An internal error occurred during: "Compute launch button tooltip".

I was editing a file somename.scala.html at the time.

java.lang.NullPointerException
at scala.tools.eclipse.util.EclipseUtils$PimpedAdaptable.adaptTo(EclipseUtils.scala:20)
at scala.tools.eclipse.launching.ScalaLaunchShortcut$.getMainMethods(ScalaLaunchShortcut.scala:208)
at scala.tools.eclipse.launching.ScalaLaunchableTester.hasMain(ScalaLaunchableTester.scala:43)
at scala.tools.eclipse.launching.ScalaLaunchableTester.test(ScalaLaunchableTester.scala:93)
at org.eclipse.core.internal.expressions.Property.test(Property.java:58)
at org.eclipse.core.internal.expressions.TestExpression.evaluate(TestExpression.java:99)
at org.eclipse.core.internal.expressions.CompositeExpression.evaluateAnd(CompositeExpression.java:53)
at org.eclipse.core.internal.expressions.AndExpression.evaluate(AndExpression.java:29)
at org.eclipse.core.internal.expressions.CompositeExpression.evaluateAnd(CompositeExpression.java:53)
at org.eclipse.core.internal.expressions.IterateExpression.evaluate(IterateExpression.java:150)
at org.eclipse.core.internal.expressions.CompositeExpression.evaluateAnd(CompositeExpression.java:53)
at org.eclipse.core.internal.expressions.WithExpression.evaluate(WithExpression.java:72)
at org.eclipse.core.internal.expressions.CompositeExpression.evaluateAnd(CompositeExpression.java:53)
at org.eclipse.core.internal.expressions.EnablementExpression.evaluate(EnablementExpression.java:53)
at org.eclipse.debug.internal.ui.launchConfigurations.LaunchShortcutExtension.evalEnablementExpression(LaunchShortcutExtension.java:287)
at org.eclipse.debug.internal.ui.contextlaunching.LaunchingResourceManager.getShortcutsForSelection(LaunchingResourceManager.java:452)
at org.eclipse.debug.internal.ui.contextlaunching.LaunchingResourceManager.computeLabels(LaunchingResourceManager.java:237)
at org.eclipse.debug.internal.ui.contextlaunching.LaunchingResourceManager$2.run(LaunchingResourceManager.java:138)
at org.eclipse.core.internal.jobs.Worker.run(Worker.java:54)