"dotnet run" for project targeting .NET Framework fails with unhelpful error on Linux

[dsplaisted]

Trying to dotnet run a project targeting .NET Framework fails with the following error on Linux (and probably Mac):

System.ComponentModel.Win32Exception (8): Exec format error
   at System.Diagnostics.Process.ForkAndExecProcess(String filename, String[] argv, String[] envp, String cwd, Boolean redirectStdin, Boolean redirectStdout, Boolean redirectStderr, Boolean setCredentials, UInt32 userId, UInt32 groupId, UInt32[] groups, Int32& stdinFd, Int32& stdoutFd, Int32& stderrFd, Boolean usesTerminal, Boolean throwOnNoExec)
   at System.Diagnostics.Process.StartCore(ProcessStartInfo startInfo)

We should fail with a more graceful error.

[peterhuene]

I think corefx should probably provide one and not the CLI. This is a generic error message (i.e. strerror) that could be improved upon there, I think (although this error can occur for missing shebangs in scripts or other binfmt_misc errors, afaik).

[dsplaisted]

I'm not sure of the details of how it all works, but I think to .NET Core / the OS it's simply an invalid file to execute, while the .NET Core SDK knows that it's a .NET Framework project which would be useful to include in the error.

[peterhuene]

That's fair, although users would probably then expect that dotnet run when you've set RuntimeIdentifier to a RID other than your current platform to behave the same, which becomes trickier to implement. It would either need to know the RID graph or we'd just check for a few known RID prefixes (e.g. win-, linux-, osx-, etc), although that won't help for say running a linux-arm64 executable on a linux-x64 host (which might even work thanks to binfmt_misc).

[github-actions]

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