macro imports don't work when there are _two_ imported attributes

[Manishearth]

// crate must be on rust 2018
// OR add an `extern crate serde_derive`

use serde_derive::Deserialize;

#[derive(Deserialize)]
#[serde(rename_all = "kebab-case")]
#[serde(deny_unknown_fields)]
enum Foo {
    A(u8)
}

This is the code you are supposed to use according to the macro_use_extern_crate lint.

It fails to compile, with

   Compiling t v0.1.0 (file:///home/manishearth/sand/bar/t)                                                              
error: cannot find attribute macro `serde` in this scope=========>      ] 9/10: t                                        
  --> src/main.rs:11:3
   |
11 | #[serde(deny_unknown_fields)]
   |   ^^^^^

It compiles fine if you use just one of the two attributes. Swapping attribute order makes it complain about the last non-derive attribute.

This seems broken?

cc @dtolnay @alexcrichton

[dtolnay]

Confirmed, this behavior is broken. Possibly related to #52226. @petrochenkov

[dtolnay]

As a workaround specific to serde_derive, we allow multiple elements within one #[serde(...)] attribute.

#[derive(Deserialize)]
#[serde(rename_all = "kebab-case", deny_unknown_fields)]
enum Foo {
    A(u8)
}

[Manishearth]

yeah, that's what I ended up doing

…

-Manish Goregaokar

On Thu, Jul 19, 2018 at 12:17 AM David Tolnay ***@***.***> wrote: As a workaround specific to serde_derive, we allow multiple elements within one #[serde(...)] attribute. #[derive(Deserialize)] #[serde(rename_all = "kebab-case", deny_unknown_fields)]enum Foo { A(u8) } — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <#52525 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/ABivSF1JPzq8S2-yOddn4qtf11a0DgvGks5uIDJ0gaJpZM4VV3H-> .

[alexcrichton]

This should be fixed in #52539