Incorrect COMReference entry when using Office interop

[JohnyL]

To include Excel interop libraries in .NET Core app, I do the following: Dependencies -> Add Reference -> COM -> Microsoft Excel 14.0 Object Library. When I do this, I get the following ItemGroup:

<ItemGroup>
    <COMReference Include="Microsoft.Office.Excel.dll">
        <Guid>00020813-0000-0000-c000-000000000046</Guid>
        <VersionMajor>1</VersionMajor>
        <VersionMinor>7</VersionMinor>
        <WrapperTool>tlbimp</WrapperTool>
        <Lcid>0</Lcid>
        <Isolated>false</Isolated>
    </COMReference>
</ItemGroup>

However, I get the following runtime error:

Unhandled exception. System.IO.FileNotFoundException: Could not load file or assembly 'office, Version=15.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c'. The system cannot find the file specified.

In order to work, I have created .NET Framework app, added COM reference there and copied its COMReference - and it works:

<ItemGroup>
    <COMReference Include="Microsoft.Office.Interop.Excel">
        <Guid>{00020813-0000-0000-C000-000000000046}</Guid>
        <VersionMajor>1</VersionMajor>
	<VersionMinor>7</VersionMinor>
	<Lcid>0</Lcid>
	<WrapperTool>primary</WrapperTool>
	<Isolated>False</Isolated>
	<EmbedInteropTypes>True</EmbedInteropTypes>
    </COMReference>
</ItemGroup>

As noted here, in order to fix the situation, the project system needs to add <EmbedInteropTypes>True</EmbedInteropTypes>.

[drewnoakes]

Repro steps:

1. New netcoreapp3.1 console application
2. Right-click Dependencies node
3. Select "Add Reference..."
4. Select "COM"
5. Select "Microsoft Excel 16.0 Object Library"
6. Reference a type within code (e.g. Microsoft.Office.Interop.Excel.Chart)
7. Try to run the console app. It fails as described.
8. Add <EmbedInteropTypes>True</EmbedInteropTypes>
9. Running now works

netcoreapp3.1

  <ItemGroup>
    <COMReference Include="Microsoft.Office.Excel.dll">
      <Guid>00020813-0000-0000-c000-000000000046</Guid>
      <VersionMajor>1</VersionMajor>
      <VersionMinor>9</VersionMinor>
      <WrapperTool>tlbimp</WrapperTool>
      <Lcid>0</Lcid>
      <Isolated>false</Isolated>
    </COMReference>
  </ItemGroup>

net471

  <ItemGroup>
    <COMReference Include="Microsoft.Office.Core">
      <Guid>{2DF8D04C-5BFA-101B-BDE5-00AA0044DE52}</Guid>
      <VersionMajor>2</VersionMajor>
      <VersionMinor>8</VersionMinor>
      <Lcid>0</Lcid>
      <WrapperTool>primary</WrapperTool>
      <Isolated>False</Isolated>
      <EmbedInteropTypes>True</EmbedInteropTypes>
    </COMReference>
    <COMReference Include="Microsoft.Office.Interop.Excel">
      <Guid>{00020813-0000-0000-C000-000000000046}</Guid>
      <VersionMajor>1</VersionMajor>
      <VersionMinor>9</VersionMinor>
      <Lcid>0</Lcid>
      <WrapperTool>primary</WrapperTool>
      <Isolated>False</Isolated>
      <EmbedInteropTypes>True</EmbedInteropTypes>
    </COMReference>
    <COMReference Include="VBIDE">
      <Guid>{0002E157-0000-0000-C000-000000000046}</Guid>
      <VersionMajor>5</VersionMajor>
      <VersionMinor>3</VersionMinor>
      <Lcid>0</Lcid>
      <WrapperTool>primary</WrapperTool>
      <Isolated>False</Isolated>
      <EmbedInteropTypes>True</EmbedInteropTypes>
    </COMReference>
  </ItemGroup>

[JohnyL]

Beg your pardon - I forgot to mention that this happens in .NET Core.

[JohnyL]

I have found out that if you use <WrapperTool>tlbimp</WrapperTool>, then interop types won't be embedded and Excel DLL is copied into app's folder, but if you use <WrapperTool>primary</WrapperTool>, then types will be embedded and Excel DLL is not copied into app's folder (of course, <EmbedInteropTypes>true</EmbedInteropTypes> must exist).

[shanselman]

I'm hitting this, just as above, in Sept of 2020. @davkean

Seems like you can't do Office Interop with Core unless you do the com reference manually?

Tooling does this (wrong:)

    <COMReference Include="Microsoft.Office.PowerPoint.dll">
      <Guid>91493440-5a91-11cf-8700-00aa0060263b</Guid>
      <VersionMajor>2</VersionMajor>
      <VersionMinor>12</VersionMinor>
      <WrapperTool>tlbimp</WrapperTool>
      <Lcid>0</Lcid>
      <Isolated>false</Isolated>
    </COMReference>
  </ItemGroup>

Correct:

    <COMReference Include="Microsoft.Office.Interop.PowerPoint">
      <Guid>{91493440-5a91-11cf-8700-00aa0060263b}</Guid>
      <VersionMajor>2</VersionMajor>
      <VersionMinor>12</VersionMinor>
      <WrapperTool>primary</WrapperTool>
      <Lcid>0</Lcid>
      <Isolated>false</Isolated>
      <EmbedInteropTypes>True</EmbedInteropTypes>
    </COMReference>
  </ItemGroup>

[JohnyL]

@shanselman Your correct variant is correct. 😉 This is what COMReference should have:

1. The value of <WrapperTool> must be primary.
2. <EmbedInteropTypes>True</EmbedInteropTypes> must be present.
3. The .dll extension in the end of file name (in Include attribute) is arbitrary.

[cartermp]

As per a chat with @shanselman this is popping up in multiple places:

dotnet/msbuild#4332
dotnet/msbuild#3986

Is the root problem the VS tooling or the MSBuild issue?

[davkean]

This is a CPS bug, we should get a Developer feedback item filed and moved to them.