Confusing result from conflict dialog

[GerdP]

What steps will reproduce the problem?

1. load attached file
2. select the two address nodes and the building, note that each has a different shop=* tag
3. press Shift+T for terrace plugin
4. make sure the dialog shows checkbox "add to existing associatedStreet relation" enabled
5. press OK

What is the expected result?

Not sure. A conflict dialog of some sort.

What happens instead?

The conflict dialog for combine ways is displayed which shows confusing hints. It seems impossible to get a resonable result, typically the associatedStreet relation will contain only one of the two buildings, but that one twice.
When I leave the dialog with Escape the relation looks fine but both buildings are tagged as shop=mall.

Please provide any additional information below. Attach a screenshot if possible.

Build-Date:2020-09-28 07:29:31
Revision:17063
Is-Local-Build:true

Identification: JOSM/1.5 (17063 SVN en) Windows 10 64-Bit
OS Build number: Windows 10 Home 2004 (19041)
Memory Usage: 1050 MB / 3641 MB (251 MB allocated, but free)
Java version: 1.8.0_191-b12, Oracle Corporation, Java HotSpot(TM) 64-Bit Server VM
Look and Feel: com.sun.java.swing.plaf.windows.WindowsLookAndFeel
Screen: \Display0 1920x1080 (scaling 1.0x1.0)
Maximum Screen Size: 1920x1080
Best cursor sizes: 16x16 -> 32x32, 32x32 -> 32x32
VM arguments: [-agentlib:jdwp=transport=dt_socket,suspend=y,address=localhost:49457, -ea, -Dfile.encoding=UTF-8]
Program arguments: [--debug]
Dataset consistency test: No problems found

Plugins:
+ OpeningHoursEditor (35414)
+ PolygonCutOut (v0.7)
+ apache-commons (35524)
+ buildings_tools (35500)
+ continuosDownload (91)
+ ejml (35313)
+ geotools (35169)
+ jaxb (35092)
+ jts (35122)
+ merge-overlap (35248)
+ o5m (35248)
+ opendata (35513)
+ pbf (35446)
+ poly (35248)
+ reverter (35556)
+ terracer (35560)
+ undelete (35521)
+ utilsplugin2 (35487)

[GerdP]

There are several problems here.

1. global field tagsInConflict might contain an empty colllection, but code only checks if it is null.
2. I think conflict resolution only works when a single node is selected. The current code iterates over the selected addr:housenumber nodes and stores conflicting elements in global fields. These global fields are evaluated only once when all changes are calculated. So, only if the last processed node creates a conflict this is presented, other conflicts are silently ignored.
3. The CombinePrimitiveResolverDialog is about combining elements, but terracer is typically splitting a single closed way into multiple closed ways and each one might produce a "combine" with a corresponding addr:housenumber node.

Each of these "combine" actions may produce different conflicts concerning different tags.

I think we either need a lot more code here or we can remove a lot of code and simply refuse to continue where any conflicts are found.

[GerdP]

One way to solve this would be to show one conflict dialog for each node that produces a conflict. Might get annoying when you have several nodes.

[GerdP]

show more than one conflict dialog if needed, don't mess up associatedStreet relation