Blittable strings generator implementation

Improvements to fixed array generator
2026-07-16 06:29:29 +00:00 · 2026-01-27 14:15:41 +01:00
parent dbdf5cfbe2
commit 2c918cf4a4
3 changed files with 194 additions and 30 deletions
@@ -0,0 +1,142 @@
+using Microsoft.CodeAnalysis;
+using Sybil;
+using System.Text;
+using System.Linq;
+
+namespace System.Extensions;
+#nullable enable
+[Generator(LanguageNames.CSharp)]
+public class BlittableStringGenerator : IIncrementalGenerator
+{
+    private const string UsingSystem = "System";
+    private const string UsingSystemRuntimeInterop = "System.Runtime.InteropServices";
+    private const string AttributeNamespace = "System.Extensions";
+    private const string AttributeName = "GenerateBlittableStringAttribute";
+    private const string AttributeShortName = "GenerateBlittableString";
+    private const string String = "String";
+    private const string Public = "public";
+    private const string Required = "required";
+    private const string Size = "Size";
+    private const string Int = "int";
+
+    public void Initialize(IncrementalGeneratorInitializationContext context)
+    {
+        context.RegisterPostInitializationOutput(context =>
+        {
+            var compilationUnitBuilder = SyntaxBuilder.CreateCompilationUnit()
+                .WithNamespace(
+                SyntaxBuilder.CreateNamespace(AttributeNamespace)
+                    .WithClass(SyntaxBuilder.CreateClass(AttributeName)
+                        .WithModifier(Public)
+                        .WithConstructor(SyntaxBuilder.CreateConstructor(AttributeName)
+                            .WithModifier(Public))
+                        .WithAttribute(SyntaxBuilder.CreateAttribute("AttributeUsage")
+                            .WithArgument(AttributeTargets.Assembly)
+                            .WithArgument("Inherited", false)
+                            .WithArgument("AllowMultiple", true))
+                        .WithProperty(SyntaxBuilder.CreateProperty(Int, Size)
+                            .WithModifier(Public)
+                            .WithModifier(Required)
+                            .WithAccessor(SyntaxBuilder.CreateGetter())
+                            .WithAccessor(SyntaxBuilder.CreateSetter()))
+                        .WithBaseClass(nameof(Attribute))));
+            var compilationUnitSyntax = compilationUnitBuilder.Build();
+            var source = compilationUnitSyntax.ToFullString();
+            context.AddSource($"{AttributeName}.g", source);
+        });
+
+        context.RegisterSourceOutput(context.CompilationProvider, (sourceProductionContext, compilation) =>
+        {
+            var assemblyAttributes =
+            compilation.Assembly.GetAttributes().Where(a => a.AttributeClass != null &&
+                        (a.AttributeClass.Name == AttributeName || a.AttributeClass.Name == AttributeShortName));
+
+            foreach (var attr in assemblyAttributes)
+            {
+                // Extract the Size parameter from the named arguments.
+                int? fixedSize = default;
+                foreach (var arg in attr.NamedArguments)
+                {
+                    if (arg.Key == Size && arg.Value.Value is int intValue)
+                    {
+                        fixedSize = intValue;
+                        break;
+                    }
+                }
+
+                if (fixedSize is null)
+                {
+                    // As Size is required, skip if not provided.
+                    continue;
+                }
+
+                Execute(sourceProductionContext, (int)fixedSize);
+            }
+        });
+    }
+
+    private static void Execute(SourceProductionContext sourceProductionContext, int size)
+    {
+        var structName = $"{String}{size}";
+        var builder = new StringBuilder();
+        builder.AppendLine($"using {UsingSystem};");
+        builder.AppendLine($"using {UsingSystemRuntimeInterop};");
+        builder.AppendLine();
+        builder.AppendLine($"namespace {AttributeNamespace};");
+        builder.AppendLine();
+        builder.AppendLine("[StructLayout(LayoutKind.Sequential, Pack = 1)]");
+        builder.AppendLine($"public unsafe partial struct {structName}");
+        builder.AppendLine("{");
+        builder.AppendLine($"    public const int Size = {size};");
+        builder.AppendLine();
+        builder.AppendLine("    public fixed char Value[Size];");
+        builder.AppendLine();
+        builder.AppendLine("    public Span<char> AsSpan()");
+        builder.AppendLine("    {");
+        builder.AppendLine("        fixed (char* ptr = this.Value)");
+        builder.AppendLine("        {");
+        builder.AppendLine("            return MemoryMarshal.CreateSpan(ref *ptr, Size);");
+        builder.AppendLine("        }");
+        builder.AppendLine("    }");
+        builder.AppendLine();
+        builder.AppendLine("    public readonly ReadOnlySpan<char> AsReadOnlySpan()");
+        builder.AppendLine("    {");
+        builder.AppendLine("        fixed (char* ptr = this.Value)");
+        builder.AppendLine("        {");
+        builder.AppendLine("            return new ReadOnlySpan<char>(ptr, Size);");
+        builder.AppendLine("        }");
+        builder.AppendLine("    }");
+        builder.AppendLine();
+        builder.AppendLine("    public void Set(ReadOnlySpan<char> value)");
+        builder.AppendLine("    {");
+        builder.AppendLine("        fixed (char* ptr = this.Value)");
+        builder.AppendLine("        {");
+        builder.AppendLine("            var span = MemoryMarshal.CreateSpan(ref *ptr, Size);");
+        builder.AppendLine("            span.Clear();");
+        builder.AppendLine("            value[..Math.Min(value.Length, Size - 1)].CopyTo(span);");
+        builder.AppendLine("        }");
+        builder.AppendLine("    }");
+        builder.AppendLine();
+        builder.AppendLine("    public override readonly string ToString()");
+        builder.AppendLine("    {");
+        builder.AppendLine("        var span = this.AsReadOnlySpan();");
+        builder.AppendLine("        var nullIndex = span.IndexOf('\\0');");
+        builder.AppendLine("        return nullIndex >= 0 ? new string(span[..nullIndex]) : new string(span);");
+        builder.AppendLine("    }");
+        builder.AppendLine();
+        builder.AppendLine($"    public static implicit operator string({structName} value) => value.ToString();");
+        builder.AppendLine();
+        builder.AppendLine($"    public static implicit operator {structName}(string value)");
+        builder.AppendLine("    {");
+        builder.AppendLine($"        var result = default({structName});");
+        builder.AppendLine("        result.Set(value);");
+        builder.AppendLine("        return result;");
+        builder.AppendLine("    }");
+        builder.AppendLine();
+        builder.AppendLine($"    public static implicit operator ReadOnlySpan<char>({structName} value) => value.AsReadOnlySpan();");
+        builder.AppendLine("}");
+
+        sourceProductionContext.AddSource($"{structName}.g.cs", builder.ToString());
+    }
+}
+#nullable disable