Using C# 7.1 with MSBuild

Question

To use the new C# 7.1 language features with Visual Studio 2017, you add the setting <LangVersion>latest</LangVersion> to your project file(s).

However, building such projects from MSBuild (version 15.3.409.57025, located at C:\Program Files (x86)\Microsoft Visual Studio\2017\Enterprise\MSBuild\15.0\Bin) results in an error:

CSC : error CS1617: Invalid option 'latest' for /langversion;
must be ISO-1, ISO-2, Default or an integer in range 1 to 6.

Is this feature just not yet supported by MSBuild, or is it possible to get this working?

This covers 200+ projects that were originally created variously in Visual Studio 2013 and 2015. They were all re-targeted to .NET 4.7 using the Target Framework Migrator tool (which saved lots of clicking and appears - based on inspecting .csproj file changes - to do the job correctly).

The projects all build successfully from Visual Studio 2017.

Where does your MSBuild reside? Here it resides in `C:\Program Files (x86)\Microsoft Visual Studio\2017\Professional\MSBuild\15.0\Bin` and adding the language element does work. Does your project build from Visual Studio? — Patrick Hofman, Sep 26 '17 at 07:12
Do the project maybe reference the `Microsoft.Net.Compilers` nuget package? if so, it needs to be updated to get a compiler version that supports this. — Martin Ullrich, Sep 26 '17 at 08:37

score 28 · Answer 1 · edited Aug 08 '18 at 06:32

28

Nuget packages

Microsoft.Net.Compilers nuget package does not work and needn't to be installed.

Set the following `project/build settings`

Set at least C# 7.1 or higher in the Debug and Release build properties. (via: Project menu > [ProjectName] Properties > Build tab > [Advanced] button > Language Version).
Setting it to latest does not work.

Also make sure that you are running the latest MSBuild version.

edited Aug 08 '18 at 06:32

S.Serpooshan

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answered Jan 10 '18 at 08:33

Dominic Jonas

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Bingo! This was the right answer for me to get it working with TFS & MSBuild. – John Mills Mar 28 '18 at 04:10
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Thanks! Removing the Microsoft.Net.Compilers fixed this issue... and made it easier to upgrade some other items. – Anthony Nichols Jul 03 '18 at 19:30
Language version drop down is disabled for my project. I'm using vs 2019 Enterprise. It is a console application project. – RBT Jul 15 '21 at 06:41

score 8 · Answer 2 · answered Sep 29 '17 at 05:19

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Add a reference to the Microsoft.Net.Compilers package (version 2.3.x, to get C# 7.1).

A short description of the package:

Microsoft.Net.Compilers

This package not only includes the C# and Visual Basic compilers, it also modifies MSBuild targets so that the included compiler versions are used rather than any system-installed versions. Once installed, this package requires Microsoft Build Tools 2015.

answered Sep 29 '17 at 05:19

Julien Couvreur

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This did the trick for me. I had the package in my main project, but today I updated a referenced project to C# 7.1 and forgot it didn't have this NuGet package. I received this exact issue - builds in VS but fails on the build server. Thanks for the tip! – Ian Yates Oct 16 '17 at 11:59
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Actually... My problem was also caused by me changing the value in DEBUG project property settings. Visiting the RELEASE settings found it was still C# (latest major version). Changing that, checking in and doing another build. Happy now :) – Ian Yates Oct 16 '17 at 12:15
Thats what fixed it for me @Ian Yates. Thanks. – John Mills Mar 28 '18 at 04:08
Only this solution helped me to fix it – Ivan Doroshenko Apr 26 '22 at 13:40

score 4 · Answer 3 · answered Sep 19 '19 at 08:45

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Make sure you have changed for "All Configuration" and not just "Debug"

else you will be baffling why it is failing at production.

answered Sep 19 '19 at 08:45

Raghav

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firepol · Answer 4 · 2018-10-08T12:09:13.010

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In case you land here because you get the error as the OP mentioned, running msbuild via command line (e.g. from a build agent such as jenkins), the solution may be as easy as to upgrade Microsoft Build Tools 2015.

You can do that via choco install microsoft-build-tools or manually via the official Microsoft Build Tools 2015 or by updating your Visual Studio 2017 installation.

edited Oct 08 '18 at 12:09

answered Oct 08 '18 at 08:50

firepol

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Richard · Answer 5 · 2017-09-26T07:50:27.167

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I've got a solution with a C# console app using C# 7.1 here.

Using the VS 2017 command line (and thus MSBuild 15.3.409.57025) it worked fine. (The .csproj does contain <LangVersion>latest</LangVersion>.)

Is this feature just not yet supported by MSBuild, or is it possible to get this working?

Yes it is.

Which instance of csc.exe is being run and what's its version? Because it looks like, despite quoting the version, you have the wrong version of csc.exe (the error message says 1-6 so not even C# 7 would work).

edited Sep 26 '17 at 07:50

answered Sep 26 '17 at 07:10

Richard

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What exactly is the solution you propose? It all seems to be running fine out of the box as described in the procedures from OP. – Patrick Hofman Sep 26 '17 at 07:15
@Richard - updated my question to address some of your queries – Richard Ev Sep 26 '17 at 07:22
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@PatrickHofman Updated to make it clear I'm addressing the existential part of the question. – Richard Sep 26 '17 at 07:51

score 2 · Accepted Answer · answered Sep 26 '17 at 23:17

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We discovered that our MVC projects were triggering this issue.

To fix, we updated the Microsoft.CodeDom.Providers.DotNetCompilerPlatform NuGet package used by these projects from version 1.0.0 to 1.0.7.

answered Sep 26 '17 at 23:17

Richard Ev

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Besides this I also had to update `Microsoft.Net.Compilers`. – Timo May 04 '18 at 13:36

Using C# 7.1 with MSBuild

6 Answers6

Nuget packages

Set the following `project/build settings`

Linked

Using C# 7.1 with MSBuild

6 Answers6

Nuget packages

Set the following project/build settings

Linked

Set the following `project/build settings`