From a6857d7d8f6f5359891df988d708b036b67f3841 Mon Sep 17 00:00:00 2001
From: Atif Aziz <code@raboof.com>
Date: Mon, 30 Jan 2023 23:05:45 +0100
Subject: [PATCH] Initial refactoring into incremental source generator

---
 Directory.Build.props                         |   2 +-
 .../CodeGeneration/CommunityToolkit.cs        | 513 ++++++++++++++++++
 .../CodeGeneration/SourceGenerator.cs         | 263 ++++-----
 src/DocoptNet/DocoptNet.csproj                |   4 +-
 .../CodeGeneration/SourceGeneratorTests.cs    |  10 +-
 tests/DocoptNet.Tests/DocoptNet.Tests.csproj  |   2 +-
 6 files changed, 658 insertions(+), 136 deletions(-)
 create mode 100644 src/DocoptNet/CodeGeneration/CommunityToolkit.cs

diff --git a/Directory.Build.props b/Directory.Build.props
index 5e8f9754..49140bc8 100644
--- a/Directory.Build.props
+++ b/Directory.Build.props
@@ -1,7 +1,7 @@
 <Project>
 
   <PropertyGroup>
-    <LangVersion>10</LangVersion>
+    <LangVersion>11</LangVersion>
     <Nullable>enable</Nullable>
     <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
     <!--
diff --git a/src/DocoptNet/CodeGeneration/CommunityToolkit.cs b/src/DocoptNet/CodeGeneration/CommunityToolkit.cs
new file mode 100644
index 00000000..92f4eeca
--- /dev/null
+++ b/src/DocoptNet/CodeGeneration/CommunityToolkit.cs
@@ -0,0 +1,513 @@
+#region Copyright .NET Foundation and Contributors. All rights reserved.
+/*
+ **************************************************************
+ * Permission is hereby granted, free of charge, to any person
+ * obtaining a copy of this software and associated documentation
+ * files (the "Software"), to deal in the Software without
+ * restriction, including without limitation the rights to use,
+ * copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following
+ * conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
+ * OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
+ * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
+ * WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
+ * OTHER DEALINGS IN THE SOFTWARE.
+ **************************************************************
+ */
+#endregion
+
+// Source: https://github.com/CommunityToolkit/dotnet/tree/v8.1.0/src/CommunityToolkit.Mvvm.SourceGenerators
+
+#pragma warning disable CS0809 // Obsolete member overrides non-obsolete member
+
+namespace DocoptNet.CodeGeneration
+{
+    using System;
+    using System.Collections;
+    using System.Collections.Generic;
+    using System.Collections.Immutable;
+    using System.ComponentModel;
+    using System.Diagnostics.CodeAnalysis;
+    using System.Linq;
+    using System.Runtime.CompilerServices;
+    using System.Security.Cryptography;
+    using Microsoft.CodeAnalysis;
+    using Microsoft.CodeAnalysis.CSharp;
+    using Microsoft.CodeAnalysis.CSharp.Syntax;
+    using Microsoft.CodeAnalysis.Text;
+
+    partial class Extensions
+    {
+        /// <summary>
+        /// Checks whether a given <see cref="TypeDeclarationSyntax"/> has or could possibly have any attributes, using only syntax.
+        /// </summary>
+        /// <param name="typeDeclaration">The input <see cref="TypeDeclarationSyntax"/> instance to check.</param>
+        /// <returns>Whether <paramref name="typeDeclaration"/> has or could possibly have any attributes.</returns>
+
+        public static bool HasOrPotentiallyHasAttributes(this TypeDeclarationSyntax typeDeclaration) =>
+            //
+            // If the type has any attributes lists, then clearly it can have attributes
+            //
+            typeDeclaration.AttributeLists.Count > 0
+            //
+            // If the declaration has no attribute lists, check if the type is partial. If it is, it means
+            // that there could be another partial declaration with some attribute lists over them.
+            //
+            || typeDeclaration.Modifiers.Any(modifier => modifier.IsKind(SyntaxKind.PartialKeyword));
+    }
+
+    /// <summary>
+    /// A model for a serializeable diagnostic info.
+    /// </summary>
+    /// <param name="Descriptor">The wrapped <see cref="DiagnosticDescriptor"/> instance.</param>
+    /// <param name="SyntaxTree">The tree to use as location for the diagnostic, if available.</param>
+    /// <param name="TextSpan">The span to use as location for the diagnostic.</param>
+    /// <param name="Arguments">The diagnostic arguments.</param>
+
+    sealed record DiagnosticInfo(
+        DiagnosticDescriptor Descriptor,
+        SyntaxTree? SyntaxTree,
+        TextSpan TextSpan,
+        EquatableArray<string> Arguments)
+    {
+        /// <summary>
+        /// Creates a new <see cref="Diagnostic"/> instance with the state from this model.
+        /// </summary>
+        /// <returns>A new <see cref="Diagnostic"/> instance with the state from this model.</returns>
+
+        public Diagnostic ToDiagnostic()
+        {
+            return Diagnostic.Create(Descriptor, SyntaxTree is { } tree ? Location.Create(tree, TextSpan) : null,
+                                     Arguments.ToArray());
+        }
+
+        /// <summary>
+        /// Creates a new <see cref="DiagnosticInfo"/> instance with the specified parameters.
+        /// </summary>
+        /// <param name="descriptor">The input <see cref="DiagnosticDescriptor"/> for the diagnostics to create.</param>
+        /// <param name="symbol">The source <see cref="ISymbol"/> to attach the diagnostics to.</param>
+        /// <param name="args">The optional arguments for the formatted message to include.</param>
+        /// <returns>A new <see cref="DiagnosticInfo"/> instance with the specified parameters.</returns>
+
+        public static DiagnosticInfo Create(DiagnosticDescriptor descriptor, ISymbol symbol, params object[] args)
+        {
+            var location = symbol.Locations.First();
+            return new(descriptor, location.SourceTree, location.SourceSpan, args.Select(static arg => arg.ToString()).ToImmutableArray());
+        }
+
+        /// <summary>
+        /// Creates a new <see cref="DiagnosticInfo"/> instance with the specified parameters.
+        /// </summary>
+        /// <param name="descriptor">The input <see cref="DiagnosticDescriptor"/> for the diagnostics to create.</param>
+        /// <param name="node">The source <see cref="SyntaxNode"/> to attach the diagnostics to.</param>
+        /// <param name="args">The optional arguments for the formatted message to include.</param>
+        /// <returns>A new <see cref="DiagnosticInfo"/> instance with the specified parameters.</returns>
+
+        public static DiagnosticInfo Create(DiagnosticDescriptor descriptor, SyntaxNode node, params object[] args)
+        {
+            var location = node.GetLocation();
+            return new(descriptor, location.SourceTree, location.SourceSpan, args.Select(static arg => arg.ToString()).ToImmutableArray());
+        }
+    }
+
+    /// <summary>
+    /// A model representing a value and an associated set of diagnostic errors.
+    /// </summary>
+    /// <typeparam name="TValue">The type of the wrapped value.</typeparam>
+    /// <param name="Value">The wrapped value for the current result.</param>
+    /// <param name="Errors">The associated diagnostic errors, if any.</param>
+
+    sealed record Result<TValue>(TValue Value, EquatableArray<DiagnosticInfo> Errors)
+        where TValue : IEquatable<TValue>?;
+
+    /// <summary>
+    /// Extensions for <see cref="EquatableArray{T}"/>.
+    /// </summary>
+
+    static class EquatableArray
+    {
+        /// <summary>
+        /// Creates an <see cref="EquatableArray{T}"/> instance from a given <see cref="ImmutableArray{T}"/>.
+        /// </summary>
+        /// <typeparam name="T">The type of items in the input array.</typeparam>
+        /// <param name="array">The input <see cref="ImmutableArray{T}"/> instance.</param>
+        /// <returns>An <see cref="EquatableArray{T}"/> instance from a given <see cref="ImmutableArray{T}"/>.</returns>
+
+        public static EquatableArray<T> AsEquatableArray<T>(this ImmutableArray<T> array)
+            where T : IEquatable<T>
+        {
+            return new(array);
+        }
+    }
+
+    /// <summary>
+    /// An immutable, equatable array. This is equivalent to <see cref="ImmutableArray{T}"/> but with value equality support.
+    /// </summary>
+    /// <typeparam name="T">The type of values in the array.</typeparam>
+    readonly struct EquatableArray<T> : IEquatable<EquatableArray<T>>, IEnumerable<T>
+        where T : IEquatable<T>
+    {
+        /// <summary>
+        /// The underlying <typeparamref name="T"/> array.
+        /// </summary>
+
+        readonly T[]? array;
+
+        /// <summary>
+        /// Creates a new <see cref="EquatableArray{T}"/> instance.
+        /// </summary>
+        /// <param name="array">The input <see cref="ImmutableArray{T}"/> to wrap.</param>
+
+        public EquatableArray(ImmutableArray<T> array)
+        {
+            this.array = Unsafe.As<ImmutableArray<T>, T[]?>(ref array);
+        }
+
+        /// <summary>
+        /// Gets a reference to an item at a specified position within the array.
+        /// </summary>
+        /// <param name="index">The index of the item to retrieve a reference to.</param>
+        /// <returns>A reference to an item at a specified position within the array.</returns>
+
+        public ref readonly T this[int index]
+        {
+            [MethodImpl(MethodImplOptions.AggressiveInlining)]
+            get => ref AsImmutableArray().ItemRef(index);
+        }
+
+        /// <summary>
+        /// Gets a value indicating whether the current array is empty.
+        /// </summary>
+
+        public bool IsEmpty
+        {
+            [MethodImpl(MethodImplOptions.AggressiveInlining)]
+            get => AsImmutableArray().IsEmpty;
+        }
+
+        /// <sinheritdoc/>
+
+        public bool Equals(EquatableArray<T> array)
+        {
+            return AsSpan().SequenceEqual(array.AsSpan());
+        }
+
+        /// <sinheritdoc/>
+
+        public override bool Equals([NotNullWhen(true)] object? obj)
+        {
+            return obj is EquatableArray<T> array && Equals(this, array);
+        }
+
+        /// <sinheritdoc/>
+
+        public override int GetHashCode()
+        {
+            if (this.array is not T[] array)
+            {
+                return 0;
+            }
+
+            HashCode hashCode = default;
+
+            foreach (var item in array)
+            {
+                hashCode.Add(item);
+            }
+
+            return hashCode.ToHashCode();
+        }
+
+        /// <summary>
+        /// Gets an <see cref="ImmutableArray{T}"/> instance from the current <see cref="EquatableArray{T}"/>.
+        /// </summary>
+        /// <returns>The <see cref="ImmutableArray{T}"/> from the current <see cref="EquatableArray{T}"/>.</returns>
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public ImmutableArray<T> AsImmutableArray()
+        {
+            return Unsafe.As<T[]?, ImmutableArray<T>>(ref Unsafe.AsRef(in this.array));
+        }
+
+        /// <summary>
+        /// Creates an <see cref="EquatableArray{T}"/> instance from a given <see cref="ImmutableArray{T}"/>.
+        /// </summary>
+        /// <param name="array">The input <see cref="ImmutableArray{T}"/> instance.</param>
+        /// <returns>An <see cref="EquatableArray{T}"/> instance from a given <see cref="ImmutableArray{T}"/>.</returns>
+
+        public static EquatableArray<T> FromImmutableArray(ImmutableArray<T> array)
+        {
+            return new(array);
+        }
+
+        /// <summary>
+        /// Returns a <see cref="ReadOnlySpan{T}"/> wrapping the current items.
+        /// </summary>
+        /// <returns>A <see cref="ReadOnlySpan{T}"/> wrapping the current items.</returns>
+
+        public ReadOnlySpan<T> AsSpan()
+        {
+            return AsImmutableArray().AsSpan();
+        }
+
+        /// <summary>
+        /// Copies the contents of this <see cref="EquatableArray{T}"/> instance. to a mutable array.
+        /// </summary>
+        /// <returns>The newly instantiated array.</returns>
+
+        public T[] ToArray()
+        {
+            return AsImmutableArray().ToArray();
+        }
+
+        /// <summary>
+        /// Gets an <see cref="ImmutableArray{T}.Enumerator"/> value to traverse items in the current array.
+        /// </summary>
+        /// <returns>An <see cref="ImmutableArray{T}.Enumerator"/> value to traverse items in the current array.</returns>
+
+        public ImmutableArray<T>.Enumerator GetEnumerator()
+        {
+            return AsImmutableArray().GetEnumerator();
+        }
+
+        /// <sinheritdoc/>
+
+        IEnumerator<T> IEnumerable<T>.GetEnumerator()
+        {
+            return ((IEnumerable<T>)AsImmutableArray()).GetEnumerator();
+        }
+
+        /// <sinheritdoc/>
+
+        IEnumerator IEnumerable.GetEnumerator()
+        {
+            return ((IEnumerable)AsImmutableArray()).GetEnumerator();
+        }
+
+        /// <summary>
+        /// Implicitly converts an <see cref="ImmutableArray{T}"/> to <see cref="EquatableArray{T}"/>.
+        /// </summary>
+        /// <returns>An <see cref="EquatableArray{T}"/> instance from a given <see cref="ImmutableArray{T}"/>.</returns>
+
+        public static implicit operator EquatableArray<T>(ImmutableArray<T> array)
+        {
+            return FromImmutableArray(array);
+        }
+
+        /// <summary>
+        /// Implicitly converts an <see cref="EquatableArray{T}"/> to <see cref="ImmutableArray{T}"/>.
+        /// </summary>
+        /// <returns>An <see cref="ImmutableArray{T}"/> instance from a given <see cref="EquatableArray{T}"/>.</returns>
+
+        public static implicit operator ImmutableArray<T>(EquatableArray<T> array)
+        {
+            return array.AsImmutableArray();
+        }
+
+        /// <summary>
+        /// Checks whether two <see cref="EquatableArray{T}"/> values are the same.
+        /// </summary>
+        /// <param name="left">The first <see cref="EquatableArray{T}"/> value.</param>
+        /// <param name="right">The second <see cref="EquatableArray{T}"/> value.</param>
+        /// <returns>Whether <paramref name="left"/> and <paramref name="right"/> are equal.</returns>
+
+        public static bool operator ==(EquatableArray<T> left, EquatableArray<T> right)
+        {
+            return left.Equals(right);
+        }
+
+        /// <summary>
+        /// Checks whether two <see cref="EquatableArray{T}"/> values are not the same.
+        /// </summary>
+        /// <param name="left">The first <see cref="EquatableArray{T}"/> value.</param>
+        /// <param name="right">The second <see cref="EquatableArray{T}"/> value.</param>
+        /// <returns>Whether <paramref name="left"/> and <paramref name="right"/> are not equal.</returns>
+
+        public static bool operator !=(EquatableArray<T> left, EquatableArray<T> right)
+        {
+            return !left.Equals(right);
+        }
+    }
+
+    /// <summary>
+    /// A polyfill type that mirrors some methods from <see cref="HashCode"/> on .NET 6.
+    /// </summary>
+    struct HashCode
+    {
+        const uint Prime1 = 2654435761U;
+        const uint Prime2 = 2246822519U;
+        const uint Prime3 = 3266489917U;
+        const uint Prime4 = 668265263U;
+        const uint Prime5 = 374761393U;
+
+        static readonly uint seed = GenerateGlobalSeed();
+
+        uint v1, v2, v3, v4;
+        uint queue1, queue2, queue3;
+        uint length;
+
+        /// <summary>
+        /// Initializes the default seed.
+        /// </summary>
+        /// <returns>A random seed.</returns>
+
+        static uint GenerateGlobalSeed()
+        {
+            var bytes = new byte[4];
+
+            RandomNumberGenerator.Create().GetBytes(bytes);
+
+            return BitConverter.ToUInt32(bytes, 0);
+        }
+
+        /// <summary>
+        /// Adds a single value to the current hash.
+        /// </summary>
+        /// <typeparam name="T">The type of the value to add into the hash code.</typeparam>
+        /// <param name="value">The value to add into the hash code.</param>
+
+        public void Add<T>(T value)
+        {
+            Add(value?.GetHashCode() ?? 0);
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        static void Initialize(out uint v1, out uint v2, out uint v3, out uint v4)
+        {
+            v1 = seed + Prime1 + Prime2;
+            v2 = seed + Prime2;
+            v3 = seed;
+            v4 = seed - Prime1;
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        static uint Round(uint hash, uint input)
+        {
+            return RotateLeft(hash + input * Prime2, 13) * Prime1;
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        static uint QueueRound(uint hash, uint queuedValue)
+        {
+            return RotateLeft(hash + queuedValue * Prime3, 17) * Prime4;
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        static uint MixState(uint v1, uint v2, uint v3, uint v4)
+        {
+            return RotateLeft(v1, 1) + RotateLeft(v2, 7) + RotateLeft(v3, 12) + RotateLeft(v4, 18);
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        static uint MixEmptyState()
+        {
+            return seed + Prime5;
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        static uint MixFinal(uint hash)
+        {
+            hash ^= hash >> 15;
+            hash *= Prime2;
+            hash ^= hash >> 13;
+            hash *= Prime3;
+            hash ^= hash >> 16;
+
+            return hash;
+        }
+
+        void Add(int value)
+        {
+            var val = (uint)value;
+            var previousLength = length++;
+            var position = previousLength % 4;
+
+            switch (position)
+            {
+                case 0: queue1 = val; break;
+                case 1: queue2 = val; break;
+                case 2: queue3 = val; break;
+                default:
+                {
+                    if (previousLength == 3)
+                        Initialize(out v1, out v2, out v3, out v4);
+
+                    v1 = Round(v1, queue1);
+                    v2 = Round(v2, queue2);
+                    v3 = Round(v3, queue3);
+                    v4 = Round(v4, val);
+                    break;
+                }
+            }
+        }
+
+        /// <summary>
+        /// Gets the resulting hashcode from the current instance.
+        /// </summary>
+        /// <returns>The resulting hashcode from the current instance.</returns>
+
+        public int ToHashCode()
+        {
+            var length = this.length;
+            var position = length % 4;
+            var hash = length < 4 ? MixEmptyState() : MixState(v1, v2, v3, v4);
+
+            hash += length * 4;
+
+            if (position > 0)
+            {
+                hash = QueueRound(hash, queue1);
+
+                if (position > 1)
+                {
+                    hash = QueueRound(hash, queue2);
+
+                    if (position > 2)
+                    {
+                        hash = QueueRound(hash, queue3);
+                    }
+                }
+            }
+
+            hash = MixFinal(hash);
+
+            return (int)hash;
+        }
+
+        /// <inheritdoc/>
+
+        [Obsolete("HashCode is a mutable struct and should not be compared with other HashCodes. Use ToHashCode to retrieve the computed hash code.", error: true)]
+        [EditorBrowsable(EditorBrowsableState.Never)]
+        public override int GetHashCode() => throw new NotSupportedException();
+
+        /// <inheritdoc/>
+
+        [Obsolete("HashCode is a mutable struct and should not be compared with other HashCodes.", error: true)]
+        [EditorBrowsable(EditorBrowsableState.Never)]
+        public override bool Equals(object? obj) => throw new NotSupportedException();
+
+        /// <summary>
+        /// Rotates the specified value left by the specified number of bits.
+        /// Similar in behavior to the x86 instruction ROL.
+        /// </summary>
+        /// <param name="value">The value to rotate.</param>
+        /// <param name="offset">The number of bits to rotate by.
+        /// Any value outside the range [0..31] is treated as congruent mod 32.</param>
+        /// <returns>The rotated value.</returns>
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        static uint RotateLeft(uint value, int offset)
+        {
+            return (value << offset) | (value >> (32 - offset));
+        }
+    }
+}
diff --git a/src/DocoptNet/CodeGeneration/SourceGenerator.cs b/src/DocoptNet/CodeGeneration/SourceGenerator.cs
index 0fd1b8bd..1614e8e6 100644
--- a/src/DocoptNet/CodeGeneration/SourceGenerator.cs
+++ b/src/DocoptNet/CodeGeneration/SourceGenerator.cs
@@ -17,8 +17,8 @@ namespace DocoptNet.CodeGeneration
     using Unit = System.ValueTuple;
     using static OptionModule;
 
-    [Generator]
-    public sealed class SourceGenerator : ISourceGenerator
+    [Generator(LanguageNames.CSharp)]
+    public sealed class SourceGenerator : IIncrementalGenerator
     {
         static readonly DiagnosticDescriptor SyntaxError =
             new DiagnosticDescriptor(id: "DCPT0001",
@@ -36,139 +36,114 @@ public sealed class SourceGenerator : ISourceGenerator
                 DiagnosticSeverity.Error,
                 isEnabledByDefault: true);
 
-        public void Initialize(GeneratorInitializationContext context) =>
-            context.RegisterForSyntaxNotifications(() => new SyntaxReceiver());
-
-        sealed class SyntaxReceiver : ISyntaxContextReceiver
-        {
-            ModelSymbols? _modelSymbols;
-
-            public List<(ClassDeclarationSyntax Class, AttributeData Attributes)> ClassAttributes { get; } = new();
-
-            sealed class ModelSymbols
-            {
-                public ModelSymbols(SemanticModel model, INamedTypeSymbol attributeType)
-                {
-                    Model = model;
-                    AttributeType = attributeType;
-                }
-
-                public SemanticModel Model { get; }
-                public INamedTypeSymbol AttributeType { get; }
-            }
-
-            ModelSymbols GetModelSymbols(SemanticModel semanticModel)
-            {
-                if (_modelSymbols is { Model: { } model } someModelSymbols && ReferenceEquals(semanticModel, model))
-                    return someModelSymbols;
-
-                const string attributeName = nameof(DocoptNet) + "." + nameof(DocoptArgumentsAttribute);
-                var attributeTypeSymbol = semanticModel.Compilation.GetTypeByMetadataName(attributeName);
-                return _modelSymbols = new ModelSymbols(semanticModel, attributeTypeSymbol ?? throw new NullReferenceException());
-            }
-
-            public void OnVisitSyntaxNode(GeneratorSyntaxContext context)
-            {
-                var attributeTypeSymbol = GetModelSymbols(context.SemanticModel).AttributeType;
-                if (context.Node is AttributeSyntax attribute
-                    && SymbolEqualityComparer.Default.Equals(attributeTypeSymbol, context.SemanticModel.GetTypeInfo(attribute).Type)
-                    && attribute.FirstAncestorOrSelf((ClassDeclarationSyntax _) => true) is { } cds
-                    && context.SemanticModel.GetDeclaredSymbol(cds)?.GetAttributes() is { } attributes)
-                {
-                    var attributeData = attributes.First(a => SymbolEqualityComparer.Default.Equals(a.AttributeClass, attributeTypeSymbol));
-                    ClassAttributes.Add((cds, attributeData));
-                }
-            }
-        }
-
-        static class Metadata
-        {
-            const string Prefix = "build_metadata.AdditionalFiles.";
-            public const string SourceItemType = Prefix + nameof(SourceItemType);
-            public const string Name = Prefix + nameof(Name);
-        }
-
-        static readonly SymbolDisplayFormat FullyQualifiedFormatWithoutGlobalNamespace =
-            SymbolDisplayFormat.FullyQualifiedFormat.WithGlobalNamespaceStyle(SymbolDisplayGlobalNamespaceStyle.Omitted);
-
-        const string DefaultHelpConstName = "Help";
-
-        public void Execute(GeneratorExecutionContext context)
+        public void Initialize(IncrementalGeneratorInitializationContext context)
         {
-            context.LaunchDebuggerIfFlagged(nameof(DocoptNet));
+            // FIXME re-instate launching debugger
+            // context.LaunchDebuggerIfFlagged(nameof(DocoptNet));
 
-            var syntaxReceiver = (SyntaxReceiver)(context.SyntaxContextReceiver ?? throw new NullReferenceException());
+            const string attributeName = $"{nameof(DocoptNet)}.{nameof(DocoptArgumentsAttribute)}";
 
-            SemanticModel? model = null;
-            SyntaxTree? modelSyntaxTree = null;
-
-            var docoptTypes = new List<(string? Namespace, string Name,
-                                        IEnumerable<TypeDeclarationSyntax> Parents,
-                                        DocoptArgumentsAttribute? ArgumentsAttribute,
-                                        SourceText Help, GenerationOptions Options)>();
-
-            foreach (var (cds, attributeData) in syntaxReceiver.ClassAttributes)
-            {
-                if (model is null || modelSyntaxTree != cds.SyntaxTree)
-                {
-                    model = context.Compilation.GetSemanticModel(cds.SyntaxTree);
-                    modelSyntaxTree = cds.SyntaxTree;
-                }
-
-                var symbol = model.GetDeclaredSymbol(cds) as INamedTypeSymbol;
-                if (symbol is null)
-                    continue;
-                // TODO emit diagnostics on nested types? symbol.ContainingType != null
-                var className = symbol.ToDisplayString(SymbolDisplayFormat.MinimallyQualifiedFormat);
-                var namespaceName =
-                    symbol.ContainingNamespace.ToDisplayString(FullyQualifiedFormatWithoutGlobalNamespace)
-                    is { Length: > 0 } s ? s : null;
-                var attribute = DocoptArgumentsAttribute.From(attributeData);
-                attribute.HelpConstName ??= DefaultHelpConstName;
-                var help = symbol.GetMembers()
-                                 .Choose(s => s is IFieldSymbol { IsConst: true, Name: var name, ConstantValue: string help }
-                                           && name == attribute.HelpConstName ? Some(help) : default)
-                                 .FirstOrDefault();
-                if (help is { } someHelp)
-                    docoptTypes.Add((namespaceName, className, cds.GetParents().Where(tds => tds is ClassDeclarationSyntax).Reverse(), attribute, SourceText.From(someHelp), GenerationOptions.SkipHelpConst));
-                else
-                    context.ReportDiagnostic(Diagnostic.Create(MissingHelpConstError, symbol.Locations.First(), symbol, attribute.HelpConstName));
-            }
-
-            var globalOptions = context.AnalyzerConfigOptions.GlobalOptions;
-            globalOptions.TryGetValue("build_property.RootNamespace", out var rootNamespace);
+            var docoptTypeResults =
+                context.SyntaxProvider
+                       .ForAttributeWithMetadataName(attributeName,
+                            static (node, _) => node is ClassDeclarationSyntax cds && cds.HasOrPotentiallyHasAttributes(),
+                            static (ctx, _) =>
+                            {
+                                var cds = (ClassDeclarationSyntax)ctx.TargetNode;
+                                var symbol = (INamedTypeSymbol)ctx.TargetSymbol;
+
+                                // TODO emit diagnostics on nested types? symbol.ContainingType != null
+                                var className = symbol.ToDisplayString(SymbolDisplayFormat.MinimallyQualifiedFormat);
+                                var namespaceName =
+                                    symbol.ContainingNamespace.ToDisplayString(FullyQualifiedFormatWithoutGlobalNamespace)
+                                        is { Length: > 0 } s ? s : null;
+                                var attributeData = ctx.Attributes[0];
+                                var attribute = DocoptArgumentsAttribute.From(attributeData);
+                                attribute.HelpConstName ??= DefaultHelpConstName;
+                                var help =
+                                    symbol.GetMembers()
+                                          .Choose(s => s is IFieldSymbol { IsConst: true, Name: var name, ConstantValue: string help }
+                                                    && name == attribute.HelpConstName ? Some(help) : default)
+                                          .FirstOrDefault();
+
+                                if (help is { } someHelp)
+                                {
+                                    return Result.Create((DocoptType?)new()
+                                    {
+                                        Namespace = namespaceName,
+                                        Name = className,
+                                        Parents = cds.GetParents()
+                                                     .Where(tds => tds is ClassDeclarationSyntax)
+                                                     .Reverse()
+                                                     .Select(p => p.Identifier.ToString())
+                                                     .ToImmutableArray(),
+                                        HelpConstName = attribute.HelpConstName,
+                                        Help = SourceText.From(someHelp),
+                                        Options = GenerationOptions.SkipHelpConst
+                                    });
+                                }
+
+                                var diagnostics = ImmutableArray.Create(DiagnosticInfo.Create(MissingHelpConstError, cds, symbol, attribute.HelpConstName));
+
+                                return new Result<DocoptType?>(null, diagnostics);
+                            });
+
+            context.RegisterSourceOutput(docoptTypeResults.Select((r, _) => r.Errors),
+                                         static (context, diagnostics) =>
+                                         {
+                                             foreach (var diagnostic in diagnostics)
+                                                 context.ReportDiagnostic(diagnostic.ToDiagnostic());
+                                         });
+
+            var docoptTypes = docoptTypeResults.Where(r => r.Value is not null)
+                                               .Select((r, _) => r.Value!);
+
+            var rootNamespace =
+                context.AnalyzerConfigOptionsProvider
+                       .Select((e, _) => e.GlobalOptions.TryGetValue("build_property.RootNamespace", out var rootNamespace) ? rootNamespace : null);
 
             var docoptSources =
-                context.AdditionalFiles
-                       .Choose(at => context.AnalyzerConfigOptions.GetOptions(at) is var options
-                                     && options.TryGetValue(Metadata.SourceItemType, out var type)
-                                     && "Docopt".Equals(type, StringComparison.OrdinalIgnoreCase)
-                                     && at.GetText() is { } text
-                                     ? Some((rootNamespace,
-                                             options.TryGetValue(Metadata.Name, out var name)
-                                             && !string.IsNullOrWhiteSpace(name)
-                                                 ? name
-                                                 : Path.GetFileName(at.Path).Partition(".").Item1 + "Arguments",
-                                             Enumerable.Empty<TypeDeclarationSyntax>(),
-                                             (DocoptArgumentsAttribute?)null,
-                                             text,
-                                             GenerationOptions.None))
-                                     : default)
-                       .ToImmutableArray();
-
-            var hintNameBuilder = new StringBuilder();
-
-            foreach (var (ns, name, parents, attribute, help, options) in docoptSources.Concat(docoptTypes))
+                context.AdditionalTextsProvider
+                       .Combine(context.AnalyzerConfigOptionsProvider)
+                       .Combine(rootNamespace)
+                       .Select((e, _) =>
+                       {
+                           var ((at, analyzerConfigOptions), ns) = e;
+                           return analyzerConfigOptions.GetOptions(at) is var options
+                                  && options.TryGetValue(Metadata.SourceItemType, out var type)
+                                  && "Docopt".Equals(type, StringComparison.OrdinalIgnoreCase)
+                                  && at.GetText() is { } text
+                                  ? (DocoptType?)new()
+                                    {
+                                        Namespace = ns,
+                                        Name = options.TryGetValue(Metadata.Name, out var name)
+                                               && !string.IsNullOrWhiteSpace(name)
+                                             ? name
+                                             : Path.GetFileName(at.Path).Partition(".").Item1 + "Arguments",
+                                        Parents = ImmutableArray<string>.Empty,
+                                        HelpConstName = null,
+                                        Help = text,
+                                        Options = GenerationOptions.None
+                                    }
+                                  : default;
+                       })
+                       .Where(e => e is not null);
+
+            context.RegisterSourceOutput(docoptSources, Generate!);
+            context.RegisterSourceOutput(docoptTypes, Generate);
+
+            static void Generate(SourceProductionContext context, DocoptType dt)
             {
+                var hintNameBuilder = new StringBuilder();
+
                 try
                 {
-                    var parentNames = parents.Select(p => p.Identifier.ToString()).ToArray();
-                    if (Generate(ns, name, parentNames, attribute?.HelpConstName, help, options) is { Length: > 0 } source)
+                    var parentNames = dt.Parents;
+                    if (SourceGenerator.Generate(dt.Namespace, dt.Name, parentNames, dt.HelpConstName, dt.Help, dt.Options)
+                        is { Length: > 0 } source)
                     {
-                        hintNameBuilder.Clear();
-                        if (ns is { } someNamespace)
-                            hintNameBuilder.Append(someNamespace).Append('.');
-                        if (parentNames.Length > 0)
+                        if (dt.Namespace is { } someNamespace) hintNameBuilder.Append(someNamespace).Append('.');
+                        if (parentNames.AsSpan().Length > 0)
                         {
                             foreach (var pn in parentNames)
                             {
@@ -178,7 +153,8 @@ public void Execute(GeneratorExecutionContext context)
                                 hintNameBuilder.Append(pn).Append('-');
                             }
                         }
-                        hintNameBuilder.Append(name);
+
+                        hintNameBuilder.Append(dt.Name);
                         context.AddSource(hintNameBuilder.Append(".cs").ToString(), source);
                     }
                 }
@@ -190,6 +166,39 @@ public void Execute(GeneratorExecutionContext context)
             }
         }
 
+        sealed record DocoptType
+        {
+            public required string? Namespace { get; init; }
+            public required string Name { get; init; }
+            public required EquatableArray<string> Parents { get; init; }
+            public required string? HelpConstName { get; init; }
+            public required SourceText Help { get; init; }
+            public required GenerationOptions Options { get; init; }
+        }
+
+        static class Result
+        {
+            public static Result<TValue> Create<TValue>(TValue value)
+                where TValue : IEquatable<TValue>? =>
+                Create(value, ImmutableArray<DiagnosticInfo>.Empty);
+
+            public static Result<TValue> Create<TValue>(TValue value, EquatableArray<DiagnosticInfo> errors)
+                where TValue : IEquatable<TValue>? =>
+                new(value, errors);
+        }
+
+        static class Metadata
+        {
+            const string Prefix = "build_metadata.AdditionalFiles.";
+            public const string SourceItemType = Prefix + nameof(SourceItemType);
+            public const string Name = Prefix + nameof(Name);
+        }
+
+        static readonly SymbolDisplayFormat FullyQualifiedFormatWithoutGlobalNamespace =
+            SymbolDisplayFormat.FullyQualifiedFormat.WithGlobalNamespaceStyle(SymbolDisplayGlobalNamespaceStyle.Omitted);
+
+        const string DefaultHelpConstName = "Help";
+
         static readonly SourceText EmptySourceText = SourceText.From(string.Empty);
         static readonly Encoding Utf8BomlessEncoding = new UTF8Encoding(encoderShouldEmitUTF8Identifier: false);
 
diff --git a/src/DocoptNet/DocoptNet.csproj b/src/DocoptNet/DocoptNet.csproj
index 75aab781..506603f9 100644
--- a/src/DocoptNet/DocoptNet.csproj
+++ b/src/DocoptNet/DocoptNet.csproj
@@ -1,4 +1,4 @@
-<Project Sdk="Microsoft.NET.Sdk">
+<Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
     <TargetFrameworks>netstandard2.1;netstandard2.0;netstandard1.5</TargetFrameworks>
@@ -50,7 +50,7 @@ Portions Copyright (C) West Wind Technologies, 2008.
   </ItemGroup>
 
   <ItemGroup Condition="'$(TargetFramework)' != 'netstandard1.5'">
-    <PackageReference Include="Microsoft.CodeAnalysis.CSharp" Version="3.10.0" PrivateAssets="all" />
+    <PackageReference Include="Microsoft.CodeAnalysis.CSharp" Version="4.3.1" PrivateAssets="all" />
     <AdditionalFiles Include="CodeGeneration\AnalyzerReleases.*.md" />
   </ItemGroup>
 
diff --git a/tests/DocoptNet.Tests/CodeGeneration/SourceGeneratorTests.cs b/tests/DocoptNet.Tests/CodeGeneration/SourceGeneratorTests.cs
index 83577dd5..57fa1887 100644
--- a/tests/DocoptNet.Tests/CodeGeneration/SourceGeneratorTests.cs
+++ b/tests/DocoptNet.Tests/CodeGeneration/SourceGeneratorTests.cs
@@ -551,7 +551,7 @@ public partial class " + ProgramArgumentsClassName + @" { }
         static readonly RsAnalyzerConfigOptions DocoptSourceItemTypeConfigOption =
             new AnalyzerConfigOptions(KeyValuePair.Create("build_metadata.AdditionalFiles.SourceItemType", "Docopt"));
 
-        internal static (CSharpGeneratorDriver, CSharpCompilation)
+        internal static (GeneratorDriver, CSharpCompilation)
             PrepareForGeneration(params (string Path, SourceText Text)[] sources)
         {
             var trees = new List<SyntaxTree>();
@@ -576,7 +576,7 @@ internal static (CSharpGeneratorDriver, CSharpCompilation)
                                  .AddReferences(MetadataReference.CreateFromFile(Path.Combine(TestContext.CurrentContext.TestDirectory, "Newtonsoft.Json.dll")))
                                  .AddReferences(MetadataReference.CreateFromFile(typeof(Docopt).Assembly.Location));
 
-            ISourceGenerator generator = new SourceGenerator();
+            IIncrementalGenerator generator = new SourceGenerator();
 
             var globalOptions = Enumerable.Empty<KeyValuePair<string, string>>();
 
@@ -586,9 +586,9 @@ internal static (CSharpGeneratorDriver, CSharpCompilation)
                     additionalTexts.Select(at => KeyValuePair.Create(at, DocoptSourceItemTypeConfigOption))
                                    .ToImmutableDictionary());
 
-            var driver = CSharpGeneratorDriver.Create(new[] { generator },
-                                                      additionalTexts,
-                                                      optionsProvider: optionsProvider);
+            GeneratorDriver driver = CSharpGeneratorDriver.Create(generator);
+            driver = driver.AddAdditionalTexts(additionalTexts.ToImmutableArray());
+            driver = driver.WithUpdatedAnalyzerConfigOptions(optionsProvider);
 
             return (driver, compilation);
         }
diff --git a/tests/DocoptNet.Tests/DocoptNet.Tests.csproj b/tests/DocoptNet.Tests/DocoptNet.Tests.csproj
index a9528233..b5665b12 100644
--- a/tests/DocoptNet.Tests/DocoptNet.Tests.csproj
+++ b/tests/DocoptNet.Tests/DocoptNet.Tests.csproj
@@ -26,7 +26,7 @@
 
   <ItemGroup>
     <PackageReference Include="Basic.Reference.Assemblies" Version="1.4.1" />
-    <PackageReference Include="Microsoft.CodeAnalysis.CSharp" Version="3.10.0" />
+    <PackageReference Include="Microsoft.CodeAnalysis.CSharp" Version="4.3.1" />
     <PackageReference Include="morelinq" Version="3.3.2" />
     <PackageReference Include="Newtonsoft.Json" Version="13.0.2" />
     <PackageReference Include="nunit" Version="3.13.3" />