sortOnly CommonSorter gets thrown away by other NavigationContent TriggerPoints

[pazi146]

How to reproduce:

Setup:

• navigationContent navA providing e1 with specific trigger points (e.g. providing and acting on .xml files)
• Object e1 belonging to navA (e.g. file foo.xml)
• Object e2 not belonging to navA and not fulfilling its trigger points/enablement (e.g. file bar.txt)
• sortOnly commonSorter sortF with the same or higher priority than navA valid for the objects (e.g. parent is IFolder)

eclipse.platform.ui/bundles/org.eclipse.ui.navigator/src/org/eclipse/ui/navigator/CommonViewerSorter.java

Lines 132 to 138 in 2cab7ac

	ViewerSorter sorter = sorterService.findSorter(descriptor, parent, e1, e2);
	if (!descriptor.isSortOnly()) { // for compatibility
	if (!(descriptor.isTriggerPoint(e1) && descriptor.isTriggerPoint(e2))) {
	return null;
	}
	}
	return sorter;

Sequence:

• sorterService.findSorter(...) will correctly return the sorter defined by sortF (implementation: org.eclipse.ui.internal.navigator.sorters.NavigatorSorterService)
• if (!descriptor.isSortOnly()) will be entered as navA can't be sortOnly
• descriptor.isTriggerPoint(e2) will be false
• sortF sorter will be wrongfully discarded

Notes:
1.
if (!descriptor.isSortOnly()) will always be entered (if my understanding is correct) as this code

eclipse.platform.ui/bundles/org.eclipse.ui.navigator/src/org/eclipse/ui/navigator/CommonViewerSorter.java

Lines 83 to 84 in 2cab7ac

	INavigatorContentDescriptor sourceOfLvalue = getSource(e1);
	INavigatorContentDescriptor sourceOfRvalue = getSource(e2);

can't ever give a sortOnly navigationContent as source (as it can't provide items per definition).
These are used in the later call:

eclipse.platform.ui/bundles/org.eclipse.ui.navigator/src/org/eclipse/ui/navigator/CommonViewerSorter.java

Lines 108 to 110 in 2cab7ac

	// findSorter returns the sorter specified at the source or if it has a higher priority a sortOnly sorter that is registered for the parent
	ViewerSorter lSorter = findApplicableSorter(sourceOfLvalue, parent, e1, e2);
	ViewerSorter rSorter = findApplicableSorter(sourceOfRvalue, parent, e1, e2);

If both navigationContents involved fail isTriggerPoint() then no sorter will ever be provided (e.g. navA as above and navB only acting on .json files)

A sortOnly commonSorter with lower priority would be a good idea in case no common sorter is found (as a fallback). That could be added right before

eclipse.platform.ui/bundles/org.eclipse.ui.navigator/src/org/eclipse/ui/navigator/CommonViewerSorter.java

Lines 118 to 120 in 2cab7ac

	if (sorter != null) {
	return sorter.compare(viewer, e1, e2);
	}