Add long path switches to config

[ccastanedaucf]

Should be safe now that we're on Dev16.

[ccastanedaucf]

@dotnet-bot test Windows_NT Build for CoreCLR please

[ccastanedaucf]

@dotnet-bot test OSX10.13 Build for CoreCLR please

[rainersigwald]

Do we also need this in unit tests . . . somehow? I have a very hazy recollection that they can consume configuration but I don't remember if that is still app.config-compatible post-xunit.

https://github.com/Microsoft/msbuild/blob/master/src/Shared/UnitTests/App.config

[ccastanedaucf]

I remember spending a while trying to figure that one out, some unit tests would use the app.config and others (I believe everything under Tasks?) would completely ignore it.

[ccastanedaucf]

I'm double checking that one since I'd have a better idea of what's going wrong now vs 5 weeks ago

[ccastanedaucf]

Completely figured it out. So .NET Framework tests can't use the two App.config switches since the tests run on 4.6.1, and .NET Core tests will already have them enabled by default. Remember the switches are so we can target 4.6.1 but still use the new long path behavior when running on > 4.6.2.

What makes it seem like App.config is being read: a bunch of tests on .NET Framework fail since they expect a PathTooLong exception that doesn't get thrown. But since most of the path-related calls on Windows net46 use native calls, it behaves as if the switches were set for many tests.

Which also means... if the remaining managed path-related calls went through FileUtilities, FileSystems, ect. where the conditional switches for native/managed calls are, long paths would actually work even when running on 4.6.1. And at that point the app.config switches wouldn't even be necessary. Would also make running tests with long paths enabled on 4.6.1 really easy since the behavior would be uniform, and not a mix of things that throw and don't throw LongPathException. But that's a whole other issue.

[hickford]

@rainersigwald So MSBuild 16.0 and later (Visual Studio 2019 and later) can handle long paths? Is this documented anywhere?

Aha https://github.com/dotnet/msbuild/releases/tag/v16.0.461.62831

MSBuild.exe now supports long paths on Windows