Replace gumdrop with clap v3?

[tony-iqlusion]

There were two primary reasons why Abscissa used gumdrop over clap v2 originally:

• Previously clap had an excessively large number of dependencies, whereas gumdrop had no dependencies other than proc-macro2, quote, and syn for its proc macro. It seems clap-v3 has done a good job of addressing this (see below).
• Custom derive support: clap's previous custom derive crate structopt was added as something of an afterthought, had a clunky attribute syntax, and generally felt pretty low quality, whereas gumdrop was effectively a "custom derive first" crate and in that regard felt much more cohesive. That said, clap-v3 now features clap_derive which largely addresses these concerns.

We're now at a crossroads where we can either upgrade to gumdrop v0.8 or consider migrating to clap-v3. Either approach seems a bit difficult as gumdrop v0.8 contains a number of API changes.

The current beta release is clap-v3 3.0.0-beta.2. They warn against depending on the API until it's stable, however.

Tracking issue for clap v3 is here: clap-rs/clap#1037

Dependencies

Here are the transitive dependencies of clap-v3 3.0.0-beta.1 (I haven't fully cross-referenced these with our current ones yet, but I see a lot of commonality):

• ansi_term 0.12.1
• atty 0.2.14
• autocfg 1.0.0
• bitflags 1.2.1
• clap-v3 3.0.0-beta.1
• clap_derive-v3 3.0.0-beta.1
• heck 0.3.1
• hermit-abi 0.1.13
• indexmap 1.4.0
• lazy_static 1.4.0
• libc 0.2.71
• proc-macro-error 0.4.12
• proc-macro-error-attr 0.4.12
• proc-macro2 1.0.18
• quote 1.0.7
• strsim 0.9.3
• syn 1.0.31
• syn-mid 0.5.0
• textwrap 0.11.0
• unicode-segmentation 1.6.0
• unicode-width 0.1.7
• unicode-xid 0.2.0
• vec_map 0.8.2
• version_check 0.9.2
• winapi 0.3.8
• winapi-i686-pc-windows-gnu 0.4.0
• winapi-x86_64-pc-windows-gnu 0.4.0

[leotaku]

Here are some advantages I personally think a switch to clap would bring:

• Clap automatically handles things like version and help subcommands and flags
  • Gumdrop struggles with this and requires additional boilerplate from abscissa (e.g. Help)
• Clap better conforms to the expected behavior for command line applications
• Clap is much more widely used by the Rust community and thus more likely to be maintained for a long time

[tony-iqlusion]

gumdrop was replaced with clapv3 in #562.