Suggest names for aliases

src/Features/CSharp/Portable/Completion/CompletionProviders/DeclarationNameCompletionProvider.DeclarationInfo.cs

@@ -24,17 +24,20 @@ internal struct NameDeclarationInfo
                 ImmutableArray<SymbolKind> possibleSymbolKinds,
                 Accessibility accessibility, 
                 DeclarationModifiers declarationModifiers, 
-                ITypeSymbol type) 
+                ITypeSymbol type, 
+                IAliasSymbol alias) 
             {
                 PossibleSymbolKinds = possibleSymbolKinds;
                 DeclaredAccessibility = accessibility;
                 Modifiers = declarationModifiers;
                 Type = type;
+                Alias = alias;
             }
 
             public ImmutableArray<SymbolKind> PossibleSymbolKinds { get; }
             public DeclarationModifiers Modifiers { get; }
             public ITypeSymbol Type { get; }
+            public IAliasSymbol Alias { get; }
             public Accessibility DeclaredAccessibility { get; }
 
             internal static async Task<NameDeclarationInfo> GetDeclarationInfo(Document document, int position, CancellationToken cancellationToken)
@@ -136,11 +139,15 @@ internal static async Task<NameDeclarationInfo> GetDeclarationInfo(Document docu
                     return default(NameDeclarationInfo);
                 }
 
+                var alias = semanticModel.GetAliasInfo(typeSyntax, cancellationToken);
+                var type = semanticModel.GetTypeInfo(typeSyntax, cancellationToken).Type;
+
                 return new NameDeclarationInfo(
                     possibleDeclarationComputer(GetDeclarationModifiers(modifiers.Value)),
                     GetAccessibility(modifiers.Value),
                     GetDeclarationModifiers(modifiers.Value),
-                    semanticModel.GetTypeInfo(typeSyntax, cancellationToken).Type);
+                    type, 
+                    alias);
             }
 
             private static NameDeclarationInfo IsLastTokenOfType<TSyntaxNode>(
@@ -178,7 +185,8 @@ internal static async Task<NameDeclarationInfo> GetDeclarationInfo(Document docu
                     possibleDeclarationComputer(GetDeclarationModifiers(modifiers.Value)),
                     GetAccessibility(modifiers.Value),
                     GetDeclarationModifiers(modifiers.Value),
-                    semanticModel.GetTypeInfo(typeSyntax, cancellationToken).Type);
+                    semanticModel.GetTypeInfo(typeSyntax, cancellationToken).Type,
+                    semanticModel.GetAliasInfo(typeSyntax, cancellationToken));
             }
 
             private static bool IsFieldDeclaration(SyntaxToken token, SemanticModel semanticModel, 
@@ -224,7 +232,8 @@ internal static async Task<NameDeclarationInfo> GetDeclarationInfo(Document docu
                         ImmutableArray.Create(SymbolKind.TypeParameter),
                         Accessibility.NotApplicable,
                         new DeclarationModifiers(),
-                        type: null);
+                        type: null,
+                        alias: null);
 
                     return true;
                 }

src/Features/CSharp/Portable/Completion/CompletionProviders/DeclarationNameCompletionProvider.cs

@@ -12,6 +12,7 @@
 using Microsoft.CodeAnalysis.Shared.Extensions;
 using Microsoft.CodeAnalysis.Simplification;
 using Microsoft.CodeAnalysis.Text;
+using Roslyn.Utilities;
 using static Microsoft.CodeAnalysis.Diagnostics.Analyzers.NamingStyles.SymbolSpecification;
 
 namespace Microsoft.CodeAnalysis.CSharp.Completion.Providers
@@ -37,14 +38,12 @@ public override async Task ProvideCompletionsAsync(CompletionContext completionC
             }
 
             var nameInfo = await NameDeclarationInfo.GetDeclarationInfo(document, position, cancellationToken).ConfigureAwait(false);
-
-            if (!IsValidType(nameInfo.Type))
+            var baseNames = GetBaseNames(semanticModel, nameInfo);
+            if (baseNames == default)
             {
                 return;
             }
 
-            var type = UnwrapType(nameInfo.Type, semanticModel.Compilation);
-            var baseNames = NameGenerator.GetBaseNames(type);
             var recommendedNames = await GetRecommendedNamesAsync(baseNames, nameInfo, context, document, cancellationToken).ConfigureAwait(false);
             int sortValue = 0;
             foreach (var (name, kind) in recommendedNames)
@@ -57,6 +56,23 @@ public override async Task ProvideCompletionsAsync(CompletionContext completionC
             completionContext.SuggestionModeItem = CommonCompletionItem.Create(CSharpFeaturesResources.Name, CompletionItemRules.Default);
         }
 
+        private ImmutableArray<IEnumerable<string>> GetBaseNames(SemanticModel semanticModel,  NameDeclarationInfo nameInfo)
+        {
+            if (nameInfo.Alias != null)
+            {
+                return ImmutableArray.Create(SpecializedCollections.SingletonEnumerable(nameInfo.Alias.Name));
+            }
+
+            if (!IsValidType(nameInfo.Type))
+            {
+                return default;
+            }
+
+            var type = UnwrapType(nameInfo.Type, semanticModel.Compilation);
+            var baseNames = NameGenerator.GetBaseNames(type);
+            return baseNames;
+        }
+
         private bool IsValidType(ITypeSymbol type)
         {
             if (type == null)