Converting integers to pointers using "as _" works, but produces error messages if a different error occurs

[jmegaffin]

This code is fine.

fn main() {
    let x: *const () = 0 as _;
}

But when the following code fails to compile because of the unresolved foo, an additional error message is generated for the integer-pointer conversion.

fn main() {
    foo();
    let x: *const () = 0 as _;
}

rustc 1.14.0 (e8a012324 2016-12-16)
error[E0425]: unresolved name `foo`
 --> <anon>:2:5
  |
2 |     foo();
  |     ^^^ unresolved name

error: non-scalar cast: `{integer}` as `*const ()`
 --> <anon>:3:24
  |
3 |     let x: *const () = 0 as _;
  |                        ^^^^^^

error: aborting due to previous error

This makes it very annoying to debug a large program with lots of this kind of integer-pointer conversion that fails for some other reason, as an extra message is generated for every conversion.

[nagisa]

This code is fine.

No it is not. usize does not implicitly convert to a pointer, raw or not.

[jmegaffin]

It compiles. If it shouldn't, well, it shouldn't.

[hanna-kruppe]

What's your Rust version? The program does not compile on current stable, beta, or nightly playground.

[petrochenkov]

http://rust.godbolt.org has quick access to all versions since 1.0 and this code fails to compile on all of them.

[jmegaffin]

Sorry, I misrepresented the issue here. It's really got to do with conversion using as _. I've updated the original post to reflect this.

[codyps]

Here's the example code fixed up. Uncomment foo() to see the failure that emits 1 expected error and a second that dislikes the cast.

https://is.gd/goAcm7

fn main() {
    //foo();
    let _x: *const () = 0 as _;
}

[Mark-Simulacrum]

Closing in favor of #35772.