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Subject: Re: [Boost-build] allowing targets to fail
From: Stefan Seefeld (stefan_at_[hidden])
Date: 2017-04-08 22:22:32

On 08.04.2017 13:31, Steven Watanabe via Boost-build wrote:
> On 04/08/2017 11:00 AM, Stefan Seefeld via Boost-build wrote:
>> Can you qualify "immediately" and "later" a little more ?
> Immediately means that we call UPDATE_NOW
> directly.

Directly where, in what phase of the workflow ? This may seem pedantic,
but I think it's important to spell out in full detail so users of those
features understand the implications.

> Later means that we add the target
> to dependency graph and assume that someone
> else will call UPDATE_NOW.

To rephrase my question above: I understand the there is a top-level
call to UPDATE_NOW, where the arguments are the targets explicitly
requested from command-line options (and associated properties). So all
those other calls to UPDATE_NOW must be triggered through some other
mechanism by which the (or another ?) dependency graph is evaluated,
eventually leading to those "immediate" targets.
In other words, it seems there are multiple ways in which the (or a)
dependency graph is traversed: the one used by the bjam engine itself
("phase 3" as per your description), and the others sometime earlier,
while that dependency graph is constructed ("phase 2" as per your

Am I capturing the situation correctly with that description ?

>> Normal targets
>> (those being built "later", that is) are only built if either explicitly
>> requested or needed by explicitly requested dependent targets.
>> But, for these "immediate" targets this doesn't seem to be possible, or
>> does it ?
> Boost.Build only generates the actual targets
> which are needed. check-target-builds will only
> be evaluated if we are building the target that
> uses it.

This is where I'm (slightly) confused: to me it doesn't look like any
real target "uses" the check-target-builds target. Rather, it's the
'main' *meta*-target that requires it in the target instantiation process.

Right ?


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