Rename rustc_unicode to std_unicode

[brson]

All other cases of the rustc "namespace" identify crates that are part
of the compiler, whereas this one is part of the standard library. By
changing the name of this crate one can count on all "librustc"
directories being part of the compiler.

This has long bugged me.

r? @alexcrichton cc @rust-lang/libs

[brson]

cc @SimonSapin

[alexcrichton]

So long as it's always super private with tons of red tape saying "please don't use this" I'm pretty much fine with w/e name. I think rustc_unicode had the connotation of "private" due to the rustc namespace, but agreed that it's not appropriate for this lib itself.

I'll give it a bit though to see if anyone objects.

[japaric]

This is going to annoying to deal with in Xargo. It currently builds the sysroot by creating an empty sysroot crate that depends on all the C-free crates and rustc_unicode is one of those dependencies. I'd have to add some logic (probably date based) to build std_unicode instead of rustc_unicode or simply stop building the unicode crate; I have no idea if anyone actually uses it.

If not a priority, I'd prefer if this rename landed after std-aware Cargo becomes a thing and Xargo is no longer necessary but perhaps that would be too late? I don't what's the stability policy around the standard crates Cargo could access to. As in: are renames possible after std-aware Cargo comes into existence?

[FenrirWolf]

Uh-oh. I'm using rustc_unicode in ctru-rs because the Nintendo 3DS uses UTF-16 filepaths and encode_utf16() isn't available in collections::string::String (or maybe it was the lack of decode_utf16() on core::char, I forget which). So if you can keep it working in Xargo, I'd love that <3

[japaric]

@FenrirWolf Noted! Since there's at least one user, Xargo will continue to supported the unicode crate.

[alexcrichton]

I think we're fine wrt renaming crates like this. We obviously can't rename a stable crate, but unstable crates can't be stably depended on anyway so I'd be fine considering this "acceptable breakage" under that banner.

[SimonSapin]

Renaming sounds fine to me, modulo xargo concerns.

@FenrirWolf can you confirm what API is missing? Sounds like we should add something to libcore or libstd.

[FenrirWolf]

Looks like it's char::decode_utf16() that I'm using from rustc_unicode. It's available in the standard library, but I'm limited to freestanding crates for this project.

Either way, will renaming the unicode crate really keep Xargo from building it? looks like it's still freestanding even with these changes.

[aturon]

I'm also fine with renaming.

[SimonSapin]

As far as I understand, the issue with xargo is to decide which sysroot crates to build. But I suppose it could check whether a std_unicode directory exists?

---

Taking another look at the naming convention: if we’re going with a std_ prefix, shouldn’t all in-tree recursive dependencies of std have it?

[japaric]

But I suppose it could check whether a std_unicode directory exists?

Sure, it can be done. It's just annoying to keep adding ad hoc logic to Xargo.

[bors]

☔ The latest upstream changes (presumably #36377) made this pull request unmergeable. Please resolve the merge conflicts.

[brson]

Since there's no pressing need to do this, I'm going to close, but we are going to rename this crate someday. Unstable things are unstable for a reason.