Overhaul how regex generated code is structured

src/libraries/System.Text.RegularExpressions/gen/RegexGenerator.Parser.cs

@@ -178,10 +178,10 @@ private static bool IsSemanticTargetForGeneration(SemanticModel semanticModel, M
             }
 
             // Parse the input pattern
-            RegexTree tree;
+            RegexTree regexTree;
             try
             {
-                tree = RegexParser.Parse(pattern, regexOptions | RegexOptions.Compiled, culture); // make sure Compiled is included to get all optimizations applied to it
+                regexTree = RegexParser.Parse(pattern, regexOptions | RegexOptions.Compiled, culture); // make sure Compiled is included to get all optimizations applied to it
             }
             catch (Exception e)
             {
@@ -192,37 +192,36 @@ private static bool IsSemanticTargetForGeneration(SemanticModel semanticModel, M
             string? ns = regexMethodSymbol.ContainingType?.ContainingNamespace?.ToDisplayString(
                 SymbolDisplayFormat.FullyQualifiedFormat.WithGlobalNamespaceStyle(SymbolDisplayGlobalNamespaceStyle.Omitted));
 
+            var regexType = new RegexType(
+                typeDec is RecordDeclarationSyntax rds ? $"{typeDec.Keyword.ValueText} {rds.ClassOrStructKeyword}" : typeDec.Keyword.ValueText,
+                ns ?? string.Empty,
+                $"{typeDec.Identifier}{typeDec.TypeParameterList}");
+
             var regexMethod = new RegexMethod(
+                regexType,
                 methodSyntax,
                 regexMethodSymbol.Name,
                 methodSyntax.Modifiers.ToString(),
                 pattern,
                 regexOptions,
                 matchTimeout ?? Timeout.Infinite,
-                tree);
-
-            var regexType = new RegexType(
-                regexMethod,
-                typeDec is RecordDeclarationSyntax rds ? $"{typeDec.Keyword.ValueText} {rds.ClassOrStructKeyword}" : typeDec.Keyword.ValueText,
-                ns ?? string.Empty,
-                $"{typeDec.Identifier}{typeDec.TypeParameterList}");
+                regexTree);
 
             RegexType current = regexType;
             var parent = typeDec.Parent as TypeDeclarationSyntax;
 
             while (parent is not null && IsAllowedKind(parent.Kind()))
             {
-                current.ParentClass = new RegexType(
-                    null,
+                current.Parent = new RegexType(
                     parent is RecordDeclarationSyntax rds2 ? $"{parent.Keyword.ValueText} {rds2.ClassOrStructKeyword}" : parent.Keyword.ValueText,
                     ns ?? string.Empty,
                     $"{parent.Identifier}{parent.TypeParameterList}");
 
-                current = current.ParentClass;
+                current = current.Parent;
                 parent = parent.Parent as TypeDeclarationSyntax;
             }
 
-            return regexType;
+            return regexMethod;
 
             static bool IsAllowedKind(SyntaxKind kind) =>
                 kind == SyntaxKind.ClassDeclaration ||
@@ -233,12 +232,16 @@ private static bool IsSemanticTargetForGeneration(SemanticModel semanticModel, M
         }
 
         /// <summary>A regex method.</summary>
-        internal sealed record RegexMethod(MethodDeclarationSyntax MethodSyntax, string MethodName, string Modifiers, string Pattern, RegexOptions Options, int MatchTimeout, RegexTree Tree);
+        internal sealed record RegexMethod(RegexType DeclaringType, MethodDeclarationSyntax MethodSyntax, string MethodName, string Modifiers, string Pattern, RegexOptions Options, int MatchTimeout, RegexTree Tree)
+        {
+            public int GeneratedId { get; set; }
+            public string GeneratedName => $"{MethodName}_{GeneratedId}";
+        }
 
         /// <summary>A type holding a regex method.</summary>
-        internal sealed record RegexType(RegexMethod? Method, string Keyword, string Namespace, string Name)
+        internal sealed record RegexType(string Keyword, string Namespace, string Name)
         {
-            public RegexType? ParentClass { get; set; }
+            public RegexType? Parent { get; set; }
         }
     }
 }

src/libraries/System.Text.RegularExpressions/gen/RegexGenerator.cs

@@ -2,11 +2,13 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System;
+using System.CodeDom.Compiler;
 using System.Collections.Generic;
 using System.Collections.Immutable;
 using System.Diagnostics;
 using System.Diagnostics.CodeAnalysis;
 using System.Diagnostics.Tracing;
+using System.IO;
 using System.Linq;
 using System.Runtime.CompilerServices;
 using System.Text;
@@ -23,65 +25,239 @@ namespace System.Text.RegularExpressions.Generator
     [Generator(LanguageNames.CSharp)]
     public partial class RegexGenerator : IIncrementalGenerator
     {
-        public void Initialize(IncrementalGeneratorInitializationContext context)
+        /// <summary>Name of the type emitted to contain helpers used by the generated code.</summary>
+        private const string HelpersTypeName = "Utilities";
+        /// <summary>Namespace containing all the generated code.</summary>
+        private const string GeneratedNamespace = "System.Text.RegularExpressions.Generated";
+        /// <summary>Code for a [GeneratedCode] attribute to put on the top-level generated members.</summary>
+        private static readonly string s_generatedCodeAttribute = $"GeneratedCodeAttribute(\"{typeof(RegexGenerator).Assembly.GetName().Name}\", \"{typeof(RegexGenerator).Assembly.GetName().Version}\")";
+        /// <summary>Header comments and usings to include at the top of every generated file.</summary>
+        private static readonly string[] s_headers = new string[]
         {
-            // To avoid invalidating the generator's output when anything from the compilation
-            // changes, we will extract from it the only thing we care about: whether unsafe
-            // code is allowed.
-            IncrementalValueProvider<bool> allowUnsafeProvider =
-                context.CompilationProvider
-                .Select((x, _) => x.Options is CSharpCompilationOptions { AllowUnsafe: true });
+            "// <auto-generated/>",
+            "#nullable enable",
+            "#pragma warning disable CS0162 // Unreachable code",
+            "#pragma warning disable CS0164 // Unreferenced label",
+            "#pragma warning disable CS0219 // Variable assigned but never used",
+        };
 
-            // Contains one entry per regex method, either the generated code for that regex method,
-            // a diagnostic to fail with, or null if no action should be taken for that regex.
+        public void Initialize(IncrementalGeneratorInitializationContext context)
+        {
+            // Produces one entry per generated regex.  This may be:
+            // - Diagnostic in the case of a failure that should end the compilation
+            // - (RegexMethod regexMethod, string runnerFactoryImplementation, Dictionary<string, string[]> requiredHelpers) in the case of valid regex
+            // - (RegexMethod regexMethod, string reason, Diagnostic diagnostic) in the case of a limited-support regex
             IncrementalValueProvider<ImmutableArray<object?>> codeOrDiagnostics =
                 context.SyntaxProvider
 
-                // Find all MethodDeclarationSyntax nodes attributed with RegexGenerator and gather the required information
+                // Find all MethodDeclarationSyntax nodes attributed with RegexGenerator and gather the required information.
                 .CreateSyntaxProvider(IsSyntaxTargetForGeneration, GetSemanticTargetForGeneration)
                 .Where(static m => m is not null)
 
-                // Pair each with whether unsafe code is allowed
-                .Combine(allowUnsafeProvider)
-
-                // Get the resulting code string or error Diagnostic for
-                // each MethodDeclarationSyntax/allow-unsafe-blocks pair
+                // Generate the RunnerFactory for each regex, if possible.  This is where the bulk of the implementation occurs.
                 .Select((state, _) =>
                 {
-                    Debug.Assert(state.Left is not null);
-                    return state.Left is RegexType regexType ? EmitRegexType(regexType, state.Right) : state.Left;
+                    if (state is not RegexMethod regexMethod)
+                    {
+                        Debug.Assert(state is Diagnostic);
+                        return state;
+                    }
+
+                    // If we're unable to generate a full implementation for this regex, report a diagnostic.
+                    // We'll still output a limited implementation that just caches a new Regex(...).
+                    if (!regexMethod.Tree.Root.SupportsCompilation(out string? reason))
+                    {
+                        return (regexMethod, reason, Diagnostic.Create(DiagnosticDescriptors.LimitedSourceGeneration, regexMethod.MethodSyntax.GetLocation()));
+                    }
+
+                    // Generate the core logic for the regex.
+                    Dictionary<string, string[]> requiredHelpers = new();
+                    var sw = new StringWriter();
+                    var writer = new IndentedTextWriter(sw);
+                    writer.Indent += 3;
+                    writer.WriteLine();
+                    EmitRegexDerivedTypeRunnerFactory(writer, regexMethod, requiredHelpers);
+                    writer.Indent -= 3;
+                    return (regexMethod, sw.ToString(), requiredHelpers);
                 })
                 .Collect();
 
+            // To avoid invalidating every regex's output when anything from the compilation changes,
+            // we extract from it the only things we care about: whether unsafe code is allowed,
+            // and a name based on the assembly's name, and only that information is then fed into
+            // RegisterSourceOutput along with all of the cached generated data from each regex.
+            IncrementalValueProvider<(bool AllowUnsafe, string? AssemblyName)> compilationDataProvider =
+                context.CompilationProvider
+                .Select((x, _) => (x.Options is CSharpCompilationOptions { AllowUnsafe: true }, x.AssemblyName));
+
             // When there something to output, take all the generated strings and concatenate them to output,
             // and raise all of the created diagnostics.
-            context.RegisterSourceOutput(codeOrDiagnostics, static (context, results) =>
+            context.RegisterSourceOutput(codeOrDiagnostics.Combine(compilationDataProvider), static (context, compilationDataAndResults) =>
             {
-                var code = new List<string>(s_headers.Length + results.Length);
-
-                // Add file header and required usings
-                code.AddRange(s_headers);
+                ImmutableArray<object?> results = compilationDataAndResults.Left;
 
+                // Report any top-level diagnostics.
+                bool allFailures = true;
                 foreach (object? result in results)
                 {
-                    switch (result)
+                    if (result is Diagnostic d)
                     {
-                        case Diagnostic d:
-                            context.ReportDiagnostic(d);
-                            break;
+                        context.ReportDiagnostic(d);
+                    }
+                    else
+                    {
+                        allFailures = false;
+                    }
+                }
+                if (allFailures)
+                {
+                    return;
+                }
+
+                // At this point we'll be emitting code.  Create a writer to hold it all.
+                var sw = new StringWriter();
+                IndentedTextWriter writer = new(sw);
+
+                // Add file headers and required usings.
+                foreach (string header in s_headers)
+                {
+                    writer.WriteLine(header);
+                }
+                writer.WriteLine();
 
-                        case ValueTuple<string, ImmutableArray<Diagnostic>> t:
-                            code.Add(t.Item1);
-                            foreach (Diagnostic d in t.Item2)
+                // For every generated type, we give it an incrementally increasing ID, in order to create
+                // unique type names even in situations where method names were the same, while also keeping
+                // the type names short.  Note that this is why we only generate the RunnerFactory implementations
+                // earlier in the pipeline... we want to avoid generating code that relies on the class names
+                // until we're able to iterate through them linearly keeping track of a deterministic ID
+                // used to name them.  The boilerplate code generation that happens here is minimal when compared to
+                // the work required to generate the actual matching code for the regex.
+                int id = 0;
+                string generatedClassName = $"__{ComputeStringHash(compilationDataAndResults.Right.AssemblyName ?? ""):x}";
+
+                // If we have any (RegexMethod regexMethod, string generatedName, string reason, Diagnostic diagnostic), these are regexes for which we have
+                // limited support and need to simply output boilerplate.  We need to emit their diagnostics.
+                // If we have any (RegexMethod regexMethod, string generatedName, string runnerFactoryImplementation, Dictionary<string, string[]> requiredHelpers),
+                // those are generated implementations to be emitted.  We need to gather up their required helpers.
+                Dictionary<string, string[]> requiredHelpers = new();
+                foreach (object? result in results)
+                {
+                    RegexMethod? regexMethod = null;
+                    if (result is ValueTuple<RegexMethod, string, Diagnostic> limitedSupportResult)
+                    {
+                        context.ReportDiagnostic(limitedSupportResult.Item3);
+                        regexMethod = limitedSupportResult.Item1;
+                    }
+                    else if (result is ValueTuple<RegexMethod, string, Dictionary<string, string[]>> regexImpl)
+                    {
+                        foreach (KeyValuePair<string, string[]> helper in regexImpl.Item3)
+                        {
+                            if (!requiredHelpers.ContainsKey(helper.Key))
                             {
-                                context.ReportDiagnostic(d);
+                                requiredHelpers.Add(helper.Key, helper.Value);
                             }
-                            break;
+                        }
+
+                        regexMethod = regexImpl.Item1;
+                    }
+
+                    if (regexMethod is not null)
+                    {
+                        regexMethod.GeneratedId = id++;
+                        EmitRegexPartialMethod(regexMethod, writer, generatedClassName);
+                        writer.WriteLine();
+                    }
+                }
+
+                // At this point we've emitted all the partial method definitions, but we still need to emit the actual regex-derived implementations.
+                // These are all emitted inside of our generated class.
+                // TODO https://github.com/dotnet/csharplang/issues/5529:
+                // When C# provides a mechanism for shielding generated code from the rest of the project, it should be employed
+                // here for the generated class.  At that point, the generated class wrapper can be removed, and all of the types
+                // generated inside of it (one for each regex as well as the helpers type) should be shielded.
+
+                writer.WriteLine($"namespace {GeneratedNamespace}");
+                writer.WriteLine($"{{");
+
+                // We emit usings here now that we're inside of a namespace block and are no longer emitting code into
+                // a user's partial type.  We can now rely on binding rules mapping to these usings and don't need to
+                // use global-qualified names for the rest of the implementation.
+                writer.WriteLine($"    using System;");
+                writer.WriteLine($"    using System.CodeDom.Compiler;");
+                writer.WriteLine($"    using System.Collections;");
+                writer.WriteLine($"    using System.ComponentModel;");
+                writer.WriteLine($"    using System.Globalization;");
+                writer.WriteLine($"    using System.Runtime.CompilerServices;");
+                writer.WriteLine($"    using System.Text.RegularExpressions;");
+                writer.WriteLine($"    using System.Threading;");
+                writer.WriteLine($"");
+                if (compilationDataAndResults.Right.AllowUnsafe)
+                {
+                    writer.WriteLine($"    [SkipLocalsInit]");
+                }
+                writer.WriteLine($"    [{s_generatedCodeAttribute}]");
+                writer.WriteLine($"    [EditorBrowsable(EditorBrowsableState.Never)]");
+                writer.WriteLine($"    internal static class {generatedClassName}");
+                writer.WriteLine($"    {{");
+
+                // Emit each Regex-derived type.
+                writer.Indent += 2;
+                foreach (object? result in results)
+                {
+                    if (result is ValueTuple<RegexMethod, string, Diagnostic> limitedSupportResult)
+                    {
+                        EmitRegexLimitedBoilerplate(writer, limitedSupportResult.Item1, limitedSupportResult.Item1.GeneratedId, limitedSupportResult.Item2);
+                        writer.WriteLine();
+                    }
+                    else if (result is ValueTuple<RegexMethod, string, Dictionary<string, string[]>> regexImpl)
+                    {
+                        EmitRegexDerivedImplementation(writer, regexImpl.Item1, regexImpl.Item1.GeneratedId, regexImpl.Item2);
+                        writer.WriteLine();
+                    }
+                }
+                writer.Indent -= 2;
+
+                // If any of the Regex-derived types asked for helper methods, emit those now.
+                if (requiredHelpers.Count != 0)
+                {
+                    writer.Indent += 2;
+                    writer.WriteLine($"private static class {HelpersTypeName}");
+                    writer.WriteLine($"{{");
+                    writer.Indent++;
+                    foreach (KeyValuePair<string, string[]> helper in requiredHelpers)
+                    {
+                        foreach (string value in helper.Value)
+                        {
+                            writer.WriteLine(value);
+                        }
+                        writer.WriteLine();
                     }
+                    writer.Indent--;
+                    writer.WriteLine($"}}");
+                    writer.Indent -= 2;
                 }
 
-                context.AddSource("RegexGenerator.g.cs", string.Join(Environment.NewLine, code));
+                writer.WriteLine($"    }}");
+                writer.WriteLine($"}}");
+
+                // Save out the source
+                context.AddSource("RegexGenerator.g.cs", sw.ToString());
             });
         }
+
+        /// <summary>Computes a hash of the string.</summary>
+        /// <remarks>
+        /// Currently an FNV-1a hash function. The actual algorithm used doesn't matter; just something
+        /// simple to create a deterministic, pseudo-random value that's based on input text.
+        /// </remarks>
+        private static uint ComputeStringHash(string s)
+        {
+            uint hashCode = 2166136261;
+            foreach (char c in s)
+            {
+                hashCode = (c ^ hashCode) * 16777619;
+            }
+            return hashCode;
+        }
     }
 }

src/libraries/System.Text.RegularExpressions/gen/System.Text.RegularExpressions.Generator.csproj

@@ -13,6 +13,7 @@
     <IsNETCoreAppAnalyzer>true</IsNETCoreAppAnalyzer>
     <AnalyzerLanguage>cs</AnalyzerLanguage>
     <IsPackable>false</IsPackable>
+    <LangVersion>Preview</LangVersion>
   </PropertyGroup>
 
   <ItemGroup>