Bug 29755 Attach source does not allow one to select a folder... [build path]
When opening some .class that does not yet have a source attachment eclipse shows a text version of the interface defintion and a button for Attaching source. When pressing this button a window appaer where one can enter the name/location of a folder, zip or jar for the source. There are also a button for choosing it via a file selection dialog and this works fine for zip and jar files - but not for selecting a directory :( Workaround is just to enter the directory manually.
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/wizards/buildpaths/SourceAttachmentBlock.java
public void changeControlPressed(DialogField field) {
			attachmentChangeControlPressed(field);			
		}
		
		
		public void dialogFieldChanged(DialogField field) {
			attachmentDialogFieldChanged(field);
		}
	}
	
	private void attachmentChangeControlPressed(DialogField field) {
		if (field == fFileNameField) {
			IPath jarFilePath= chooseExtJarFile();
			if (jarFilePath != null) {
				fFileNameField.setText(jarFilePath.toString());
			}
		}	
	}