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Moving macro metavar expressions forward #4

Open tgross35 opened 7 months ago

tgross35 commented 7 months ago

The feature macro_metavar_expr has been around since 2021 without any significant progress https://github.com/rust-lang/rust/issues/83527. There is one unresolved question listed about hygiene, but this may have since been resolved (unclear).

It would be nice to get parts of this on the path to stabilization, even if all parts of the RFC are not yet ready. Stabilizing only ${ignore(ident)} could make sense as a first step since it is is useful, has a well-defined purpose, and shouldn't suffer from the possible hygiene problem.

This is also relevant because there are other metavar expressions that we would like to eventually move forward, such as concat in https://github.com/rust-lang/rust/pull/118958#issuecomment-1988267818.

Discussion thread: https://rust-lang.zulipchat.com/#narrow/stream/404510-wg-macros/topic/Metavar.20expressions

tgross35 commented 7 months ago

@c410-f3r actually recently suggested merging all of the feature at https://github.com/rust-lang/rust/issues/83527#issuecomment-1935848469, so this is on the table too.