Description John Cortell 2009-12-09 14:59:36 EST

Extensions are touted as a lightweight means to contribute actions (e.g., menus and toolbar items) to the GUI without having to load the code that carries out those operations, instead lazy-loading the plugins when the action is actually invoked. For this reason I was surprised to see a plugin I'm working with get loaded when I move the cursor over the Debug toolbar button. Looking into it, I see that the loading is triggered by the launch shortcut support. Specifically, the debug platform is putting together the labels for the available launch shortcuts given the current selection (LaunchingResourceManager#computeLabels()). If contextual launching is turned on, it assembles the collection of LaunchShortcutExtension instances that are applicable for the current selection, then invokes logic that ultimately calls each ones LaunchShortcutExtension.getLaunchConfigurations(IEditorPart). This method requests the extension's delegate, which of course requires the bundle to load. 

If this activity operated on only a targeted set of shortcut extensions, then all this would not be THAT troubling. But what really concerns me is that we can end up with a fairly extensive set of shortcut extensions, even for a selection that they have nothing to do with. 

In the scenario I'm running, the selection is the CDT editor, yet the shortcuts identified for that selection are

   org.eclipse.cdt.debug.ui.localCShortcut
   org.eclipse.jdt.debug.ui.javaAppletShortcut
   org.eclipse.jdt.debug.ui.localJavaShortcut
   org.eclipse.jdt.junit.junitShortcut
   org.eclipse.pde.ui.junitWorkbenchShortcut
   org.eclipse.tm.tcf.debug.ui.TCFShortcut

The JDT and PDE ones don't seem to be a right match, but they end up in the list because, ironically enough, the plugins aren't loaded, and that screws up the extension enablement evaluation. To see this behavior, set a breakpoint in LaunchingResourceManager#computeLabels() and observe the result of calling

   getShortcutsForSelection(selection, group.getMode());

Thus, just hovering over the Debug toolbar button causes CDT, TCF, JDT and PDE plugins to load, even though the selection is the CDT editor. This just seems to go against the spirit of the lightweight GUI contribution mechanism in Eclipse.