Pattern Matching: Ensure that we always return a non-null instruction after successfully matching a pattern.

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

@@ -503,6 +503,66 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 			}
 		}
 
+
+		public void RecursivePattern_NullableIntField_Var(object obj)
+		{
+			if (obj is X { NullableIntField: var nullableIntField })
+			{
+				Console.WriteLine("Test " + nullableIntField.Value);
+			}
+			else
+			{
+				Console.WriteLine("not Test");
+			}
+		}
+
+		public void RecursivePattern_NullableIntProp_Const(object obj)
+		{
+			if (obj is X { NullableIntProp: 42 } x)
+			{
+				Console.WriteLine("Test " + x);
+			}
+			else
+			{
+				Console.WriteLine("not Test");
+			}
+		}
+		public void RecursivePattern_NullableIntProp_Var(object obj)
+		{
+			if (obj is X { NullableIntProp: var nullableIntProp })
+			{
+				Console.WriteLine("Test " + nullableIntProp.Value);
+			}
+			else
+			{
+				Console.WriteLine("not Test");
+			}
+		}
+
+		public void RecursivePattern_NullableCustomStructField_Const(object obj)
+		{
+			if (obj is X { NullableCustomStructField: { I: 42, Obj: not null } nullableCustomStructField })
+			{
+				Console.WriteLine("Test " + nullableCustomStructField.I);
+			}
+			else
+			{
+				Console.WriteLine("not Test");
+			}
+		}
+
+		public void RecursivePattern_NullableCustomStructField_Var(object obj)
+		{
+			if (obj is X { NullableCustomStructField: var nullableCustomStructField, Obj: null })
+			{
+				Console.WriteLine("Test " + nullableCustomStructField.Value);
+			}
+			else
+			{
+				Console.WriteLine("not Test");
+			}
+		}
+
 		public void RecursivePattern_NullableCustomStructProp_Const(object obj)
 		{
 			if (obj is X { NullableCustomStructProp: { I: 42, Obj: not null } nullableCustomStructProp })
@@ -514,6 +574,18 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 				Console.WriteLine("not Test");
 			}
 		}
+
+		public void RecursivePattern_NullableCustomStructProp_Var(object obj)
+		{
+			if (obj is X { NullableCustomStructProp: var nullableCustomStructProp, Obj: null })
+			{
+				Console.WriteLine("Test " + nullableCustomStructProp.Value);
+			}
+			else
+			{
+				Console.WriteLine("not Test");
+			}
+		}
 #endif
 		private bool F()
 		{

ICSharpCode.Decompiler/IL/Transforms/PatternMatchingTransform.cs

@@ -186,11 +186,10 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			return true;
 		}
 
-		private static ILInstruction? DetectPropertySubPatterns(MatchInstruction parentPattern, ILInstruction? trueInst,
+		private static ILInstruction DetectPropertySubPatterns(MatchInstruction parentPattern, ILInstruction trueInst,
 			ILInstruction parentFalseInst, BlockContainer container, ILTransformContext context, ref ControlFlowGraph? cfg)
 		{
-			ILInstruction? prevTrueInst = trueInst;
-			while (trueInst != null)
+			while (true)
 			{
 				Block? trueBlock = trueInst as Block;
 				if (!(trueBlock != null || trueInst.MatchBranch(out trueBlock)))
@@ -201,13 +200,17 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 				{
 					break;
 				}
-				trueInst = DetectPropertySubPattern(parentPattern, trueBlock, parentFalseInst, context, ref cfg);
-				if (trueInst != null)
+				var nextTrueInst = DetectPropertySubPattern(parentPattern, trueBlock, parentFalseInst, context, ref cfg);
+				if (nextTrueInst != null)
 				{
-					prevTrueInst = trueInst;
+					trueInst = nextTrueInst;
+				}
+				else
+				{
+					break;
 				}
 			}
-			return prevTrueInst;
+			return trueInst;
 		}
 
 		private static ILInstruction? DetectPropertySubPattern(MatchInstruction parentPattern, Block block,
@@ -288,7 +291,8 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 
 				if (targetVariable.Type.IsKnownType(KnownTypeCode.NullableOfT))
 				{
-					return MatchNullableHasValueCheckPattern(block, varPattern, parentFalseInst, context, ref cfg);
+					return MatchNullableHasValueCheckPattern(block, varPattern, parentFalseInst, context, ref cfg)
+						?? block;
 				}
 
 				var instructionAfterNullCheck = MatchNullCheckPattern(block, varPattern, parentFalseInst, context);
@@ -339,6 +343,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			block.Instructions.Add(trueInst);
 			return trueInst;
 		}
+
 		private static ILInstruction? MatchNullableHasValueCheckPattern(Block block, MatchInstruction varPattern,
 			ILInstruction parentFalseInst, ILTransformContext context, ref ControlFlowGraph? cfg)
 		{