Classify string fields with embedded languages if we can see their va…

…lues passed to a StringSyntax api (#77199)

Fixes #77189

src/EditorFeatures/CSharpTest/Classification/SemanticClassifierTests_Regex.cs

@@ -1312,4 +1312,70 @@ void Goo()
             Namespace("RegularExpressions"),
             Keyword("var"));
     }
+
+    [Theory, CombinatorialData]
+    [WorkItem("https://github.com/dotnet/roslyn/issues/77189")]
+    public async Task TestStringFieldUsedLater_ProperModifiers(
+        TestHost testHost,
+        [CombinatorialValues("const", "static readonly")] string modifiers)
+    {
+        await TestAsync(
+            $$"""
+            using System.Diagnostics.CodeAnalysis;
+            using System.Text.RegularExpressions;
+
+            class Program
+            {
+                private {{modifiers}} string regexValue = [|@"$(\a\t\u0020)"|];
+
+                void Goo()
+                {
+                    Bar(regexValue);
+                }
+
+                void Bar([StringSyntax(StringSyntaxAttribute.Regex)] string p)
+                {
+                }
+            }
+            """ + EmbeddedLanguagesTestConstants.StringSyntaxAttributeCodeCSharp,
+            testHost,
+            Regex.Anchor("$"),
+            Regex.Grouping("("),
+            Regex.OtherEscape("\\"),
+            Regex.OtherEscape("a"),
+            Regex.OtherEscape("\\"),
+            Regex.OtherEscape("t"),
+            Regex.OtherEscape("\\"),
+            Regex.OtherEscape("u"),
+            Regex.OtherEscape("0020"),
+            Regex.Grouping(")"));
+    }
+
+    [Theory, CombinatorialData]
+    [WorkItem("https://github.com/dotnet/roslyn/issues/77189")]
+    public async Task TestStringFieldUsedLater_ImproperModifiers(
+        TestHost testHost,
+        [CombinatorialValues("", "static", "readonly")] string modifiers)
+    {
+        await TestAsync(
+            $$"""
+            using System.Diagnostics.CodeAnalysis;
+            using System.Text.RegularExpressions;
+
+            class Program
+            {
+                private {{modifiers}} string regexValue = [|@"$(\a\t\u0020)"|];
+
+                void Goo()
+                {
+                    Bar(regexValue);
+                }
+
+                void Bar([StringSyntax(StringSyntaxAttribute.Regex)] string p)
+                {
+                }
+            }
+            """ + EmbeddedLanguagesTestConstants.StringSyntaxAttributeCodeCSharp,
+            testHost);
+    }
 }

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

@@ -20,7 +20,7 @@ internal abstract class AbstractLanguageDetector<TOptions>(
     where TOptions : struct, Enum
 {
     protected readonly EmbeddedLanguageInfo Info = info;
-    protected readonly EmbeddedLanguageDetector Detector = new EmbeddedLanguageDetector(info, languageIdentifiers, commentDetector);
+    protected readonly EmbeddedLanguageDetector Detector = new(info, languageIdentifiers, commentDetector);
 
     /// <summary>
     /// Whether or not this is an argument to a well known api for this language (like Regex.Match or JToken.Parse).

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

@@ -322,7 +322,8 @@ private bool IsEmbeddedLanguageStringLiteralToken(
                 semanticModel.GetDeclaredSymbol(variableDeclarator, cancellationToken) ??
                 semanticModel.GetDeclaredSymbol(syntaxFacts.GetIdentifierOfVariableDeclarator(variableDeclarator).GetRequiredParent(), cancellationToken);
 
-            return IsLocalConsumedByApiWithStringSyntaxAttribute(symbol, container, semanticModel, cancellationToken, out identifier);
+            return IsLocalConsumedByApiWithStringSyntaxAttribute(symbol, container, semanticModel, cancellationToken, out identifier) ||
+                   IsFieldConsumedByApiWithStringSyntaxAttribute(symbol, container, semanticModel, cancellationToken, out identifier);
         }
 
         return false;
@@ -336,46 +337,83 @@ private bool IsLocalConsumedByApiWithStringSyntaxAttribute(
         [NotNullWhen(true)] out string? identifier)
     {
         identifier = null;
-        if (symbol is not ILocalSymbol localSymbol)
+        if (symbol is not ILocalSymbol { Name: not "" } localSymbol)
             return false;
 
         var blockFacts = this.Info.BlockFacts;
-        var syntaxFacts = this.Info.SyntaxFacts;
 
         var block = tokenParent.AncestorsAndSelf().FirstOrDefault(blockFacts.IsExecutableBlock);
         if (block is null)
             return false;
 
-        var localName = localSymbol.Name;
-        if (localName == "")
-            return false;
-
         // Now look at the next statements that follow for usages of this local variable.
         foreach (var statement in blockFacts.GetExecutableBlockStatements(block))
         {
-            foreach (var descendent in statement.DescendantNodesAndSelf())
-            {
-                cancellationToken.ThrowIfCancellationRequested();
+            if (CheckDescendants(localSymbol, semanticModel, statement, cancellationToken, out identifier))
+                return true;
+        }
 
-                if (!syntaxFacts.IsIdentifierName(descendent))
-                    continue;
+        return false;
+    }
 
-                var identifierToken = syntaxFacts.GetIdentifierOfIdentifierName(descendent);
-                if (identifierToken.ValueText != localName)
-                    continue;
+    private bool IsFieldConsumedByApiWithStringSyntaxAttribute(
+        ISymbol? symbol,
+        SyntaxNode tokenParent,
+        SemanticModel semanticModel,
+        CancellationToken cancellationToken,
+        [NotNullWhen(true)] out string? identifier)
+    {
+        identifier = null;
+        if (symbol is not IFieldSymbol { Name: not "" } fieldSymbol)
+            return false;
 
-                var otherSymbol = semanticModel.GetSymbolInfo(descendent, cancellationToken).GetAnySymbol();
+        var isConst = fieldSymbol.IsConst;
+        var isStaticReadonly = fieldSymbol.IsStatic && fieldSymbol.IsReadOnly;
+        if (!isConst && !isStaticReadonly)
+            return false;
 
-                // Only do a direct check here.  We don't want to continually do indirect checks where a string literal
-                // is assigned to one local, assigned to another local, assigned to another local, and so on.
-                if (localSymbol.Equals(otherSymbol) &&
-                    IsEmbeddedLanguageStringLiteralToken_Direct(identifierToken, semanticModel, cancellationToken, out identifier))
-                {
-                    return true;
-                }
+        var syntaxFacts = this.Info.SyntaxFacts;
+
+        var typeDeclaration = tokenParent.AncestorsAndSelf().FirstOrDefault(syntaxFacts.IsTypeDeclaration);
+        if (typeDeclaration is null)
+            return false;
+
+        return CheckDescendants(fieldSymbol, semanticModel, typeDeclaration, cancellationToken, out identifier);
+    }
+
+    private bool CheckDescendants(
+        ISymbol symbol,
+        SemanticModel semanticModel,
+        SyntaxNode node,
+        CancellationToken cancellationToken,
+        [NotNullWhen(true)] out string? identifier)
+    {
+        var symbolName = symbol.Name;
+        var syntaxFacts = this.Info.SyntaxFacts;
+
+        foreach (var descendent in node.DescendantNodesAndSelf())
+        {
+            cancellationToken.ThrowIfCancellationRequested();
+
+            if (!syntaxFacts.IsIdentifierName(descendent))
+                continue;
+
+            var identifierToken = syntaxFacts.GetIdentifierOfIdentifierName(descendent);
+            if (identifierToken.ValueText != symbolName)
+                continue;
+
+            var otherSymbol = semanticModel.GetSymbolInfo(descendent, cancellationToken).GetAnySymbol();
+
+            // Only do a direct check here.  We don't want to continually do indirect checks where a string literal
+            // is assigned to one local, assigned to another local, assigned to another local, and so on.
+            if (symbol.Equals(otherSymbol) &&
+                IsEmbeddedLanguageStringLiteralToken_Direct(identifierToken, semanticModel, cancellationToken, out identifier))
+            {
+                return true;
             }
         }
 
+        identifier = null;
         return false;
     }