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Assets/FastScriptReload/Scripts/Editor/Compilation/McsExeDynamicCompilation.cs

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+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using UnityEngine;
+
+#if FastScriptReload_CompileViaMCS
+public class McsExeDynamicCompilation : DynamicCompilationBase
+{
+    private const int ReferenceLenghtCountWarningThreshold = 32767 - 2000; //windows can accept up to 32767 chars as args, then it starts thorowing exceptions. MCS.exe is adding references via command /r:<full path>
+    
+    private static CompileResult Compile(List<string> filePathsWithSourceCode)
+    {
+        var fileSourceCode = filePathsWithSourceCode.Select(File.ReadAllText);
+
+        var providerOptions = new Dictionary<string, string>();
+        var provider = new Microsoft.CSharp.CSharpCodeProvider(providerOptions);
+        var param = new  System.CodeDom.Compiler.CompilerParameters();
+
+        var excludeAssyNames = new List<string> 
+        {
+            "mscorlib"
+        };
+        var referencesToAdd = ResolveReferencesToAdd(excludeAssyNames);
+
+        var referencePathCharLenght = referencesToAdd.Sum(r => r.Length);
+        if (referencePathCharLenght > ReferenceLenghtCountWarningThreshold)
+        {
+            LoggerScoped.LogWarning(
+                "Windows can accept up to 32767 chars as args, then it starts throwing exceptions. Dynamic compilation will use MCS.exe and will add references via command /r:<full path>, " +
+                $"currently your assembly have {referencesToAdd.Count} references which full paths amount to: {referencePathCharLenght} chars." +
+                $"\r\nIf you see this warning likely compilation will fail, you can:" +
+                $"\r\n1) Move your project to be more top-level, as references take full paths, eg 'c:\\my-source\\stuff\\unity\\my-project\\' - this then gets repeated for many references, moving it close to top level will help" +
+                $"\r\n2) Remove some of the assemblies if you don't need them" +
+                "\r\n Please let me know via support email if that's causing you issues, there may be a fix if it's affecting many users, sorry about that!");
+
+            //TODO: the process is started from Microsoft.CSharp.CSharpCodeGenerator.FromFileBatch, potentially all it'd be possible to patch that class to maybe copy all
+            //assemblies to some top-level location and change parameters to run from this folder, with a working directory set, this would drastically reduce char count used by full refs
+            //also mcs.exe allows to compile with -pkg:package1[,packageN], which somewhat bundles multiple references, maybe all unity engine refs could go in there, or all refs in general
+        }
+
+        param.ReferencedAssemblies.AddRange(referencesToAdd.ToArray());
+        param.GenerateExecutable = false;
+        param.GenerateInMemory = false;
+        providerOptions.Add(PatchMcsArgsGeneration.PreprocessorDirectivesProviderOptionsKey,
+            string.Join(";", ActiveScriptCompilationDefines));
+        
+        var sourceCodeCombined = CreateSourceCodeCombinedContents(fileSourceCode);
+        var result = provider.CompileAssemblyFromSource(param, sourceCodeCombined, DynamicallyCreatedAssemblyAttributeSourceCode);
+        var errors = new List<string>();
+        foreach (var error in result.Errors)
+        {
+            errors.Add(error.ToString());
+        }
+        return new CompileResult(
+            result.CompiledAssembly.FullName,
+            errors,
+            result.NativeCompilerReturnValue,
+            result.CompiledAssembly,
+            sourceCodeCombined,
+            string.Empty
+        );
+    }
+}
+#endif