This is a fork of Pathoschild/Harmony, itself a fork of Harmony 2.4.2. See pardeike/Harmony for documentation and usage.

What's different from Pathoschild's fork

MonoILFixup

A post-transpiler IL fixup pass that corrects invalid IL that CoreCLR's JIT silently accepts but Mono's JIT strictly rejects. Runs after all transpilers complete but before IL emission, and fixes:

1. int*float mul type mismatch

   • Inserts conv.r4/conv.i4 where CoreCLR silently coerces int*float results but Mono throws "Invalid IL code" errors.

2. Stale Nullable<T> constructor after call replacement

   • When a transpiler replaces Method(Nullable<T>) with Method(T) without removing the preceding newobj, the extra hasValue bytes corrupt value type fields on Mono. Uses stack-depth tracking to distinguish this from legitimate Nullable usage.

3. Raw local variable index type mismatch

   • Transpilers using raw integer indices instead of LocalBuilder references can produce type mismatches that CoreCLR ignores but Mono throws InvalidProgramException for. Infers correct types from surrounding IL, declares new typed locals, and redirects references. Handles shifted local indices from game recompilation.

Other Mono compatibility fixes

• By-ref parameter handling

  • On Mono, ldnull is incompatible with by-ref parameters (type &), causing "Invalid IL code" errors. Static method patches now use a default-initialized temp local and pass its address instead.

• HasDefault parameter attribute stripping

  • DMD wrappers don't need default values, and copying them causes Cecil to resolve the parameter type at write time, which fails for game assembly types. This strips HasDefault to prevent crashes on Mono.

• CodeMatcher insert validation fix

  • Fixes insert position validation to use Pos < 0 || Pos > Length instead of IsInvalid, allowing inserts at the end of the instruction list.

• DMD diagnostic dump

  • When InvalidProgramException occurs during patching, dumps assembly references, mismatched assemblies, and token resolution info for debugging.

Build changes

• Targets net8.0 only (removed netstandard2.0 and multi-targeting)
• SDK 8.0.100 with latestMajor rollforward

What's different from upstream Harmony

Same as Pathoschild's fork: generated method names include the patching Harmony IDs to help troubleshoot error logs:

// with original Harmony
   at StardewValley.Farm.resetLocalState_Patch1(Object )

// with fork
   at StardewValley.Farm.resetLocalState_PatchedBy<Pathoschild.SmallBeachFarm>(Object )

How to build

Requires .NET SDK 8.0 or later.

git clone https://github.com/Ekyso/Harmony.git
cd Harmony
dotnet build Lib.Harmony.Thin -c Release

Output in Lib.Harmony.Thin/bin/Release/net8.0/:

• 0Harmony.dll — Harmony library
• Mono.Cecil*.dll — IL/metadata manipulation
• MonoMod.*.dll — runtime detour and utilities

Build variants

The SMAPI community uses the Lib.Harmony.Thin version, since SMAPI manages the other dependencies.