Google.Protobuf.Tools and Grpc.Tools proto compilation is only supported by default in a C# project (extension .csproj)

[jozefizso]

What version of gRPC and what language are you using?

grpc 1.18.0

What operating system (Linux, Windows,...) and version?

Windows

What runtime / compiler are you using (e.g. python version or version of gcc)

.NET Framework 4.7.2
Grpc.Tools 1.18.0

What did you do?

When I open .NET project in VS 2017 and/or 2019 and I run build, Grpc.Tools often reports this error: Google.Protobuf.Tools proto compilation is only supported by default in a C# project (extension .csproj)

This error is mostly reported on a project which was recently checked out and it's nuget packages are missing. After restoring packages and running build, msbuild will likely report this error.

When I run Build > Build Solution several times in a row, the project finally build correctly. As I change the .proto file in the project and run Build again, I got the error message again.

This causes issues with build machines which do clean builds and are thus failing the build. And it causes to developers as they local builds are often reported as failed.

What did you expect to see?

Project should build correctly.

What did you see instead?

msbuild error: Google.Protobuf.Tools proto compilation is only supported by default in a C# project (extension .csproj)

Full build log: https://gist.github.com/jozefizso/383d6d1346a0ffcd8dde5e5955384070

[jozefizso]

Moved to protocolbuffers/protobuf#6740 as it seams more appropriate place for this issue.

[jtattermusch]

Looks like this is impacting Grpc.Tools as well: protocolbuffers/protobuf#6740 (comment)

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[jtattermusch]

I can actually reproduce this issue with VS2019 by getting a clean checkout of the helloworld example in a "classic" csproj:

1 get a clean checkout of https://github.com/grpc/grpc/tree/master/examples/csharp/HelloworldLegacyCsproj
2. open https://github.com/grpc/grpc/blob/master/examples/csharp/HelloworldLegacyCsproj/Greeter.sln in VS2019
3. click "Build solution", I get the error Google.Protobuf.Tools proto compilation is only supported by default in a C# project (extension .csproj)

As described above, after a few rebuild attempts this problem goes away by itself and I can build just fine from that moment onward. (I can even clean and rebuild and things just continue working fine)

I don't know what's causing the problem and it almost looks like a VS or msbuild bug.
The problem doesn't affect the new dotnet-style projects so I don't think it's realistic to expect that this it's going to be fixed.
The workaround is just to wait a few minutes / attempts until the builds starts working normally.