VB: Do not use overload resolution while lowering interpolated strings

src/Compilers/VisualBasic/Portable/Binding/Binder_Conversions.vb

@@ -1618,7 +1618,9 @@ DoneWithDiagnostics:
 
             If (convKind And ConversionKind.InterpolatedString) = ConversionKind.InterpolatedString Then
                 Debug.Assert(targetType.Equals(Compilation.GetWellKnownType(WellKnownType.System_IFormattable)) OrElse targetType.Equals(Compilation.GetWellKnownType(WellKnownType.System_FormattableString)))
-                Return New BoundConversion(tree, node, ConversionKind.InterpolatedString, False, isExplicit, targetType)
+                Return New BoundConversion(tree,
+                                           BindUnconvertedInterpolatedStringToFormattable(tree, node, targetType, diagnostics),
+                                           ConversionKind.InterpolatedString, False, isExplicit, targetType)
             End If
 
             Return node

src/Compilers/VisualBasic/Portable/Binding/Binder_Expressions.vb

@@ -1400,6 +1400,10 @@ Namespace Microsoft.CodeAnalysis.VisualBasic
                         Throw ExceptionUtilities.UnexpectedValue(propertyAccess.AccessKind)
                 End Select
 
+            ElseIf expr.Kind = BoundKind.InterpolatedStringExpression Then
+
+                expr = BindUnconvertedInterpolatedStringToString(DirectCast(expr, BoundInterpolatedStringExpression), diagnostics)
+
             ElseIf expr.IsLateBound() Then
 
                 Select Case expr.GetLateBoundAccessKind()

src/Compilers/VisualBasic/Portable/Binding/Binder_InterpolatedString.vb

@@ -29,7 +29,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic
                 End Select
             Next
 
-            Return New BoundInterpolatedStringExpression(syntax, contentBuilder.ToImmutableAndFree(), binder:=Me, type:=GetSpecialType(SpecialType.System_String, syntax, diagnostics))
+            Return New BoundInterpolatedStringExpression(syntax, contentBuilder.ToImmutableAndFree(), constructionOpt:=Nothing, type:=GetSpecialType(SpecialType.System_String, syntax, diagnostics))
 
         End Function
 
@@ -72,5 +72,174 @@ Namespace Microsoft.CodeAnalysis.VisualBasic
 
         End Function
 
+        Private Function BindUnconvertedInterpolatedStringToString(node As BoundInterpolatedStringExpression, diagnostics As BindingDiagnosticBag) As BoundExpression
+
+            Debug.Assert(node.Type.SpecialType = SpecialType.System_String)
+
+            ' We lower an interpolated string into an invocation of String.Format or System.Runtime.CompilerServices.FormattableStringFactory.Create.
+            ' For example, we translate the expression:
+            '
+            '     $"Jenny, don't change your number: {phoneNumber:###-####}."
+            '
+            ' into
+            '
+            '     String.Format("Jenny, don't change your number: {0:###-####}.", phoneNumber)
+            '
+            ' TODO: A number of optimizations would be beneficial in the generated code.
+            ' 
+            ' (1) If there is no width or format, and the argument is a value type, call .ToString()
+            '     on it directly so that we avoid the boxing overhead.
+            '
+            ' (2) For the built-in types, we can use .ToString(string format) for some format strings.
+            '     Detect those cases that can be handled that way and take advantage of them.
+            If node.IsEmpty OrElse Not node.HasInterpolations Then
+                Return node
+            End If
+
+            Return node.Update(node.Contents,
+                               constructionOpt:=TryInvokeInterpolatedStringFactory(node,
+                                                                                   factoryType:=node.Type,
+                                                                                   factoryMethodName:="Format",
+                                                                                   targetType:=node.Type,
+                                                                                   diagnostics),
+                               node.Type)
+        End Function
+
+        Private Function BindUnconvertedInterpolatedStringToFormattable(syntax As SyntaxNode, node As BoundInterpolatedStringExpression, targetType As TypeSymbol, diagnostics As BindingDiagnosticBag) As BoundExpression
+
+            Debug.Assert(targetType.Equals(Compilation.GetWellKnownType(WellKnownType.System_FormattableString)) OrElse
+                         targetType.Equals(Compilation.GetWellKnownType(WellKnownType.System_IFormattable)))
+
+            ' We lower an interpolated string into an invocation of System.Runtime.CompilerServices.FormattableStringFactory.Create.
+            ' For example, we translate the expression:
+            '
+            '     $"Jenny, don't change your number: {phoneNumber:###-####}."
+            '
+            ' into
+            '
+            '     FormattableStringFactory.Create("Jenny, don't change your number: {0:###-####}.", phoneNumber)
+            '
+            ' TODO: A number of optimizations would be beneficial in the generated code.
+            ' 
+            ' (1) If there is no width or format, and the argument is a value type, call .ToString()
+            '     on it directly so that we avoid the boxing overhead.
+            '
+            ' (2) For the built-in types, we can use .ToString(string format) for some format strings.
+            '     Detect those cases that can be handled that way and take advantage of them.
+
+            Return node.Update(node.Contents,
+                               constructionOpt:=TryInvokeInterpolatedStringFactory(node,
+                                                                                   factoryType:=GetWellKnownType(WellKnownType.System_Runtime_CompilerServices_FormattableStringFactory, syntax, diagnostics),
+                                                                                   factoryMethodName:="Create",
+                                                                                   targetType,
+                                                                                   diagnostics),
+                               node.Type)
+        End Function
+
+        Private Function TryInvokeInterpolatedStringFactory(node As BoundInterpolatedStringExpression, factoryType As TypeSymbol, factoryMethodName As String, targetType As TypeSymbol, diagnostics As BindingDiagnosticBag) As BoundExpression
+
+            Dim hasErrors As Boolean = False
+
+            If factoryType.IsErrorType() OrElse
+               node.HasErrors OrElse
+               node.Contents.OfType(Of BoundInterpolation)().Any(
+                    Function(interpolation) interpolation.Expression.HasErrors OrElse
+                                            (interpolation.AlignmentOpt IsNot Nothing AndAlso
+                                             Not (interpolation.AlignmentOpt.IsConstant AndAlso interpolation.AlignmentOpt.ConstantValueOpt.IsIntegral))) Then
+                Return Nothing
+            End If
+
+            Dim lookup = LookupResult.GetInstance()
+            Dim useSiteInfo = GetNewCompoundUseSiteInfo(diagnostics)
+
+            LookupMember(lookup, factoryType, factoryMethodName, 0, LookupOptions.MustNotBeInstance Or LookupOptions.MethodsOnly Or LookupOptions.AllMethodsOfAnyArity, useSiteInfo)
+
+            diagnostics.Add(node, useSiteInfo)
+
+            If lookup.Kind = LookupResultKind.Inaccessible Then
+                hasErrors = True
+            ElseIf Not lookup.IsGood Then
+                lookup.Free()
+                GoTo Report_ERR_InterpolatedStringFactoryError
+            End If
+
+            Dim methodGroup = New BoundMethodGroup(node.Syntax, Nothing, lookup.Symbols.ToDowncastedImmutable(Of MethodSymbol), lookup.Kind, Nothing, QualificationKind.QualifiedViaTypeName).MakeCompilerGenerated()
+            lookup.Free()
+
+            Dim formatStringBuilderHandle = PooledStringBuilder.GetInstance()
+            Dim arguments = ArrayBuilder(Of BoundExpression).GetInstance()
+            Dim interpolationOrdinal = -1
+
+            arguments.Add(Nothing) ' Placeholder for format string.
+
+            For Each item In node.Contents
+
+                Select Case item.Kind
+
+                    Case BoundKind.Literal
+
+                        formatStringBuilderHandle.Builder.Append(DirectCast(item, BoundLiteral).Value.StringValue)
+
+                    Case BoundKind.Interpolation
+
+                        interpolationOrdinal += 1
+
+                        Dim interpolation = DirectCast(item, BoundInterpolation)
+
+                        With formatStringBuilderHandle.Builder
+
+                            .Append("{"c)
+
+                            .Append(interpolationOrdinal.ToString(Globalization.CultureInfo.InvariantCulture))
+
+                            If interpolation.AlignmentOpt IsNot Nothing Then
+                                Debug.Assert(interpolation.AlignmentOpt.IsConstant AndAlso interpolation.AlignmentOpt.ConstantValueOpt.IsIntegral)
+                                .Append(","c)
+                                .Append(interpolation.AlignmentOpt.ConstantValueOpt.Int64Value.ToString(Globalization.CultureInfo.InvariantCulture))
+                            End If
+
+                            If interpolation.FormatStringOpt IsNot Nothing Then
+                                .Append(":")
+                                .Append(interpolation.FormatStringOpt.Value.StringValue)
+                            End If
+
+                            .Append("}"c)
+                        End With
+
+                        arguments.Add(interpolation.Expression)
+
+                    Case Else
+                        Throw ExceptionUtilities.Unreachable()
+                End Select
+
+            Next
+
+            arguments(0) = CreateStringLiteral(node.Syntax, formatStringBuilderHandle.ToStringAndFree(), compilerGenerated:=True, diagnostics)
+
+            Dim result As BoundExpression = MakeRValue(BindInvocationExpression(node.Syntax,
+                                                                                node.Syntax,
+                                                                                TypeCharacter.None,
+                                                                                methodGroup,
+                                                                                arguments.ToImmutableAndFree(),
+                                                                                Nothing,
+                                                                                diagnostics,
+                                                                                callerInfoOpt:=Nothing,
+                                                                                forceExpandedForm:=True), diagnostics).MakeCompilerGenerated()
+
+            If Not result.Type.Equals(targetType) Then
+                result = ApplyImplicitConversion(node.Syntax, targetType, result, diagnostics).MakeCompilerGenerated()
+            End If
+
+            If hasErrors OrElse result.HasErrors Then
+                GoTo Report_ERR_InterpolatedStringFactoryError
+            End If
+
+            Return result
+
+Report_ERR_InterpolatedStringFactoryError:
+            ReportDiagnostic(diagnostics, node.Syntax, ErrorFactory.ErrorInfo(ERRID.ERR_InterpolatedStringFactoryError, factoryType.Name, factoryMethodName))
+            Return Nothing
+        End Function
+
     End Class
 End Namespace

src/Compilers/VisualBasic/Portable/Binding/Binder_XmlLiterals.vb

@@ -1048,7 +1048,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic
         End Function
 
         Private Function CreateStringLiteral(
-                                            syntax As VisualBasicSyntaxNode,
+                                            syntax As SyntaxNode,
                                             str As String,
                                             compilerGenerated As Boolean,
                                             diagnostics As BindingDiagnosticBag,

src/Compilers/VisualBasic/Portable/BoundTree/BoundNodes.xml

@@ -1927,7 +1927,7 @@
     <!-- Type is required for this node type; may not be null -->
     <Field Name="Type" Type="TypeSymbol" Override="true" Null="disallow"/>
     <Field Name="Contents" Type="ImmutableArray(Of BoundNode)"/>
-    <Field Name="Binder" Type="Binder" Null="disallow" />
+    <Field Name="ConstructionOpt" Type="BoundExpression" Null="allow" SkipInVisitor="true"/>
   </Node>
 
   <!-- There is no BoundInterpolatedStringText because we use BoundLiteral of type string for this purpose. -->

src/Compilers/VisualBasic/Portable/Lowering/Diagnostics/DiagnosticsPass_ExpressionLambdas.vb

@@ -405,6 +405,10 @@ lSelect:
             Me._diagnostics.Add(New VBDiagnostic(ErrorFactory.ErrorInfo(code), node.Syntax.GetLocation()))
         End Sub
 
+        Public Overrides Function VisitInterpolatedStringExpression(node As BoundInterpolatedStringExpression) As BoundNode
+            Visit(node.ConstructionOpt)
+            Return MyBase.VisitInterpolatedStringExpression(node)
+        End Function
     End Class
 
 End Namespace