Testing libc++ ToT against Clang ToT

Note: I'm sending this to cfe-dev because I want to have more exposure than only libcxx-dev.


Two recent changes in Clang broke libc++ tests:

r343131: https://bugs.llvm.org/show_bug.cgi?id=39232
r342605: http://bugs.llvm.org/show_bug.cgi?id=39234

Those failures were apparently not caught by the builders because we don't seem to test libc++ ToT against Clang ToT (aka Stage 2 build). In the future, it would be great to catch those failures earlier and notify the commit authors instead of having to painstakingly bisect the errors after the fact.

I have the following questions:
1. Is there currently a build bot that tests libc++ ToT against Clang ToT?
2. If not, is it easy for someone to set one up?


I maintain most of the bots in question here.

I attempt to keep the Clang version under test as close to ToT as possible, but it’s still a manual process.

I don’t want to force most libc++ bots to build Clang before running the tests, as rebuilding Clang all the time will take a long time.
However, I’ll look into setting up a bot that does a full bootstrap which includes testing libc++.