Oh, running with --debug-loading reports suggests that we're loading Jamroot when this error happens.
Indeed, here's what Jamroot says:

5a86ed2c Jamroot    (Beman           2013-12-24 15:48:03 -0500 250) use-project /boost/tools/inspect : tools/inspect/build ;
51bc0b6a Jamroot    (Eric Niebler    2014-01-15 09:20:43 -0800 251) use-project /boost/libs/wave/tool : libs/wave/tool/build ;

So it seems like the current behaviour was around for a while. I've checked in the below to develop:

        https://github.com/boostorg/boost/commit/a7d89154ad4b9ab29a441d137d46c4e9b4933a91

Could you see whether it helped?


So, I tried applying those changes to my 1.57.0 version, along with the bcp develop, and got a new error:

error: Unable to find file or target named
error:     '/boost/system//boost_system'
error: referred to from project at
error:     'libs/chrono/build'
error: could not resolve project reference '/boost/system'

 Here is the output from debug-loading:

Initializing project 'test-config'
Assigned project target object(project-target)@62 to 'test-config'
Initializing project 'site-config'
Assigned project target object(project-target)@64 to 'site-config'
Initializing project 'user-config'
Assigned project target object(project-target)@66 to 'user-config'
Loading Jamfile at '.'
Initializing project 'Jamfile<E:\boost\myboost>'
Assigned project target object(project-target)@107 to 'Jamfile<E:\boost\myboost>'
Loading Jamfile at 'libs/atomic/build'
Initializing project 'Jamfile<E:\boost\myboost\libs\atomic\build>'
Assigned project target object(project-target)@169 to 'Jamfile<E:\boost\myboost\libs\atomic\build>'
Loading Jamfile at 'libs/chrono/build'
Initializing project 'Jamfile<E:\boost\myboost\libs\chrono\build>'
Assigned project target object(project-target)@207 to 'Jamfile<E:\boost\myboost\libs\chrono\build>'
Loading Jamfile at 'libs/container/build'
Initializing project 'Jamfile<E:\boost\myboost\libs\container\build>'
Assigned project target object(project-target)@216 to 'Jamfile<E:\boost\myboost\libs\container\build>'
Loading Jamfile at 'libs/date_time/build'
Initializing project 'Jamfile<E:\boost\myboost\libs\date_time\build>'
Assigned project target object(project-target)@245 to 'Jamfile<E:\boost\myboost\libs\date_time\build>'
Loading Jamfile at 'libs/exception/build'
Initializing project 'Jamfile<E:\boost\myboost\libs\exception\build>'
Assigned project target object(project-target)@276 to 'Jamfile<E:\boost\myboost\libs\exception\build>'
Loading Jamfile at 'libs/filesystem/build'
Initializing project 'Jamfile<E:\boost\myboost\libs\filesystem\build>'
Assigned project target object(project-target)@306 to 'Jamfile<E:\boost\myboost\libs\filesystem\build>'
Loading Jamfile at 'libs/random/build'
Initializing project 'Jamfile<E:\boost\myboost\libs\random\build>'
Assigned project target object(project-target)@342 to 'Jamfile<E:\boost\myboost\libs\random\build>'
Loading Jamfile at 'libs/regex/build'
Initializing project 'Jamfile<E:\boost\myboost\libs\regex\build>'
Assigned project target object(project-target)@373 to 'Jamfile<E:\boost\myboost\libs\regex\build>'
Loading Jamfile at 'libs/serialization/build'
Initializing project 'Jamfile<E:\boost\myboost\libs\serialization\build>'
Assigned project target object(project-target)@464 to 'Jamfile<E:\boost\myboost\libs\serialization\build>'
Loading Jamfile at 'libs/test/build'
Initializing project 'Jamfile<E:\boost\myboost\libs\test\build>'
Assigned project target object(project-target)@498 to 'Jamfile<E:\boost\myboost\libs\test\build>'
Loading Jamfile at 'libs/thread/build'
Initializing project 'Jamfile<E:\boost\myboost\libs\thread\build>'
Assigned project target object(project-target)@539 to 'Jamfile<E:\boost\myboost\libs\thread\build>'
Loading Jamfile at 'libs/timer/build'
Initializing project 'Jamfile<E:\boost\myboost\libs\timer\build>'
Assigned project target object(project-target)@562 to 'Jamfile<E:\boost\myboost\libs\timer\build>'

Building the Boost C++ Libraries.


error: Unable to find file or target named
error:     '/boost/system//boost_system'
error: referred to from project at
error:     'libs/chrono/build'
error: could not resolve project reference '/boost/system'

Am I heading down a rabbit hole?  I'm okay with moving to bcp-develop, but will that throw off the dependencies in the rest of my build's modules, if they are from 1.57?

Regards,
Kevin