Fix BadImageFormatException on .NET Core 3.0

[lg2de]

This is a PR to provide testing environment for .NET Core for now. We would like to verify e.g. #1047.
Later this PR can be used to add the target for 3.0 in next release.

Regarding double format changes please note https://devblogs.microsoft.com/dotnet/floating-point-parsing-and-formatting-improvements-in-net-core-3-0/

I would recommend to adopt the expectation because this seems to be default behavior in .NET Core 3.

[dennisdoomen]

I think this doesn't work because we still use msbuild (through a Cake API).

[jnyrup]

Also from build.cake

settings.ToolVersion = MSBuildToolVersion.VS2017;

[jnyrup]

And from https://github.com/cake-build/cake/releases there has been some updates from the 0.30.0 that we use to 0.33.0 about NugetRestore and msbuild 16.

[lg2de]

With the recent comment the build.ps1 was running fine on my PC.
I guess the build server need to have installed the .NET Core 3 SDK.

Lets retry when appveyor has finished the VS2019 (16.1) image.

[jnyrup]

Could it be that the build server do have 3.0 installed, but since it's preview it's not picked by default?

[jnyrup]

Hmm... I can't really see from the build logs if:

• .net core 3.0 is not installed,
• Restore-NuGet-Packages can't find .net core 3.0, or
• Restore-NuGet-Packages actively chooses .net core 2.2 over .net core 3.0

Raising the logging level from DotNetCoreVerbosity.Normal to DotNetCoreVerbosity.Diagnostic
could maybe shed some light on those questions.

Maybe related links:
https://help.appveyor.com/discussions/problems/22448-dotnet-core-30-and-netstandard-21
cake-build/cake#2519

[dennisdoomen]

I pushed a commit that switched our Nuget restore and build steps to dotnet. The Visual Studio 2019 Preview agent has SDK 3.0.100-preview-009812 installed. It now complains about C# issues.

[jnyrup]

I don't see any complaints about C# issues?
It fails before finishing restoring nuget packages.

Do we want to add a netcoreapp3.0 target of the Library?
It should suffice to add a netcoreapp3.0 test project.

[dennisdoomen]

I don't see any complaints about C# issues?

I got the entire script running on my local machine, and it even reports the IL errors reported in #1047.

Do we want to add a netcoreapp3.0 target of the Library?

Not until we need to support assertions on specific types introduced by .NET Core 3.0

[jnyrup]

Aha, the #1047 c# issues causing runtime problems.
I thought you were calling out some sort of c# compile time issues.

[dennisdoomen]

I thought you were calling out some sort of c# compile time issues.

As well. But that's probably because that agent is using an old preview of .NET Core 3.0

C:\projects\fluentassertions\Tests\Shared.Specs\MethodBaseAssertionSpecs.cs(829,77): error CS8107: Feature 'private protected' is not available in C# 7.0. Please use language version 7.2 or greater.

I'm trying to figure out a way to install the right dotnet SDK as part of our build process. We do this as well in our projects.

[jnyrup]

@lg2de As #1060 has been merged it should now be possible to build .net core 3.0 targets.
As we're not utilizing any .net core 3.0 features (yet!), please remove that from the core library target frameworks.
When I tried locally I could reproduce #1047 with a netcoreapp2.0 core library and a netcoreapp3.0 test project.

[lg2de]

I have reworked as requested and added the fix mentioned by @jnyrup.
Please review my changes and comment the TODOs added.
The build failed now "only" due to timing issues.

[dennisdoomen]

Great work. Only one remark.

[jnyrup]

Thanks for the rework, only a few comments from here.
(I really dislike that GitHub marks "request changes" with a big red alarming cross) It has changed

[jnyrup]

Looks great!