Disclaimer: I accept that I have trouble navigating the docs at times and don’t do MSIs for a living.

I have a solution with a bunch of projects, one being the Installer and one – for the sake of this discussion – a windows service Foo.

FooInstaller
-> WiX here
Foo
-> Dotnet core windows service here
Foo.sln

In my installer project I have a file like this

<Include xmlns="http://wixtoolset.org/schemas/v4/wxs">
    <?ifndef $(env.CI)?>
    <?include SourcePaths.Local.wxi?>
    <?else?>
    <?if $(env.CI) != ""?>
    <?include SourcePaths.CI.wxi?>
    <?else?>
    <?include SourcePaths.Local.wxi?>
    <?endif?>
    <?endif?>
</Include>

which for Some Reasons™ defines a different set of paths for CI and local builds. It looks like this in my v4 project:

<Include xmlns="http://wixtoolset.org/schemas/v4/wxs">
    <?warning This is NOT a CI build (local?)?>
    <?define FooSource = "SourceDir"?> <!-- in the .Local variant. In the .CI variant it's an absolute path -->
</Include>

The component then is using the WiX4 style heat based harvesting to generate a huge file, with gazillion entries that look like this (after a search/replace to use my path)

<Component Id="cmpDufKoLsEXviYiwOW8uU0YqqkTrU" Directory="foodir" Guid="{BD9D7EF7-C97D-48DB-B0B6-1F5CBA3E2DE9}">
    <File Id="filPesrMHNYqq.3oDZxmNT0UmP9XUI" KeyPath="yes" Source="$(FooSource)appsettings.json" />
</Component>

.. and that works fine for CI and local builds. $(FooSource) is either a full path or it is ‘SourceDir’ which to me is undocumented black magic that just works and fishes the files from the project references and their output folders.

Now I wanted to cut down on these auto-generated files and use the new WiX 5 features. My naive attempt looked like this (relevant snippet):

<Fragment>
        <?include SourcePaths.wxi?>
        <ComponentGroup Id="foofiles">
            <Files Include="$(FooSource)**">
                <!--
                Don't harvest the service because it needs manual authoring (below).
                -->
                <Exclude Files="$(FooSource)foo-service.exe" />
            </Files>

which I was hoping to be a drop-in replacement for the working WiX 4 version. But unfortunately this warns me during build-time:

warning WIX8601: Missing directory for harvesting files: Could not find a part of the path 'D:FooFooInstallerSourceDir'

which is .. unsurprising. That takes SourceDir literally and that directory doesn’t exist. Is there a way to make this work or am I stuck with the WiX4 way of manually generating my files with heat and then manually editing them (say to reference my path variable, to exclude the service etc etc)? Where did my SourceDir magic go?