Add support for "definitely assigned if true/false" to data flow analysis.

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

@@ -77,6 +77,7 @@
   <ItemGroup>
     <Compile Include="DisassemblerPrettyTestRunner.cs" />
     <Compile Include="TestCases\ILPretty\ConstantBlobs.cs" />
+    <Compile Include="TestCases\Pretty\OutVariables.cs" />
     <None Include="TestCases\ILPretty\DirectCallToExplicitInterfaceImpl.cs" />
     <Compile Include="TestCases\ILPretty\Issue1389.cs" />
     <Compile Include="TestCases\ILPretty\Issue1454.cs" />

ICSharpCode.Decompiler.Tests/PrettyTestRunner.cs

@@ -239,6 +239,12 @@ namespace ICSharpCode.Decompiler.Tests
 			RunForLibrary(cscOptions: cscOptions, asmOptions: AssemblerOptions.UseOwnDisassembler);
 		}
 
+		[Test]
+		public void OutVariables([ValueSource(nameof(roslynOnlyOptions))] CompilerOptions cscOptions)
+		{
+			RunForLibrary(cscOptions: cscOptions);
+		}
+
 		[Test]
 		public void InitializerTests([ValueSource(nameof(defaultOptions))] CompilerOptions cscOptions)
 		{

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

@@ -0,0 +1,45 @@
+// Copyright (c) AlphaSierraPapa for the SharpDevelop Team
+// 
+// Permission is hereby granted, free of charge, to any person obtaining a copy of this
+// software and associated documentation files (the "Software"), to deal in the Software
+// without restriction, including without limitation the rights to use, copy, modify, merge,
+// publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons
+// to whom the Software is furnished to do so, subject to the following conditions:
+// 
+// The above copyright notice and this permission notice shall be included in all copies or
+// substantial portions of the Software.
+// 
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
+// INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
+// PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE
+// FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
+// OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+// DEALINGS IN THE SOFTWARE.
+
+using System;
+using System.Collections.Generic;
+
+namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
+{
+	public class PatternMatching
+	{
+		public static void OutVarInShortCircuit(Dictionary<int, string> d)
+		{
+			if (d.Count > 2 && d.TryGetValue(42, out string value)) {
+				Console.WriteLine(value);
+			}
+		}
+
+		public static Action CapturedOutVarInShortCircuit(Dictionary<int, string> d)
+		{
+			// Note: needs reasoning about "definitely assigned if true"
+			// to ensure that the value is initialized when the delegate is declared.
+			if (d.Count > 2 && d.TryGetValue(42, out string value)) {
+				return delegate {
+					Console.WriteLine(value);
+				};
+			}
+			return null;
+		}
+	}
+}

ICSharpCode.Decompiler/FlowAnalysis/DataFlowVisitor.cs

@@ -603,16 +603,60 @@ namespace ICSharpCode.Decompiler.FlowAnalysis
 		protected internal override void VisitIfInstruction(IfInstruction inst)
 		{
 			DebugStartPoint(inst);
-			inst.Condition.AcceptVisitor(this);
-			State branchState = state.Clone();
+			var (beforeThen, beforeElse) = EvaluateCondition(inst.Condition);
+			state = beforeThen;
 			inst.TrueInst.AcceptVisitor(this);
 			State afterTrueState = state;
-			state = branchState;
+			state = beforeElse;
 			inst.FalseInst.AcceptVisitor(this);
 			state.JoinWith(afterTrueState);
 			DebugEndPoint(inst);
 		}
 
+		/// <summary>
+		/// Evaluates the condition of an if.
+		/// </summary>
+		/// <returns>
+		/// A pair of:
+		///  * The state after the condition evaluates to true
+		///  * The state after the condition evaluates to false
+		/// </returns>
+		/// <remarks>
+		/// <c>this.state</c> is invalid after this function was called, and must be overwritten
+		/// with one of the return values.
+		/// </remarks>
+		(State OnTrue, State OnFalse) EvaluateCondition(ILInstruction inst)
+		{
+			if (inst is IfInstruction ifInst) {
+				// 'if (a?b:c)' or similar.
+				// This also includes conditions that are logic.not, logic.and, logic.or.
+				DebugStartPoint(ifInst);
+				var (beforeThen, beforeElse) = EvaluateCondition(ifInst.Condition);
+				state = beforeThen;
+				var (afterThenTrue, afterThenFalse) = EvaluateCondition(ifInst.TrueInst);
+				state = beforeElse;
+				var (afterElseTrue, afterElseFalse) = EvaluateCondition(ifInst.FalseInst);
+
+				var onTrue = afterThenTrue;
+				onTrue.JoinWith(afterElseTrue);
+				var onFalse = afterThenFalse;
+				onFalse.JoinWith(afterElseFalse);
+
+				DebugEndPoint(ifInst);
+				return (onTrue, onFalse);
+			} else if (inst is LdcI4 constant) {
+				if (constant.Value == 0) {
+					return (bottomState.Clone(), state);
+				} else {
+					return (state, bottomState.Clone());
+				}
+			} else {
+				// other kind of condition
+				inst.AcceptVisitor(this);
+				return (state, state.Clone());
+			}
+		}
+
 		protected internal override void VisitNullCoalescingInstruction(NullCoalescingInstruction inst)
 		{
 			HandleBinaryWithOptionalEvaluation(inst, inst.ValueInst, inst.FallbackInst);