Make deprecated_cfg_attr_crate_type_name a hard error

[est31]

Turns the forward compatibility lint added by #83744 into a hard error, so now, while the #![crate_name] and #![crate_type] attributes are still allowed in raw form, they are now forbidden to be nested inside a #![cfg_attr()] attribute.

The following will now be an error:

#![cfg_attr(foo, crate_name = "foobar")]
#![cfg_attr(foo, crate_type = "bin")]

This code will continue working and is not deprecated:

#![crate_name = "foobar"]
#![crate_type = "lib"]

The reasoning for this is explained in #83744: it allows us to not have to cfg-expand in order to determine the crate's type and name.

As of filing the PR, exactly two years have passed since #99784 has been merged, which has turned the lint's default warning level into an error, so there has been ample time to move off the now-forbidden syntax.

cc #91632 - tracking issue for the lint

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[bors]

☔ The latest upstream changes (presumably #129665) made this pull request unmergeable. Please resolve the merge conflicts.

[traviscross]

@rfcbot fcp merge

We discussed this is the meeting today and were feeling positively toward it.

[rfcbot]

Team member @traviscross has proposed to merge this. The next step is review by the rest of the tagged team members:

• @joshtriplett
• @nikomatsakis
• @pnkfelix
• @scottmcm
• @tmandry
• @traviscross

No concerns currently listed.

Once a majority of reviewers approve (and at most 2 approvals are outstanding), this will enter its final comment period. If you spot a major issue that hasn't been raised at any point in this process, please speak up!

cc @rust-lang/lang-advisors: FCP proposed for lang, please feel free to register concerns.
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[rfcbot]

🔔 This is now entering its final comment period, as per the review above. 🔔

[nikomatsakis]

@rfcbot reviewed

This seems like a good simplification, but we should notify crate authors that may be affected with at least a ping. I'd like to know if there is truly no way to support their use case.

[joshtriplett]

Documenting some supporting rationale:

1. We're assuming that --crate-type will be sufficient to migrate to.

2. We expect that if the warned-about (and later errored-about) thing being allowed was an issue for anyone, the affected crates would have raised this upstream.

[nikomatsakis]

Based on a google code search, I want to give a headsup to

• wasmerio/wasmer -- cc @syrusakbary and @Hywan (top two contributors) -- allows the lint here

[bjorn3]

The usage in wasmer seems to be entirely ineffective:

$ cargo +stable build --no-default-features --features "wasmer/js wasmer/std" -p wasmer --target wasm32-unknown-unknown
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.09s
$ ls target/wasm32-unknown-unknown/debug
build  deps  examples  incremental  libwasmer.d  libwasmer.rlib
$ ls target/wasm32-unknown-unknown/debug/deps | grep wasmer
libwasmer-aac61f984f72830e.rlib
libwasmer-aac61f984f72830e.rmeta
libwasmer_types-e9cfd7530a67cd97.rlib
libwasmer_types-e9cfd7530a67cd97.rmeta
wasmer-aac61f984f72830e.d
wasmer_types-e9cfd7530a67cd97.d

No .wasm file is produced that would be expected from a cdylib.

On the other hand even if I remove #![cfg_attr(feature = "js", crate_type = "cdylib")], cargo +stable rustc --no-default-features --features "wasmer/js wasmer/std" -p wasmer --target wasm32-unknown-unknown --crate-type cdylib produces a wasmer.wasm file. The usage of cargo rustc + --crate-type cdylib instead of cargo build is what causes the crate type to be changed to cdylib.

[RalfJung]

When a lint is removed, it must be added to the removed lint list. (This is explained at the top of this file.) That seems to be missing from this PR.

[RalfJung]

So this has not gone through a "report in deps" stage. Fine for me, but I just wanted to call it out for awareness.