Support the StringSyntax attribute actually being used on an attribute parameter.

src/EditorFeatures/CSharpTest/Classification/SemanticClassifierTests.cs

@@ -3559,6 +3559,35 @@ void Goo()
 EnumMember("IgnorePatternWhitespace"));
         }
 
+        [Theory]
+        [CombinatorialData]
+        public async Task TestRegexOnApiWithStringSyntaxAttribute_Attribute(TestHost testHost)
+        {
+            await TestAsync(
+@"
+using System;
+using System.Diagnostics.CodeAnalysis;
+using System.Text.RegularExpressions;
+
+[AttributeUsage(AttributeTargets.Field)]
+class RegexTestAttribute : Attribute
+{
+    public RegexTestAttribute([StringSyntax(StringSyntaxAttribute.Regex)] string value) { }
+}
+
+class Program
+{
+    [|[RegexTest(@""$\a(?#comment)"")]|]
+    private string field;
+}" + EmbeddedLanguagesTestConstants.StringSyntaxAttributeCodeCSharp,
+testHost,
+Class("RegexTest"),
+Regex.Anchor("$"),
+Regex.OtherEscape("\\"),
+Regex.OtherEscape("a"),
+Regex.Comment("(?#comment)"));
+        }
+
         [Theory]
         [CombinatorialData]
         public async Task TestIncompleteRegexLeadingToStringInsideSkippedTokensInsideADirective(TestHost testHost)

src/EditorFeatures/VisualBasicTest/Classification/SemanticClassifierTests.vb

@@ -654,6 +654,39 @@ Regex.Anchor("z"),
 Regex.Grouping(")"))
         End Function
 
+        <WpfTheory, CombinatorialData>
+        Public Async Function TestRegexStringSyntaxAttribute_Attribute(testHost As TestHost) As Task
+            Await TestAsync(
+"
+imports system
+imports System.Diagnostics.CodeAnalysis
+imports System.Text.RegularExpressions
+
+<AttributeUsage(AttributeTargets.Field)>
+class RegexTestAttribute 
+    inherits Attribute
+
+    public sub new(<StringSyntax(StringSyntaxAttribute.Regex)> value as string)
+    end sub
+end class
+
+class Program
+    [|<RegexTest(""$(\b\G\z)"")>|]
+    dim field as string
+end class" & EmbeddedLanguagesTestConstants.StringSyntaxAttributeCodeVB,
+                testHost,
+[Class]("RegexTest"),
+Regex.Anchor("$"),
+Regex.Grouping("("),
+Regex.Anchor("\"),
+Regex.Anchor("b"),
+Regex.Anchor("\"),
+Regex.Anchor("G"),
+Regex.Anchor("\"),
+Regex.Anchor("z"),
+Regex.Grouping(")"))
+        End Function
+
         <WpfTheory, CombinatorialData>
         Public Async Function TestRegexStringSyntaxAttribute_Property(testHost As TestHost) As Task
             Await TestAsync(

src/Features/Core/Portable/EmbeddedLanguages/AbstractLanguageDetector.cs

@@ -3,6 +3,7 @@
 // See the LICENSE file in the project root for more information.
 
 using System;
+using System.Diagnostics.CodeAnalysis;
 using System.Text.RegularExpressions;
 using System.Threading;
 using Microsoft.CodeAnalysis.EmbeddedLanguages.LanguageServices;
@@ -150,6 +151,12 @@ private bool IsEmbeddedLanguageStringLiteralToken(SyntaxToken token, SemanticMod
                 if (IsArgumentToParameterWithMatchingStringSyntaxAttribute(semanticModel, argument, cancellationToken, out options))
                     return true;
             }
+            else if (syntaxFacts.IsAttributeArgument(parent.Parent))
+            {
+                var argument = parent.Parent;
+                if (IsArgumentToAttributeParameterWithMatchingStringSyntaxAttribute(semanticModel, argument, cancellationToken, out options))
+                    return true;
+            }
             else
             {
                 var statement = parent.FirstAncestorOrSelf<SyntaxNode>(syntaxFacts.IsStatement);
@@ -167,13 +174,24 @@ private bool IsEmbeddedLanguageStringLiteralToken(SyntaxToken token, SemanticMod
             return false;
         }
 
-        private bool IsArgumentToParameterWithMatchingStringSyntaxAttribute(SemanticModel semanticModel, SyntaxNode argumentNode, CancellationToken cancellationToken, out TOptions options)
+        private bool IsArgumentToAttributeParameterWithMatchingStringSyntaxAttribute(
+            SemanticModel semanticModel, SyntaxNode argument, CancellationToken cancellationToken, out TOptions options)
+        {
+            var parameter = Info.SemanticFacts.FindParameterForAttributeArgument(semanticModel, argument, cancellationToken);
+            return IsParameterWithMatchingStringSyntaxAttribute(semanticModel, argument, parameter, cancellationToken, out options);
+        }
+
+        private bool IsArgumentToParameterWithMatchingStringSyntaxAttribute(SemanticModel semanticModel, SyntaxNode argument, CancellationToken cancellationToken, out TOptions options)
         {
-            var operation = semanticModel.GetOperation(argumentNode, cancellationToken);
-            if (operation is IArgumentOperation { Parameter: { } parameter } &&
-                HasMatchingStringSyntaxAttribute(parameter))
+            var parameter = Info.SemanticFacts.FindParameterForArgument(semanticModel, argument, cancellationToken);
+            return IsParameterWithMatchingStringSyntaxAttribute(semanticModel, argument, parameter, cancellationToken, out options);
+        }
+
+        private bool IsParameterWithMatchingStringSyntaxAttribute(SemanticModel semanticModel, SyntaxNode argument, IParameterSymbol parameter, CancellationToken cancellationToken, out TOptions options)
+        {
+            if (HasMatchingStringSyntaxAttribute(parameter))
             {
-                options = GetOptionsFromSiblingArgument(argumentNode, semanticModel, cancellationToken) ??
+                options = GetOptionsFromSiblingArgument(argument, semanticModel, cancellationToken) ??
                           GetStringSyntaxDefaultOptions();
                 return true;
             }
@@ -190,12 +208,15 @@ private bool IsFieldOrPropertyWithMatchingStringSyntaxAttribute(
                 HasMatchingStringSyntaxAttribute(symbol);
         }
 
-        private bool HasMatchingStringSyntaxAttribute(ISymbol symbol)
+        private bool HasMatchingStringSyntaxAttribute([NotNullWhen(true)] ISymbol? symbol)
         {
-            foreach (var attribute in symbol.GetAttributes())
+            if (symbol != null)
             {
-                if (IsMatchingStringSyntaxAttribute(attribute))
-                    return true;
+                foreach (var attribute in symbol.GetAttributes())
+                {
+                    if (IsMatchingStringSyntaxAttribute(attribute))
+                        return true;
+                }
             }
 
             return false;
@@ -241,18 +262,22 @@ private bool IsMatchingStringSyntaxAttribute(AttributeData attribute)
         }
 
         protected TOptions? GetOptionsFromSiblingArgument(
-            SyntaxNode argumentNode,
+            SyntaxNode argument,
             SemanticModel semanticModel,
             CancellationToken cancellationToken)
         {
             var syntaxFacts = Info.SyntaxFacts;
-            var argumentList = argumentNode.GetRequiredParent();
-            var arguments = syntaxFacts.GetArgumentsOfArgumentList(argumentList);
+            var argumentList = argument.GetRequiredParent();
+            var arguments = syntaxFacts.IsArgument(argument)
+                ? syntaxFacts.GetArgumentsOfArgumentList(argumentList)
+                : syntaxFacts.GetArgumentsOfAttributeArgumentList(argumentList);
             foreach (var siblingArg in arguments)
             {
-                if (siblingArg != argumentNode)
+                if (siblingArg != argument)
                 {
-                    var expr = syntaxFacts.GetExpressionOfArgument(siblingArg);
+                    var expr = syntaxFacts.IsArgument(argument)
+                        ? syntaxFacts.GetExpressionOfArgument(siblingArg)
+                        : syntaxFacts.GetExpressionOfAttributeArgument(siblingArg);
                     if (expr != null)
                     {
                         var exprType = semanticModel.GetTypeInfo(expr, cancellationToken);

src/Workspaces/SharedUtilitiesAndExtensions/Compiler/CSharp/Services/SemanticFacts/CSharpSemanticFacts.cs

@@ -269,8 +269,11 @@ public IEnumerable<ISymbol> GetDeclaredSymbols(
             }
         }
 
-        public IParameterSymbol FindParameterForArgument(SemanticModel semanticModel, SyntaxNode argumentNode, CancellationToken cancellationToken)
-            => ((ArgumentSyntax)argumentNode).DetermineParameter(semanticModel, allowParams: false, cancellationToken);
+        public IParameterSymbol FindParameterForArgument(SemanticModel semanticModel, SyntaxNode argument, CancellationToken cancellationToken)
+            => ((ArgumentSyntax)argument).DetermineParameter(semanticModel, allowParams: false, cancellationToken);
+
+        public IParameterSymbol FindParameterForAttributeArgument(SemanticModel semanticModel, SyntaxNode argument, CancellationToken cancellationToken)
+            => ((AttributeArgumentSyntax)argument).DetermineParameter(semanticModel, allowParams: false, cancellationToken);
 
         public ImmutableArray<ISymbol> GetBestOrAllSymbols(SemanticModel semanticModel, SyntaxNode node, SyntaxToken token, CancellationToken cancellationToken)
         {

src/Workspaces/SharedUtilitiesAndExtensions/Compiler/CSharp/Services/SyntaxFacts/CSharpSyntaxFacts.cs

@@ -1183,6 +1183,9 @@ public SeparatedSyntaxList<SyntaxNode> GetArgumentsOfObjectCreationExpression(Sy
         public SeparatedSyntaxList<SyntaxNode> GetArgumentsOfArgumentList(SyntaxNode argumentList)
             => ((BaseArgumentListSyntax)argumentList).Arguments;
 
+        public SeparatedSyntaxList<SyntaxNode> GetArgumentsOfAttributeArgumentList(SyntaxNode argumentList)
+            => ((AttributeArgumentListSyntax)argumentList).Arguments;
+
         public bool IsRegularComment(SyntaxTrivia trivia)
             => trivia.IsRegularComment();
 

src/Workspaces/SharedUtilitiesAndExtensions/Compiler/Core/Services/SemanticFacts/ISemanticFacts.cs

@@ -89,7 +89,8 @@ internal partial interface ISemanticFacts
 
         IEnumerable<ISymbol> GetDeclaredSymbols(SemanticModel semanticModel, SyntaxNode memberDeclaration, CancellationToken cancellationToken);
 
-        IParameterSymbol FindParameterForArgument(SemanticModel semanticModel, SyntaxNode argumentNode, CancellationToken cancellationToken);
+        IParameterSymbol FindParameterForArgument(SemanticModel semanticModel, SyntaxNode argument, CancellationToken cancellationToken);
+        IParameterSymbol FindParameterForAttributeArgument(SemanticModel semanticModel, SyntaxNode argument, CancellationToken cancellationToken);
 
 #nullable enable
         ImmutableArray<ISymbol> GetBestOrAllSymbols(SemanticModel semanticModel, SyntaxNode? node, SyntaxToken token, CancellationToken cancellationToken);

src/Workspaces/SharedUtilitiesAndExtensions/Compiler/Core/Services/SyntaxFacts/ISyntaxFacts.cs

@@ -324,6 +324,7 @@ void GetPartsOfInterpolationExpression(SyntaxNode node,
         SeparatedSyntaxList<SyntaxNode> GetArgumentsOfInvocationExpression(SyntaxNode node);
         SeparatedSyntaxList<SyntaxNode> GetArgumentsOfObjectCreationExpression(SyntaxNode node);
         SeparatedSyntaxList<SyntaxNode> GetArgumentsOfArgumentList(SyntaxNode node);
+        SeparatedSyntaxList<SyntaxNode> GetArgumentsOfAttributeArgumentList(SyntaxNode node);
 
         bool IsUsingDirectiveName([NotNullWhen(true)] SyntaxNode? node);
 

src/Workspaces/SharedUtilitiesAndExtensions/Compiler/VisualBasic/Services/SemanticFacts/VisualBasicSemanticFacts.vb

@@ -99,11 +99,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic
             Return False
         End Function
 
-        Public ReadOnly Property SupportsParameterizedProperties As Boolean Implements ISemanticFacts.SupportsParameterizedProperties
-            Get
-                Return True
-            End Get
-        End Property
+        Public ReadOnly Property SupportsParameterizedProperties As Boolean = True Implements ISemanticFacts.SupportsParameterizedProperties
 
         Public Function TryGetSpeculativeSemanticModel(oldSemanticModel As SemanticModel, oldNode As SyntaxNode, newNode As SyntaxNode, <Out> ByRef speculativeModel As SemanticModel) As Boolean Implements ISemanticFacts.TryGetSpeculativeSemanticModel
             Debug.Assert(oldNode.Kind = newNode.Kind)
@@ -230,8 +226,12 @@ Namespace Microsoft.CodeAnalysis.VisualBasic
             Return SpecializedCollections.SingletonEnumerable(semanticModel.GetDeclaredSymbol(memberDeclaration, cancellationToken))
         End Function
 
-        Public Function FindParameterForArgument(semanticModel As SemanticModel, argumentNode As SyntaxNode, cancellationToken As CancellationToken) As IParameterSymbol Implements ISemanticFacts.FindParameterForArgument
-            Return DirectCast(argumentNode, ArgumentSyntax).DetermineParameter(semanticModel, allowParamArray:=False, cancellationToken)
+        Public Function FindParameterForArgument(semanticModel As SemanticModel, argument As SyntaxNode, cancellationToken As CancellationToken) As IParameterSymbol Implements ISemanticFacts.FindParameterForArgument
+            Return DirectCast(argument, ArgumentSyntax).DetermineParameter(semanticModel, allowParamArray:=False, cancellationToken)
+        End Function
+
+        Public Function FindParameterForAttributeArgument(semanticModel As SemanticModel, argument As SyntaxNode, cancellationToken As CancellationToken) As IParameterSymbol Implements ISemanticFacts.FindParameterForAttributeArgument
+            Return FindParameterForArgument(semanticModel, argument, cancellationToken)
         End Function
 
         Public Function GetBestOrAllSymbols(semanticModel As SemanticModel, node As SyntaxNode, token As SyntaxToken, cancellationToken As CancellationToken) As ImmutableArray(Of ISymbol) Implements ISemanticFacts.GetBestOrAllSymbols

src/Workspaces/SharedUtilitiesAndExtensions/Compiler/VisualBasic/Services/SyntaxFacts/VisualBasicSyntaxFacts.vb

@@ -1222,6 +1222,10 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.LanguageServices
             Return DirectCast(node, ArgumentListSyntax).Arguments
         End Function
 
+        Public Function GetArgumentsOfAttributeArgumentList(node As SyntaxNode) As SeparatedSyntaxList(Of SyntaxNode) Implements ISyntaxFacts.GetArgumentsOfAttributeArgumentList
+            Return GetArgumentsOfArgumentList(node)
+        End Function
+
         Public Function ConvertToSingleLine(node As SyntaxNode, Optional useElasticTrivia As Boolean = False) As SyntaxNode Implements ISyntaxFacts.ConvertToSingleLine
             Return node.ConvertToSingleLine(useElasticTrivia)
         End Function

src/Workspaces/SharedUtilitiesAndExtensions/Workspace/Core/LanguageServices/SemanticsFactsService/AbstractSemanticFactsService.cs

@@ -157,6 +157,9 @@ public IEnumerable<ISymbol> GetDeclaredSymbols(SemanticModel semanticModel, Synt
         public IParameterSymbol FindParameterForArgument(SemanticModel semanticModel, SyntaxNode argumentNode, CancellationToken cancellationToken)
             => SemanticFacts.FindParameterForArgument(semanticModel, argumentNode, cancellationToken);
 
+        public IParameterSymbol FindParameterForAttributeArgument(SemanticModel semanticModel, SyntaxNode argumentNode, CancellationToken cancellationToken)
+            => SemanticFacts.FindParameterForAttributeArgument(semanticModel, argumentNode, cancellationToken);
+
         public ImmutableArray<ISymbol> GetBestOrAllSymbols(SemanticModel semanticModel, SyntaxNode node, SyntaxToken token, CancellationToken cancellationToken)
             => SemanticFacts.GetBestOrAllSymbols(semanticModel, node, token, cancellationToken);