Generate shell-completions and man pages in build.rs

[ducaale]

Although build.rs cannot import modules from xh, it is possible to use the include!() to paste the content of src/cli.rs into build.rs.

See https://kbknapp.dev/shell-completions/

[blyxxyz]

I considered doing it at build time, but I didn't like it.

build.rs generating files that are checked into source control is seemingly discouraged. cargo will refuse to upload if a build script changes the contents of src. You're supposed to put them in $OUT_DIR, which isn't ergonomic.

The man pages are generated with help2man, and I don't think we can expect everyone to have that installed.

OTOH ripgrep has build.rs generate completions and build a man page (with asciidoctor): https://github.com/BurntSushi/ripgrep/blob/3ca324fda75885bf3523762ed57811d80abb3b00/FAQ.md#does-ripgrep-have-a-man-page

It only generates the man page if it can find the tools. I didn't think of that.

But it has to do some work to find the files it generates: https://github.com/BurntSushi/ripgrep/blob/20534fad0404417487318dcc7d6fb5a91835a278/ci/cargo-out-dir

Not sure if this is a good idea, but it's worth another look.