Merge pull request #3878 from ds5678/issue3877

Handle negative dictionary capacity in string switch transform

ICSharpCode.Decompiler.Tests/PrettyTestRunner.cs

@@ -836,6 +836,12 @@ namespace ICSharpCode.Decompiler.Tests
 			await RunForLibrary(cscOptions: cscOptions);
 		}
 
+		[Test]
+		public async Task Issue3877([ValueSource(nameof(roslyn2OrNewerWithNet40Options))] CompilerOptions cscOptions)
+		{
+			await RunForLibrary(cscOptions: cscOptions);
+		}
+
 		[Test]
 		public async Task AssemblyCustomAttributes([ValueSource(nameof(defaultOptions))] CompilerOptions cscOptions)
 		{

ICSharpCode.Decompiler.Tests/TestCases/Pretty/Issue3877.cs

@@ -0,0 +1,65 @@
+using System.Collections.Generic;
+using System.Runtime.CompilerServices;
+
+namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
+{
+	internal static class Issue3877
+	{
+		[CompilerGenerated]
+		private static Dictionary<string, int> backingField;
+
+		public static void M(string s)
+		{
+			N(0);
+			if (s != null)
+			{
+				if (backingField == null)
+				{
+#if OPT
+					backingField = new Dictionary<string, int>(-87) {
+						{ "string0", 0 },
+						{ "string1", 1 },
+						{ "string2", 2 },
+						{ "string3", 3 },
+						{ "string4", 4 }
+					};
+#else
+					Dictionary<string, int> dictionary = new Dictionary<string, int>(-87);
+					dictionary.Add("string0", 0);
+					dictionary.Add("string1", 1);
+					dictionary.Add("string2", 2);
+					dictionary.Add("string3", 3);
+					dictionary.Add("string4", 4);
+					backingField = dictionary;
+#endif
+				}
+				if (backingField.TryGetValue(s, out var value))
+				{
+					switch (value)
+					{
+						case 0:
+							N(10);
+							break;
+						case 1:
+							N(20);
+							break;
+						case 2:
+							N(30);
+							break;
+						case 3:
+							N(40);
+							break;
+						case 4:
+							N(50);
+							break;
+					}
+				}
+			}
+			N(60);
+		}
+
+		public static void N(int i)
+		{
+		}
+	}
+}

ICSharpCode.Decompiler/IL/Transforms/SwitchOnStringTransform.cs

@@ -818,6 +818,8 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 				if (!newObj.Arguments[0].MatchLdcI4(out valuesLength))
 					return false;
 			}
+			if (valuesLength < 0)
+				return false;
 			values = new List<(string, int)>(valuesLength);
 			int i = 0;
 			while (MatchAddCall(dictionaryType, block.Instructions[i + 1], dictVar, out var index, out var value))