Port #[used] to new attribute parsing infrastructure

[JonathanBrouwer]

Ports used to the new attribute parsing infrastructure for #131229 (comment)

r? @jdonszelmann

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[rustbot]

Some changes occurred in compiler/rustc_attr_parsing

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Some changes occurred in compiler/rustc_codegen_ssa

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Some changes occurred in compiler/rustc_codegen_ssa/src/codegen_attrs.rs

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Some changes occurred in compiler/rustc_attr_data_structures

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Some changes occurred in compiler/rustc_passes/src/check_attr.rs

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[JonathanBrouwer]

@rustbot author

[rustbot]

Reminder, once the PR becomes ready for a review, use @rustbot ready.

[bors]

☔ The latest upstream changes (presumably #142826) made this pull request unmergeable. Please resolve the merge conflicts.

[JonathanBrouwer]

@rustbot ready
Implemented ratcheting behaviour & reverted change to the warning

[JonathanBrouwer]

Rebased to solve merge conflicts

[bors]

☔ The latest upstream changes (presumably #142878) made this pull request unmergeable. Please resolve the merge conflicts.

[jdonszelmann]

just to be clear @JonathanBrouwer, is the behavior right now exactly the same as before with regards to errors and which attribute applies in case of duplicates or not?

[JonathanBrouwer]

@jdonszelmann
The behaviour regarding errors and duplicates is exactly the same when multiple identical attributes are specified. This provides a warning "unused attribute" without stating it will be removed.

When multiple different attributes are applied the behaviour has changed. This is fine because [used(arg)] with an argument is unstable.

What has changed:

#[used]
#[used(linker)]

Before: Error, "compiler and linker can't be used together". This is a wrong error since #[used] should be equivalent to #[used(linker)]
After: Changed: now a warning, unused attribute

#[used]
#[used(compiler)]

Before: No error, ratcheting behaviour so "linker " is used
After: unchanged

#[used(linker)]
#[used(compiler)]

Before: Error
After: Changed: Now also does ratcheting to linker.