Clean leaves bind intermediates behind (cabcache, extracted wixext resources) - bug or by design?

[bugale]

Question

Observed with WixToolset.Sdk 5.0.2 (MSBuild 18.9, Windows): MSBuild /t:Clean deletes the MSI/wixpdb but leaves two kinds of bind intermediates behind in $(IntermediateOutputPath):

• cabcache\#cab1.cab (with <ReuseCabinetCache>true</ReuseCabinetCache>)
• WixToolset.UI.wixext_<hash>\wix-ir\* (resources extracted from extension wixlibs: ico/bmp/rtf, custom action .dll-N files)

Minimal repro - three files:

ReproMsi.wixproj:

<Project Sdk="WixToolset.Sdk/5.0.2">
  <PropertyGroup>
    <ReuseCabinetCache>true</ReuseCabinetCache>
  </PropertyGroup>
  <ItemGroup>
    <PackageReference Include="WixToolset.UI.wixext" Version="5.0.2" />
  </ItemGroup>
</Project>

Package.wxs:

<Wix xmlns="http://wixtoolset.org/schemas/v4/wxs" xmlns:ui="http://wixtoolset.org/schemas/v4/wxs/ui">
  <Package Name="Repro" Version="1.0.0" Manufacturer="Repro" UpgradeCode="6f2c78e5-3f24-4a4e-9d1c-6d1f6a3b9c01">
    <MediaTemplate EmbedCab="yes" />
    <ui:WixUI Id="WixUI_Minimal" />
    <StandardDirectory Id="ProgramFilesFolder">
      <Directory Id="INSTALLFOLDER" Name="Repro" />
    </StandardDirectory>
    <Feature Id="Main">
      <Component Directory="INSTALLFOLDER">
        <File Source="payload.txt" />
      </Component>
    </Feature>
  </Package>
</Wix>

payload.txt: any content.

msbuild ReproMsi.wixproj -restore /p:Configuration=Release
msbuild ReproMsi.wixproj /t:Clean /p:Configuration=Release

After Clean, obj\Release still contains cabcache\#cab1.cab and the whole WixToolset.UI.wixext_HAq...\wix-ir\ tree (msi/wixpdb/BindTracking are correctly gone).

Why it happens (from the wix sources): both file kinds are written to the BindTracking-neutral.txt file, but typed Intermediate:

Intermediate	...\obj\Release\cabcache\#cab1.cab
Intermediate	...\obj\Release\WixToolset.UI.wixext_HAq...\wix-ir\bannrbmp.bmp

ReadTracking.Outputs only surfaces BuiltOutputs + CopiedOutputs (ReadTracking.cs), and UpdateFileWritesWithBindInformation in wix.targets feeds only Outputs into @(FileWrites) - so Intermediate-typed entries never reach CoreClean and survive every Clean.

Question: is that by design or a bug?

• For cabcache I can imagine a "caches survive clean" argument (though Clean is normally expected to reset build state).
• For the wix-ir extractions I can't: ExtractEmbeddedFilesCommand re-extracts unconditionally on every bind (ExtractToFile(overwrite: true)), so a surviving copy is never reused as-is - it's just a stale leftover.

If you consider it a bug I'm happy to turn this into a proper issue. Our current workaround in the wixproj:

<ItemGroup>
  <Clean Include="$(IntermediateOutputPath)cabcache\**;$(IntermediateOutputPath)WixToolset.*.wixext_*\**" />
</ItemGroup>

Open Source Maintenance Fee

• I (or an organization I'm a member of) pay the Open Source Maintenance Fee by sponsoring the wixtoolset project because I support the maintainers.

[robmen]

Those sound like bugs. I'd have to double check cabcache as it might not be intended to be cleaned but the WixExtension internals are not expected to hang around.