Improve test helpers

Author: leotsarev

Tsarev.Analyzer.Helpers/TypeHelpers.cs

@@ -1,4 +1,5 @@
-using Microsoft.CodeAnalysis;
+using JetBrains.Annotations;
+using Microsoft.CodeAnalysis;
 using Microsoft.CodeAnalysis.CSharp.Syntax;
 using Microsoft.CodeAnalysis.Diagnostics;
 
@@ -36,11 +37,47 @@ public static bool IsExpressionOfType<T>(this ExpressionSyntax createNode, Synta
     }
 
     /// <summary>
-    /// Gets matching type in context
+    /// Determines if some expression is actually of type T or of type derived from T
     /// </summary>
-    public static INamedTypeSymbol GetType<T>(this SyntaxNodeAnalysisContext context)
+    public static bool IsExpressionOfTypeOrDerived<T>(this ExpressionSyntax createNode, SyntaxNodeAnalysisContext context)
     {
-      return context.SemanticModel.Compilation.GetTypeByMetadataName(typeof(T).FullName);
+      var targetType = GetType<T>(context);
+      return createNode.IsExpressionOfTypeOrDerived(context, targetType);
     }
+
+    /// <summary>
+    /// Determines if some expression is actually of type T or of type derived from T
+    /// </summary>
+    public static bool IsExpressionOfTypeOrDerived(this ExpressionSyntax createNode,
+      SyntaxNodeAnalysisContext context, INamedTypeSymbol targetType)
+    {
+      var actualType = context.SemanticModel.GetTypeInfo(createNode).Type as INamedTypeSymbol;
+
+      var searchType = actualType;
+
+      while (searchType != null)
+      {
+        if (Equals(searchType, targetType))
+        {
+          return true;
+        }
+
+        searchType = searchType.BaseType;
+      }
+
+      return false;
+    }
+
+    /// <summary>
+    /// Gets matching type in context
+    /// </summary>
+    [CanBeNull]
+    public static INamedTypeSymbol GetType<T>(this SyntaxNodeAnalysisContext context) => context.SemanticModel.Compilation.GetType<T>();
+
+    /// <summary>
+    /// Gets matching type in context
+    /// </summary>
+    [CanBeNull]
+    public static INamedTypeSymbol GetType<T>(this Compilation semanticModelCompilation) => semanticModelCompilation.GetTypeByMetadataName(typeof(T).FullName);
   }
 }