Replace proc-macro-error with proc-macro2-diagnostics

[tamird]

See individual commits.

I realize this crate is deprecated in favor of clap, but it still seems to enjoy some 10,000-40,000 downloads per day over the past three months. Updating to syn@2 is likely to have positive effect on compilation time for dependents.

See https://crates.io/crates/structopt-derive for download graphs.

[tamird]

@TeXitoi could you have a look please?

[TeXitoi]

That’s a big change for a frozen crate. I’ll try to have a look, but no promise.

[epage]

I realize this crate is deprecated in favor of clap, but it still seems to enjoy some 10,000-40,000 downloads per day over the past three months. Updating to syn@2 is likely to have positive effect on compilation time for dependents.

imo that effort would be better spent migrating some of the more popular users.

[tamird]

You mean like this? https://github.com/rust-lang/git2-rs/pull/1007 https://github.com/brendanzab/codespan/pull/357 https://github.com/marshallpierce/rust-base64/pull/262

[TeXitoi]

I close this MR as there is no activity.

[tamird]

If you can close it, maybe you can also review and accept it?

[TeXitoi]

Sorry. I don't want a regression, and there is one.

Also, I'm quite anxious at this PR as this is a big library change, and it might cause a behavior change.

I know that you worked in this and that closing this deny your work, but it adds more risk than advantages for my point of view.

[tamird]

Ack. Salvaged some useful stuff into #542 + added GitHub CI.