Fix #1906: RRs for default expressions of primitive types should use the correct constant value.

VB's `New Long()` is emitted as `initobj` whereas C#'s `default(long)` is emitted as `ldc.i4.0; conv.i8`.

ICSharpCode.Decompiler.Tests/ICSharpCode.Decompiler.Tests.csproj

@@ -82,6 +82,7 @@
     <Compile Include="DisassemblerPrettyTestRunner.cs" />
     <Compile Include="TestCases\Correctness\StringConcat.cs" />
     <Compile Include="TestCases\Ugly\NoLocalFunctions.cs" />
+    <Compile Include="TestCases\VBPretty\Issue1906.cs" />
     <Compile Include="TestCases\VBPretty\Select.cs" />
     <None Include="TestCases\ILPretty\WeirdEnums.cs" />
     <Compile Include="TestCases\ILPretty\ConstantBlobs.cs" />
@@ -93,6 +94,7 @@
     <Compile Include="TestCases\Ugly\NoForEachStatement.cs" />
     <None Include="TestCases\Ugly\NoExtensionMethods.Expected.cs" />
     <Compile Include="TestCases\Ugly\NoExtensionMethods.cs" />
+    <None Include="TestCases\VBPretty\Issue1906.vb" />
     <None Include="TestCases\VBPretty\Select.vb" />
     <None Include="TestCases\VBPretty\VBCompoundAssign.cs" />
     <Compile Include="TestCases\Pretty\ThrowExpressions.cs" />

ICSharpCode.Decompiler.Tests/TestCases/VBPretty/Issue1906.cs

@@ -0,0 +1,9 @@
+using System;
+
+public class Issue1906
+{
+	public void M()
+	{
+		Console.WriteLine(Math.Min(Math.Max(long.MinValue, default(long)), long.MaxValue));
+	}
+}

ICSharpCode.Decompiler.Tests/TestCases/VBPretty/Issue1906.vb

@@ -0,0 +1,6 @@
+Imports System
+Public Class Issue1906
+	Public Sub M()
+		Console.WriteLine(Math.Min(Math.Max(Int64.MinValue, New Long), Int64.MaxValue))
+	End Sub
+End Class

ICSharpCode.Decompiler.Tests/VBPrettyTestRunner.cs

@@ -78,6 +78,12 @@ namespace ICSharpCode.Decompiler.Tests
 			Run(options: options | CompilerOptions.Library);
 		}
 
+		[Test]
+		public void Issue1906([ValueSource(nameof(defaultOptions))] CompilerOptions options)
+		{
+			Run(options: options | CompilerOptions.Library);
+		}
+
 		void Run([CallerMemberName] string testName = null, CompilerOptions options = CompilerOptions.UseDebug, DecompilerSettings settings = null)
 		{
 			var vbFile = Path.Combine(TestCasePath, testName + ".vb");

ICSharpCode.Decompiler/CSharp/ExpressionBuilder.cs

@@ -536,14 +536,17 @@ namespace ICSharpCode.Decompiler.CSharp
 		{
 			Expression expr;
 			IType constantType;
+			object constantValue;
 			if (type.IsReferenceType == true || type.IsKnownType(KnownTypeCode.NullableOfT)) {
 				expr = new NullReferenceExpression();
 				constantType = SpecialType.NullType;
+				constantValue = null;
 			} else {
 				expr = new DefaultValueExpression(ConvertType(type));
 				constantType = type;
+				constantValue = CSharpResolver.GetDefaultValue(type);
 			}
-			return expr.WithRR(new ConstantResolveResult(constantType, null));
+			return expr.WithRR(new ConstantResolveResult(constantType, constantValue));
 		}
 		
 		protected internal override TranslatedExpression VisitSizeOf(SizeOf inst, TranslationContext context)