cargo fix --edition-idioms: "failed to automatically apply fixes suggested by rustc to crate"

[SimonSapin]

• Clone Servo at commit 6878dbbbeaa59b21a7b3608b6d6a911e88c1e443 (current HEAD)
• cd components/profile
• cargo +nightly fix --edition-idioms

rustc 1.32.0-nightly (13dab66a6 2018-11-05)
cargo 1.32.0-nightly (1fa3088 2018-10-31)

    Checking profile v0.0.1 (/home/simon/servo/components/profile)                                                     
warning: failed to automatically apply fixes suggested by rustc to crate `profile`                                     

after fixes were automatically applied the compiler reported errors within these files:

  * components/profile/lib.rs

This likely indicates a bug in either rustc or cargo itself,
and we would appreciate a bug report! You're likely to see 
a number of compiler warnings after this message which cargo
attempted to fix but failed. If you could open an issue at
https://github.com/rust-lang/cargo/issues
quoting the full output of this command we'd be very appreciative!

warning: unused extern crate                                                                                           
 --> components/profile/lib.rs:9:1                                                                                     
  |                                                                                                                    
9 | extern crate influent;                                                                                             
  | ^^^^^^^^^^^^^^^^^^^^^^ help: remove it                                                                             
  |                                                                                                                    
  = note: `-W unused-extern-crates` implied by `-W rust-2018-idioms`                                                   
                                                                                                                       
warning: unused extern crate                                                                                           
  --> components/profile/lib.rs:10:1                                                                                   
   |                                                                                                                   
10 | extern crate ipc_channel;                                                                                         
   | ^^^^^^^^^^^^^^^^^^^^^^^^^ help: remove it                                                                         
                                                                                                                       
warning: unused extern crate                                                                                           
  --> components/profile/lib.rs:14:1                                                                                   
   |                                                                                                                   
13 | / #[cfg(not(target_os = "windows"))]                                                                              
14 | | extern crate libc;                                                                                              
   | | ^^^^^^^^^^^^^^^^^-                                                                                              
   | |__________________|                                                                                              
   |                    help: remove it                                                                                
                                                                                                                       
warning: unused extern crate                                                                                           
  --> components/profile/lib.rs:20:1                                                                                   
   |                                                                                                                   
19 | / #[cfg(target_os = "linux")]                                                                                     
20 | | extern crate regex;                                                                                             
   | | ^^^^^^^^^^^^^^^^^^-                                                                                             
   | |___________________|                                                                                             
   |                     help: remove it                                                                               
                                                                                                                       
warning: unused extern crate                                                                                           
  --> components/profile/lib.rs:23:1                                                                                   
   |                                                                                                                   
23 | extern crate serde_json;                                                                                          
   | ^^^^^^^^^^^^^^^^^^^^^^^^ help: remove it                                                                          
                                                                                                                       
warning: unused extern crate                                                                                           
  --> components/profile/lib.rs:24:1                                                                                   
   |                                                                                                                   
24 | extern crate servo_config;                                                                                        
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^ help: remove it                                                                        
                                                                                                                       
warning: `extern crate` is not idiomatic in the new edition                                                            
  --> components/profile/lib.rs:27:1                                                                                   
   |                                                                                                                   
27 | extern crate time as std_time;                                                                                    
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: convert it to a `use`                                                        
                                                                                                                       
warning: unused extern crate                                                                                           
  --> components/profile/lib.rs:28:1                                                                                   
   |                                                                                                                   
28 | extern crate tokio;                                                                                               
   | ^^^^^^^^^^^^^^^^^^^ help: remove it                                                                               
                                                                                                                       
warning: unused extern crate                                                                                           
 --> components/profile/lib.rs:9:1                                                                                     
  |                                                                                                                    
9 | extern crate influent;                                                                                             
  | ^^^^^^^^^^^^^^^^^^^^^^ help: remove it                                                                             
  |                                                                                                                    
  = note: `-W unused-extern-crates` implied by `-W rust-2018-idioms`                                                   
                                                                                                                       
warning: unused extern crate                                                                                           
  --> components/profile/lib.rs:10:1                                                                                   
   |                                                                                                                   
10 | extern crate ipc_channel;                                                                                         
   | ^^^^^^^^^^^^^^^^^^^^^^^^^ help: remove it                                                                         
                                                                                                                       
warning: unused extern crate                                                                                           
  --> components/profile/lib.rs:14:1                                                                                   
   |                                                                                                                   
13 | / #[cfg(not(target_os = "windows"))]                                                                              
14 | | extern crate libc;                                                                                              
   | | ^^^^^^^^^^^^^^^^^-                                                                                              
   | |__________________|                                                                                              
   |                    help: remove it                                                                                
                                                                                                                       
warning: unused extern crate                                                                                           
  --> components/profile/lib.rs:20:1                                                                                   
   |                                                                                                                   
19 | / #[cfg(target_os = "linux")]                                                                                     
20 | | extern crate regex;                                                                                             
   | | ^^^^^^^^^^^^^^^^^^-                                                                                             
   | |___________________|                                                                                             
   |                     help: remove it                                                                               
                                                                                                                       
warning: unused extern crate                                                                                           
  --> components/profile/lib.rs:23:1                                                                                   
   |                                                                                                                   
23 | extern crate serde_json;                                                                                          
   | ^^^^^^^^^^^^^^^^^^^^^^^^ help: remove it                                                                          
                                                                                                                       
warning: unused extern crate                                                                                           
  --> components/profile/lib.rs:24:1                                                                                   
   |                                                                                                                   
24 | extern crate servo_config;                                                                                        
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^ help: remove it                                                                        
                                                                                                                       
warning: `extern crate` is not idiomatic in the new edition                                                            
  --> components/profile/lib.rs:27:1                                                                                   
   |                                                                                                                   
27 | extern crate time as std_time;                                                                                    
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: convert it to a `use`                                                        
                                                                                                                       
warning: unused extern crate                                                                                           
  --> components/profile/lib.rs:28:1                                                                                   
   |                                                                                                                   
28 | extern crate tokio;                                                                                               
   | ^^^^^^^^^^^^^^^^^^^ help: remove it                                                                               
                                                                                                                       
    Finished dev [unoptimized + debuginfo] target(s) in 1.62s                                                          

[ehuss]

A smaller reproduction, try cargo +nightly fix --edition-idioms with:
Cargo.toml:

[package]
name = "foo"
version = "0.1.0"
edition = "2018"

[dependencies]
time = "0.1"

src/lib.rs:

extern crate time as std_time;
pub mod time {
    pub fn f() {
        println!("{:?}", crate::std_time::now());
    }
}

It replaces extern crate with use time as std_time; which runs afoul of the uniform_paths future-proofing error. I would guess this code needs to know if it should use the :: prefix.

[SimonSapin]

Thanks for reducing this @ehuss! This is a good hint to work around this bug. After some manual fixes I’ve managed to make cargo fix --edition-idioms apply fixes in several more crates. However components/canvas_traits is another case of this “failed to automatically apply fixes” error message even though it does not use extern crate … as …;

[alexcrichton]

Yes thanks @ehuss! I've moved this over to rust-lang/rust#55759 with the reproduction, and let's track it there as it's a rustc issue.

@SimonSapin do you have logs from the other failure? FWIW these sorts of bugs nowadays are typically one fix that fails to get applied, and it's a bit of a whack-a-mole game to figure out which one!

[ehuss]

Here's a repro for the second one.

macro_rules! foo {
    ($name:ident) => {
        pub struct $name;
        impl ::std::fmt::Debug for $name {
            fn fmt(&self, _fmt: &mut ::std::fmt::Formatter) -> Result<(), ::std::fmt::Error> {
                Ok(())
            }
        }
    }
}

foo!{One}
foo!{Two}

Fixing it attempts to add <'_> to the Formatter once for each use, ending up with Formatter<'_><'_>.

[alexcrichton]

Perfect! I've opened that as rust-lang/rust#55768. I'm gonna close this for now but if more come up we can open more issues and/or coordinate!