E0593 regression when mismatched argument count leads to other errors in Beta/Nightly

[Rantanen]

Playground

use std::collections::HashMap;
fn main() {
    
    let m = HashMap::new();
    m.insert( "foo", "bar" );
    
    m.iter().map( |_, b| { // Stable ONLY:
                           // > [E0593]: closure is expected to take a single tuple as argument

        b.to_string()      // Stable + Beta + Nightly:
                           // > [E0619]: the type of this value must be known in this context
    });
}

Commenting out the b.to_string() will yield the [E0593] error in all toolchains.

The [E0619] alone makes for a very confusing error message, as the user's assumption is that the type of b is correct.

[nikomatsakis]

cc @estebank -- was this fixed by #47747 ? Any idea what the problem is here?

[nikomatsakis]

triage: P-high

[estebank]

I don't think the presentation changes that that PR (and the one it's supplementing) introduced. It looks to me that it doesn't actually get to check E0593. I'll dig deeper.

[nikomatsakis]

@estebank great, if you don't have time, lemme know

[estebank]

@nikomatsakis I didn't have time to look into this and will unlikely have time to perform a bisect during the week. I can confirm that this was introduced earlier than #47747.

[nikomatsakis]

cc @rust-lang/compiler -- can somebody pick this up to try and get to the bottom of it?

[kennytm]

Bisection result is #45879.

Details

Test script:

#!/bin/sh
$RUSTC_RELATIVE -V
! ( $RUSTC_RELATIVE 1.rs 2>&1 | grep E0593 )

1.rs is the source in the bug report.

Output:

$ RUST_LOG=rust_sysroot=info target/release/bisect --preserve --test test.sh --start 33374fa9d09e2a790979b31e61100dfed4b44139 --end b65f0bedd2f22d9661ecb7092f07746dc2ccfb0d
INFO:rust_sysroot: Getting commits from the git checkout in 33374fa9d09e2a790979b31e61100dfed4b44139...b65f0bedd2f22d9661ecb7092f07746dc2ccfb0d
INFO:rust_sysroot: Received 272 commits
Searching in 272 commits; about 9 steps
rustc 1.24.0-nightly (830599b19 2017-12-11)
rustc 1.24.0-nightly (315fbf751 2017-12-01)
rustc 1.23.0-nightly (2f84fb5cc 2017-11-26)
rustc 1.23.0-nightly (0916bbc00 2017-11-23)
rustc 1.23.0-nightly (96e9cee77 2017-11-22)
rustc 1.23.0-nightly (ebda7662d 2017-11-21)
error[E0593]: closure is expected to take a single tuple as argument, but it takes 2 distinct arguments
rustc 1.23.0-nightly (63739ab7b 2017-11-21)
error[E0593]: closure is expected to take a single tuple as argument, but it takes 2 distinct arguments
rustc 1.23.0-nightly (d6d09e0b4 2017-11-21)
searched commits 33374fa9d09e2a790979b31e61100dfed4b44139 through b65f0bedd2f22d9661ecb7092f07746dc2ccfb0d
regression in 7; Some(Commit { sha: "d6d09e0b4dac93ae07dae6206bf95e7cea0124a2", date: 2017-11-21T22:52:19Z, summary: "Auto merge of #45879 - nikomatsakis:nll-kill-cyclic-closures, r=arielb1" })

[nikomatsakis]

D'oh, that's my pr :)