What is the best way to validate a property in a .props file?

[sanderobdeijn]

I'm making a .props file that reads some properties in a .csproj and then sets other properties and loads some nugetpackages.
I want to add errors or warnings when the properties are empty. So I added a warning tag that looks for a empty property.
But I got an error that the warning tag can no longer be placed directly into the project tag. So I added an target tag and placed the warning tag into the target tag.
And to make sure the properties are always checked I have added the target to the the InitialTargets attribute in the Project tag. Is this the correct way, or will I now override the InitialTargets attribute in the csproj file.
Also I would like to add a link to a support page in visual studio. I used the HelpKeyword attribute but visual seems to mangle the url. Can an url be added to this attribute.

Here is my code:

<Project InitialTargets="ValidateProjectParameters">
    <Target Name="ValidateProjectParameters">
        <Warning Text="The property TestProperty is empty in the projectfile"
                 Condition="'$(TestProperty)' == ''"
                 Code="1"
                 HelpKeyword="http://bfy.tw/19ge"/>
    </Target>
</Project>

[rainersigwald]

That's a pretty good way to do this. InitialTargets are additive (PR to mention this in the docs: MicrosoftDocs/visualstudio-docs#1737) so you won't be clobbering anything.

One consideration: projects are built in several contexts that aren't normal builds. Most important is probably Visual Studio's "design-time build" which is used to extract information about the project to drive IntelliSense and other IDE features. You should be careful to only fail design-time builds in very broken circumstances. Since this target emits a warning, rather than an error, it's fine.

As a general guideline, please provide a more specific error code than 1. Users can suppress warnings using the code, so it should ideally be unique to your project. This is often done with 3- or 4-letter prefixes (like MSBuild's MSBxxxx or C#'s CS1234).

Would you mind opening a separate bug about the HelpKeyword? Someone would need to dig into that a bit to figure out what's mangling the URL and whether that's intentional.