'Unity "Multiple precompiled assemblies with the same name" using external dll

I have a "Shared" project where I share code between my client (unity) and my server (C# server)

Both projects require Newtonsoft.Json.dll

When I compile the Shared.dll and put it inside of Unity's Resources folder (so it's included in the build), I get this error :

PrecompiledAssemblyException: Multiple precompiled assemblies with the same name Newtonsoft.Json.dll included or the current platform. Only one assembly with the same name is allowed per platform. Assembly paths: 
Assets/Resources/Shared/Newtonsoft.Json.dll
C:/Users/rotmg/Documents/GitHub/AG-LNL/AG-LNL-Client/Library/PackageCache/[email protected]/Runtime/Newtonsoft.Json.dll

I realise it's a conflict between Unity's dependency on Newtonsoft.Json and my Shared.dll's.

This answer :

https://answers.unity.com/questions/1697304/how-to-resolve-multiple-precompiled-assemblies-err.html

Says to use "merge all the dependencies into one .dll"

So I tried using Costura.Fody to build a single .dll that bundles all dependencies, but then I get an error saying that I should add references to the dependencies that Shared has. (NLog, BouncyCastle, etc.)

How can I resolve this conflict?

c++sharpunity3d


Solution 1:[1]

In my case after updating from Unity 2020.3.8f1 to 2020.3.17f1 and package com.unity.collab-proxy from 1.3.9 to 1.7.1 it got dependency com.unity.nuget.newtonsoft-json which was conflicting with my manually imported JsonDotNet package in Assets folder.

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Removing my manually imported JsonDotNet package from Assets folder helped. After removing close Unity, delete folders YouProjectFolder\Library\PackageCache and YouProjectFolder\Library\ScriptAssemblies and restart Unity.

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Solution 2:[2]

based on this answer: https://www.gitmemory.com/issue/juicycleff/flutter-unity-view-widget/414/859018825

best way is to import project without JsonDotNet folder or remove JsonDotNet folder before importing.

JsonDotNet folder

Solution 3:[3]

I got this issue after adding another package using Newtonsoft.Json.dll, causing a conflict. For me removing one of the duplicates resolved the issue.

Sources

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Source: Stack Overflow

Solution Source
Solution 1
Solution 2 Omid Fast
Solution 3 user16189729

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