Initialize naming style preferences when language is added to workspace

src/Features/Core/Portable/Options/EditorConfig/EditorConfigFileGenerator.cs

@@ -40,7 +40,10 @@ public static string Generate(
 
         foreach ((var feature, var options) in groupedOptions)
         {
-            AppendOptionsToEditorConfig(configOptions, feature, options, language, editorconfig);
+            if (!options.Contains(NamingStyleOptions.NamingPreferences))
+            {
+                AppendOptionsToEditorConfig(configOptions, feature, options, language, editorconfig);
+            }
         }
 
         if (configOptions.TryGetOption(new OptionKey2(NamingStyleOptions.NamingPreferences, language), out NamingStylePreferences namingStylePreferences))

src/Features/Core/Portable/Options/EditorConfig/EditorConfigOptionsEnumerator.cs

@@ -54,7 +54,9 @@ internal sealed class EditorConfigOptionsEnumerator(
         yield return (WorkspacesResources.dot_NET_Coding_Conventions,
         [
             .. GenerationOptions.EditorConfigOptions,
-            .. CodeStyleOptions2.EditorConfigOptions
+            .. CodeStyleOptions2.EditorConfigOptions,
         ]);
+
+        yield return (CompilerExtensionsResources.Naming_styles, NamingStyleOptions.EditorConfigOptions);
     }
 }

src/LanguageServer/Protocol/Features/Options/ClientFallbackAnalyzerConfigOptionsProvider.cs

@@ -33,11 +33,7 @@ public StructuredAnalyzerConfigOptions GetOptions(string language)
             foreach (var option in options)
             {
                 var value = globalOptions.GetOption<object>(new OptionKey2(option, option.IsPerLanguage ? language : null));
-
-                var configName = option.Definition.ConfigName;
-                var configValue = option.Definition.Serializer.Serialize(value);
-
-                builder.Add(configName, configValue);
+                EditorConfigValueSerializer.Serialize(builder, option, language, value);
             }
         }
 

src/LanguageServer/Protocol/Features/Options/SolutionAnalyzerConfigOptionsUpdater.cs

@@ -84,23 +84,8 @@ Solution UpdateOptions(Solution oldSolution)
                             }
                         }
 
-                        // update changed values:
-                        var configName = key.Option.Definition.ConfigName;
-                        if (value is NamingStylePreferences preferences)
-                        {
-                            NamingStylePreferencesEditorConfigSerializer.WriteNamingStylePreferencesToEditorConfig(
-                                preferences.SymbolSpecifications,
-                                preferences.NamingStyles,
-                                preferences.Rules.NamingRules,
-                                language,
-                                entryWriter: (name, value) => lazyBuilder[name] = value,
-                                triviaWriter: null,
-                                setPrioritiesToPreserveOrder: true);
-                        }
-                        else
-                        {
-                            lazyBuilder[configName] = key.Option.Definition.Serializer.Serialize(value);
-                        }
+                        // update changed value:
+                        EditorConfigValueSerializer.Serialize(lazyBuilder, key.Option, language, value);
                     }
 
                     if (lazyBuilder != null)

src/LanguageServer/ProtocolUnitTests/Options/SolutionAnalyzerConfigOptionsUpdaterTests.cs

@@ -107,6 +107,14 @@ public void FlowsNamingStylePreferencesToWorkspace()
     {
         using var workspace = CreateWorkspace();
 
+        Assert.Empty(workspace.CurrentSolution.Projects);
+        var globalOptions = workspace.GetService<IGlobalOptionService>();
+
+        var initialPeferences = OptionsTestHelpers.CreateNamingStylePreferences(
+            ([SymbolKind.Property], Capitalization.AllUpper, ReportDiagnostic.Error));
+
+        globalOptions.SetGlobalOption(NamingStyleOptions.NamingPreferences, LanguageNames.CSharp, initialPeferences);
+
         var testProjectWithoutConfig = new TestHostProject(workspace, "proj_without_config", LanguageNames.CSharp);
 
         testProjectWithoutConfig.AddDocument(new TestHostDocument("""
@@ -135,21 +143,28 @@ class MyClass2;
             """,
             filePath: Path.Combine(TempRoot.Root, "proj_with_config", "test.cs")));
 
+        // No fallback options before a project is added.
+        Assert.False(workspace.CurrentSolution.FallbackAnalyzerOptions.TryGetValue(LanguageNames.CSharp, out _));
+
         workspace.AddTestProject(testProjectWithoutConfig);
         workspace.AddTestProject(testProjectWithConfig);
 
-        var globalOptions = workspace.GetService<IGlobalOptionService>();
+        // Once a C# project is added the preferences stored in global options should be applied to fallback options:
+        Assert.True(workspace.CurrentSolution.FallbackAnalyzerOptions.TryGetValue(LanguageNames.CSharp, out var fallbackOptions));
+        AssertEx.SequenceEqual(
+            initialPeferences.Rules.NamingRules.Select(r => r.Inspect()),
+            fallbackOptions.GetNamingStylePreferences().Rules.NamingRules.Select(r => r.Inspect()));
 
         var hostPeferences = OptionsTestHelpers.CreateNamingStylePreferences(
             ([MethodKind.Ordinary], Capitalization.PascalCase, ReportDiagnostic.Error),
             ([MethodKind.Ordinary, SymbolKind.Field], Capitalization.PascalCase, ReportDiagnostic.Error));
 
         globalOptions.SetGlobalOption(NamingStyleOptions.NamingPreferences, LanguageNames.CSharp, hostPeferences);
 
-        Assert.True(workspace.CurrentSolution.FallbackAnalyzerOptions.TryGetValue(LanguageNames.CSharp, out var fallbackOptions));
-
+        // Initial preferences should be replaced by host preferences.
         // Note: rules are ordered but symbol and naming style specifications are not.
-        AssertEx.Equal(
+        Assert.True(workspace.CurrentSolution.FallbackAnalyzerOptions.TryGetValue(LanguageNames.CSharp, out fallbackOptions));
+        AssertEx.SequenceEqual(
             hostPeferences.Rules.NamingRules.Select(r => r.Inspect()),
             fallbackOptions.GetNamingStylePreferences().Rules.NamingRules.Select(r => r.Inspect()));
 

src/Workspaces/SharedUtilitiesAndExtensions/Compiler/Core/NamingStyles/NamingStyleOptions.cs

@@ -2,10 +2,9 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
-using System.Threading;
-using System.Threading.Tasks;
 using Microsoft.CodeAnalysis.Diagnostics.Analyzers.NamingStyles;
 using Microsoft.CodeAnalysis.Options;
+using System.Collections.Immutable;
 
 #if !CODE_STYLE
 using Microsoft.CodeAnalysis.Host;
@@ -26,6 +25,11 @@ internal static class NamingStyleOptions
         defaultValue: NamingStylePreferences.Default,
         isEditorConfigOption: true,
         serializer: EditorConfigValueSerializer<NamingStylePreferences>.Unsupported);
+
+    /// <summary>
+    /// Options that we expect the user to set in editorconfig.
+    /// </summary>
+    internal static readonly ImmutableArray<IOption2> EditorConfigOptions = [NamingPreferences];
 }
 
 internal interface NamingStylePreferencesProvider

src/Workspaces/SharedUtilitiesAndExtensions/Compiler/Core/Options/EditorConfigValueSerializer.cs

@@ -7,6 +7,7 @@
 using System.Collections.Immutable;
 using System.Linq;
 using Microsoft.CodeAnalysis.CodeStyle;
+using Microsoft.CodeAnalysis.Diagnostics.Analyzers.NamingStyles;
 using Roslyn.Utilities;
 
 namespace Microsoft.CodeAnalysis.Options;
@@ -170,4 +171,36 @@ private static bool TryParseEnum<T>(string str, out T result) where T : struct,
 
         return Enum.TryParse(str, ignoreCase: true, out result);
     }
+
+    /// <summary>
+    /// Serializes arbitrary editorconfig option value (including naming style preferences) into a given builder.
+    /// Replaces existing value if present.
+    /// </summary>
+    public static void Serialize(IDictionary<string, string> builder, IOption2 option, string language, object? value)
+    {
+        if (value is NamingStylePreferences preferences)
+        {
+            // remove existing naming style values:
+            foreach (var name in builder.Keys)
+            {
+                if (name.StartsWith("dotnet_naming_rule.") || name.StartsWith("dotnet_naming_symbols.") || name.StartsWith("dotnet_naming_style."))
+                {
+                    builder.Remove(name);
+                }
+            }
+
+            NamingStylePreferencesEditorConfigSerializer.WriteNamingStylePreferencesToEditorConfig(
+                preferences.SymbolSpecifications,
+                preferences.NamingStyles,
+                preferences.Rules.NamingRules,
+                language,
+                entryWriter: (name, value) => builder[name] = value,
+                triviaWriter: null,
+                setPrioritiesToPreserveOrder: true);
+        }
+        else
+        {
+            builder[option.Definition.ConfigName] = option.Definition.Serializer.Serialize(value);
+        }
+    }
 }