Ensure script compilations properly inherit return type from first compilation

Use ScriptCompilationInfo.ReturnTypeOpt instead of ReturnType when
chaining off a previous compilation to ensure that the derived
ScriptCompilationInfo has the same ReturnType.

src/Compilers/CSharp/Portable/Compilation/CSharpCompilation.cs

@@ -510,7 +510,7 @@ public CSharpCompilation WithScriptCompilationInfo(CSharpScriptCompilationInfo i
                 _options,
                 this.ExternalReferences,
                 info?.PreviousScriptCompilation,
-                info?.ReturnType,
+                info?.ReturnTypeOpt,
                 info?.GlobalsType,
                 info != null,
                 _referenceManager,

src/Compilers/CSharp/Portable/Compilation/CSharpScriptCompilationInfo.cs

@@ -20,7 +20,7 @@ internal CSharpScriptCompilationInfo(CSharpCompilation previousCompilationOpt, T
         internal override Compilation CommonPreviousScriptCompilation => PreviousScriptCompilation;
 
         public CSharpScriptCompilationInfo WithPreviousScriptCompilation(CSharpCompilation compilation) =>
-            (compilation == PreviousScriptCompilation) ? this : new CSharpScriptCompilationInfo(compilation, ReturnType, GlobalsType);
+            (compilation == PreviousScriptCompilation) ? this : new CSharpScriptCompilationInfo(compilation, ReturnTypeOpt, GlobalsType);
 
         internal override ScriptCompilationInfo CommonWithPreviousScriptCompilation(Compilation compilation) =>
             WithPreviousScriptCompilation((CSharpCompilation)compilation);

src/Compilers/CSharp/Test/Symbol/Compilation/CompilationAPITests.cs

@@ -1583,6 +1583,7 @@ class A
         }
 
         [WorkItem(8506, "https://github.com/dotnet/roslyn/issues/8506")]
+        [WorkItem(17403, "https://github.com/dotnet/roslyn/issues/17403")]
         [Fact]
         public void CrossCorlibSystemObjectReturnType_Script()
         {
@@ -1592,21 +1593,42 @@ public void CrossCorlibSystemObjectReturnType_Script()
             //
             // In the original bug, Xamarin iOS, Android, and Mac Mobile profile corlibs were
             // realistic cross-compilation targets.
-            var compilation = CSharpCompilation.CreateScriptCompilation(
-                "submission-assembly",
-                references: new [] { MinAsyncCorlibRef },
+
+            void AssertCompilationCorlib(CSharpCompilation compilation)
+            {
+                Assert.True(compilation.IsSubmission);
+
+                var taskOfT = compilation.GetWellKnownType(WellKnownType.System_Threading_Tasks_Task_T);
+                var taskOfObject = taskOfT.Construct(compilation.ObjectType);
+                var entryPoint = compilation.GetEntryPoint(default(CancellationToken));
+
+                Assert.Same(compilation.ObjectType.ContainingAssembly, taskOfT.ContainingAssembly);
+                Assert.Same(compilation.ObjectType.ContainingAssembly, taskOfObject.ContainingAssembly);
+                Assert.Equal(taskOfObject, entryPoint.ReturnType);
+            }
+
+            var firstCompilation = CSharpCompilation.CreateScriptCompilation(
+                "submission-assembly-1",
+                references: new[] { MinAsyncCorlibRef },
                 syntaxTree: Parse("true", options: TestOptions.Script)
             ).VerifyDiagnostics();
 
-            Assert.True(compilation.IsSubmission);
+            AssertCompilationCorlib(firstCompilation);
+
+            var secondCompilation = CSharpCompilation.CreateScriptCompilation(
+                "submission-assembly-2",
+                previousScriptCompilation: firstCompilation,
+                syntaxTree: Parse("false", options: TestOptions.Script))
+                .WithScriptCompilationInfo(new CSharpScriptCompilationInfo(firstCompilation, null, null))
+                .VerifyDiagnostics();
+
+            AssertCompilationCorlib(secondCompilation);
 
-            var taskOfT = compilation.GetWellKnownType(WellKnownType.System_Threading_Tasks_Task_T);
-            var taskOfObject = taskOfT.Construct(compilation.ObjectType);
-            var entryPoint = compilation.GetEntryPoint(default(CancellationToken));
+            Assert.Same(firstCompilation.ObjectType, secondCompilation.ObjectType);
 
-            Assert.Same(compilation.ObjectType.ContainingAssembly, taskOfT.ContainingAssembly);
-            Assert.Same(compilation.ObjectType.ContainingAssembly, taskOfObject.ContainingAssembly);
-            Assert.Equal(taskOfObject, entryPoint.ReturnType);
+            Assert.Null(new CSharpScriptCompilationInfo(null, null, null)
+                .WithPreviousScriptCompilation(firstCompilation)
+                .ReturnTypeOpt);
         }
 
         [WorkItem(3719, "https://github.com/dotnet/roslyn/issues/3719")]

src/Compilers/VisualBasic/Portable/Compilation/VisualBasicCompilation.vb

@@ -669,7 +669,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic
                 _embeddedTrees,
                 _declarationTable,
                 info?.PreviousScriptCompilation,
-                info?.ReturnType,
+                info?.ReturnTypeOpt,
                 info?.GlobalsType,
                 info IsNot Nothing,
                 _referenceManager,

src/Compilers/VisualBasic/Portable/Compilation/VisualBasicScriptCompilationInfo.vb

@@ -21,7 +21,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic
         End Property
 
         Public Shadows Function WithPreviousScriptCompilation(compilation As VisualBasicCompilation) As VisualBasicScriptCompilationInfo
-            Return If(compilation Is PreviousScriptCompilation, Me, New VisualBasicScriptCompilationInfo(compilation, ReturnType, GlobalsType))
+            Return If(compilation Is PreviousScriptCompilation, Me, New VisualBasicScriptCompilationInfo(compilation, ReturnTypeOpt, GlobalsType))
         End Function
 
         Friend Overrides Function CommonWithPreviousScriptCompilation(compilation As Compilation) As ScriptCompilationInfo

src/Compilers/VisualBasic/Test/Semantic/Compilation/CompilationAPITests.vb

@@ -1544,6 +1544,7 @@ End Class
         End Sub
 
         <WorkItem(8506, "https://github.com/dotnet/roslyn/issues/8506")>
+        <WorkItem(17403, "https://github.com/dotnet/roslyn/issues/17403")>
         <Fact()>
         Public Sub CrossCorlibSystemObjectReturnType_Script()
             ' MinAsyncCorlibRef corlib Is used since it provides just enough corlib type definitions
@@ -1552,21 +1553,40 @@ End Class
             '
             ' In the original bug, Xamarin iOS, Android, And Mac Mobile profile corlibs were
             ' realistic cross-compilation targets.
-            Dim compilation = VisualBasicCompilation.CreateScriptCompilation(
-                "submission-assembly",
+
+            Dim AssertCompilationCorlib As Action(Of VisualBasicCompilation) =
+                Sub(compilation As VisualBasicCompilation)
+                    Assert.True(compilation.IsSubmission)
+
+                    Dim taskOfT = compilation.GetWellKnownType(WellKnownType.System_Threading_Tasks_Task_T)
+                    Dim taskOfObject = taskOfT.Construct(compilation.ObjectType)
+                    Dim entryPoint = compilation.GetEntryPoint(Nothing)
+
+                    Assert.Same(compilation.ObjectType.ContainingAssembly, taskOfT.ContainingAssembly)
+                    Assert.Same(compilation.ObjectType.ContainingAssembly, taskOfObject.ContainingAssembly)
+                    Assert.Equal(taskOfObject, entryPoint.ReturnType)
+                End Sub
+
+            Dim firstCompilation = VisualBasicCompilation.CreateScriptCompilation(
+                "submission-assembly-1",
                 references:={MinAsyncCorlibRef},
                 syntaxTree:=Parse("? True", options:=TestOptions.Script)
             ).VerifyDiagnostics()
 
-            Assert.True(compilation.IsSubmission)
+            AssertCompilationCorlib(firstCompilation)
+
+            Dim secondCompilation = VisualBasicCompilation.CreateScriptCompilation(
+                "submission-assembly-2",
+                previousScriptCompilation:=firstCompilation,
+                syntaxTree:=Parse("? False", options:=TestOptions.Script)
+            ).WithScriptCompilationInfo(New VisualBasicScriptCompilationInfo(firstCompilation, Nothing, Nothing)
+            ).VerifyDiagnostics()
+
+            AssertCompilationCorlib(secondCompilation)
 
-            Dim taskOfT = compilation.GetWellKnownType(WellKnownType.System_Threading_Tasks_Task_T)
-            Dim taskOfObject = taskOfT.Construct(compilation.ObjectType)
-            Dim entryPoint = compilation.GetEntryPoint(Nothing)
+            Assert.Same(firstCompilation.ObjectType, secondCompilation.ObjectType)
 
-            Assert.Same(compilation.ObjectType.ContainingAssembly, taskOfT.ContainingAssembly)
-            Assert.Same(compilation.ObjectType.ContainingAssembly, taskOfObject.ContainingAssembly)
-            Assert.Equal(taskOfObject, entryPoint.ReturnType)
+            Assert.Null(New VisualBasicScriptCompilationInfo(Nothing, Nothing, Nothing).WithPreviousScriptCompilation(firstCompilation).ReturnTypeOpt)
         End Sub
 
         <WorkItem(3719, "https://github.com/dotnet/roslyn/issues/3719")>