BUGFIX IDISP003 when assitgned in ctor expression body.

Fix #183.

Author: JohanLarsson

IDisposableAnalyzers.Test/IDISP003DisposeBeforeReassigningTests/Valid.cs

@@ -1308,5 +1308,25 @@ protected virtual void Dispose(bool disposing)
 
             RoslynAssert.Valid(Analyzer, code);
         }
+
+        [Test]
+        public static void AssigningFieldInExpressionBodyCtor()
+        {
+            var code = @"
+namespace N
+{
+    using System;
+    using System.Threading;
+
+    public class C
+    {
+        private readonly IDisposable disposable;
+
+        public C()=> this.disposable = new CancellationTokenSource();
+    }
+}";
+
+            RoslynAssert.Valid(Analyzer, code);
+        }
     }
 }

IDisposableAnalyzers/Helpers/Disposable.IsCreation.cs

@@ -17,6 +17,12 @@ internal static Result IsAlreadyAssignedWithCreated(ExpressionSyntax disposable,
                 return Result.No;
             }
 
+            if (disposable is { Parent: AssignmentExpressionSyntax { Parent: ArrowExpressionClauseSyntax { Parent: ConstructorDeclarationSyntax _} } })
+            {
+                assignedSymbol = null;
+                return Result.No;
+            }
+
             var symbol = semanticModel.GetSymbolSafe(disposable, cancellationToken);
             if (symbol is null)
             {

IDisposableAnalyzers/Helpers/Walkers/DisposableWalker.Returns.cs

@@ -3,6 +3,7 @@
     using System.Threading;
     using Gu.Roslyn.AnalyzerExtensions;
     using Microsoft.CodeAnalysis;
+    using Microsoft.CodeAnalysis.CSharp;
     using Microsoft.CodeAnalysis.CSharp.Syntax;
 
     internal sealed partial class DisposableWalker
@@ -48,8 +49,8 @@ private static bool Returns(ExpressionSyntax candidate, Recursion recursion)
             {
                 { Parent: ReturnStatementSyntax _ }
                 => true,
-                { Parent: ArrowExpressionClauseSyntax _ }
-                => true,
+                { Parent: ArrowExpressionClauseSyntax { Parent: { } parent } }
+                => !parent.IsKind(SyntaxKind.ConstructorDeclaration),
                 { Parent: EqualsValueClauseSyntax { Parent: VariableDeclaratorSyntax variableDeclarator } }
                 => recursion.Target(variableDeclarator) is { } target &&
                    Returns(target, recursion),