Fix #2541: Add explicit `unchecked()` around non-constant cast of constant to `nint`

ICSharpCode.Decompiler.Tests/RoundtripAssembly.cs

@@ -103,14 +103,12 @@ namespace ICSharpCode.Decompiler.Tests
 		}
 
 		[Test]
-		[Ignore("See https://github.com/icsharpcode/ILSpy/issues/2541 - Waiting for https://github.com/dotnet/roslyn/issues/45929")]
 		public void ExplicitConversions_With_NativeInts()
 		{
 			RunWithOutput("Random Tests\\TestCases", "ExplicitConversions.exe", LanguageVersion.CSharp9_0);
 		}
 
 		[Test]
-		[Ignore("See https://github.com/icsharpcode/ILSpy/issues/2541 - Waiting for https://github.com/dotnet/roslyn/issues/45929")]
 		public void ExplicitConversions_32_With_NativeInts()
 		{
 			RunWithOutput("Random Tests\\TestCases", "ExplicitConversions_32.exe", LanguageVersion.CSharp9_0);

ICSharpCode.Decompiler.Tests/TestCases/Pretty/NativeInts.cs

@@ -205,5 +205,17 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 		{
 			return (nint)(0 - x);
 		}
+
+		public nint SignedNotFittingIn32Bits()
+		{
+			// Explicit `unchecked` is necessary when casting oversized constant to nint
+			return unchecked((nint)9123123123123L);
+		}
+
+		public nuint UnsignedNotFittingIn32Bits()
+		{
+			// Explicit `unchecked` is necessary when casting oversized constant to nuint
+			return unchecked((nuint)9123123123123uL);
+		}
 	}
 }

ICSharpCode.Decompiler/CSharp/ExpressionBuilder.cs

@@ -120,10 +120,12 @@ namespace ICSharpCode.Decompiler.CSharp
 				else if (rr.Type.IsCSharpSmallIntegerType())
 				{
 					expr = new CastExpression(new PrimitiveType(KnownTypeReference.GetCSharpNameByTypeCode(rr.Type.GetDefinition().KnownTypeCode)), expr);
+					// Note: no unchecked annotation necessary, because the constant was folded to be in-range
 				}
 				else if (rr.Type.IsCSharpNativeIntegerType())
 				{
 					expr = new CastExpression(new PrimitiveType(rr.Type.Name), expr);
+					// Note: no unchecked annotation necessary, because the rr wouldn't be a constant if the value wasn't in-range on 32bit
 				}
 			}
 			var exprRR = expr.Annotation<ResolveResult>();

ICSharpCode.Decompiler/CSharp/Transforms/AddCheckedBlocks.cs

@@ -35,10 +35,16 @@ namespace ICSharpCode.Decompiler.CSharp.Transforms
 			/// true=checked, false=unchecked
 			/// </summary>
 			public bool IsChecked;
+
+			/// <summary>
+			/// Require an explicit unchecked block (can't rely on the project-level unchecked context)
+			/// </summary>
+			public bool IsExplicit;
 		}
 
 		public static readonly object CheckedAnnotation = new CheckedUncheckedAnnotation { IsChecked = true };
 		public static readonly object UncheckedAnnotation = new CheckedUncheckedAnnotation { IsChecked = false };
+		public static readonly object ExplicitUncheckedAnnotation = new CheckedUncheckedAnnotation { IsChecked = false, IsExplicit = true };
 		#endregion
 
 		/* 
@@ -114,7 +120,6 @@ namespace ICSharpCode.Decompiler.CSharp.Transforms
 			/// <summary>
 			/// Gets the new cost if an expression with this cost is wrapped in a checked/unchecked expression.
 			/// </summary>
-			/// <returns></returns>
 			internal Cost WrapInCheckedExpr()
 			{
 				if (Expressions == 0)
@@ -349,13 +354,27 @@ namespace ICSharpCode.Decompiler.CSharp.Transforms
 				CheckedUncheckedAnnotation annotation = expr.Annotation<CheckedUncheckedAnnotation>();
 				if (annotation != null)
 				{
-					// If the annotation requires this node to be in a specific context, add a huge cost to the other context
-					// That huge cost gives us the option to ignore a required checked/unchecked expression when there wouldn't be any
-					// solution otherwise. (e.g. "for (checked(M().x += 1); true; unchecked(M().x += 2)) {}")
-					if (annotation.IsChecked)
-						result.CostInUncheckedContext += new Cost(10000, 0);
+					if (annotation.IsExplicit)
+					{
+						// We don't yet support distinguishing CostInUncheckedContext vs. CostInExplicitUncheckedContext,
+						// so we always force an unchecked() expression here.
+						if (annotation.IsChecked)
+							throw new NotImplementedException("explicit checked"); // should not be needed
+						result.CostInCheckedContext = result.CostInUncheckedContext.WrapInCheckedExpr();
+						result.CostInUncheckedContext = result.CostInUncheckedContext.WrapInCheckedExpr();
+						result.NodesToInsertInUncheckedContext += new InsertedExpression(expr, annotation.IsChecked);
+						result.NodesToInsertInCheckedContext = result.NodesToInsertInUncheckedContext;
+					}
 					else
-						result.CostInCheckedContext += new Cost(10000, 0);
+					{
+						// If the annotation requires this node to be in a specific context, add a huge cost to the other context
+						// That huge cost gives us the option to ignore a required checked/unchecked expression when there wouldn't be any
+						// solution otherwise. (e.g. "for (checked(M().x += 1); true; unchecked(M().x += 2)) {}")
+						if (annotation.IsChecked)
+							result.CostInUncheckedContext += new Cost(10000, 0);
+						else
+							result.CostInCheckedContext += new Cost(10000, 0);
+					}
 				}
 				// Embed this node in an checked/unchecked expression:
 				if (expr.Parent is ExpressionStatement)

ICSharpCode.Decompiler/CSharp/TranslatedExpression.cs

@@ -569,7 +569,22 @@ namespace ICSharpCode.Decompiler.CSharp
 			bool needsCheckAnnotation = targetUType.GetStackType().IsIntegerType();
 			if (needsCheckAnnotation)
 			{
-				castExpr.AddAnnotation(checkForOverflow ? AddCheckedBlocks.CheckedAnnotation : AddCheckedBlocks.UncheckedAnnotation);
+				if (checkForOverflow)
+				{
+					castExpr.AddAnnotation(AddCheckedBlocks.CheckedAnnotation);
+				}
+				else if (ResolveResult.IsCompileTimeConstant && targetUType.IsCSharpNativeIntegerType())
+				{
+					// unchecked potentially-overflowing cast of constant to n(u)int:
+					// Placement in implicitly unchecked context is not good enough when applied to compile-time constant,
+					// the constant must be placed into an explicit unchecked block.
+					// (note that non-potentially-overflowing casts will be handled by constant folding and won't get here)
+					castExpr.AddAnnotation(AddCheckedBlocks.ExplicitUncheckedAnnotation);
+				}
+				else
+				{
+					castExpr.AddAnnotation(AddCheckedBlocks.UncheckedAnnotation);
+				}
 			}
 			return castExpr.WithoutILInstruction().WithRR(rr);
 		}