Remove --crate-type=metadata deprecation warning

[citizen428]

Fixes #38640

[rust-highfive]

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[Mark-Simulacrum]

Looks like there's a warning you'll need to fix:

[00:06:12] error: variable does not need to be mutable
[00:06:12]     --> /checkout/src/librustc/session/config.rs:1634:9
[00:06:12]      |
[00:06:12] 1634 |     let mut emit_metadata = false;
[00:06:12]      |         ^^^^^^^^^^^^^^^^^
[00:06:12]      |
[00:06:12]      = note: #[deny(unused_mut)] implied by #[deny(warnings)]
[00:06:12] note: lint level defined here
[00:06:12]     --> /checkout/src/librustc/lib.rs:23:9
[00:06:12]      |
[00:06:12] 23   | #![deny(warnings)]
[00:06:12]      |         ^^^^^^^^
[00:06:12] 
[00:06:12] error: aborting due to previous error

[citizen428]

@Mark-Simulacrum I know, thanks. Basically just did that in a rush earlier and pushed it up, figured I'll look at the Travis output later. I can't seem to manage labels, can you change it to S-waiting-on-author please?

[citizen428]

@Mark-Simulacrum I removed the mut which should fix the warning. I'm just wondering if that variable can be removed completely?

let emit_metadata = false;
...
return Ok((crate_types, emit_metadata));

It's only called in one location in the same file (line 1357) and I think it might be better to completely remove it.

cc @nikomatsakis

[Mark-Simulacrum]

Yeah, remove emit_metadata here, and if you follow that change through (change the return type of parse_crate_types_from_list and go from there, you'll find that OutputType::Metadata can probably be removed as well (removing a bunch of cruft from the compiler that's no longer needed since this is always false).

[citizen428]

Just FYI, I'm working my way through this. Properly removing the flag instead of having it permanently set to false is somewhat more effort than originally outlined in the mentoring description, but seems to be worth it.

[Mark-Simulacrum]

src/test/run-pass/auxiliary/rmeta_rmeta.rs and src/test/run-pass/rmeta.rs need to be deleted since they are testing --emit=metadata.

[citizen428]

@Mark-Simulacrum src/test/run-pass/auxiliary/rmeta_rmeta.rs is already removed as you can see in the file list. But thanks for confirming that they can indeed be remove. There are still a few leftovers like meta_stats etc. that I'm a bit unsure about. If we do this, we might as well rip out everything that's not necessary anymore.

[Mark-Simulacrum]

Actually, I think I lied; we do want to keep --emit=metadata, it's the crate type that is gone. I think rmeta_meta should've been kept actually, as should at least most of the other tests. Sorry about the run-around. This may mean that some of the code that you've removed needs to be re-added..

[citizen428]

@Mark-Simulacrum I went back to a very early version of this PR, basically just removing the code snippet that had the deprecation warning, the related emit_metadata variable and its use at the callsite.

[citizen428]

@Mark-Simulacrum This PR is S-waiting-on-review again.

[nikomatsakis]

@bors r+ -- thanks @citizen428 !

[bors]

📌 Commit 9873acc has been approved by nikomatsakis

[Mark-Simulacrum]

@bors rollup