Expand root outline view in outline view by default (#1048)

Before this commit, the outline view is drawn with all elements
collapsed by default. This often results in plenty of wasted space in
the UI and low information density.

Instead, as discussed in #693, it would be preferable to draw the
outline view with its first level expanded by default (i.e., displaying
the root node and its immediate children by default).

Issue: #693

org.eclipse.lsp4e/src/org/eclipse/lsp4e/outline/LSSymbolsContentProvider.java

@@ -333,16 +333,22 @@ protected void refreshTreeContentFromLS() {
  return;
  }
 
+ final int EXPAND_ROOT_LEVEL = 2; // Expansion level that displays root node and its children
  if (isQuickOutline) {
  viewer.refresh();
+ viewer.expandToLevel(EXPAND_ROOT_LEVEL);
  } else {
  TreePath[] expandedElements = viewer.getExpandedTreePaths();
  TreePath[] initialSelection = ((ITreeSelection) viewer.getSelection()).getPaths();
  viewer.refresh();
- viewer.setExpandedTreePaths(Arrays.stream(expandedElements).map(symbolsModel::toUpdatedSymbol)
+ if (expandedElements.length > 0) {
+ viewer.setExpandedTreePaths(Arrays.stream(expandedElements).map(symbolsModel::toUpdatedSymbol)
  .filter(Objects::nonNull).toArray(TreePath[]::new));
- viewer.setSelection(new TreeSelection(Arrays.stream(initialSelection)
- .map(symbolsModel::toUpdatedSymbol).filter(Objects::nonNull).toArray(TreePath[]::new)));
+ viewer.setSelection(new TreeSelection(Arrays.stream(initialSelection)
+ .map(symbolsModel::toUpdatedSymbol).filter(Objects::nonNull).toArray(TreePath[]::new)));
+ } else {
+ viewer.expandToLevel(EXPAND_ROOT_LEVEL);
+ }
  }
 
  if (linkWithEditor) {