discord-bot/SourceGenerators/Win32ErrorsSourceGenerator.cs

using System;
using System.IO;
using System.Linq;
using System.Text;
using System.Text.RegularExpressions;
using Microsoft.CodeAnalysis;
using Microsoft.CodeAnalysis.Text;

namespace SourceGenerators;

[Generator]
public class Win32ErrorsSourceGenerator : ISourceGenerator
{
    private const string Indent = "    ";
    private static readonly char[] Separator = {'\t'};
        
    private static readonly DiagnosticDescriptor Win32ErrorFormatError = new(
        id: "WIN32CODE001",
        title: "Invalid Win32 error code line",
        messageFormat: "Error while parsing win32 error code description. Code: '{0}', description: '{1}'.",
        category: nameof(Win32ErrorsSourceGenerator),
        DiagnosticSeverity.Error,
        isEnabledByDefault: true
    );

    public void Initialize(GeneratorInitializationContext context)
    {
    }

    public void Execute(GeneratorExecutionContext context)
    {
        var resourceName = context.AdditionalFiles
            .OrderBy(f => f.Path, StringComparer.OrdinalIgnoreCase)
            .LastOrDefault(f => Path.GetFileName(f.Path) is string fname && fname.StartsWith("win32_error_codes", StringComparison.OrdinalIgnoreCase) && fname.EndsWith(".txt", StringComparison.OrdinalIgnoreCase));
        if (resourceName is null)
            return;
            
        using var stream = File.Open(resourceName.Path, FileMode.Open, FileAccess.Read, FileShare.Read);
        if (stream is null)
            throw new InvalidOperationException("Failed to get win32_error_codes txt stream");

        if (!context.AnalyzerConfigOptions.GlobalOptions.TryGetValue("build_property.RootNamespace", out var ns))
            ns = context.Compilation.AssemblyName;
        var cn = "Win32ErrorCodes";
        var result = new StringBuilder()
            .AppendLine("using System.Collections.Generic;")
            .AppendLine()
            .AppendLine($"namespace {ns}")
            .AppendLine("{")
            .AppendLine($"{Indent}public static class {cn}")
            .AppendLine($"{Indent}{{")
            .AppendLine($"{Indent}{Indent}public static readonly Dictionary<int, (string name, string description)> Map = new()")
            .AppendLine($"{Indent}{Indent}{{");

        var previousPos = 0;
        var line = 0;
        var codeLine = 0;
        var descLine = 0;
        using var reader = new StreamReader(stream, Encoding.UTF8, false);
        while (reader.ReadLine() is string errorCodeLine)
        {
            line++;
            if (string.IsNullOrWhiteSpace(errorCodeLine))
                continue;

            codeLine = line - 1;
            string errorNameAndDescriptionLine;
            do
            {
                errorNameAndDescriptionLine = reader.ReadLine();
                line++;
            } while (string.IsNullOrWhiteSpace(errorNameAndDescriptionLine));
            descLine = line - 1;
                
            var nameDescParts = errorNameAndDescriptionLine.Split(Separator, 2);
            if (nameDescParts.Length != 2 || !Regex.IsMatch(errorCodeLine, @"0x[0-9a-f]+"))
            {
                context.ReportDiagnostic(Diagnostic.Create(
                    Win32ErrorFormatError,
                    Location.Create(
                        resourceName.Path,
                        TextSpan.FromBounds(
                            previousPos,
                            (int)stream.Position
                        ),
                        new(
                            new(codeLine, 0),
                            new(descLine, errorNameAndDescriptionLine.Length)
                        )),
                    errorCodeLine,
                    errorNameAndDescriptionLine));
                previousPos = (int)stream.Position;
                continue;
            }
            previousPos = (int)stream.Position;

            var name = nameDescParts[0];
            var desc = nameDescParts[1].Replace("\\", "\\\\").Replace("\"", "\\\"");
            result.AppendLine($"{Indent}{Indent}{Indent}[{errorCodeLine.Trim()}] = (\"{name.Trim()}\", \"{desc.Trim()}\"),");
        }

        result.AppendLine($"{Indent}{Indent}}};")
            .AppendLine($"{Indent}}}")
            .AppendLine("}");
            
        context.AddSource($"{cn}.Generated.cs", SourceText.From(result.ToString(), Encoding.UTF8));
    }
}