Visibility tokens on types in extern { ... } blocks are no longer given to procedural macros #69315

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1. jonas-schievink

   added

   A-visibilityArea: Visibility / privacyArea: Visibility / privacy

   C-bugCategory: This is a bug.Category: This is a bug.

   I-nominated

   regression-from-stable-to-nightlyPerformance or correctness regression from stable to nightly.Performance or correctness regression from stable to nightly.

   T-compilerRelevant to the compiler team, which will review and decide on the PR/issue.Relevant to the compiler team, which will review and decide on the PR/issue.

   on Feb 20, 2020
2. Centril

   added

   A-parserArea: The lexing & parsing of Rust source code to an ASTArea: The lexing & parsing of Rust source code to an AST

   E-needs-mcveCall for participation: This issue has a repro, but needs a Minimal Complete and Verifiable ExampleCall for participation: This issue has a repro, but needs a Minimal Complete and Verifiable Example

   and removed

   C-bugCategory: This is a bug.Category: This is a bug.

   on Feb 20, 2020
3. petrochenkov commented on Feb 20, 2020

   

   petrochenkov

   on Feb 20, 2020

   Contributor

   More actions

   The large parser PR from @Centril (#69194) could also cause something like this.
4. petrochenkov

   self-assigned this

   on Feb 20, 2020
5. petrochenkov commented on Feb 20, 2020

   

   petrochenkov

   on Feb 20, 2020

   Contributor

   More actions

   I'll be able to look at this during the weekend, but it would be great if someone could come up with a minimal reproduction before that.
6. alexcrichton commented on Feb 20, 2020

   

   alexcrichton

   on Feb 20, 2020

   MemberAuthor

   More actions

   Ok, wanted to get a gut-check to see if it was known what was happening. Did some reduction and it looks like the macro no longer gets the pub token for the input type.

   Given this input:

   pub mod wasm {
       #[the_macro::the_macro]
       extern "C" {
           pub type Memory;
       }
   }
   
   fn main() {
       let _: wasm::Memory;
   }

   then with this macro:

   extern crate proc_macro;
   
   use proc_macro::*;
   
   #[proc_macro_attribute]
   pub fn the_macro(_attr: TokenStream, body: TokenStream) -> TokenStream {
       let g = match body.clone().into_iter().nth(2) {
           Some(TokenTree::Group(g)) => g,
           _ => panic!("unexpected input"),
       };
       let tokens = g.stream().into_iter().collect::<Vec<_>>();
       assert_eq!(tokens[0].to_string(), "pub");
       return body;
   }

   it fails with:

   $ cargo +nightly build
      Compiling wut v0.1.0 (/home/alex/code/wut)
   error: custom attribute panicked
    --> src/main.rs:2:5
     |
   2 |     #[the_macro::the_macro]
     |     ^^^^^^^^^^^^^^^^^^^^^^^
     |
     = help: message: assertion failed: `(left == right)`
               left: `"type"`,
              right: `"pub"`
   
   error: aborting due to previous error
   
   error: could not compile `wut`.
   
   To learn more, run the command again with --verbose.
   

   On stable it yields the expected error[E0658]: extern types are experimental error which indicates that the pub token was fed to the macro.

   If the #[wasm_bindgen] macro doesn't see the pub token it doesn't make the final result public, which is why the privacy error happened in the first place.
7. alexcrichton

   changed the title [-]Macro-expanded public struct no longer considered public[/-] [+]Visibility tokens on types in `extern { ... }` blocks are no longer given to procedural macros[/+] on Feb 20, 2020
8. alexcrichton commented on Feb 20, 2020

   

   alexcrichton

   on Feb 20, 2020

   MemberAuthor

   More actions

   (updated the issue title to reflect what appears to be the actual bug)
9. Centril

   self-assigned this

   on Feb 20, 2020
10. Centril

    removed

    E-needs-mcveCall for participation: This issue has a repro, but needs a Minimal Complete and Verifiable ExampleCall for participation: This issue has a repro, but needs a Minimal Complete and Verifiable Example

    on Feb 20, 2020
11. Centril commented on Feb 21, 2020

    

    Centril

    on Feb 21, 2020

    Contributor

    More actions

    Fixed by #69334.
12. Centril

    removed

    I-nominated

    on Feb 21, 2020
13. bors

    added 2 commits that reference this issue on Feb 22, 2020

    Auto merge of #69334 - Centril:nested-item-vis-def, r=petrochenkov

    ...

    a82d3cf

    Auto merge of #69334 - Centril:nested-item-vis-def, r=petrochenkov

    ...

    1484196
14. bors

    closed this as completedin 1484196on Feb 23, 2020