Bogus unknown attribute errors in newest nightly

[sfackler]

log4rs no longer builds on nightly with bogus unknown attribute errors:

 ❯ cargo +nightly build                                                                                                                                                                                                                                             [log4rs/master=]
   Compiling log4rs v0.8.0 (file:///home/sfackler/rust/log4rs)                                                                                                                                                                                                                      
error[E0658]: The attribute `serde` is currently unknown to the compiler and may have meaning added to it in the future (see issue #29642)                                                                                                                                         
  --> src/append/file.rs:25:1                                                                                                                                                                                                                                                      
   |                                                                                                                                                                                                                                                                               
25 | #[serde(deny_unknown_fields)]                                                                                                                                                                                                                                                 
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^                                                                                                                                                                                                                                                 
   |                                                                                                                                                                                                                                                                               
   = help: add #![feature(custom_attribute)] to the crate attributes to enable                                                                                                                                                                                                     
                                                                                                                                                                                                                                                                                   
error[E0658]: The attribute `serde` is currently unknown to the compiler and may have meaning added to it in the future (see issue #29642)                                                                                                                                         
  --> src/append/console.rs:24:1                                                                                                                                                                                                                                                   
   |                                                                                                                                                                                                                                                                               
24 | #[serde(deny_unknown_fields)]                                                                                                                                                                                                                                                 
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^                                                                                                                                                                                                                                                 
   |                                                                                                                                                                                                                                                                               
   = help: add #![feature(custom_attribute)] to the crate attributes to enable                                                                                                                                                                                                     
                                                                                                                                                                                                                                                                                   
error[E0658]: The attribute `serde` is currently unknown to the compiler and may have meaning added to it in the future (see issue #29642)                                                                                                                                         
  --> src/append/rolling_file/policy/compound/roll/delete.rs:16:1                                                                                                                                                                                                                  
   |                                                                                                                                                                                                                                                                               
16 | #[serde(deny_unknown_fields)]                                                                                                                                                                                                                                                 
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^                                                                                                                                                                                                                                                 
   |                                                                                                                                                                                                                                                                               
   = help: add #![feature(custom_attribute)] to the crate attributes to enable                                                                                                                                                                                                     
                                                                                                                                                                                                                                                                                   
error[E0658]: The attribute `serde` is currently unknown to the compiler and may have meaning added to it in the future (see issue #29642)                                                                                                                                         
  --> src/append/rolling_file/policy/compound/roll/fixed_window.rs:17:1                                                                                                                                                                                                            
   |                                                                                                                                                                                                                                                                               
17 | #[serde(deny_unknown_fields)]                                                                                                                                                                                                                                                 
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^                                                                                                                                                                                                                                                 
   |                                                                                                                                                                                                                                                                               
   = help: add #![feature(custom_attribute)] to the crate attributes to enable                                                                                                                                                                                                     
                                                                                                                                                                                                                                                                                   
error[E0658]: The attribute `serde` is currently unknown to the compiler and may have meaning added to it in the future (see issue #29642)                                                                                                                                         
  --> src/append/rolling_file/policy/compound/trigger/size.rs:21:1                                                                                                                                                                                                                 
   |                                                                                                                                                                                                                                                                               
21 | #[serde(deny_unknown_fields)]                                                                                                                                                                                                                                                 
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^                                                                                                                                                                                                                                                 
   |                                                                                                                                                                                                                                                                               
   = help: add #![feature(custom_attribute)] to the crate attributes to enable                                                                                                                                                                                                     
                                                                                                                                                                                                                                                                                   
error[E0658]: The attribute `serde` is currently unknown to the compiler and may have meaning added to it in the future (see issue #29642)                                                                                                                                         
  --> src/append/rolling_file/policy/compound/mod.rs:24:1                                                                                                                                                                                                                          
   |                                                                                                                                                                                                                                                                               
24 | #[serde(deny_unknown_fields)]                                                                                                                                                                                                                                                 
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^                                                                                                                                                                                                                                                 
   |                                                                                                                                                                                                                                                                               
   = help: add #![feature(custom_attribute)] to the crate attributes to enable                                                                                                                                                                                                     
                                                                                                                                                                                                                                                                                   
error[E0658]: The attribute `serde` is currently unknown to the compiler and may have meaning added to it in the future (see issue #29642)                                                                                                                                         
  --> src/append/rolling_file/mod.rs:46:1                                                                                                                                                                                                                                          
   |                                                                                                                                                                                                                                                                               
46 | #[serde(deny_unknown_fields)]                                                                                                                                                                                                                                                 
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^                                                                                                                                                                                                                                                 
   |                                                                                                                                                                                                                                                                               
   = help: add #![feature(custom_attribute)] to the crate attributes to enable                                                                                                                                                                                                     
                                                                                                                                                                                                                                                                                   
error: aborting due to 7 previous errors                                                                                                                                                                                                                                           
                                                                                                                                                                                                                                                                                   
For more information about this error, try `rustc --explain E0658`.                                                                                                                                                                                                                
error: Could not compile `log4rs`.                                                                                                                                                                                                                                                 
                                                                                                                                                                                                                                                                                   
To learn more, run the command again with --verbose.

Those attributes are used on types with #[derive(Deserialize)] so the serde attribute should be whitelisted: https://github.com/sfackler/log4rs/blob/master/src/append/file.rs#L22-L30

estk/log4rs#75

[petrochenkov]

Unfortunately, feature gate errors are fatal (this needs to be fixed), so in this case they hide the true issue:

error: cannot determine resolution for the derive macro `Deserialize`
  --> src/append/file.rs:24:10
   |
24 | #[derive(Deserialize)]
   |          ^^^^^^^^^^^
   |
   = note: import resolution is stuck, try simplifying macro imports

All in all, this happens due to #[derive(Deserialize)] being in the same scope with use file::Deserialize;, but I'm not yet sure about details.
I'll try to minimize the issue and find out why resolution is stuck.

The workaround is to avoid use file::Deserialize; imports and to use ::file::Deserialize explicitly.

[petrochenkov]

Minimized:

#[macro_use]
extern crate serde_derive;

mod m1 {
    use m2::Deserialize;

    #[derive(Deserialize)] //~ ERROR cannot determine resolution for the derive macro `Deserialize`
    struct A {}
}

mod m2 {
    pub type Deserialize = u8;

    #[derive(Deserialize)]
    #[serde]
    struct B {}
}

[tomhoule]

I believe my project is hitting a similar issue: see the travis CI runs for this PR: graphql-rust/graphql-client#79

error: cannot determine resolution for the attribute macro `serde`
  --> tests/subscriptions.rs:19:10
   |
19 | #[derive(GraphQLQuery)]
   |          ^^^^^^^^^^^^
   |
   = note: import resolution is stuck, try simplifying macro imports

(happens only on nightly)

[petrochenkov]

Fixed in #53587

[pnkfelix]

visiting for triage. P-high. (Hopefully the aforementioned PR will land before next week's meeting.)

[dtolnay]

For those looking for a nightly to use, nightly-2018-08-17 is the newest that does not hit this issue.

rustup install nightly-2018-08-17

[petrochenkov]

Fixed in #54086