Use incremental source generator

README.md

@@ -17,7 +17,7 @@ C# and Razor compiler playground in the browser via Blazor WebAssembly. https://
 - VSCode Monaco Editor.
 - Multiple input sources (especially useful for interlinked Razor components).
 - C# Language Services (completions, live diagnostics) - experimental.
-- Configuring any C# parse options (e.g., LangVersion, Features).
+- Configuring any C# options (e.g., LangVersion, Features, OptimizationLevel, AllowUnsafe).
 
 ## Development
 

src/App/Lab/InitialCode.cs

@@ -2,6 +2,26 @@
 
 internal sealed record InitialCode
 {
+    public static readonly InitialCode CSharp = new("Program.cs", """
+        using System;
+        using System.Collections.Generic;
+        using System.Collections.Immutable;
+        using System.Diagnostics;
+        using System.Diagnostics.CodeAnalysis;
+        using System.Linq;
+        using System.Threading;
+        using System.Threading.Tasks;
+
+        class Program
+        {
+            static void Main()
+            {
+                Console.WriteLine("Hello.");
+            }
+        }
+
+        """);
+
     public static readonly InitialCode Razor = new("TestComponent.razor", """
         <TestComponent Param="1" />
 
@@ -25,26 +45,6 @@ @using Microsoft.JSInterop
 
         """);
 
-    public static readonly InitialCode CSharp = new("Program.cs", """
-        using System;
-        using System.Collections.Generic;
-        using System.Collections.Immutable;
-        using System.Diagnostics;
-        using System.Diagnostics.CodeAnalysis;
-        using System.Linq;
-        using System.Threading;
-        using System.Threading.Tasks;
-
-        class Program
-        {
-            static void Main()
-            {
-                Console.WriteLine("Hello.");
-            }
-        }
-
-        """);
-
     public static readonly InitialCode Cshtml = new("TestPage.cshtml", """
         @page
         @using System.ComponentModel.DataAnnotations

src/App/Lab/SavedState.cs

@@ -14,8 +14,8 @@ static WellKnownSlugs()
     {
         IEnumerable<(string Shorthand, string Title, SavedState State)> entries =
         [
-            ("razor", "Razor", SavedState.Razor),
             ("csharp", "C#", SavedState.CSharp),
+            ("razor", "Razor", SavedState.Razor),
             ("cshtml", "CSHTML", SavedState.Cshtml),
         ];
 
@@ -190,20 +190,20 @@ internal sealed record SavedState
         RazorToolchain = RazorToolchain.SourceGeneratorOrInternalApi,
     };
 
-    public static SavedState Initial => Razor;
-
-    public static SavedState Razor { get; } = defaults with
-    {
-        Inputs = [InitialCode.Razor.ToInputCode(), InitialCode.RazorImports.ToInputCode()],
-        SelectedOutputType = "gcs",
-    };
+    public static SavedState Initial => CSharp;
 
     public static SavedState CSharp { get; } = defaults with
     {
         Inputs = [InitialCode.CSharp.ToInputCode()],
         SelectedOutputType = "run",
     };
 
+    public static SavedState Razor { get; } = defaults with
+    {
+        Inputs = [InitialCode.Razor.ToInputCode(), InitialCode.RazorImports.ToInputCode()],
+        SelectedOutputType = "gcs",
+    };
+
     public static SavedState Cshtml { get; } = defaults with
     {
         Inputs = [InitialCode.Cshtml.ToInputCode()],

src/Compiler/Compiler.cs

@@ -22,6 +22,11 @@ You can try selecting different Razor toolchain in Settings / Advanced.
 
     private (CompilationInput Input, CompiledAssembly Output)? lastResult;
 
+    /// <summary>
+    /// Reused for incremental source generation.
+    /// </summary>
+    private GeneratorDriver? generatorDriver;
+
     public CompiledAssembly Compile(
         CompilationInput input,
         ImmutableDictionary<string, ImmutableArray<byte>>? assemblies,
@@ -338,18 +343,28 @@ static CSharpCompilationOptions createCompilationOptions(OutputKind outputKind)
                 references: references,
                 options: options);
 
-            var driver = CSharpGeneratorDriver.Create(
-                generators: [new RazorSourceGenerator().AsSourceGenerator()],
-                additionalTexts: additionalTextsBuilder.ToImmutable(),
-                parseOptions: parseOptions,
-                optionsProvider: optionsProvider);
+            if (generatorDriver is null)
+            {
+                generatorDriver = CSharpGeneratorDriver.Create(
+                    generators: [new RazorSourceGenerator().AsSourceGenerator()],
+                    additionalTexts: additionalTextsBuilder.ToImmutable(),
+                    parseOptions: parseOptions,
+                    optionsProvider: optionsProvider);
+            }
+            else
+            {
+                generatorDriver = generatorDriver
+                    .ReplaceAdditionalTexts(additionalTextsBuilder.ToImmutable())
+                    .WithUpdatedParseOptions(parseOptions)
+                    .WithUpdatedAnalyzerConfigOptions(optionsProvider);
+            }
 
-            driver = (CSharpGeneratorDriver)driver.RunGeneratorsAndUpdateCompilation(
+            generatorDriver = (CSharpGeneratorDriver)generatorDriver.RunGeneratorsAndUpdateCompilation(
                 initialCompilation,
                 out var finalCommonCompilation,
                 out var generatorDiagnostics);
 
-            razorResult = driver.GetRunResult().Results.FirstOrDefault();
+            razorResult = generatorDriver.GetRunResult().Results.FirstOrDefault();
 
             var finalCompilation = (CSharpCompilation)finalCommonCompilation;