Project reference modifiers

We identify the following modifiers are impacting how copy items are handled across P2P references:

• Private defaults to true. When false, means the project's outputs are public somehow (e.g. in the GAC) and don't need to be copied to the output directory.
• EmbedInteropTypes defaults to false. When true means the referenced project's types should be embedded and its compilation outputs not copied.
• ReferenceOutputAssembly defaults to true. When false means what the name implies, though also relates to other compilation outputs such as PDB and XML documentation.

These may be combined.

Scenarios

We have several .NET projects arranged in the following P2P graph:

graph LR
    Main --> Normal
    Main -->|Private=False| NonPrivate --> NonPrivateRef
    Main -->|ReferenceOutputAssembly=False| NoReferenceOutput --> NoReferenceOutputRef
    Main -->|EmbedInteropTypes=True| EmbedInteropTypes --> EmbedInteropTypesRef
    Main -->|Private=False,ReferenceOutputAssembly=False| NonPrivateAndNoReferenceOutput --> NonPrivateAndNoReferenceOutputRef
    Main -->|Private=False,EmbedInteropTypes=True| NonPrivateAndEmbedInteropTypes --> NonPrivateAndEmbedInteropTypesRef
    Main -->|Private=False,EmbedInteropTypes=True,ReferenceOutputAssembly=False| NonPrivateAndEmbedInteropTypesAndNoReferenceOutput --> NonPrivateAndEmbedInteropTypesAndNoReferenceOutputRef
    Main -->|EmbedInteropTypes=True,ReferenceOutputAssembly=False| EmbedInteropTypesAndNoReferenceOutput --> EmbedInteropTypesAndNoReferenceOutputRef
	subgraph Single modifiers
        NonPrivate
        NonPrivateRef
        NoReferenceOutput
        NoReferenceOutputRef
        EmbedInteropTypes
        EmbedInteropTypesRef
    end
    subgraph Modifier combinations
	    NonPrivateAndNoReferenceOutput
        NonPrivateAndNoReferenceOutputRef
        NonPrivateAndEmbedInteropTypes
        NonPrivateAndEmbedInteropTypesRef
        NonPrivateAndEmbedInteropTypesAndNoReferenceOutput
        NonPrivateAndEmbedInteropTypesAndNoReferenceOutputRef
        EmbedInteropTypesAndNoReferenceOutput
        EmbedInteropTypesAndNoReferenceOutputRef
    end

Each project has a CopyToOutputDirectory="PreserveNewest" item with that project's name and extension .txt.

Building the Main project produces the following files in its output Main\bin\Debug\net6.0:

• EmbedInteropTypes.txt
• EmbedInteropTypesAndNoReferenceOutput.txt
• EmbedInteropTypesAndNoReferenceOutputRef.txt
• EmbedInteropTypesRef.dll
• EmbedInteropTypesRef.pdb
• EmbedInteropTypesRef.txt
• EmbedInteropTypesRef.xml
• Main.dll
• Main.pdb
• Main.txt
• Main.xml
• NonPrivateAndEmbedInteropTypesRef.dll
• NonPrivateAndEmbedInteropTypesRef.pdb
• NonPrivateAndEmbedInteropTypesRef.txt
• NonPrivateAndEmbedInteropTypesRef.xml
• NonPrivateRef.dll
• NonPrivateRef.pdb
• NonPrivateRef.txt
• NonPrivateRef.xml
• NoReferenceOutput.txt
• NoReferenceOutputRef.txt
• Normal.dll
• Normal.pdb
• Normal.txt
• Normal.xml

We can observe:

• EmbedInteropTypes=True only excludes the directly referenced project's compilation outputs (DLL/PDB/XML)
  • SkipCompilationOutputsOnce
• Private=False excludes everything from the referenced project, but allows further transitive references
  • SkipAllOutputsOnce
• ReferenceOutputAssembly=False excludes the output assembly of all transitively referenced projects
  • SkipCompilationOutputsTransitively

Completely missing from the output directory are any files from projects NonPrivateAndNoReferenceOutput and NonPrivateAndEmbedInteropTypesAndNoReferenceOutput. It appears that the combination of Private=False,ReferenceOutputAssembly=False results in nothing being copied at all.

To implement this, the FUTDC will need:

1. To distinguish between compilation outputs (DLL/PDB/XML) and other copy items. We will update our design-time target to add extra metadata to these items accordingly.
2. To model Private, EmbedInteropTypes and ReferenceOutputAssembly metadata on P2P references (or some proxy for these)

NuGet packages

The copying of files from NuGet packages varies by target framework! Eg. net472 copies NuGet DLLs to the out dir, while net6.0 does not (using a .deps.json file instead). Thankfully the FUTDC ignores copying of items from NuGet packages, so we don't have to worry about this distinction.