Build generates multiple tlog folders

[tersers]

When building my project, I'm getting a warning from MSBuild saying:

MSB8028: The intermediate directory (<intermediate directory here>) contains files shared from another project (<project name here>)

What's interesting is the shared project name is the exact same as the project I'm currently building. Upon investigation into the folder it complains about, I noticed MSBuild is sometimes creating multiple tlog folders. Since the name of my project is long, the folder hierarchy looks something like this:

|-IntermediateDir
    |-MyProjectNameIsL.123454678.tlog
    |-MyProjectNameIsL.ABCDEFGH.tlog

Note that MyProjectNameIsL is not a typo, it is to exemplify the length of my project's name and why MSBuild appears to serialize it. For the purpose of this question the name of the project is MyProjectNameIsLong.

If I delete these folders, it works fine for the first build but reports a warning for the second. It appears that MSBuild forgets about the existence of the original tlog folder and just creates a new one. Why is this the case?

[rainersigwald]

This message comes from the C++ targets. On my machine it's from c:\Program Files (x86)\MSBuild\Microsoft.Cpp\v4.0\V140\Microsoft.CppBuild.targets:

<!-- lastbuildstate is a unique file writen to by each build. Multiple of this file can mean that the IntDir is shared by more the one project. -->
<ItemGroup>
  <AllTlogLocation Include="$(IntDir)*.tlog\*.lastbuildstate" Exclude="$(LastBuildState)" Condition="'$(IntDirSharingDetected)' == ''"/>
</ItemGroup>

<PropertyGroup>
  <IntDirSharingDetected Condition="'@(AllTlogLocation)' != ''">true</IntDirSharingDetected>
  <IntDirSharingProjects Condition="'@(AllTlogLocation)' != ''">@(AllTlogLocation->'%(Filename).vcxproj', ', ')</IntDirSharingProjects>
</PropertyGroup>

<VCMessage Code="MSB8028" Type="Warning" Arguments="$(IntDirSharingProjects);$(IntDir)" Condition="'$(IgnoreWarnIntDirSharingDetected)' != 'true' and '$(IntDirSharingDetected)' == 'true'"/>

LastBuildState is written to TLogLocation, which is defined in C:\Program Files (x86)\MSBuild\Microsoft.Cpp\v4.0\V140\Microsoft.BuildSteps.Targets:

<!-- TLogLocation requires trailing slash. -->
<TLogLocation Condition="'$(TLogLocation)' == '' and '$(ProjectName)' != '' and '$(ProjectGuid)' != '' and '$(ProjectName.Length)' &gt; '16'">$(IntDir)$(ProjectName.Substring(0,8)).$(ProjectGuid.Substring(1,8)).tlog\</TLogLocation>
<TLogLocation Condition="'$(TLogLocation)' == ''">$(IntDir)$(ProjectName).tlog\</TLogLocation>

That explains the truncated names and the numbers. Do you perhaps have multiple projects with the same name prefix and different project GUIDs?

The C++ targets aren't open source and are supported by the C++ team, not the MSBuild team that works in this repo, so the best thing to do would be to use their support channels. But the IgnoreWarnIntDirSharingDetected property looks interesting . . .