ACP: [perf] `proc-macro` `Ident` should have method `as_str`

Proposal

Problem statement

Motivating examples or use cases

According to https://doc.rust-lang.org/proc_macro/struct.Ident.html

There are

• pub fn new(string: &str, span: Span) -> Ident

• ident.to_string()

Should provide below for performance

• ident.as_str()

Very common actual usage

ident_string = ident.to_string()

match ident_string.as_str() { ... }

Solution sketch

Expect usage

match ident.as_str() { ... }

Alternatives

Links and related work

https://github.com/rust-lang/rust/issues/139953

What happens now?

This issue contains an API change proposal (or ACP) and is part of the libs-api team feature lifecycle. Once this issue is filed, the libs-api team will review open proposals as capability becomes available. Current response times do not have a clear estimate, but may be up to several months.

Possible responses

The libs team may respond in various different ways. First, the team will consider the problem (this doesn't require any concrete solution or alternatives to have been proposed):

• We think this problem seems worth solving, and the standard library might be the right place to solve it.
• We think that this probably doesn't belong in the standard library.

Second, if there's a concrete solution:

• We think this specific solution looks roughly right, approved, you or someone else should implement this. (Further review will still happen on the subsequent implementation PR.)
• We're not sure this is the right solution, and the alternatives or other materials don't give us enough information to be sure about that. Here are some questions we have that aren't answered, or rough ideas about alternatives we'd want to see discussed.

Start by reading the proposal and the linked Rust issue #139953, then review the libs-api feature lifecycle linked in the issue. No implementation file or test is named; the work is done when the libs-api team reaches a decision on the proposed Ident::as_str API and its implementation scope.