added source generator for Combine methods

JustDotNet.Railway.sln

@@ -7,6 +7,8 @@ Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Railway", "Railway\Railway.
 EndProject
 Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Raliway.Tests", "Raliway.Tests\Raliway.Tests.csproj", "{607F91E4-83A2-48C4-BAC2-2205BEE81D93}"
 EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Railway.SourceGenerator", "Railway.SourceGenerator\Railway.SourceGenerator.csproj", "{1A3B8F0A-7A30-4AA8-BC15-47FA2D75B6BF}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -24,5 +26,9 @@ Global
 		{607F91E4-83A2-48C4-BAC2-2205BEE81D93}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{607F91E4-83A2-48C4-BAC2-2205BEE81D93}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{607F91E4-83A2-48C4-BAC2-2205BEE81D93}.Release|Any CPU.Build.0 = Release|Any CPU
+		{1A3B8F0A-7A30-4AA8-BC15-47FA2D75B6BF}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{1A3B8F0A-7A30-4AA8-BC15-47FA2D75B6BF}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{1A3B8F0A-7A30-4AA8-BC15-47FA2D75B6BF}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{1A3B8F0A-7A30-4AA8-BC15-47FA2D75B6BF}.Release|Any CPU.Build.0 = Release|Any CPU
 	EndGlobalSection
 EndGlobal

Railway.SourceGenerator/Constants.cs

@@ -0,0 +1,7 @@
+namespace Just.Railway.SourceGen;
+
+internal static class Constants
+{
+    public const int MaxResultTupleSize = 4;
+    
+}

Railway.SourceGenerator/Railway.SourceGenerator.csproj

@@ -0,0 +1,20 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>netstandard2.0</TargetFramework>
+    <LangVersion>latest</LangVersion>
+    <IsPackable>false</IsPackable>
+    <RootNamespace>Just.Railway.SourceGen</RootNamespace>
+    
+    <EnforceExtendedAnalyzerRules>true</EnforceExtendedAnalyzerRules>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Microsoft.CodeAnalysis.Analyzers" Version="3.3.4">
+      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+      <PrivateAssets>all</PrivateAssets>
+    </PackageReference>
+    <PackageReference Include="Microsoft.CodeAnalysis.CSharp" Version="4.8.0" />
+  </ItemGroup>
+
+</Project>

Railway.SourceGenerator/ResultCombineGenerator.cs

@@ -0,0 +1,214 @@
+using System;
+using System.Collections.Generic;
+using System.Collections.Immutable;
+using System.Linq;
+using System.Text;
+using Microsoft.CodeAnalysis;
+
+namespace Just.Railway.SourceGen;
+
+[Generator]
+public class ResultCombineGenerator : IIncrementalGenerator
+{
+    public ResultCombineGenerator()
+    {
+    }
+
+    public void Initialize(IncrementalGeneratorInitializationContext context)
+    {
+        context.RegisterSourceOutput(context.CompilationProvider, Execute);
+    }
+
+    private void Execute(SourceProductionContext context, Compilation source)
+    {
+        var methods = GenerateCombineMethods();
+        var code = $$"""
+        #nullable enable
+        using System;
+        using System.Collections.Generic;
+        using System.Diagnostics.Contracts;
+        using System.CodeDom.Compiler;
+
+        namespace Just.Railway;
+
+        public readonly partial struct Result
+        {
+        {{methods}}
+        }
+        """;
+
+        context.AddSource("Result.Combine.g.cs", code);
+    }
+
+    private string GenerateCombineMethods()
+    {
+        var sb = new StringBuilder();
+
+        for (int i = 2; i <= Constants.MaxResultTupleSize; i++)
+        {
+            GenerateCombineMethodsForArgCount(sb, argCount: i);
+        }
+
+        return sb.ToString();
+    }
+
+    private void GenerateCombineMethodsForArgCount(StringBuilder sb, int argCount)
+    {
+        sb.AppendLine($"#region Combine {argCount} Results");
+
+        GenerateGetBottomMethod(sb, argCount);
+
+        var argsResultTupleSizes = new List<ImmutableArray<int>>();
+        Span<int> templateCounts = stackalloc int[argCount];
+
+        Permute(templateCounts, argsResultTupleSizes);
+
+        foreach (var argResultTupleSizes in argsResultTupleSizes)
+        {
+            sb.AppendLine(GenerateCombineMethodBody(argResultTupleSizes));
+        }
+
+        sb.AppendLine("#endregion");
+
+        static void Permute(Span<int> templateCounts, ICollection<ImmutableArray<int>> argsResultTupleSizes, int lvl = 0)
+        {
+            int sum = 0;
+            for (int i = 0; i < lvl; i++)
+            {
+                sum += templateCounts[i];
+            }
+            for (templateCounts[lvl] = 0; templateCounts[lvl] <= Constants.MaxResultTupleSize - sum; templateCounts[lvl]++)
+            {
+                if (lvl == templateCounts.Length - 1)
+                {
+                    argsResultTupleSizes.Add(templateCounts.ToImmutableArray());
+                    continue;
+                }
+                Permute(templateCounts, argsResultTupleSizes, lvl + 1);
+            }
+        }
+    }
+
+    private static void GenerateGetBottomMethod(StringBuilder sb, int argCount)
+    {
+        var args = Enumerable.Range(1, argCount)
+            .Select(i => $"result{i}")
+            .ToImmutableArray();
+        var argsDecl = string.Join(", ", args.Select(x => $"ResultState {x}"));
+        sb.AppendLine($"[GeneratedCodeAttribute(\"{nameof(ResultCombineGenerator)}\", \"1.0.0.0\")]");
+        sb.AppendLine($"private static IEnumerable<string> GetBottom({argsDecl})");
+        sb.AppendLine("{");
+        foreach (var arg in args)
+        {
+            sb.AppendLine($"    if ({arg} == ResultState.Bottom) yield return \"{arg}\";");
+        }
+        sb.AppendLine("}");
+    }
+
+    private string GenerateCombineMethodBody(ImmutableArray<int> argResultTupleSizes)
+    {
+        var resultTupleSize = argResultTupleSizes.Sum();
+
+        var paramNames = Enumerable.Range(1, argResultTupleSizes.Length)
+            .Select(i => $"result{i}")
+            .ToImmutableArray();
+        var templateArgNames = Enumerable.Range(1, resultTupleSize)
+            .Select(i => $"T{i}")
+            .ToImmutableArray();
+
+        string templateDecl = templateArgNames.IsEmpty 
+            ? string.Empty
+            : $"<{string.Join(", ", templateArgNames)}>";
+        string resultTypeDecl = GetResultTypeDecl(templateArgNames);
+        string paramDecl;
+        {
+            var paramDeclBuilder = new StringBuilder();
+            int currentTemplateArg = 0;
+            for (int i = 0; i < argResultTupleSizes.Length; i++)
+            {
+                var argResultTupleSize = argResultTupleSizes[i];
+                string currentParamType = GetResultTypeDecl(templateArgNames.Slice(currentTemplateArg, argResultTupleSize));
+                currentTemplateArg += argResultTupleSize;
+                paramDeclBuilder.Append($"in {currentParamType} {paramNames[i]}, ");
+            }
+            paramDeclBuilder.Remove(paramDeclBuilder.Length-2, 2);
+            paramDecl = paramDeclBuilder.ToString();
+        }
+
+        var paramNameStates = paramNames.Select(x => $"{x}.State")
+            .ToImmutableArray();
+        string bottomStateCheck = string.Join(" & ", paramNameStates);
+        string statesSeparatedList = string.Join(", ", paramNameStates);
+
+        string failureChecks;
+        {
+            var failureChecksBuilder = new StringBuilder();
+            foreach (var paramName in paramNames)
+            {
+                failureChecksBuilder.AppendLine($"    if ({paramName}.IsFailure) error += {paramName}.Error;");
+            }
+            failureChecks = failureChecksBuilder.ToString();
+        }
+        string resultExpansion;
+        switch (resultTupleSize)
+        {
+            case 0:
+            resultExpansion = "null";
+            break;
+
+            case 1:
+            resultExpansion = $"{paramNames[argResultTupleSizes.IndexOf(1)]}.Value";
+            break;
+            
+            default:
+            var resultExpansionBuilder = new StringBuilder();
+            resultExpansionBuilder.Append("(");
+            for (int i = 0; i < argResultTupleSizes.Length; i++)
+            {
+                if (argResultTupleSizes[i] == 0) continue;
+                if (argResultTupleSizes[i] == 1)
+                {
+                    resultExpansionBuilder.Append($"{paramNames[i]}.Value, ");
+                    continue;
+                }
+                
+                for (int valueIndex = 1; valueIndex <= argResultTupleSizes[i]; valueIndex++)
+                {
+                    resultExpansionBuilder.Append($"{paramNames[i]}.Value.Item{valueIndex}, ");
+                }
+            }
+            resultExpansionBuilder.Remove(resultExpansionBuilder.Length - 2, 2);
+            resultExpansionBuilder.Append(")");
+            resultExpansion = resultExpansionBuilder.ToString();
+            break;
+        }
+        
+        string returnExpr = $"return error is null ? new({resultExpansion}) : new(error);";
+        var method = $$"""
+        [GeneratedCodeAttribute("{{nameof(ResultCombineGenerator)}}", "1.0.0.0")]
+        [PureAttribute]
+        public static {{resultTypeDecl}} Combine{{templateDecl}}({{paramDecl}})
+        {
+            if (({{bottomStateCheck}}) == ResultState.Bottom)
+            {
+                throw new ResultNotInitializedException(string.Join(';', GetBottom({{statesSeparatedList}})));
+            }
+            Error? error = null;
+        {{failureChecks}}
+            {{returnExpr}}
+        }
+        """;
+        return method;
+
+        static string GetResultTypeDecl(IReadOnlyList<string> templateArgNames)
+        {
+            return templateArgNames.Count switch
+            {
+                0 => "Result",
+                1 => $"Result<{templateArgNames[0]}>",
+                _ => $"Result<({string.Join(", ", templateArgNames)})>"
+            };
+        }
+    }
+}
+

Railway/Railway.csproj

@@ -4,6 +4,7 @@
     <TargetFramework>net8.0</TargetFramework>
     <ImplicitUsings>enable</ImplicitUsings>
     <Nullable>enable</Nullable>
+    <EmitCompilerGeneratedFiles Condition="'$(Configuration)'=='Debug'">true</EmitCompilerGeneratedFiles>
 
     <AssemblyName>Just.Railway</AssemblyName>
     <RootNamespace>Just.Railway</RootNamespace>
@@ -19,4 +20,10 @@
     <InternalsVisibleTo Include="$(AssemblyName).Tests" />
   </ItemGroup>
 
+  <ItemGroup>
+    <ProjectReference Include="..\Railway.SourceGenerator\Railway.SourceGenerator.csproj"
+                      OutputItemType="Analyzer"
+                      ReferenceOutputAssembly="false" />
+  </ItemGroup>
+  
 </Project>