Function cargo_update::ops::update_index

pub fn update_index<W: Write, A: AsRef<str>, I: Iterator<Item = A>>(
    index_repo: &mut Registry,
    repo_url: &str,
    packages: I,
    http_proxy: Option<&str>,
    fork_git: bool,
    out: &mut W
) -> Result<(), String>

Update the specified index repository from the specified URL.

Historically, cargo search was used, first of an empty string, then a ZWNJ (why?).

The need for this in-house has first emerged with #93: since cargo v1.29.0-nightly, the registry was no longer updated. So a two-year-old cargo issue was dug up, asking for a cargo update-registry command, followed by a PR implementing this. Up to this point, there was no good substitute: cargo install lazy_static, the poster-child of replacements errored out and left garbage in the console, making it unsuitable.

But then, a man of steel eyes and hawk will has emerged, seemingly from nowhere, remarking:

[21:09] Eh2406: https://github.com/rust-lang/cargo/blob/1ee1ef0ea7ab47d657ca675e3b1bd2fcd68b5aab/src/cargo/sources/registry/remote. rs#L204
[21:10] Eh2406: looks like it is a git fetch of “refs/heads/master:refs/remotes/origin/master”
[21:11] Eh2406: You are already poking about in cargos internal representation of the index, is this so much more?

It, well, isn’t. And with some cargo maintainers being firmly against blind-merging that cargo update-registry PR, here I go recycling the same old song that implementation (but simpler, and badlier).

Honourable mentions:

• @joshtriplett, for being a bastion for the people and standing with me in advocacy for cargo update-registry (NB: it was his issue from 2016 requesting it, funny how things turn around)
• @alexcrichton, for not getting overly too fed up with me while managing that PR and producing a brilliant argument list for doing it in-house (as well as suggesting I write another crate for this)
• And lastly, because mostly, @Eh2406, for swooping in and saving me in my hour of need not having a good replacement.

Most of this would have been impossible, of course, without the rust-lang Discord server, so shoutout to whoever convinced people that Discord is actually good.

Sometimes, however, even this isn’t enough (see https://github.com/nabijaczleweli/cargo-update/issues/163), hence fork_git, which actually runs $GIT (default: git).

Sparse indices

Have a .cache under the obvious path, then the usual ca/rg/cargo-update, but the file is different than the standard format: it starts with a ^A or ^C (I’m assuming these are versions, and if I looked at more files I would also’ve seen ^C), then Some Binary Data, then the ETag(?), then {NUL, version, NUL, usual JSON blob line} repeats.

I do not wanna be touching that shit. Just suck off all the files.
Shoulda stored the blobs verbatim and used If-Modified-Since. Too me.

Only in this mode is the package list used.