Let actions download parents when JOSM cannot be sure if they are completely known

[GerdP]

Since r19078 we have a new flag isReferrersDownloaded which is used the check if parents are fully downloaded. Before we used the (problematic) test whether a node is inside a download area.
With this flag we should now implement an automatic download of parent objects whereever actions need this to make sure that no parent object is corrupted, esp. "Split ...", "Combine ..." and "Join ..." actions need this.
With the old code OSM data loaded from file was considered "complete" when the file contained one or more "bounds" and the data was within those bounds. Since r19078 no such assumptions are made reg. the flag isReferrersDownloaded.

With the new flag I see two possible enhancements:
1) Add a new button "Download now" to the existing dialog which warns about missing parents.
2) Add a new preference auto-download.parents and - if true - let all actions download the needed parents for objects where isReferrersDownloaded.

Maybe a mixture of both.

[MSiipola]

What defines a "Referee" and "Parent"?

[MSiipola]

I using 19096, and have two ways which both have "State: all-referrers-downloaded modified", but they can't be combined.
I this a bug which this ticket will solve?

[GerdP]

Replying to MSiipola:

What defines a "Referee" and "Parent"?

A way refers to (consists of) nodes, so the way is one parent object for the nodes. Several ways may share a node, each of them is a parent.
A relation refers to nodes or ways or other relations (as members) and is thus a parent object to each of them.

[GerdP]

Replying to MSiipola:

I using 19096, and have two ways which both have "State: all-referrers-downloaded modified", but they can't be combined.
I this a bug which this ticket will solve?

No, this is a special case because the test wrongly checks if the way end nodes have the "all-referrers-downloaded" state. This was already fixed with r19119, see #23735.