[Patch] Add action to select shared/common child objects

[Woazboat]

It would be quite useful to have an action that allows you to select all common child objects that are shared between all currently selected objects.

E.g.:

• select all nodes that are shared between ways
• select all common members of relations

​https://github.com/JOSM/josm/pull/125

[taylor.smock]

I was going to apply this today.

I didn't, since when a single way is selected, the behavior is very similar to SelectWayNodesAction from utilsplugin2.

I'm kind of inclined to (a) set the default shortcut to ctrl+shift+n (same as utilsplugin2) and modify utilsplugin2 to not add that action when running a JOSM version with this patch.

Question:

• Did you intend to replace or partly replace SelectWayNodesAction? Or should we modify updateEnabledState to check to see if there are at least two selected objects?

[taylor.smock]

NVM. A use case I didn't think about for SelectWayNodesAction was to select all way nodes in the current selection.

[taylor.smock]

In 18814/josm:

Fix #23105: Add action to select shared/common child objects (patch by Woazboat, modified)

Modifications are as follows:

• Basic test added
• Icon added (copied and modified from selectall.svg)
• default methods for IPrimitive.getChildren were moved to the appropriate locations
• Lint cleanups in modified files

Additional notes:

• The behavior when only one way is selected is very similar to SelectWayNodesAction from utilsplugin2

[Woazboat]

Sorry, I didn't have much time in the last weeks to follow up on this or the comments on the github pull request. Thanks for modifying and applying the patch!

[gaben]

Does it have documentation yet?

[taylor.smock]

Initial documentation added via https://josm.openstreetmap.de/wiki/Help/Menu/Selection?action=diff&version=24 .

[gaben]

Thank you!

@Woazboat, could you please detail the function in a few sentences on the wiki?