From 5ce700e74eb18fa1e04ae91c31ecadb47795f15f Mon Sep 17 00:00:00 2001
From: Jake Bailey <5341706+jakebailey@users.noreply.github.com>
Date: Mon, 5 Aug 2019 13:27:16 -0700
Subject: [PATCH] Prevent crashes when the AST happens to be null

---
 .../Impl/Indexing/MostRecentDocumentSymbols.cs   | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/src/LanguageServer/Impl/Indexing/MostRecentDocumentSymbols.cs b/src/LanguageServer/Impl/Indexing/MostRecentDocumentSymbols.cs
index 2096e26fc..fe8b6969b 100644
--- a/src/LanguageServer/Impl/Indexing/MostRecentDocumentSymbols.cs
+++ b/src/LanguageServer/Impl/Indexing/MostRecentDocumentSymbols.cs
@@ -7,6 +7,7 @@
 using Microsoft.Python.Analysis.Documents;
 using Microsoft.Python.Core;
 using Microsoft.Python.Core.Diagnostics;
+using Microsoft.Python.Parsing.Ast;
 
 namespace Microsoft.Python.LanguageServer.Indexing {
     class MostRecentDocumentSymbols : IMostRecentDocumentSymbols {
@@ -120,7 +121,20 @@ public void Dispose() {
         }
 
         private async Task<IReadOnlyList<HierarchicalSymbol>> IndexAsync(IDocument doc, CancellationToken indexCt) {
-            var ast = await doc.GetAstAsync(indexCt);
+            PythonAst ast = null;
+
+            for (var i = 0; i < 5; i++) {
+                ast = await doc.GetAstAsync(indexCt);
+                if (ast != null) {
+                    break;
+                }
+                await Task.Delay(100);
+            }
+
+            if (ast == null) {
+                return Array.Empty<HierarchicalSymbol>();
+            }
+
             indexCt.ThrowIfCancellationRequested();
             var walker = new SymbolIndexWalker(ast);
             ast.Walk(walker);