Limit the maximum number of outline symbols to 5000 to avoid UI freezes

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

@@ -33,6 +33,12 @@
 
 public class SymbolsModel {
 
+	/**
+	 * maximal number of symbols provided for the outline. limiting the number
+	 * prevents the UI from freezing and becoming unusable.
+	 */
+	private static final int MAX_SYMBOLS = 5_000;
+
 	private static final SymbolInformation ROOT_SYMBOL_INFORMATION = new SymbolInformation();
 	private static final Object[] EMPTY = new Object[0];
 
@@ -112,24 +118,56 @@ public synchronized boolean update(List<Either<SymbolInformation, DocumentSymbol
 			final var parentStack = new ArrayDeque<SymbolInformation>();
 			parentStack.push(ROOT_SYMBOL_INFORMATION);
 			SymbolInformation previousSymbol = null;
+
+			int symbolsCount = 0;
+
 			for (Either<SymbolInformation, DocumentSymbol> either : response) {
+
+				if (symbolsCount >= MAX_SYMBOLS)
+					break;
+
+				// handle deprecated SymbolInformation elements
 				if (either.isLeft()) {
 					SymbolInformation symbol = either.getLeft();
 					if (isIncluded(previousSymbol, symbol)) {
 						parentStack.push(previousSymbol);
 						addChild(newChildrenMap, parentStack.peek(), symbol);
+						symbolsCount++;
 					} else if (isIncluded(parentStack.peek(), symbol)) {
 						addChild(newChildrenMap, parentStack.peek(), symbol);
+						symbolsCount++;
 					} else {
 						while (!isIncluded(parentStack.peek(), symbol)) {
 							parentStack.pop();
 						}
 						addChild(newChildrenMap, parentStack.peek(), symbol);
+						symbolsCount++;
 						parentStack.push(symbol);
 					}
 					previousSymbol = symbol;
+
+					// handle DocumentSymbol elements
 				} else if (either.isRight()) {
-					newRootSymbols.add(either.getRight());
+					final var docSym = either.getRight();
+					newRootSymbols.add(docSym);
+					symbolsCount++;
+
+					// count number of symbols and remove child symbols if MAX_SYMBOLS is reached
+					if (docSym.getChildren() != null) {
+						final var q = new ArrayDeque<DocumentSymbol>();
+						q.add(docSym);
+						while (!q.isEmpty()) {
+							final var parent = q.poll();
+							final var children = parent.getChildren();
+							if (children != null) {
+								if (symbolsCount + children.size() >= MAX_SYMBOLS) {
+									children.subList(MAX_SYMBOLS - symbolsCount, children.size()).clear();
+								}
+								symbolsCount += children.size();
+								q.addAll(children);
+							}
+						}
+					}
 				}
 			}