Add pretty test for C# 9 pattern combinator round-trips

Pins which C# 9 pattern-matching-improvement forms the decompiler already reconstructs or canonicalizes today. Green round-trips: 'not <constant>' subpatterns (int, char, enum, float, double), nested and mixed with 'not null'. EXPECTED_OUTPUT pins document deliberate canonical forms whose IL is indistinguishable from the pattern source: 'is not null' prints as '!= null' (or '.HasValue' on nullables), 'is not T' as '!(x is T)', 'x is > c' on a typed value as a plain comparison, 'B: not true' as 'B: false', and 'case 1 or 2 or 3:' as separate case labels. Assisted-by: Claude:claude-fable-5:Claude Code
2026-10-12 02:15:58 +00:00 · 2026-07-29 07:19:30 +02:00
parent d7bbf17e2e
commit 3d057d4bcd
2 changed files with 167 additions and 0 deletions
@@ -488,6 +488,12 @@ namespace ICSharpCode.Decompiler.Tests
 			await RunForLibrary(cscOptions: cscOptions);
 		}

+		[Test]
+		public async Task PatternMatchingCombinators([ValueSource(nameof(roslyn3OrNewerOptions))] CompilerOptions cscOptions)
+		{
+			await RunForLibrary(cscOptions: cscOptions);
+		}
+
 		[Test]
 		public async Task InitializerTests([ValueSource(nameof(defaultOptions))] CompilerOptions cscOptions)
 		{
@@ -0,0 +1,161 @@
+using System;
+
+namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
+{
+	public class PatternMatchingCombinators
+	{
+		public enum Color
+		{
+			Red,
+			Green,
+			Blue
+		}
+
+		public class X
+		{
+			public int I { get; set; }
+			public char Ch { get; set; }
+			public bool B { get; set; }
+			public float F { get; set; }
+			public double D { get; set; }
+			public Color Col { get; set; }
+			public string Text { get; set; }
+			public object Obj { get; set; }
+			public X Next { get; set; }
+		}
+
+		public void NotConstantInt(object x)
+		{
+			if (x is X { I: not 5 } x2)
+			{
+				Console.WriteLine(x2.Text);
+			}
+		}
+
+		public void NotConstantChar(object x)
+		{
+			if (x is X { Ch: not 'a' } x2)
+			{
+				Console.WriteLine(x2.Text);
+			}
+		}
+
+		public void NotConstantEnum(object x)
+		{
+			if (x is X { Col: not Color.Red } x2)
+			{
+				Console.WriteLine(x2.Text);
+			}
+		}
+
+		public void NotConstantFloat(object x)
+		{
+			if (x is X { F: not 1.5f } x2)
+			{
+				Console.WriteLine(x2.Text);
+			}
+		}
+
+		public void NotConstantDouble(object x)
+		{
+			if (x is X { D: not 2.5 } x2)
+			{
+				Console.WriteLine(x2.Text);
+			}
+		}
+
+		public void NotConstantNested(object x)
+		{
+			if (x is X { Next: { I: not 5 } } x2)
+			{
+				Console.WriteLine(x2.Text);
+			}
+		}
+
+		public void NotConstantAndNotNull(object x)
+		{
+			if (x is X { I: not 0, Obj: not null } x2)
+			{
+				Console.WriteLine(x2.Text);
+			}
+		}
+
+		public void NotTruePrintsAsFalse(object x)
+		{
+#if EXPECTED_OUTPUT
+			if (x is X { B: false } x2)
+#else
+			if (x is X { B: not true } x2)
+#endif
+			{
+				Console.WriteLine(x2.Text);
+			}
+		}
+
+		public bool IsNotNull(object x)
+		{
+#if EXPECTED_OUTPUT
+			return x != null;
+#else
+			return x is not null;
+#endif
+		}
+
+		public bool IsNotNullNullableInt(int? x)
+		{
+#if EXPECTED_OUTPUT
+			return x.HasValue;
+#else
+			return x is not null;
+#endif
+		}
+
+		public bool IsNotType(object x)
+		{
+#if EXPECTED_OUTPUT
+			return !(x is string);
+#else
+			return x is not string;
+#endif
+		}
+
+		public bool RelationalOnInt(int i)
+		{
+#if EXPECTED_OUTPUT
+			return i > 5;
+#else
+			return i is > 5;
+#endif
+		}
+
+		public bool RelationalOnEnum(Color c)
+		{
+#if EXPECTED_OUTPUT
+			return c > Color.Red;
+#else
+			return c is > Color.Red;
+#endif
+		}
+
+		public string OrPatternMergesToCaseLabels(int i)
+		{
+			switch (i)
+			{
+#if EXPECTED_OUTPUT
+			case 1:
+			case 2:
+			case 3:
+				return "small";
+#else
+				case 1 or 2 or 3:
+					return "small";
+#endif
+				case 4:
+				case 5:
+					return "medium";
+				default:
+					return "other";
+			}
+		}
+	}
+}