This has been implemented for 3 years without much traction for
finishing it up.
The subcommand use case can be worked around by creating `Command`s that
just include the relevant logic, very similar to the default subcommand
examples in `git` / `git-derive`.
Using this for flags is covered by #4793.
Without `unstable-replace` being enabled, this still cut 5 KiB from
`cargo bloat --release --example git`.
Closes#2836Closes#2011
For now, we are still treating `clap` as the user facing API for both
builder and derive, making this an internal change as we don't expect
this to negatively impact builder build times all that much. We can
re-evaluate at a later time and consider having distinct top-level
crates for builder and derive.
Looking at `--timings` on my machine
- `clap` only took 0.04s to build and it happened in
parallel to `clap_builder` codegen
- this saved 1.7s for derive build times, with `clap_builder` building
in parallel to `syn` and `clap_builder` and `clap_derive` finishing
around the same time.
This was discussed some at https://rust-lang.zulipchat.com/#narrow/stream/220302-wg-cli/topic/clap.20build.20times.20and.20.60clap_derive.60.3A.20a.20crazy.20idea
