Project doesn't compile after upgrading from Visual Studio 2017 to 2019

Question

I can't understand the warnings and errors from Visual Studio 2019. It seems that all the references to the packages of the project are no longer working after the upgrade from Visual Studio 2017. There are the initial lines of the log when I compile the solution.

1>------ Build started: Project: ClientServerUpload, Configuration: Debug Any CPU ------
1>C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\MSBuild\Current\Bin\Microsoft.Common.CurrentVersion.targets(2106,5): warning MSB3245: Could not resolve this reference. Could not locate the assembly "System.Text.Encoding.CodePages". Check to make sure the assembly exists on disk. If this reference is required by your code, you may get compilation errors.
1>C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\MSBuild\Current\Bin\Microsoft.Common.CurrentVersion.targets(2106,5): warning MSB3243: No way to resolve conflict between "System.Text.Encoding.CodePages, Version=4.1.3.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" and "System.Text.Encoding.CodePages". Choosing "System.Text.Encoding.CodePages, Version=4.1.3.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" arbitrarily.
1>      No way to resolve conflict between "FSharp.Core, Version=4.4.1.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" and "FSharp.Core, Version=4.3.1.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a". Choosing "FSharp.Core, Version=4.4.1.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" arbitrarily.
1>      No way to resolve conflict between "FSharp.Core, Version=4.4.3.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" and "FSharp.Core, Version=4.4.1.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a". Choosing "FSharp.Core, Version=4.4.3.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" arbitrarily.
1>      Consider app.config remapping of assembly "FSharp.Core, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" from Version "4.4.3.0" [] to Version "4.7.0.0" [\\mypath\packages\FSharp.Core.4.7.0\lib\net45\FSharp.Core.dll] to solve conflict and get rid of warning.

There are many other lines after the above, but anyway I can't see what is going wrong. For example, I pick the first message, about "System.Text.Encoding.CodePages". There a warning saying "Could not locate the assembly" and another about a conflict between Version=4.1.3.0 and a reference with no version. But from where does it look at Version=4.1.3.0? In the pacakge.config there is a line:

 <package id="System.Text.Encoding.CodePages" version="4.7.0" targetFramework="net461" />

and if I edit the .proj file I see:

<Reference Include="System.Text.Encoding.CodePages">      <HintPath>..\packages\System.Text.Encoding.CodePages.4.7.0\lib\net461\System.Text.Encoding.CodePages.dll</HintPath>
</Reference>

and the HintPath is indeed there. Similar doubts for all the other messages and errors. Only another example, why is it searching FSharp.Core, Version=4.4.1.0? Again I have

  <ItemGroup>
    <Reference Include="FSharp.Core">
      <HintPath>..\packages\FSharp.Core.4.7.0\lib\net45\FSharp.Core.dll</HintPath>
    </Reference>

in the proj file and in the packages.config

  <package id="FSharp.Core" version="4.7.0" targetFramework="net461" />

All the configurations I'm aware of seem correct to me, and the whole solution was completely fine with Visual Studio 2017. The project was built with WebSharper template, I don't know if/how this is relevant, however I also reinstalled WebSharper VSIX, after upgrading to Visual Studio 2019, and I didn't receive any error. Aside from deleting and restoring all the packages, looking at the .proj file, cleaning and rebuilding the solution, what other options do I have? At what else should I look? I know I can add remapping to the Web.config, but I don't think it is the solution (not even a workaround). For your info, after many hours I managed to get a release with many (strange) lines of remapping and by manually (!) copying some files (including FSharp.Core) from the packages to the bin folder, that is clearly not an acceptable way to proceed.

Answer 1

I seem to recall something similar when I upgraded an F# project from VS2015 to 2017.

The solution was to update the version of the F# runtime (FSharp.Core.dll) in the project properties.

Looking at the .fsproj for a .NET Core 3.0 F# project: the F# runtime is not actually listed, so must be an implicit dependency: maybe removing it would also work.

Answer 2

Step 0

I've restored an old commit of my project to better describe the original situation and to track all the steps to resolve it. Before the following 2 operations, I had to nuget upgrade from FSharp.Core 4.6 to 4.7, for a problem specific to WebSharper: the Scripts were not produced.

Step 1

I had to edit the .proj file to delete some reference lines, sort of duplicated. Here is an example for FSharp.Core, but I did the same for many others (I don't know what exactly originated this problem but removing those lines seems to have done the trick for me)

<Reference Include="FSharp.Core">
  <HintPath>..\packages\FSharp.Core.4.7.0\lib\net45\FSharp.Core.dll</HintPath>
</Reference>
<Reference Include="FSharp.Core" />

In the above case I deleted the last line (and all the other similar lines without a version reference under a tag containing the version of the same package)

Step 2

Then I copied and pasted all the <dependentAssembly> from the Visual Studio output to the Web.config. Again I don't understand wht they are many more than the ones needed for Visual Studio 2017, but these 2 operations apparently solved my issue.