Spurious dead_code warning

[tomdale]

Rust is telling us that a method is not being called, but we're pretty sure that it is. There is no warning any other methods that call into it, and we believe the program would not work if this method was indeed not being called. :P

To reproduce, check out our protobuf library at the specific SHA here: https://github.com/tildeio/buffoon/tree/a6793623c496e83d578866e7f7ea34ae22370f96

Then compile the protobuf library by running:

cd src
rustc --rlib buffoon/lib.rs

(You can also just type rake from the top-level directory if you have Ruby installed.)

This is the error message we're getting:

buffoon/wire_type.rs:10:0: 19:1 warning: code is never used: `wire_type_bits`, #[warn(dead_code)] on by default
buffoon/wire_type.rs:10 pub fn wire_type_bits(wire_type: WireType) -> u64 {
buffoon/wire_type.rs:11   match wire_type {
buffoon/wire_type.rs:12     Varint => 0,
buffoon/wire_type.rs:13     SixtyFourBit => 1,
buffoon/wire_type.rs:14     LengthDelimited => 2,
buffoon/wire_type.rs:15     StartGroup => 3,

This function gets called from src/buffoon/output_stream.rs:66, which, as you can see, does not get a dead code warning.

[emberian]

cc @ktt3ja

[alexcrichton]

Minimized test case:

#[crate_type = "lib"];

mod inner {                      
    pub trait Trait {            
        fn f(&self) { f(); }     
    }                            

    impl Trait for int {}        

    fn f() {}                    
}                                

pub fn foo() {                   
    let a = &1 as &inner::Trait; 
    a.f();                       
}                                

[ktt3ja]

Thanks for the test case. I'll work on it tomorrow.

[alexcrichton]

I have a fix for this which also fixes on program in #11225, still working on the second program.

[ktt3ja]

I fixed this by checking the method source when a provided method is used. Since you have already fixed it, I'll leave it to you to decide whether it should be included.