As a smith I do not want to have compile errors after oomphing

[jpilgrim]

After freshely "oomphing" N4JS with latest Eclipse version (Eclipse IDE for Eclipse Committers, 2019-06) and I got two problems:

• org.eclipse.n4js.model/emf-gen
  The whole folder contains errors due to wrong code generation. How can we fix that? Do we need a different EMF version somewhere? Current workaround: Replace the folder with HEAD version (and discard changes).
• AstSelectionProvider2PluginUITest.xtend contains errors. Current workaround: It needs to be "touched" (i.e. changed, saved, undo change, save) in order to work

[jpilgrim]

Screenshot of the two workaround:

1. emf-gen:

2. AstSelectionProvider2PluginUITest.xtend

[mmews-n4]

#1390 fixes first item

[szarnekow]

The other problem appears to be caused by a wrongly computed build order. Investigating.

[szarnekow]

Further analysis revealed the following causal chain for the observed problem:

• We use bundle fragment to implement tests, lets say n4js.runner.ui.tests is a fragment for n4js.runner.ui
• The fragments required bundles, e.g. n4js.ui.tests.helper are hoisted into the host bundles dependencies internally by PDE
• Now we have a dependency from n4js.runner.ui to n4js.ui.tests.helper that is considered by the Eclipse incremental project builder.
• n4jsui.tests.helper depends again on n4js.runner.ui which forms a cyclic dependency.
• Cyclic dependencies are evil and cause the problem with the bogus error markers.
• Potential workaround: Refactor test fragments to bundles.

[szarnekow]

see also https://bugs.eclipse.org/bugs/show_bug.cgi?id=536592
which is solved for Eclipse 2019-12 as it seems.