Add null-ckeck analyzer and code fix

Source/CSharpEssentials.Tests/CSharpEssentials.Tests.csproj

@@ -59,6 +59,8 @@
     <Compile Include="ConvertToInterpolatedString\ConvertToInterpolatedStringRefactoringTests.cs" />
     <Compile Include="DocumentExtensions.cs" />
     <Compile Include="ExpandExpressionBodiedMember\ExpandExpressionBodiedMemberRefactoringTests.cs" />
+    <Compile Include="NullCheckToNullConditional\NullCheckToNullConditionalAnalyzerTests.cs" />
+    <Compile Include="NullCheckToNullConditional\NullCheckToNullConditionalCodeFixTests.cs" />
     <Compile Include="Properties\AssemblyInfo.cs" />
     <Compile Include="UseExpressionBodiedMember\UseExpressionBodiedMemberAnalyzerTests.cs" />
     <Compile Include="UseExpressionBodiedMember\UseExpressionBodiedMemberCodeFixTests.cs" />

Source/CSharpEssentials.Tests/NullCheckToNullConditional/NullCheckToNullConditionalAnalyzerTests.cs

@@ -0,0 +1,54 @@
+using RoslynNUnitLight;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using Microsoft.CodeAnalysis.Diagnostics;
+using Microsoft.CodeAnalysis;
+using CSharpEssentials.NullCheckToNullConditional;
+using NUnit.Framework;
+
+namespace CSharpEssentials.Tests.NullCheckToNullConditional
+{
+    class NullCheckToNullConditionalAnalyzerTests : AnalyzerTestFixture
+    {
+        protected override string LanguageName => LanguageNames.CSharp;
+
+        protected override DiagnosticAnalyzer CreateAnalyzer() => new NullCheckToNullConditionalAnalyzer();
+
+        [Test]
+        public void TestNoFixOnComipleError()
+        {
+            const string markup = @"
+class C
+{
+    void M(object o)
+    {
+        if(o.GetType != null){
+            o.GetType.ToString()
+        }
+    }
+}
+";
+            NoDiagnostic(markup, DiagnosticIds.UseNullConditional);
+        }
+
+        [Test]
+        public void TestNoFixOnNoneInvocationBody()
+        {
+            const string markup = @"
+class C
+{
+    object M(object o)
+    {
+        if(o != null){
+            return o;
+        }
+    }
+}
+";
+            NoDiagnostic(markup, DiagnosticIds.UseNullConditional);
+        }
+    }
+}

Source/CSharpEssentials.Tests/NullCheckToNullConditional/NullCheckToNullConditionalCodeFixTests.cs

@@ -0,0 +1,105 @@
+using RoslynNUnitLight;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using Microsoft.CodeAnalysis.CodeRefactorings;
+using Microsoft.CodeAnalysis;
+using CSharpEssentials.NullCheckToNullConditional;
+using NUnit.Framework;
+using Microsoft.CodeAnalysis.CodeFixes;
+using Microsoft.CodeAnalysis.Text;
+using Microsoft.CodeAnalysis.CSharp.Syntax;
+
+namespace CSharpEssentials.Tests.NullCheckToNullConditional
+{
+    class NullCheckToNullConditionalCodeFixTests : CodeFixTestFixture
+    {
+        protected override string LanguageName => LanguageNames.CSharp;
+        protected override CodeFixProvider CreateProvider() => new NullCheckToNullConditionalCodeFix();
+
+        const string codeBase = @"
+class SuperAwesomeCode
+{
+    interface A { B b(); }
+    interface B { C c { get; } }
+    interface C { DHolder this[int i] { get; } }
+    interface DHolder { D d { get; } }
+    interface D { void m(object o1, object o2); MyStruct? myStruct{ get; } }
+    struct MyStruct { int this[int i] => i; }
+    void M(A a, B b, C c, DHolder dHolder, D d, object blah, dynamic dyn)
+    {
+        <<<<<code>>>>>
+    }
+}
+";
+        string InsertCode(string s) => codeBase.Replace("<<<<<code>>>>>", s);
+
+        [Test]
+        public void SimpleTest()
+        {
+            var markupCode = InsertCode("[|if (null != d )  d.m(blah, blah);|]");
+            var expected = InsertCode("d?.m(blah, blah);");
+            TestCodeFix(markupCode, expected, DiagnosticDescriptors.UseNullConditionalMemberAccess);
+        }
+
+        [Test]
+        public void TestPropertyAccessor()
+        {
+            var markupCode = InsertCode("[|if (b != null)  b.c.ToString();|]");
+            var expected = InsertCode("b?.c.ToString();");
+            TestCodeFix(markupCode, expected, DiagnosticDescriptors.UseNullConditionalMemberAccess);
+        }
+
+        [Test]
+        public void TestIndexer()
+        {
+            var markupCode = InsertCode("[|if (b.c != null)  b.c[0].ToString();|]");
+            var expected = InsertCode("b.c?[0].ToString();");
+            TestCodeFix(markupCode, expected, DiagnosticDescriptors.UseNullConditionalMemberAccess);
+        }
+
+        [Test]
+        public void TestNullableValueType()
+        {
+            var markupCode = InsertCode("[|if (d.myStruct != null)  d.myStruct.Value[0].CompareTo(42).ToString();|]");
+            var expected = InsertCode("d.myStruct?[0].CompareTo(42).ToString();");
+            TestCodeFix(markupCode, expected, DiagnosticDescriptors.UseNullConditionalMemberAccess);
+        }
+
+        [Test]
+        public void TestDynamicExpression()
+        {
+            var markupCode = InsertCode("[|if (dyn.x.y.z != null) dyn.x.y.z.m();|]");
+            var expected = InsertCode("dyn.x.y.z?.m();");
+            TestCodeFix(markupCode, expected, DiagnosticDescriptors.UseNullConditionalMemberAccess);
+        }
+
+        [Test]
+        public void TestBlockStatement()
+        {
+            var markupCode = InsertCode("[|if (a.b() != null) { a.b().c[0].ToString(); }|]");
+            var expected = InsertCode("a.b()?.c[0].ToString();");
+            TestCodeFix(markupCode, expected, DiagnosticDescriptors.UseNullConditionalMemberAccess);
+        }
+
+        [Test]
+        public void TestInvocationStartsWith()
+        {
+            var code = InsertCode("[|if (a != null)  a.b().c[1].d.m(blah, blah);|]");
+            var expeced = InsertCode("a?.b().c[1].d.m(blah, blah);");
+
+            Document doc;
+            TextSpan span;
+            TestHelpers.TryGetDocumentAndSpanFromMarkup(code, LanguageNames.CSharp, out doc, out span);
+            var root = doc.GetSyntaxRootAsync().Result;
+            var ifStatement = root.FindNode(span) as IfStatementSyntax;
+            var exp = (ifStatement.Condition as BinaryExpressionSyntax).Left;
+            var chain = (ifStatement.Statement as ExpressionStatementSyntax).Expression;
+            ExpressionSyntax _;
+            Assert.True(NullCheckToNullConditionalCodeFix.MemberAccessChainExpressionStartsWith(chain, exp, out _));
+
+        }
+    }
+}

Source/CSharpEssentials/CSharpEssentials.csproj

@@ -11,6 +11,8 @@
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="ConvertToInterpolatedString\ConvertToInterpolatedStringRefactoring.cs" />
+    <Compile Include="NullCheckToNullConditional\NullCheckToNullConditionalCodeFix.cs" />
+    <Compile Include="NullCheckToNullConditional\NullCheckToNullConditionalAnalyzer.cs" />
     <Compile Include="DiagnosticCategories.cs" />
     <Compile Include="DiagnosticDescriptors.cs" />
     <Compile Include="DiagnosticIds.cs" />

Source/CSharpEssentials/DiagnosticDescriptors.cs

@@ -37,5 +37,22 @@ public static class DiagnosticDescriptors
             category: DiagnosticCategories.Language,
             defaultSeverity: DiagnosticSeverity.Warning,
             isEnabledByDefault: true);
+
+        public static readonly DiagnosticDescriptor UseNullConditionalMemberAccess = new DiagnosticDescriptor(
+            id: DiagnosticIds.UseNullConditional,
+            title: "Replace null-check if statement with null-conditional member access",
+            messageFormat: "Consider replacing the null-check if statement with null-conditional member access",
+            category: DiagnosticCategories.Language,
+            defaultSeverity: DiagnosticSeverity.Info,
+            isEnabledByDefault: true);
+
+        public static readonly DiagnosticDescriptor UseNullConditionalMemberAccessFadedToken = new DiagnosticDescriptor(
+            id: "UseNullConditionalMemberAccessFadedToken",
+            title: UseNullConditionalMemberAccess.Title,
+            messageFormat: UseNullConditionalMemberAccess.MessageFormat,
+            category: DiagnosticCategories.Language,
+            defaultSeverity: DiagnosticSeverity.Hidden,
+            isEnabledByDefault: true,
+            customTags: new[] { WellKnownDiagnosticTags.Unnecessary });
     }
 }

Source/CSharpEssentials/DiagnosticIds.cs

@@ -5,5 +5,6 @@ internal static class DiagnosticIds
         public const string UseNameOf = "CSE0001";
         public const string UseGetterOnlyAutoProperty = "CSE0002";
         public const string UseExpressionBodiedMember = "CSE0003";
+        public const string UseNullConditional = "CSE0004";
     }
 }

Source/CSharpEssentials/NullCheckToNullConditional/NullCheckToNullConditionalAnalyzer.cs

@@ -0,0 +1,59 @@
+using System;
+using System.Threading;
+using System.Threading.Tasks;
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.CodeActions;
+using Microsoft.CodeAnalysis.CodeRefactorings;
+using Microsoft.CodeAnalysis.CSharp;
+using Microsoft.CodeAnalysis.CSharp.Syntax;
+using Microsoft.CodeAnalysis.Formatting;
+using System.Collections.Immutable;
+using Microsoft.CodeAnalysis.Simplification;
+using Microsoft.CodeAnalysis.Diagnostics;
+using Microsoft.CodeAnalysis.Text;
+
+namespace CSharpEssentials.NullCheckToNullConditional
+{
+    [DiagnosticAnalyzer(LanguageNames.CSharp)]
+    public class NullCheckToNullConditionalAnalyzer : DiagnosticAnalyzer
+    {
+        public override ImmutableArray<DiagnosticDescriptor> SupportedDiagnostics => ImmutableArray.Create(DiagnosticDescriptors.UseNullConditionalMemberAccessFadedToken, DiagnosticDescriptors.UseNullConditionalMemberAccess);
+
+        private static async void AnalyzeThat(SyntaxNodeAnalysisContext context)
+        {
+            var ifStatement = context.Node.FindNode(context.Node.Span, getInnermostNodeForTie: true)?.FirstAncestorOrSelf<IfStatementSyntax>();
+            try
+            {
+                if (await NullCheckToNullConditionalCodeFix.GetCodeFixAsync(() => Task.FromResult(context.SemanticModel), ifStatement) != null)
+                {
+                    if (ifStatement.SyntaxTree.IsGeneratedCode(context.CancellationToken))
+                        return;
+                    var fadeoutLocations = ImmutableArray.CreateBuilder<Location>();
+                    fadeoutLocations.Add(Location.Create(context.Node.SyntaxTree, TextSpan.FromBounds(ifStatement.IfKeyword.SpanStart, ifStatement.Statement.SpanStart)));
+
+                    var statementBlock = ifStatement.Statement as BlockSyntax;
+                    if (statementBlock != null)
+                    {
+                        fadeoutLocations.Add(Location.Create(context.Node.SyntaxTree, (statementBlock.OpenBraceToken.Span)));
+                        fadeoutLocations.Add(Location.Create(context.Node.SyntaxTree, (statementBlock.CloseBraceToken.Span)));
+                    }
+                    foreach (var location in fadeoutLocations)
+                    {
+                        context.ReportDiagnostic(Diagnostic.Create(DiagnosticDescriptors.UseNullConditionalMemberAccessFadedToken, location));
+                    }
+                    context.ReportDiagnostic(Diagnostic.Create(DiagnosticDescriptors.UseNullConditionalMemberAccess,
+                        Location.Create(context.Node.SyntaxTree, ifStatement.Span)));
+                }
+            }
+            catch (OperationCanceledException ex) when (ex.CancellationToken == context.CancellationToken)
+            {
+                // we should ignore cancellation exceptions, instead of blowing up the universe!
+            }
+        }
+
+        public override void Initialize(AnalysisContext context)
+        {
+            context.RegisterSyntaxNodeAction(AnalyzeThat, ImmutableArray.Create(SyntaxKind.IfStatement));
+        }
+    }
+}