Recognize condition with logical negation

src/EditorFeatures/CSharpTest/UseNullPropagation/UseNullPropagationTests.cs

@@ -506,7 +506,7 @@ void M(C c)
 
         [WorkItem(23043, "https://github.com/dotnet/roslyn/issues/23043")]
         [Fact, Trait(Traits.Feature, Traits.Features.CodeActionsUseNullPropagation)]
-        public async Task TestWithNullableTypeAndReferenceEquals()
+        public async Task TestWithNullableTypeAndReferenceEquals1()
         {
             await TestInRegularAndScriptAsync(
 @"
@@ -531,7 +531,7 @@ void M(C c)
 
         [WorkItem(23043, "https://github.com/dotnet/roslyn/issues/23043")]
         [Fact, Trait(Traits.Feature, Traits.Features.CodeActionsUseNullPropagation)]
-        public async Task TestWithNullableTypeAndReferenceEqualsReversed()
+        public async Task TestWithNullableTypeAndReferenceEquals2()
         {
             await TestInRegularAndScriptAsync(
 @"
@@ -556,7 +556,7 @@ void M(C c)
 
         [WorkItem(23043, "https://github.com/dotnet/roslyn/issues/23043")]
         [Fact, Trait(Traits.Feature, Traits.Features.CodeActionsUseNullPropagation)]
-        public async Task TestWithNullableTypeAndReferenceEqualsWithObject()
+        public async Task TestWithNullableTypeAndReferenceEqualsWithObject1()
         {
             await TestInRegularAndScriptAsync(
 @"
@@ -581,7 +581,7 @@ void M(C c)
 
         [WorkItem(23043, "https://github.com/dotnet/roslyn/issues/23043")]
         [Fact, Trait(Traits.Feature, Traits.Features.CodeActionsUseNullPropagation)]
-        public async Task TestWithNullableTypeAndReferenceEqualsWithObjectReversed()
+        public async Task TestWithNullableTypeAndReferenceEqualsWithObject2()
         {
             await TestInRegularAndScriptAsync(
 @"
@@ -595,6 +595,181 @@ void M(C c)
 }",
 @"
 class C
+{
+    public int? f;
+    void M(C c)
+    {
+        int? x = c?.f;
+    }
+}");
+        }
+
+        [WorkItem(23043, "https://github.com/dotnet/roslyn/issues/23043")]
+        [Fact, Trait(Traits.Feature, Traits.Features.CodeActionsUseNullPropagation)]
+        public async Task TestWithNullableTypeAndNotIsNull()
+        {
+            await TestInRegularAndScriptAsync(
+@"
+class C
+{
+    public int? f;
+    void M(C c)
+    {
+        int? x = [||]!(c is null) ? c.f : null;
+    }
+}",
+@"
+class C
+{
+    public int? f;
+    void M(C c)
+    {
+        int? x = c?.f;
+    }
+}");
+        }
+
+        [WorkItem(23043, "https://github.com/dotnet/roslyn/issues/23043")]
+        [Fact, Trait(Traits.Feature, Traits.Features.CodeActionsUseNullPropagation)]
+        public async Task TestWithNullableTypeAndLogicalNotReferenceEquals1()
+        {
+            await TestInRegularAndScriptAsync(
+@"
+class C
+{
+    public int? f;
+    void M(C c)
+    {
+        int? x = [||]!ReferenceEquals(c, null) ? c.f : null;
+    }
+}",
+@"
+class C
+{
+    public int? f;
+    void M(C c)
+    {
+        int? x = c?.f;
+    }
+}");
+        }
+
+        [WorkItem(23043, "https://github.com/dotnet/roslyn/issues/23043")]
+        [Fact, Trait(Traits.Feature, Traits.Features.CodeActionsUseNullPropagation)]
+        public async Task TestWithNullableTypeAndLogicalNotReferenceEquals2()
+        {
+            await TestInRegularAndScriptAsync(
+@"
+class C
+{
+    public int? f;
+    void M(C c)
+    {
+        int? x = [||]!ReferenceEquals(null, c) ? c.f : null;
+    }
+}",
+@"
+class C
+{
+    public int? f;
+    void M(C c)
+    {
+        int? x = c?.f;
+    }
+}");
+        }
+
+        [WorkItem(23043, "https://github.com/dotnet/roslyn/issues/23043")]
+        [Fact, Trait(Traits.Feature, Traits.Features.CodeActionsUseNullPropagation)]
+        public async Task TestWithNullableTypeAndLogicalNotReferenceEqualsWithObject1()
+        {
+            await TestInRegularAndScriptAsync(
+@"
+class C
+{
+    public int? f;
+    void M(C c)
+    {
+        int? x = [||]!object.ReferenceEquals(c, null) ? c.f : null;
+    }
+}",
+@"
+class C
+{
+    public int? f;
+    void M(C c)
+    {
+        int? x = c?.f;
+    }
+}");
+        }
+
+        [WorkItem(23043, "https://github.com/dotnet/roslyn/issues/23043")]
+        [Fact, Trait(Traits.Feature, Traits.Features.CodeActionsUseNullPropagation)]
+        public async Task TestWithNullableTypeAndLogicalNotReferenceEqualsWithObject2()
+        {
+            await TestInRegularAndScriptAsync(
+@"
+class C
+{
+    public int? f;
+    void M(C c)
+    {
+        int? x = [||]!object.ReferenceEquals(null, c) ? c.f : null;
+    }
+}",
+@"
+class C
+{
+    public int? f;
+    void M(C c)
+    {
+        int? x = c?.f;
+    }
+}");
+        }
+
+        [WorkItem(23043, "https://github.com/dotnet/roslyn/issues/23043")]
+        [Fact, Trait(Traits.Feature, Traits.Features.CodeActionsUseNullPropagation)]
+        public async Task TestEqualsWithLogicalNot()
+        {
+            await TestInRegularAndScriptAsync(
+@"
+class C
+{
+    public int? f;
+    void M(C c)
+    {
+        int? x = [||]!(c == null) ? c.f : null;
+    }
+}",
+@"
+class C
+{
+    public int? f;
+    void M(C c)
+    {
+        int? x = c?.f;
+    }
+}");
+        }
+
+        [WorkItem(23043, "https://github.com/dotnet/roslyn/issues/23043")]
+        [Fact, Trait(Traits.Feature, Traits.Features.CodeActionsUseNullPropagation)]
+        public async Task TestNotEqualsWithLogicalNot()
+        {
+            await TestInRegularAndScriptAsync(
+@"
+class C
+{
+    public int? f;
+    void M(C c)
+    {
+        int? x = [||]!(c != null) ? null : c.f;
+    }
+}",
+@"
+class C
 {
     public int? f;
     void M(C c)

src/EditorFeatures/VisualBasicTest/UseNullPropagation/UseNullPropagationTests.vb

@@ -326,7 +326,7 @@ End Class")
 
         <WorkItem(23043, "https://github.com/dotnet/roslyn/issues/23043")>
         <Fact, Trait(Traits.Feature, Traits.Features.CodeActionsUseNullPropagation)>
-        Public Async Function TestWithNullableTypeAndReferenceEquals() As Task
+        Public Async Function TestWithNullableTypeAndReferenceEquals1() As Task
             Await TestInRegularAndScriptAsync(
 "
 Imports System
@@ -348,7 +348,7 @@ End Class")
 
         <WorkItem(23043, "https://github.com/dotnet/roslyn/issues/23043")>
         <Fact, Trait(Traits.Feature, Traits.Features.CodeActionsUseNullPropagation)>
-        Public Async Function TestWithNullableTypeAndReferenceEqualsReversed() As Task
+        Public Async Function TestWithNullableTypeAndReferenceEquals2() As Task
             Await TestInRegularAndScriptAsync(
 "
 Imports System
@@ -370,7 +370,7 @@ End Class")
 
         <WorkItem(23043, "https://github.com/dotnet/roslyn/issues/23043")>
         <Fact, Trait(Traits.Feature, Traits.Features.CodeActionsUseNullPropagation)>
-        Public Async Function TestWithNullableTypeAndReferenceEqualsWithObject() As Task
+        Public Async Function TestWithNullableTypeAndReferenceEqualsWithObject1() As Task
             Await TestInRegularAndScriptAsync(
 "
 Imports System
@@ -392,7 +392,7 @@ End Class")
 
         <WorkItem(23043, "https://github.com/dotnet/roslyn/issues/23043")>
         <Fact, Trait(Traits.Feature, Traits.Features.CodeActionsUseNullPropagation)>
-        Public Async Function TestWithNullableTypeAndReferenceEqualsWithObjectReversed() As Task
+        Public Async Function TestWithNullableTypeAndReferenceEqualsWithObject2() As Task
             Await TestInRegularAndScriptAsync(
 "
 Imports System
@@ -439,5 +439,116 @@ Class C
     End Sub
 End Class")
         End Function
+
+        <WorkItem(23043, "https://github.com/dotnet/roslyn/issues/23043")>
+        <Fact, Trait(Traits.Feature, Traits.Features.CodeActionsUseNullPropagation)>
+        Public Async Function TestWithNullableTypeAndLogicalNotReferenceEquals1() As Task
+            Await TestInRegularAndScriptAsync(
+"
+Imports System
+
+Class C
+    Sub M(o As Object)
+        Dim v = [||]If (Not ReferenceEquals(o, Nothing), o.ToString(), Nothing)
+    End Sub
+End Class",
+"
+Imports System
+
+Class C
+    Sub M(o As Object)
+        Dim v = o?.ToString()
+    End Sub
+End Class")
+        End Function
+
+        <WorkItem(23043, "https://github.com/dotnet/roslyn/issues/23043")>
+        <Fact, Trait(Traits.Feature, Traits.Features.CodeActionsUseNullPropagation)>
+        Public Async Function TestWithNullableTypeAndLogicalNotReferenceEquals2() As Task
+            Await TestInRegularAndScriptAsync(
+"
+Imports System
+
+Class C
+    Sub M(o As Object)
+        Dim v = [||]If (Not ReferenceEquals(Nothing, o), o.ToString(), Nothing)
+    End Sub
+End Class",
+"
+Imports System
+
+Class C
+    Sub M(o As Object)
+        Dim v = o?.ToString()
+    End Sub
+End Class")
+        End Function
+
+        <WorkItem(23043, "https://github.com/dotnet/roslyn/issues/23043")>
+        <Fact, Trait(Traits.Feature, Traits.Features.CodeActionsUseNullPropagation)>
+        Public Async Function TestWithNullableTypeAndLogicalNotReferenceEqualsWithObject1() As Task
+            Await TestInRegularAndScriptAsync(
+"
+Imports System
+
+Class C
+    Sub M(o As Object)
+        Dim v = [||]If (Not Object.ReferenceEquals(o, Nothing), o.ToString(), Nothing)
+    End Sub
+End Class",
+"
+Imports System
+
+Class C
+    Sub M(o As Object)
+        Dim v = o?.ToString()
+    End Sub
+End Class")
+        End Function
+
+        <WorkItem(23043, "https://github.com/dotnet/roslyn/issues/23043")>
+        <Fact, Trait(Traits.Feature, Traits.Features.CodeActionsUseNullPropagation)>
+        Public Async Function TestEqualsWithLogicalNot() As Task
+            Await TestInRegularAndScriptAsync(
+"
+Imports System
+
+Class C
+    Sub M(o As Object)
+        Dim v = [||]If (Not (o Is Nothing), o.ToString(), Nothing)
+    End Sub
+End Class",
+"
+Imports System
+
+Class C
+    Sub M(o As Object)
+        Dim v = o?.ToString()
+    End Sub
+End Class")
+        End Function
+
+        <WorkItem(23043, "https://github.com/dotnet/roslyn/issues/23043")>
+        <Fact, Trait(Traits.Feature, Traits.Features.CodeActionsUseNullPropagation)>
+        Public Async Function TestNotEqualsWithLogicalNot() As Task
+            Await TestInRegularAndScriptAsync(
+"
+Imports System
+
+Class C
+    Sub M(o As Object)
+        Dim v = [||]If (Not (o IsNot Nothing), Nothing, o.ToString())
+    End Sub
+End Class",
+"
+Imports System
+
+Class C
+    Sub M(o As Object)
+        Dim v = o?.ToString()
+    End Sub
+End Class")
+        End Function
+
     End Class
 End Namespace

src/Features/Core/Portable/UseNullPropagation/AbstractUseNullPropagationDiagnosticAnalyzer.cs

@@ -100,6 +100,14 @@ private void AnalyzeSyntax(SyntaxNodeAnalysisContext context, INamedTypeSymbol e
 
             conditionNode = syntaxFacts.WalkDownParentheses(conditionNode);
 
+            var conditionIsNegated = false;
+            if (syntaxFacts.IsLogicalNotExpression(conditionNode))
+            {
+                conditionIsNegated = true;
+                conditionNode = syntaxFacts.WalkDownParentheses(
+                    syntaxFacts.GetOperandOfPrefixUnaryExpression(conditionNode));
+            }
+
             var isEqualityLikeCondition = TryAnalyzeCondition(
                 context, syntaxFacts, referenceEqualsMethodOpt, conditionNode,
                 out var conditionPartToCheck, out var isEquals);
@@ -108,6 +116,11 @@ private void AnalyzeSyntax(SyntaxNodeAnalysisContext context, INamedTypeSymbol e
                 return;
             }
 
+            if (conditionIsNegated)
+            {
+                isEquals = !isEquals;
+            }
+
             // Needs to be of the form:
             //      x == null ? null : ...    or
             //      x != null ? ...  : null;