chime-flux-proc-macro-0.3.0/log.txt

[INFO] [stdout] warning: unused import: `quote::*`
[INFO] [stdout]  --> src/lib.rs:3:5
[INFO] [stdout]   |
[INFO] [stdout] 3 | use quote::*;
[INFO] [stdout]   |     ^^^^^^^^
[INFO] [stdout]   |
[INFO] [stdout]   = note: `#[warn(unused_imports)]` on by default
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stdout] error[E0599]: the method `to_token_stream` exists for reference `&Stmt`, but its trait bounds were not satisfied
[INFO] [stdout]    --> src/lib.rs:175:9
[INFO] [stdout]     |
[INFO] [stdout] 175 |                           s.to_token_stream()
[INFO] [stdout]     |                             ^^^^^^^^^^^^^^^
[INFO] [stdout]     |
[INFO] [stdout]    ::: /opt/rustwide/cargo-home/registry/src/index.crates.io-6f17d22bba15001f/syn-2.0.90/src/stmt.rs:18:1
[INFO] [stdout]     |
[INFO] [stdout] 18  | / ast_enum! {
[INFO] [stdout] 19  | |     /// A statement, usually ending in a semicolon.
[INFO] [stdout] 20  | |     #[cfg_attr(docsrs, doc(cfg(feature = "full")))]
[INFO] [stdout] 21  | |     pub enum Stmt {
[INFO] [stdout] ...   |
[INFO] [stdout] 37  | |     }
[INFO] [stdout] 38  | | }
[INFO] [stdout]     | |_- doesn't satisfy `Stmt: proc_macro::ToTokens`
[INFO] [stdout]     |
[INFO] [stdout]     = note: the following trait bounds were not satisfied:
[INFO] [stdout]             `Stmt: proc_macro::ToTokens`
[INFO] [stdout]             which is required by `&Stmt: proc_macro::ToTokens`
[INFO] [stdout]     = help: items from traits can only be used if the trait is in scope
[INFO] [stdout] help: trait `ToTokens` which provides `to_token_stream` is implemented but not in scope; perhaps you want to import it
[INFO] [stdout]     |
[INFO] [stdout] 1   + use quote::ToTokens;
[INFO] [stdout]     |

[jieyouxu]

This was introduced by #131441. I'm not sure if it's avoidable in general given this pattern of glob imports, seems like the code was just waiting to have a glob import ambiguity :'(

Seems like we may need to just accept that this can break code that was using glob imports in this fashion (I think this is glob-vs-glob?), unless we manage to never add things to proc_macros, which is also undesirable... I suppose we could notify the crates that broke?

Not sure what else can be done, outside of better advertisement/awareness-raising about breakages that can happen from glob-vs-glob imports between multiple imported crates?

[compiler-errors]

Yeah, but that's probably a call that's best left for T-libs-api since they could presumably opt to mitigate this breakage some other way (like renaming the trait to have fewer conflicts or something, though I don't personally think that needs to get done)