After making some changes to the build definition of one of the dotnet core repositories, we started observing this error with the SonarQube tasks inside the build definition in VSTS:

When we checked the complete logs, we observed below issue:

2018-09-07T03:09:54.8236958Z WARNING: The following projects do not have a valid ProjectGuid and were not built using a valid solution (.sln) thus will be skipped from analysis…
2018-09-07T03:09:54.9185769Z WARNING: Duplicate ProjectGuid: “00000000-0000-0000-0000-000000000000”. The project will not be analyzed by SonarQube. Project file: “D:\a\1\s\xx\xx.csproj”
2018-09-07T03:09:54.9187236Z WARNING: Duplicate ProjectGuid: “00000000-0000-0000-0000-000000000000”. The project will not be analyzed by SonarQube. Project file: “D:\a\1\s\xx\xx.csproj”
2018-09-07T03:09:54.9187871Z WARNING: Duplicate ProjectGuid: “00000000-0000-0000-0000-000000000000”. The project will not be analyzed by SonarQube. Project file: “D:\a\1\sxx\sxx.csproj”
2018-09-07T03:09:54.9188705Z WARNING: Duplicate ProjectGuid: “00000000-0000-0000-0000-000000000000”. The project will not be analyzed by SonarQube. Project file: “D:\a\1\s\yyy\yyy.csproj”
2018-09-07T03:09:54.9189254Z WARNING: Duplicate ProjectGuid: “00000000-0000-0000-0000-000000000000”. The project will not be analyzed by SonarQube. Project file: “D:\a\1\s\zzzz\zzzz.csproj”
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As its pretty clear from first line that we were supposed to build our solution using a Visual Studio Solution file using dotnet core. This was exactly the change that we made. Earlier we were using command dotnet build *.sln and we changed to using **/*.csproj files using dotnet core build tasks.

We checked further and found that unlike .NET framework based project files, dotnet core project files (i.e. csproj files) do not have a project GUID associated with them inside tag PropertyGroup. To fix this, we needed to edit the csproj files to add tags like below:

A visual studio solution file does have project GUIDs to reference to the projects. So that’s why it would not throw error if code was build using solution file.