Azure DevOps - conditional package restoration - msbuild

Question

A solution that is built via Azure DevOps pipeline has some projects that use conditional package references such as:
<Choose>
<When Condition="'$(Configuration)'=='Debug'">
<ItemGroup>
<PackageReference Include="Mock.MyPackage" Version="1.0.0" />
</ItemGroup>
</When>
<Otherwise>
<ItemGroup>
<PackageReference Include="MyPackage" Version="1.2.0" />
</ItemGroup>
</Otherwise>
</Choose>
The package source is a private NuGet feed.
The dotnet restore task does not respect the conditional package selection. (it restores Mock.MyPackage)
Question:
how can I conditionally restore packages (based on a $Configuration) ?
Remarks:
I have also tried restoring during Visual Studio Build task by specifying an MsBuild argument: /t:restore.
In that case it fails with a message: Failed to retrieve information about XX from remote source. If this command can restore packages how can I specify authorization args for the private feed ?
There is an issue on Github: https://github.com/NuGet/Home/issues/5895 where such issue is mentioned at the end.

Answer 1

Azure DevOps - conditional package restoration
This issue should be related your specify requirement and the limitation for current Visual Studio Build task/dotnet restore.
Just as you test, if we use the restore task, we could not specify the configuration parameter with this task. Since there is no such option to receive the configuration parameter for the restore task. That is the reason why it always restores the default package Mock.MyPackage.
If you use the Visual Studio build task, we could not to specify authorization args for the private feed.
To resolve this issue, I use the Command line V1 task to invoke MSBuild to restore and build the project with following MSBuild argument:
-t:restore;build "CoreConditionRestore/CoreConditionRestore/CoreConditionRestore.csproj" -p:RestoreSources="<MyFeed>/v3/index.json" -p:RestoreConfigFile="<MyNugetConfigPath>\nuget.config" /p:Configuration=Debug
Note: we could save the authorization args for the private feed in the nuget.config file.
As test, it works fine on my side with Devops.
Hope this helps.

Answer 2

A much, much simpler answer is to add in NUGET_RESTORE_MSBUILD_ARGS with a value of /p:Configuration=$(BuildConfiguration) to your pipeline variables. This will actually just pass your build configuration to the NuGet restore task.
This is incredibly poorly documented and it took scouring github bug requests to find it
Environment variable documentation:
https://learn.microsoft.com/en-us/nuget/reference/cli-reference/cli-ref-environment-variables
Github issue I found this on:
https://github.com/NuGet/Home/issues/7575
Not sure why this isn't enabled by default, either.
As a note, you still need to do the (imo strange)
<Choose>
<When Condition="'$(Configuration)'=='Debug'">
<ItemGroup>
<PackageReference Include="Mock.MyPackage" Version="1.0.0" />
</ItemGroup>
</When>
</Choose>
in your project file rather than the more intuitive:
<PackageReference Include="Mock.MyPackage" Version="1.0.0" Condition="'$(Configuration)' == 'Debug'" />
...which does work with normal Reference directives eg:
<Reference Include="MOCK_DLL" Condition="'$(Configuration)' == 'Debug'">
<HintPath>..\References\MOCK_DLL.dll</HintPath>
</Reference>

Answer 3

I wanted minimal change in deployment configuration, so the following was acceptable.
An empty project is created and all packages which are restored conditionally are referenced there (without any conditions).
Additional argument to msbuild task is added: '/t:restore'
During build the following will happen:
'dotnet restore' will restore all the packages thanks to 1).
Since it does not know a selected configuration it may pick a wrong package (Mock.MyPackage instead of MyPackage).
That is where 2) comes, where msbuild task will restore packages from a local cache made by 'dotnet restore'.
Remarks:
As #(Leo Liu-MSFT) wrote, dotnet restore can authenticate but it does not know configuration, and msbuild knows configuration but it can not authenticate, so package restoration in AzDevOps from private feeds is tricky.