On 22 March 2017 at 11:49, Peter Dimov via Boost
Well currently, "b2 doc" would fail for everyone using Visual Studio 2013/2015/2017 or g++ 6. It would have failed for me had I not been using the ancient 8.0 as a default.
Then they file a bug report, and I fix it at a leisurely pace, suggesting they use a binary from the last release that worked. It's not ideal, but that's life for you.
In general, and this is not directed at you personally, the point of testing develop against boostorg:develop is to catch such breaking changes as the current string_ref one early, before they reach the release. Downstream dependencies effectively serve as an integration test for lower-level libraries.
Travis is an awful mechanism for doing that as it only runs when there's a commit to the submodule being tested, which might not be regular. As it happens, the change to string_ref that caused this issue was on the 13th of February, the last commit to quickbook before you reported this was on the 12th of February.