On Tue, Jun 16, 2015 at 9:41 AM, Vladimir Prus <vladimir.prus@gmail.com> wrote:
On 6/11/2015 5:13 PM, Rene Rivera wrote:
The use case is one that I've run into since the git transition and doing Predef development. And recently I
also see it in the BPL development. For Predef my normal way to work on it is to clone *only* the Predef repo as
it's an entirely standalone library (doesn't depend on anything). Then I have a jamroot file above the cloned
Predef, as it's required to build anything with BBv2. It's easy enough for me to do this of course. But I would
like to make it easier for *users* to just get the Predef library and say, run tests and build without special
instructions or having the whole of the Boost super project. But at the same time I can't just include a jamroot
in the Predef project because it would break (in silent and strange ways) when it's part of the Boost super project.


could you describe in more detail how you envision this feature to be used? While predef is entirely standalone,
that does not appear to be a typical case, so I think we need to decide how a typical case should work, and
optimize for that case.

True, it's not typical at the moment..  But it's becoming more prevalent (slowly).

Say, a Boost library can be built either inside the tree, or outside the tree. In the former cases, it automatically gets access to:

- Requirements from Boost's Jamroot
- constants
- helper functions

In the standalone case, how would a library access all that?

Generally a non-standalone outside-the-tree library build (or test) would get that information from the "system" and/or from BB. Part of the information would come from the boost.jam module <https://github.com/boostorg/build/blob/develop/src/contrib/boost.jam>. Which might need to be extended to support more of the Boost helper functions. The goal would be to accommodate two cases: the standalone build as BPL wants (i.e. build against a system available Boost), and the testing build where we obtain the dependencies and perhaps use modular.jam to synthesize the dependencies <https://github.com/boostorg/build/blob/develop/src/contrib/modular.jam>.

In other words the information would be either in the an available Boost or already in BB (boost.jam).

Sorry I don't have any more detail than that. But I'm addressing issues as I try to get to the goal (i.e. the two use cases above).

-- Rene Rivera
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