Using .NET SDK 6 RC2 and getting 'Predefined type 'System....' is not defined or imported (csharp CS0518)

[schaveyt]

Issue Description

Using .NET SDK 6 RC2 and getting 'Predefined type 'System....' is not defined or imported (csharp CS0518)

Steps to Reproduce

1. Install .NET SDK 6 RC2
2. Install C# extension 1.23.16
3. Create a new ASP.NET project

cd \temp
dotnet new blazorserver -o test_app
code test_app

1. Open the Program.cs file

Expected Behavior

The Program.cs file should have no squiggles or reported issues.

Actual Behavior

Various lines of code are reporting squiggles for the error:
'Predefined type 'System....' is not defined or imported (csharp CS0518)

Logs

OmniSharp log

Starting OmniSharp server at 10/16/2021, 5:52:36 PM Target: c:\temp\test-app

OmniSharp server started.
Path: c:\Users\210053326.vscode\extensions\ms-dotnettools.csharp-1.23.16.omnisharp\1.37.16\OmniSharp.exe
PID: 18732

Starting OmniSharp on Windows 6.2.9200.0 (x64)
info: OmniSharp.Services.DotNetCliService
Checking the 'DOTNET_ROOT' environment variable to find a .NET SDK
info: OmniSharp.Services.DotNetCliService
Using the 'dotnet' on the PATH.
info: OmniSharp.Services.DotNetCliService
DotNetPath set to dotnet
info: OmniSharp.MSBuild.Discovery.MSBuildLocator
Located 4 MSBuild instance(s)
1: Visual Studio Professional 2017 15.9.28307.1000 15.9.21 - "C:\Program Files (x86)\Microsoft Visual Studio\2017\Professional\MSBuild\15.0\Bin"
2: Visual Studio Community 2019 16.9.31205.134 16.9.0 - "C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\MSBuild\Current\Bin"
3: Visual Studio Build Tools 2019 16.8.30907.101 16.8.3 - "C:\Program Files (x86)\Microsoft Visual Studio\2019\BuildTools\MSBuild\Current\Bin"
4: StandAlone 17.0.0 - "c:\Users\210053326.vscode\extensions\ms-dotnettools.csharp-1.23.16.omnisharp\1.37.16.msbuild\Current\Bin"
info: OmniSharp.MSBuild.Discovery.MSBuildLocator
Registered MSBuild instance: Visual Studio Community 2019 16.9.31205.134 16.9.0 - "C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\MSBuild\Current\Bin"
info: OmniSharp.WorkspaceInitializer
Invoking Workspace Options Provider: OmniSharp.Roslyn.CSharp.Services.CSharpFormattingWorkspaceOptionsProvider, Order: 0
info: OmniSharp.WorkspaceInitializer
Invoking Workspace Options Provider: OmniSharp.Roslyn.CSharp.Services.Completion.CompletionOptionsProvider, Order: 0
info: OmniSharp.WorkspaceInitializer
Invoking Workspace Options Provider: OmniSharp.Roslyn.CSharp.Services.RenameWorkspaceOptionsProvider, Order: 100
info: OmniSharp.WorkspaceInitializer
Invoking Workspace Options Provider: OmniSharp.Roslyn.CSharp.Services.ImplementTypeWorkspaceOptionsProvider, Order: 110
info: OmniSharp.WorkspaceInitializer
Invoking Workspace Options Provider: OmniSharp.Roslyn.CSharp.Services.BlockStructureWorkspaceOptionsProvider, Order: 140
info: OmniSharp.Cake.CakeProjectSystem
Detecting Cake files in 'c:\temp\test-app'.
info: OmniSharp.Cake.CakeProjectSystem
Could not find any Cake files
info: OmniSharp.MSBuild.ProjectSystem
No solution files found in 'c:\temp\test-app'
info: OmniSharp.MSBuild.ProjectManager
Queue project update for 'c:\temp\test-app\test-app.csproj'
info: OmniSharp.Script.ScriptProjectSystem
Detecting CSX files in 'c:\temp\test-app'.
info: OmniSharp.Script.ScriptProjectSystem
Could not find any CSX files
info: OmniSharp.WorkspaceInitializer
Configuration finished.
info: OmniSharp.Stdio.Host
Omnisharp server running using Stdio at location 'c:\temp\test-app' on host 16920.
info: OmniSharp.MSBuild.ProjectManager
Loading project: c:\temp\test-app\test-app.csproj
info: OmniSharp.MSBuild.ProjectManager
Successfully loaded project file 'c:\temp\test-app\test-app.csproj'.
info: OmniSharp.MSBuild.ProjectManager
Adding project 'c:\temp\test-app\test-app.csproj'
info: OmniSharp.MSBuild.ProjectManager
Update project: test-app
Received response for /v2/getcodeactions but could not find request.
[warn]: OmniSharp.Roslyn.CSharp.Services.Navigation.FindUsagesService
No symbol found. File: c:\temp\test-app\Program.cs, Line: 4, Column: 16.
[warn]: OmniSharp.Roslyn.CSharp.Services.Navigation.FindUsagesService
No symbol found. File: c:\temp\test-app\Program.cs, Line: 7, Column: 29.

C# log

It is blank

Environment information

VSCode version: 1.61.1
C# Extension: 1.23.16

Dotnet Information

.NET SDK (reflecting any global.json): Version: 6.0.100-rc.2.21505.57 Commit: ab39070116

Runtime Environment:
OS Name: Windows
OS Version: 10.0.18363
OS Platform: Windows
RID: win10-x64
Base Path: C:\Program Files\dotnet\sdk\6.0.100-rc.2.21505.57\

Host (useful for support):
Version: 6.0.0-rc.2.21480.5
Commit: 6b11d64e7e

.NET SDKs installed:
3.0.100 [C:\Program Files\dotnet\sdk]
3.1.101 [C:\Program Files\dotnet\sdk]
3.1.118 [C:\Program Files\dotnet\sdk]
5.0.104 [C:\Program Files\dotnet\sdk]
5.0.202 [C:\Program Files\dotnet\sdk]
5.0.206 [C:\Program Files\dotnet\sdk]
6.0.100-rc.2.21505.57 [C:\Program Files\dotnet\sdk]

.NET runtimes installed:
Microsoft.AspNetCore.All 2.1.26 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
Microsoft.AspNetCore.All 2.1.27 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
Microsoft.AspNetCore.App 2.1.26 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 2.1.27 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 3.0.0 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 3.1.1 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 3.1.14 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 3.1.18 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 5.0.4 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 5.0.5 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 5.0.9 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 6.0.0-rc.2.21480.10 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.NETCore.App 2.1.26 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 2.1.27 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 3.0.0 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 3.1.1 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 3.1.8 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 3.1.14 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 3.1.18 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 5.0.4 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 5.0.5 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 5.0.9 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 6.0.0-rc.2.21480.5 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.WindowsDesktop.App 3.0.0 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 3.1.1 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 3.1.8 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 3.1.14 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 3.1.18 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 5.0.4 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 5.0.5 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 5.0.9 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 6.0.0-rc.2.21501.6 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]

To install additional .NET runtimes or SDKs:
https://aka.ms/dotnet-download

Visual Studio Code Extensions

Extension	Author	Version
asciidoctor-vscode	asciidoctor	2.8.9
beautify	HookyQR	1.5.0
bracket-pair-colorizer-2	CoenraadS	0.2.1
code-spell-checker	streetsidesoftware	2.0.10
cpptools	ms-vscode	1.7.0
csharp	ms-dotnettools	1.23.16
csharpfixformat	Leopotam	0.0.84
docomment	k--kato	0.1.20
dotnet-test-explorer	formulahendry	0.7.7
git-graph	mhutchie	1.30.0
github-vscode-theme	GitHub	5.0.0
gitlens	eamodio	11.6.1
jenkinsfile-support	ivory-lab	1.1.0
jupyter	ms-toolsai	2021.9.1101343141
jupyter-keymap	ms-toolsai	1.0.0
jupyter-renderers	ms-toolsai	1.0.3
LiveServer	ritwickdey	5.6.1
markdown-all-in-one	yzhang	3.4.0
material-theme	zhuangtongfa	3.13.2
matlab	Gimly81	2.2.0
mf-ide	geas-platform-tools	0.1.9-mtr-50
partial-diff	ryu1kn	1.4.3
pdf	tomoki1207	1.1.0
powershell	ms-vscode	2021.10.0
python	ms-python	2021.10.1336267007
remote-containers	ms-vscode-remote	0.202.4
remote-ssh	ms-vscode-remote	0.65.8
remote-ssh-edit	ms-vscode-remote	0.65.8
remote-wsl	ms-vscode-remote	0.58.2
selectline-statusbar	tomoki1207	0.0.2
theme-dracula	dracula-theme	2.24.0
todo-tree	Gruntfuggly	0.0.214
vscode-commons	redhat	0.0.6
vscode-docker	ms-azuretools	1.17.0
vscode-hexdump	slevesque	1.8.1
vscode-icons	vscode-icons-team	11.6.0
vscode-markdownlint	DavidAnson	0.44.4
vscode-nuget-gallery	patcx	0.0.24
vscode-pylance	ms-python	2021.10.1
vscode-remote-extensionpack	ms-vscode-remote	0.21.0
vscode-todo-highlight	wayou	1.0.4
vscode-xml	redhat	0.18.0
xml	DotJoshJohnson	2.5.1
yang	marko2276	0.1.3

[schaveyt]

Looking at the log. I wonder if it has something to do with the fact that the MSBuildLocator is registering the old 16.9 rather than the new 17.0.0:

[schaveyt]

Yup. I followed the advise of creating an omnisharp.json file in the root of the project and populating as described here et viola...it works!

{
    "msbuild": {
        "useBundledOnly": true
    }
}

[JoeRobich]

Without a global.json pinning the SDK to 5.x the 6 RC2 SDK would be used during build operations. The minimal supported version of MSBuild for RC2 is 16.10. We should improve the MSBuild locator in OmniSharp-Roslyn to fallback to the Standalone MSBuild when an installed VS does not meet the minimum version requirement. Moving to OmniSharp-Roslyn.