rust-src component is incomplete in recent nightlies

[japaric]

The component is missing compiler-rt, jemalloc and other git submodules required to compile the std crate. This broke Xargo's use case of cross compiling the std crate.

Affected version: nightly-2017-05-04 and newer

Workaround

Switch to an older nightly version:

Known good version: nightly-2017-04-27 (still bisecting)

cc @brson @alexcrichton Do you know of any changes that may have caused this? It seems that the rust-src component has been trimmed to not include rustc source?

[alexcrichton]

cc @cuviper, maybe related to #41546?

[cuviper]

Yeah, it's surely related. If we want this to work, we'll have to augment std_src_dirs with more paths, and maybe do a full compilation in the distcheck.

At first glance, we'll need at least compiler-rt, jemalloc, and libbacktrace. I'm a little sad to add compiler-rt as that's 35M added to the current 8.4M. But 28M of that is compiler-rt/test, so maybe it can be pruned. There's only 1.5M in compiler-rt/lib/builtins.

[RalfJung]

So, say I wanted to try and fix this -- how would I go about testing the fix? Is there a way to (a) create that rust-src package locally (./x.py dist src or ./x.py dist, I guess), and (b) tell rustup to install this package such that one could actually see whether xargo works now?

[ids1024]

(b) tell rustup to install this package such that one could actually see whether xargo works now?

You can set $XARGO_RUST_SRC to tell xargo where to find the source for Rust, instead of messing with rustup.

[cuviper]

Yes, ./x.py dist src will suffice. I don't know how to get rustup to install it, but you can manually extract it and run ./install.sh --prefix ~/.rustup/toolchains/nightly-$TARGET.

[RalfJung]

Thanks, sounds like I have two options to play with then :)
I'm still fighting other issues though; right now, a working xargo wouldn't even help. If I manage to solve them, I will come back to this one, but please don't hold your breath.

[RalfJung]

All right, I got things to work with xargo on old Rust nightlies, so I submitted #42214 to fix this bug.