MSBuild: How may I access built-in properties while defining my own custom properties? - msbuild

Question

I have a file named Common.targets defined like so:
<Project>
<PropertyGroup>
<TlbExpPath>"c:\Program Files (x86)\Microsoft SDKs\Windows\v10.0A\bin\NETFX 4.6.1 Tools\x64\tlbexp"</TlbExpPath>
<TlbOutPath>"$(OutDir)..\TLB\$(TargetName).tlb"</TlbOutPath>
</PropertyGroup>
<Target Name="TlbExp" AfterTargets="CopyFilesToOutputDirectory" Inputs="$(TargetPath)" Outputs="$(TlbOutPath)">
<Exec Command='$(TlbExpPath) "$(TargetPath)" /nologo /win64 /out:$(TlbOutPath) /verbose' />
</Target>
</Project>
When I inspect the output of the TlbOutPath property, it looks like:
"..\TLB\.tlb"
Apparently, $(OutDir) and $(TargetName) produce nothing when used within a PropertyGroup. I'm not sure why. How can I make these paths/values reusable while still having access to built-in properties when they are defined?
I'm using MSBuild that comes bundled with Visual Studio 2019. I add an Import element to my actual .csproj projects to include this target where I need it. The csproj projects use the SDK format for the projects, e.g. <Project Sdk="Microsoft.NET.Sdk">.
Here is an example of what the import looks like:
<Project Sdk="Microsoft.NET.Sdk">
<!-- etc -->
<ItemGroup>
<Reference Include="Microsoft.CSharp" />
<!-- etc -->
</ItemGroup>
<Import Project="$(RepositoryRoot)\Common.targets" />
</Project>

Answer 1

MSBuild: How may I access built-in properties while defining my own
custom properties?
This is quite an issue in the new sdk format project. I have tested it and got the same issue as you said which quite bother me a lot. Like $(OutDir),$(TargetName),$(OutputPath),$(TargetPath) and some other common system properties cannot be used in a new property while $(Configuration) and $(AssemblyName) works well.
And not only us but also someone else also face the same issue about it.See this thread.
For the traditional old csproj format project, there was no problem with these properties being used this way, but in the new SDK format project, it is impossible to assign some common properties such as $(OutDir),$(TargetName) and $(TargetPath) to a new property. As we know, most of the common properties are defined in the Microsoft.Common.props file(old csproj format) which is quite different from the new sdk format project which does not have such file.
In order to get an answer,l have reported this issue to DC Forum. See this.You can enter this link and add any detailed comments to describe this issue. And anyone who interested in this issue will also vote it so that it will get more Microsoft staff's attention. All these efforts will speed up and get the final answer.
This process may take a while or you could try my suggestion.
Suggestion
1) You can customize this property $(OutDir) in Common.targets file, and use $(TargetFramework) instead of $(TargetName) since $(TargetFramework) is defined in the xxxx.csproj file.
<Project>
<PropertyGroup>
<OutDir>bin\$(Configuration)\$(TargetFramework)\$(AssemblyName)\</OutDir>
<TlbExpPath>"c:\Program Files (x86)\Microsoft SDKs\Windows\v10.0A\bin\NETFX 4.6.1 Tools\x64\tlbexp"</TlbExpPath>
<TlbOutPath>"$(OutDir)..\TLB\$(TargetName).tlb"</TlbOutPath>
<TargetPath>xxxx\xxxx.dll(exe)</TargetPath>--------the absolute path of the output file
</PropertyGroup>
<Target Name="TlbExp" AfterTargets="CopyFilesToOutputDirectory" Inputs="$(TargetPath)" Outputs="$(TlbOutPath)">
<Exec Command='$(TlbExpPath) "$(TargetPath)" /nologo /win64 /out:$(TlbOutPath) /verbose' />
</Target>
</Project>
2) use Directory.Build.targets file rather than a custom targets file.
A) You should add a file named Directory.Build.targets(it must be named this and have its own rule to be imported into xxx.csproj) under the project folder.
B) add the content of Common.targets into it without any changes and then build your project directly. The Directory.Build.targets will be imported into your project automatically while build.
This function works well and will not lose any properties. However, l stil bother why it works.
Conclusion
I think #2 is more suitable and easier for you to achieve your goal.