Properly handle conditional access combined with conditional method.

src/Compilers/CSharp/Portable/Lowering/LocalRewriter/LocalRewriter_ConditionalAccess.cs

@@ -97,10 +97,22 @@ internal BoundExpression RewriteConditionalAccess(BoundConditionalAccess node, b
                     throw ExceptionUtilities.UnexpectedValue(loweringKind);
             }
 
-            BoundExpression loweredAccessExpression = used ?
-                        this.VisitExpression(node.AccessExpression) :
-                        this.VisitUnusedExpression(node.AccessExpression);
+            BoundExpression loweredAccessExpression;
+
+            if (used)
+            {
+                loweredAccessExpression = this.VisitExpression(node.AccessExpression);
+            }
+            else
+            {
+                loweredAccessExpression = this.VisitUnusedExpression(node.AccessExpression);
+                if (loweredAccessExpression == null)
+                {
+                    return null;
+                }
+            }
 
+            Debug.Assert(loweredAccessExpression != null);
             _currentConditionalAccessTarget = previousConditionalAccessTarget;
 
             TypeSymbol type = this.VisitType(node.Type);

src/Compilers/CSharp/Test/Semantic/Semantics/ConditionalOperatorTests.cs

@@ -1400,5 +1400,69 @@ static void Main()
 
             Assert.Null(model.GetSymbolInfo(access).Symbol);
         }
+
+        [Fact(), WorkItem(4615, "https://github.com/dotnet/roslyn/issues/4615")]
+        public void ConditionalAndConditionalMethods()
+        {
+            string source = @"
+class Program
+{
+    static void Main(string[] args)
+    {
+        TestClass.Create().Test();
+        TestClass.Create().Self().Test();
+        System.Console.WriteLine(""---"");
+        TestClass.Create()?.Test();
+        TestClass.Create()?.Self().Test();
+        TestClass.Create()?.Self()?.Test();
+     }
+}
+
+class TestClass
+{
+    [System.Diagnostics.Conditional(""DEBUG"")]
+    public void Test() 
+    { 
+        System.Console.WriteLine(""Test"");
+    }
+
+    public static TestClass Create()
+    {
+        System.Console.WriteLine(""Create"");
+        return new TestClass();
+    }
+
+    public TestClass Self()
+    {
+        System.Console.WriteLine(""Self"");
+        return this;
+    }
+}
+";
+
+            var compilation = CreateCompilationWithMscorlib(source, options: TestOptions.DebugExe,
+                                                            parseOptions: CSharpParseOptions.Default.WithPreprocessorSymbols("DEBUG"));
+
+            CompileAndVerify(compilation, expectedOutput:
+@"Create
+Test
+Create
+Self
+Test
+---
+Create
+Test
+Create
+Self
+Test
+Create
+Self
+Test
+");
+
+            compilation = CreateCompilationWithMscorlib(source, options: TestOptions.ReleaseExe);
+
+            CompileAndVerify(compilation, expectedOutput:"---");
+        }
     }
 }

src/Compilers/VisualBasic/Portable/Lowering/LocalRewriter/LocalRewriter_ExpressionStatement.vb

@@ -26,9 +26,17 @@ Namespace Microsoft.CodeAnalysis.VisualBasic
         End Function
 
         Private Function IsOmittedBoundCall(expression As BoundExpression) As Boolean
-            Return (Me._flags And RewritingFlags.AllowOmissionOfConditionalCalls) = RewritingFlags.AllowOmissionOfConditionalCalls AndAlso
-                expression.Kind = BoundKind.Call AndAlso
-                DirectCast(expression, BoundCall).Method.CallsAreOmitted(expression.Syntax, expression.SyntaxTree)
+            If (Me._flags And RewritingFlags.AllowOmissionOfConditionalCalls) = RewritingFlags.AllowOmissionOfConditionalCalls Then
+                Select Case expression.Kind
+                    Case BoundKind.ConditionalAccess
+                        Return IsOmittedBoundCall(DirectCast(expression, BoundConditionalAccess).AccessExpression)
+
+                    Case BoundKind.Call
+                        Return DirectCast(expression, BoundCall).Method.CallsAreOmitted(expression.Syntax, expression.SyntaxTree)
+                End Select
+            End If
+
+            Return False
         End Function
     End Class
 End Namespace

src/Compilers/VisualBasic/Test/Semantic/Semantics/ConditionalAccessTests.vb

@@ -9432,5 +9432,70 @@ BC32022: 'Public Event TestEvent As Action' is an event, and cannot be called di
             Assert.False(info.CandidateSymbols.Any())
         End Sub
 
+        <Fact(), WorkItem(4615, "https://github.com/dotnet/roslyn/issues/4615")>
+        Public Sub ConditionalAndConditionalMethods()
+
+            Dim compilationDef =
+<compilation>
+    <file name="a.vb"><![CDATA[
+Class Program
+    Shared Sub Main()
+        TestClass.Create().Test()
+        TestClass.Create().Self().Test()
+        System.Console.WriteLine("---")
+        TestClass.Create()?.Test()
+        TestClass.Create()?.Self().Test()
+        TestClass.Create()?.Self()?.Test()
+    End Sub
+End Class
+
+Class TestClass
+    <System.Diagnostics.Conditional("DEBUG")>
+    Public Sub Test()
+        System.Console.WriteLine("Test")
+    End Sub
+
+    Shared Function Create() As TestClass
+        System.Console.WriteLine("Create")
+        return new TestClass()
+    End Function
+
+    Function Self() As TestClass
+        System.Console.WriteLine("Self")
+        return Me
+    End Function
+End Class
+    ]]></file>
+</compilation>
+
+            Dim compilation = CompilationUtils.CreateCompilationWithMscorlib(compilationDef, TestOptions.DebugExe,
+                                                                             parseOptions:=VisualBasicParseOptions.Default.WithPreprocessorSymbols({New KeyValuePair(Of String, Object)("DEBUG", True)}))
+
+            Dim verifier = CompileAndVerify(compilation, expectedOutput:=
+            <![CDATA[
+Create
+Test
+Create
+Self
+Test
+---
+Create
+Test
+Create
+Self
+Test
+Create
+Self
+Test
+]]>)
+
+            compilation = CompilationUtils.CreateCompilationWithMscorlib(compilationDef, TestOptions.ReleaseExe)
+
+            verifier = CompileAndVerify(compilation, expectedOutput:=
+            <![CDATA[
+---
+]]>)
+        End Sub
+
     End Class
 End Namespace