Fix to unused value assignment analyzer for #31583

1. Do not offer remove unused local assignment for locals with error type
2. Make sure that this code fix is ordered after Add usings code fix, in case there are more similar unknown cases, by adding the ExtensionOrder attribute

Fixes #31583

src/EditorFeatures/CSharpTest/RemoveUnusedParametersAndValues/RemoveUnusedValueAssignmentTests.cs

@@ -7,6 +7,7 @@
 using Microsoft.CodeAnalysis.CSharp.CodeStyle;
 using Microsoft.CodeAnalysis.Options;
 using Microsoft.CodeAnalysis.Test.Utilities;
+using Roslyn.Test.Utilities;
 using Xunit;
 
 namespace Microsoft.CodeAnalysis.Editor.CSharp.UnitTests.RemoveUnusedParametersAndValues
@@ -5777,5 +5778,21 @@ bool M2(out char x)
     }
 }", options: PreferDiscard);
         }
+
+        [WorkItem(31583, "https://github.com/dotnet/roslyn/issues/31583")]
+        [Theory, Trait(Traits.Feature, Traits.Features.CodeActionsRemoveUnusedValues)]
+        [InlineData(nameof(PreferDiscard))]
+        [InlineData(nameof(PreferUnusedLocal))]
+        public async Task MissingImports(string optionName)
+        {
+            await TestMissingInRegularAndScriptAsync(
+@"class C
+{
+    void M()
+    {
+        List<int> [|x|] = null;
+    }
+}", optionName);
+        }
     }
 }

src/Features/CSharp/Portable/RemoveUnusedParametersAndValues/CSharpRemoveUnusedParametersAndValuesDiagnosticAnalyzer.cs

 // Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
+using Microsoft.CodeAnalysis.CodeFixes;
 using Microsoft.CodeAnalysis.CodeStyle;
 using Microsoft.CodeAnalysis.CSharp.CodeStyle;
 using Microsoft.CodeAnalysis.CSharp.Syntax;
@@ -11,6 +12,7 @@
 namespace Microsoft.CodeAnalysis.CSharp.RemoveUnusedParametersAndValues
 {
     [DiagnosticAnalyzer(LanguageNames.CSharp)]
+    [ExtensionOrder(After = PredefinedCodeFixProviderNames.AddImport)]
     internal class CSharpRemoveUnusedParametersAndValuesDiagnosticAnalyzer : AbstractRemoveUnusedParametersAndValuesDiagnosticAnalyzer
     {
         protected override Option<CodeStyleOption<UnusedValuePreference>> UnusedValueExpressionStatementOption

src/Features/Core/Portable/RemoveUnusedParametersAndValues/AbstractRemoveUnusedParametersAndValuesDiagnosticAnalyzer.SymbolStartAnalyzer.BlockAnalyzer.cs

@@ -366,7 +366,8 @@ private void AnalyzeOperationBlockEnd(OperationBlockAnalysisContext context)
                         out ImmutableDictionary<string, string> properties)
                     {
                         properties = null;
-                        if (_options.UnusedValueAssignmentSeverity == ReportDiagnostic.Suppress)
+                        if (_options.UnusedValueAssignmentSeverity == ReportDiagnostic.Suppress ||
+                            symbol.GetSymbolType().IsErrorType())
                         {
                             return false;
                         }

src/Features/VisualBasic/Portable/RemoveUnusedParametersAndValues/VisualBasicRemoveUnusedParametersAndValuesDiagnosticAnalyzer.vb

 ' Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
+Imports Microsoft.CodeAnalysis.CodeFixes
 Imports Microsoft.CodeAnalysis.CodeStyle
 Imports Microsoft.CodeAnalysis.Diagnostics
 Imports Microsoft.CodeAnalysis.Operations
@@ -11,6 +12,7 @@ Imports Microsoft.CodeAnalysis.VisualBasic.Syntax
 Namespace Microsoft.CodeAnalysis.VisualBasic.RemoveUnusedParametersAndValues
 
     <DiagnosticAnalyzer(LanguageNames.VisualBasic)>
+    <ExtensionOrder(After:=PredefinedCodeFixProviderNames.AddImport)>
     Friend NotInheritable Class VisualBasicRemoveUnusedParametersAndValuesDiagnosticAnalyzer
         Inherits AbstractRemoveUnusedParametersAndValuesDiagnosticAnalyzer
         Protected Overrides ReadOnly Property UnusedValueExpressionStatementOption As [Option](Of CodeStyleOption(Of UnusedValuePreference))