From b5df6688680036539860b3cb767debe9fe67844a Mon Sep 17 00:00:00 2001
From: Dongbo Wang <dongbow@microsoft.com>
Date: Thu, 5 Dec 2019 15:21:42 -0800
Subject: [PATCH] Fix NullReferenceException in CompletionCompleters public
 methods

---
 .../CommandCompletion/CompletionCompleters.cs | 32 +++++++++++--------
 .../Host/TabCompletion/BugFix.Tests.ps1       | 10 ++++++
 2 files changed, 29 insertions(+), 13 deletions(-)

diff --git a/src/System.Management.Automation/engine/CommandCompletion/CompletionCompleters.cs b/src/System.Management.Automation/engine/CommandCompletion/CompletionCompleters.cs
index 415471362c8..07953a757d5 100644
--- a/src/System.Management.Automation/engine/CommandCompletion/CompletionCompleters.cs
+++ b/src/System.Management.Automation/engine/CommandCompletion/CompletionCompleters.cs
@@ -4581,7 +4581,7 @@ internal static List<CompletionResult> CompleteVariable(CompletionContext contex
             var wordToComplete = context.WordToComplete;
             var colon = wordToComplete.IndexOf(':');
 
-            var lastAst = context.RelatedAsts.Last();
+            var lastAst = context.RelatedAsts?.Last();
             var variableAst = lastAst as VariableExpressionAst;
             var prefix = variableAst != null && variableAst.Splatted ? "@" : "$";
 
@@ -5998,19 +5998,22 @@ internal static List<CompletionResult> CompleteType(CompletionContext context, s
             }
 
             // this is a temporary fix. Only the type defined in the same script get complete. Need to use using Module when that is available.
-            var scriptBlockAst = (ScriptBlockAst)context.RelatedAsts[0];
-            var typeAsts = scriptBlockAst.FindAll(ast => ast is TypeDefinitionAst, false).Cast<TypeDefinitionAst>();
-            foreach (var typeAst in typeAsts.Where(ast => pattern.IsMatch(ast.Name)))
+            if (context.RelatedAsts != null && context.RelatedAsts.Count > 0)
             {
-                string toolTipPrefix = string.Empty;
-                if (typeAst.IsInterface)
-                    toolTipPrefix = "Interface ";
-                else if (typeAst.IsClass)
-                    toolTipPrefix = "Class ";
-                else if (typeAst.IsEnum)
-                    toolTipPrefix = "Enum ";
+                var scriptBlockAst = (ScriptBlockAst)context.RelatedAsts[0];
+                var typeAsts = scriptBlockAst.FindAll(ast => ast is TypeDefinitionAst, false).Cast<TypeDefinitionAst>();
+                foreach (var typeAst in typeAsts.Where(ast => pattern.IsMatch(ast.Name)))
+                {
+                    string toolTipPrefix = string.Empty;
+                    if (typeAst.IsInterface)
+                        toolTipPrefix = "Interface ";
+                    else if (typeAst.IsClass)
+                        toolTipPrefix = "Class ";
+                    else if (typeAst.IsEnum)
+                        toolTipPrefix = "Enum ";
 
-                results.Add(new CompletionResult(prefix + typeAst.Name + suffix, typeAst.Name, CompletionResultType.Type, toolTipPrefix + typeAst.Name));
+                    results.Add(new CompletionResult(prefix + typeAst.Name + suffix, typeAst.Name, CompletionResultType.Type, toolTipPrefix + typeAst.Name));
+                }
             }
 
             results.Sort((c1, c2) => string.Compare(c1.ListItemText, c2.ListItemText, StringComparison.OrdinalIgnoreCase));
@@ -6019,7 +6022,10 @@ internal static List<CompletionResult> CompleteType(CompletionContext context, s
 
         private static string GetNamespaceToRemove(CompletionContext context, TypeCompletionBase completion)
         {
-            if (completion is NamespaceCompletion) { return null; }
+            if (completion is NamespaceCompletion || context.RelatedAsts == null || context.RelatedAsts.Count == 0)
+            {
+                return null;
+            }
 
             var typeCompletion = completion as TypeCompletion;
             string typeNameSpace = typeCompletion != null
diff --git a/test/powershell/Host/TabCompletion/BugFix.Tests.ps1 b/test/powershell/Host/TabCompletion/BugFix.Tests.ps1
index f463d95e8aa..89b91b6cfba 100644
--- a/test/powershell/Host/TabCompletion/BugFix.Tests.ps1
+++ b/test/powershell/Host/TabCompletion/BugFix.Tests.ps1
@@ -34,6 +34,16 @@ Describe "Tab completion bug fix" -Tags "CI" {
         $result.CompletionMatches[2].CompletionText | Should -BeExactly "-NoOverwrite"
     }
 
+    It "Issue#11227 - [CompletionCompleters]::CompleteVariable and [CompletionCompleters]::CompleteType should work" {
+        $result = [System.Management.Automation.CompletionCompleters]::CompleteType("CompletionComple")
+        $result.Count | Should -BeExactly 1
+        $result[0].CompletionText | Should -BeExactly 'System.Management.Automation.CompletionCompleters'
+
+        $result = [System.Management.Automation.CompletionCompleters]::CompleteVariable("errorAction")
+        $result.Count | Should -BeExactly 1
+        $result[0].CompletionText | Should -BeExactly '$ErrorActionPreference'
+    }
+
     Context "Issue#3416 - 'Select-Object'" {
         BeforeAll {
             $DatetimeProperties = @((Get-Date).psobject.baseobject.psobject.properties) | Sort-Object -Property Name