Code fix turns simple lambda into parameterized #119 (#124)

* Code fix turns simple lambda into parameterized #119

* Update CHANGELOG.md

Author: marinasundstrom

CHANGELOG.md

@@ -10,7 +10,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Added
 
-- PR [#117](https://github.com/marinasundstrom/CheckedExceptions/pull/#117) Handle redundant typed catch #114
+- PR [#117](https://github.com/marinasundstrom/CheckedExceptions/pull/#117) Handle redundant typed catch
+- PR [#124](https://github.com/marinasundstrom/CheckedExceptions/pull/#124) Code fix turns simple lambda into parameterized
 
 ### Fixed
 

CheckedExceptions.CodeFixes/AddThrowsAttributeCodeFixProvider.cs

@@ -158,11 +158,19 @@ private async Task<Document> AddThrowsAttributeAsync(Document document, SyntaxNo
         }
         else if (ancestor is LambdaExpressionSyntax lambdaExpression)
         {
+            if (existingAttributeList is null && lambdaExpression is SimpleLambdaExpressionSyntax simpleLambda)
+            {
+                lambdaExpression = ParenthesizedLambdaExpression(
+                    ParameterList(
+                        SeparatedList([simpleLambda.Parameter])),
+                    simpleLambda.Body);
+            }
+
             lambdaExpression = existingAttributeList is not null
                 ? lambdaExpression.ReplaceNode(existingAttributeList!, attributeList)
                 : lambdaExpression
                     .WithoutLeadingTrivia()
-                    .AddAttributeLists(attributeList);
+                    .AddAttributeLists(attributeList.WithoutTrailingTrivia());
 
             newAncestor = lambdaExpression
                     .WithLeadingTrivia(ancestor.GetLeadingTrivia())

CheckedExceptions.Tests/CodeFixes/AddThrowsAttributeCodeFixProviderTests.cs

@@ -153,8 +153,7 @@ public class TestClass
         [Throws(typeof(ArgumentNullException))]
         public void TestMethod()
         {
-            Action action = [Throws(typeof(ArgumentNullException))]
-            () =>
+            Action action = [Throws(typeof(ArgumentNullException))] () =>
             {
                 // Should trigger THROW001
                 throw new ArgumentNullException();
@@ -172,6 +171,60 @@ public void TestMethod()
         await Verifier.VerifyCodeFixAsync(testCode, expectedDiagnostic, fixedCode, expectedIncrementalIterations: 2);
     }
 
+    [Fact]
+    public async Task AddsThrowsAttribute_ToSimpleLambda_TurnIntoParameterizedLambda()
+    {
+        var testCode = /* lang=c#-test */  """
+using System;
+using System.Linq;
+
+namespace TestNamespace
+{
+    public class TestClass
+    {
+        public void TestMethod()
+        {
+            Action<int> action = x => 
+            {
+                // Should trigger THROW001
+                throw new ArgumentNullException();
+            };
+            
+            action(42);
+        }
+    }
+}
+""";
+
+        var fixedCode = /* lang=c#-test */  """
+using System;
+using System.Linq;
+
+namespace TestNamespace
+{
+    public class TestClass
+    {
+        [Throws(typeof(ArgumentNullException))]
+        public void TestMethod()
+        {
+            Action<int> action = [Throws(typeof(ArgumentNullException))] (x) =>
+            {
+                // Should trigger THROW001
+                throw new ArgumentNullException();
+            };
+
+            action(42);
+        }
+    }
+}
+""";
+
+        var expectedDiagnostic = Verifier.UnhandledException("ArgumentNullException")
+            .WithSpan(13, 17, 13, 51);
+
+        await Verifier.VerifyCodeFixAsync(testCode, expectedDiagnostic, fixedCode, expectedIncrementalIterations: 2);
+    }
+
     [Fact]
     public async Task AddsThrowsAttribute_ToLocalFunction_WhenUnhandledExceptionThrown()
     {