Do not treat text as json when passed to api that explicit says it is not

src/EditorFeatures/CSharpTest/Classification/SemanticClassifierTests.cs

@@ -3,13 +3,15 @@
 // See the LICENSE file in the project root for more information.
 
 using System.Collections.Immutable;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 using System.Threading.Tasks;
 using Microsoft.CodeAnalysis.Classification;
 using Microsoft.CodeAnalysis.CSharp.Test.Utilities;
 using Microsoft.CodeAnalysis.Editor.Shared.Utilities;
 using Microsoft.CodeAnalysis.Editor.Tagging;
 using Microsoft.CodeAnalysis.Editor.UnitTests;
+using Microsoft.CodeAnalysis.Editor.UnitTests.Classification;
 using Microsoft.CodeAnalysis.Options;
 using Microsoft.CodeAnalysis.Remote.Testing;
 using Microsoft.CodeAnalysis.Shared.Extensions;
@@ -27,7 +29,7 @@
 namespace Microsoft.CodeAnalysis.Editor.CSharp.UnitTests.Classification;
 
 [Trait(Traits.Feature, Traits.Features.Classification)]
-public partial class SemanticClassifierTests : AbstractCSharpClassifierTests
+public sealed partial class SemanticClassifierTests : AbstractCSharpClassifierTests
 {
     protected override async Task<ImmutableArray<ClassifiedSpan>> GetClassificationSpansAsync(string code, ImmutableArray<TextSpan> spans, ParseOptions? options, TestHost testHost)
     {
@@ -37,6 +39,14 @@ protected override async Task<ImmutableArray<ClassifiedSpan>> GetClassificationS
         return await GetSemanticClassificationsAsync(document, spans);
     }
 
+    private new Task TestAsync(
+        [StringSyntax("C#-Test")] string code,
+        TestHost testHost,
+        params FormattedClassification[] expected)
+    {
+        return base.TestAsync(code, testHost, expected);
+    }
+
     [Theory, CombinatorialData]
     public async Task GenericClassDeclaration(TestHost testHost)
     {

src/EditorFeatures/CSharpTest/Classification/SemanticClassifierTests_Json.cs

@@ -222,6 +222,28 @@ void Goo()
             Json.Array("]"));
     }
 
+    [Theory, CombinatorialData]
+    [WorkItem("https://github.com/dotnet/roslyn/issues/74020")]
+    public async Task TestJsonOnApiWithStringSyntaxAttribute_OtherLanguage_Field(TestHost testHost)
+    {
+        await TestAsync(
+            """
+            using System.Diagnostics.CodeAnalysis;
+
+            class Program
+            {
+                [StringSyntax("notjson")]
+                private string field;
+                void Goo()
+                {
+                    [|this.field = @"[{ 'goo': 0}]";|]
+                }
+            }
+            """ + EmbeddedLanguagesTestConstants.StringSyntaxAttributeCodeCSharp,
+            testHost,
+            Field("field"));
+    }
+
     [Theory, CombinatorialData]
     public async Task TestJsonOnApiWithStringSyntaxAttribute_Property(TestHost testHost)
     {

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

@@ -13,21 +13,14 @@
 
 namespace Microsoft.CodeAnalysis.Features.EmbeddedLanguages;
 
-internal abstract class AbstractLanguageDetector<TOptions>
+internal abstract class AbstractLanguageDetector<TOptions>(
+    EmbeddedLanguageInfo info,
+    ImmutableArray<string> languageIdentifiers,
+    EmbeddedLanguageCommentDetector commentDetector)
     where TOptions : struct, Enum
 {
-    protected readonly EmbeddedLanguageInfo Info;
-
-    private readonly EmbeddedLanguageDetector _detector;
-
-    protected AbstractLanguageDetector(
-        EmbeddedLanguageInfo info,
-        ImmutableArray<string> languageIdentifiers,
-        EmbeddedLanguageCommentDetector commentDetector)
-    {
-        Info = info;
-        _detector = new EmbeddedLanguageDetector(info, languageIdentifiers, commentDetector);
-    }
+    protected readonly EmbeddedLanguageInfo Info = info;
+    protected readonly EmbeddedLanguageDetector Detector = new EmbeddedLanguageDetector(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).
@@ -64,7 +57,7 @@ public bool IsEmbeddedLanguageToken(
 
         // First check for the standard pattern of either a `// lang=...` comment or an API annotated with the
         // [StringSyntax] attribute.
-        if (_detector.IsEmbeddedLanguageToken(token, semanticModel, cancellationToken, out _, out var stringOptions))
+        if (Detector.IsEmbeddedLanguageToken(token, semanticModel, cancellationToken, out _, out var stringOptions))
         {
             // If we got string-options back, then we were on a comment string (e.g. `// lang=regex,option1,option2`).
             // Attempt to convert the string options to actual options requested.

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

@@ -42,6 +42,19 @@ public bool IsEmbeddedLanguageToken(
         return LanguageIdentifiers.Contains(identifier);
     }
 
+    public string? TryGetEmbeddedLanguageTokenIdentifier(
+        SyntaxToken token,
+        SemanticModel semanticModel,
+        CancellationToken cancellationToken)
+    {
+        return IsEmbeddedLanguageTokenWorker(token, semanticModel, cancellationToken, out var identifier, out _)
+            ? identifier
+            : null;
+    }
+
+    public bool IsEmbeddedLanguageIdentifier(string identifier)
+        => LanguageIdentifiers.Contains(identifier);
+
     private bool IsEmbeddedLanguageTokenWorker(
         SyntaxToken token,
         SemanticModel semanticModel,

src/Features/Core/Portable/EmbeddedLanguages/Json/LanguageServices/JsonLanguageDetector.cs

@@ -73,7 +73,14 @@ protected override JsonOptions GetStringSyntaxDefaultOptions()
             return result;
 
         if (includeProbableStrings && IsProbablyJson(token, out var tree))
-            return tree;
+        {
+            // We have a string that looks like json.  Treat it as such *unless* we see that it was *explicitly* marked
+            // as belonging to some other language.  This allows us to light up on strings that are very likely to be
+            // json while not misclassifying strings that are actually meant to be something else.
+            var languageIdentifier = this.Detector.TryGetEmbeddedLanguageTokenIdentifier(token, semanticModel, cancellationToken);
+            if (languageIdentifier is null || this.Detector.IsEmbeddedLanguageIdentifier(languageIdentifier))
+                return tree;
+        }
 
         return null;
     }