Adding "append" Feature to p2asmaven plugin

[hacki11]

On a dependency change in the p2asmaven plugin config the whole already downloaded repository is deleted and redownloaded.

The p2.mirror ant tasks supports an "append" feature where one can set true for keeping the downloaded dependencies and just adding the new. Setting this to false will remove all deps from the target repository beforehand. During integration of the plugin, it is often needed to add dependencies incrementally and a whole rebuild is needed (up to 40 minutes).

To add this feature i think the following would have to be changed:

Instead of it should be called

goomph/src/main/java/com/diffplug/gradle/p2/P2Model.java

Line 249 in a2dbf4c

destination.attributes().put("location", FileMisc.asUrl(dstFolder));

https://wiki.eclipse.org/Equinox/p2/Ant_Tasks#Simple_Examples

Instead of deleting the directory:

goomph/src/main/java/com/diffplug/gradle/p2/AsMavenGroupImpl.java

Line 71 in a2dbf4c

FileMisc.cleanDir(dirP2());

a method "append(boolean)" can be introduced inside P2Model. If set, the ant task will clean the target dir.

This will improve the time of getting an application compiled in eclipse against all the needed dependencies without the redownload hassle (i installed a nexus p2 mirror but still costs time)

are you interested in a pull request regarding this feature?

[nedtwigg]

A PR for this would be fantastic!

Here's one use case to consider:

p2repository = '4.4'
dependencies {
    compile 'p2asmaven:org.eclipse.somejar:+'
}
... run build A ...
p2repository = '4.3'
... run build B ....

If changing the repository from 4.4 to 4.3 triggers a clean, then build A has an artifact from 4.4, and build B has an artifact from 4.3. If I understand this append mode correctly, both builds would have 4.4.

Because of that, I think that this new feature (which would be super useful for 99% of cases) ought to be enabled by a flag, such as:

p2asmaven {
    append = true // default is false, which forces a full redownload for any change

or

p2asmaven {
    cleanOnChange = false // default is true, which forces a full redownload for any change

I'm not sure which is easier to understand for the user. I lean towards append since it matches the implementation better, but it's implementor's choice.

[hacki11]

Yes, i would also recommend to have append = false as default to avoid changing current behavior. Append would also reference better to the backed p2.mirror feature.

[nedtwigg]

Shipped in 3.9.0.