MSBuildWorkspace.OpenSolutionAsync fails with the new slnx files

[virzak]

Version Used: Microsoft.CodeAnalysis.Workspaces.MSBuild 4.9.2

Steps to Reproduce:

1. Create a solution file
2. Save As slnx using Visual Studio Version 17.10.0 Preview 3.0 or later
3. Add reference to Microsoft.CodeAnalysis.Workspaces.MSBuild
4. Try opening the solution

var workspace = MSBuildWorkspace.Create();
var solution = await workspace.OpenSolutionAsync(@"C:\PathTo\ExampleSlnx.slnx").ConfigureAwait(false);

Expected Behavior:

Should have no exception. It doesn't occur when opening "ExampleSlnx.sln"

Actual Behavior:

Microsoft.Build.Exceptions.InvalidProjectFileException
HResult=0x80131500
Message=No file format header found. Q:\Code\Sandbox\ExampleSlnx\ExampleSlnx.slnx
Source=Microsoft.Build
StackTrace:
at Microsoft.Build.Shared.ProjectFileErrorUtilities.VerifyThrowInvalidProjectFile(Boolean condition, String errorSubCategoryResourceName, BuildEventFileInfo projectFile, Exception innerException, String resourceName, Object[] args)
at Microsoft.Build.Shared.ProjectFileErrorUtilities.VerifyThrowInvalidProjectFile(Boolean condition, String errorSubCategoryResourceName, BuildEventFileInfo projectFile, String resourceName, Object[] args)
at Microsoft.Build.Construction.SolutionFile.ParseFileHeader()
at Microsoft.Build.Construction.SolutionFile.ParseSolution()
at Microsoft.Build.Construction.SolutionFile.ParseSolutionFile()
at Microsoft.Build.Construction.SolutionFile.Parse(String solutionFile)
at Microsoft.CodeAnalysis.MSBuild.MSBuildProjectLoader.d__22.MoveNext()
at Microsoft.CodeAnalysis.MSBuild.MSBuildWorkspace.d__24.MoveNext()
at Program.<

$>d__0.MoveNext() in Q:\Code\Sandbox\ExampleSlnx\ExampleSlnx\Program.cs:line 9

[huoyaoyuan]

The stack trace belongs to MSBuild, not roslyn.
As the new format is still in development, integration with MSBuild is simply not done yet.

[virzak]

@huoyaoyuan Moving to dotnet/msbuild#10012