[Development] Notes on "Qt Build Systems" @ QtCon 2016

Oswald Buddenhagen oswald.buddenhagen at qt.io
Thu Sep 15 08:57:14 CEST 2016

On Wed, Sep 14, 2016 at 12:05:15PM +0200, Stephen Kelly via Development wrote:
> I want to understand Qbs and what it can do with a dynamic build graph
> which CMake can't do.
there is no such thing, as after full expansion the graph has to be
static by definition (the output artifacts are expected to be
deterministic, after all). the difference is in when you determine the
final graph. as cmake is a meta build tool, it artificially creates two
phases. as it creates inputs for static build tools, it has to execute
all the dynamic parts itself, which makes the "preparation" phase
actually a partial "execution" phase, and thus slower than it is
supposed to be.

having said that, qbs also has a "meta" mode, to make ide project
generation possible. also, as shown in the bootstrapping discussion,
we'll probably need a simple makefile generator as well.

and as christian already pointed out, in qbs there is also the
fundamental split between preparation and execution phases, only that
they could be scheduled much better for individual artifacts (but as
also pointed out, this isn't taken advantage of yet).

so what it all comes down to is that qbs is, as in pretty much every
other regard, simply more elegant than cmake, not a magic solution for
problems yet to be found.

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