Wix 4 Rc2: Better error message if directory for HarvestDirectory cannot be found

[ChristianSauer]

Feature requests

I have a HarvestDirectory Item on my WixProj like this:

 <ItemGroup>
        <HarvestDirectory Include="..\Release\SomeRelease">
            <DirectoryRefId>INSTALLFOLDER</DirectoryRefId>
            <PreprocessorVariable>var.HarvestPath</PreprocessorVariable>
            <ComponentGroupName>SomeFiles</ComponentGroupName>
            <AutogenerateGuids>true</AutogenerateGuids>
            <SuppressRegistry>true</SuppressRegistry>
            <SuppressFragments>true</SuppressFragments>
            <SuppressCom>true</SuppressCom>
            <SuppressRootDirectory>true</SuppressRootDirectory>
        </HarvestDirectory>
    </ItemGroup>

When the directory does not exist Wix fails with this message:

  My.wxs(7): [WIX0094] The identifier 'WixComponentGroup:SomeFiles' could not be found. Ensure you have typed the reference correctly and that all the necessary inputs are provided to the linker.

This message is less than helpful. It would be great if the error directly mentions that the Directory does not exist.
The problem is not even in the log, so finding this issue is annopying.

[BryanCrotaz]

I've had a (brief) conversation about this #7806 (comment) with @robmen and my suggestion was:

• Directory doesn't exist: Log error and fail the build - the task can't do what I asked, so the fault is mine
• Directory is empty: Log warning and generate empty component