[Qbs] Deployment and dependency bundling

[Oswald Buddenhagen]

On Fri, Dec 27, 2019 at 06:04:08PM +0300, Alberto Mardegan wrote:
>I agree that in many cases the Depends item is the one who has the best
>information on how to handle its deployment. For example, the QtGui
>module will know which platform plugins need to be deployed, and the
>QtQml module could know which QML modules need to be deployed and how.
>
you're mixing up two separate issues.

"deployment" (you actually mean dependency embedding) is just a special 
form of "linking" dependencies. you should be able to make a fully 
static build or a bundle with embedded dlls and plugins from the same 
project, by flipping a single bit. similarly, for qml, you could select 
whether the qml files are compiled (with the old qml compiler) or 
embedded as-is.

_what_ gets depended upon is a policy decision that is independent from 
the mechanism that does the linking.
plugins specify a type, while modules declare what types of plugins they 
want to pull in. that makes this policy implicit, and a manual override 
is provided. that was actually already implemented for the qt port.
qml modules should be typically found by qmlimportscanner or an 
equivalent mechanism. there should be probably a mechnism to exclude 
unnecessary transitive dependencies.

>Project {
>  QtGuiApplication {
>    Depends {
>      name: "QtGui"
>
>      /* Or should this be automatically detected depending on
>       * the target? Maybe one should have a "deployed-app" product,
>       * and deployment should be triggered if and only if qbs is
>       * asked to build that target?
>       */
>
you are merely asking about the default of that property, which 
definitely should be specific to the particular Depends item. an 
expression that depends on a project-wide setting whether the result 
should be self-contaiend even when doing a dynamic build would certainly 
make sense.

>     * Additional properties could be used to exclude some libraries
>     * from being deployed (because we assume they exist in the
>     * target system).
>     */
>    deployment.excludePatterns: [ "libstdc++.so*", "libxcb.so*" ]
>
the embedding property should apply to abstract modules (and their 
"slices", i.e., files that fall into a particular category), not 
os-specific files.  yes, that means that there need to be modules for 
"system" dependencies, and they should be declared as such (so that 
projects don't need to repeat the exclusions each time).