Using PublishSingleFile and IncludeNativeLibrariesForSelfExtract on macOS causes a "Class PlaceholderObject is implemented in both" warning

[KTSnowy]

Describe the bug

We're using a native C library for some performance critical parts of our application. This library gets called from our C# code using PInvoke. Recently we've been experimenting with single file publish which would allow us to package the native library with the application, but we're getting the following warning every time the application starts with dotnet run:

objc[4948]: Class PlaceholderObject is implemented in both
/<project-dir>/bin/Debug/net7.0/osx-x64/<project-name> (0x104e20400) 
and /<project-dir>/bin/Debug/net7.0/osx-x64/libSystem.Native.dylib (0x1061ad6a0). 
One of the two will be used. Which one is undefined.

To Reproduce

As far as I've tested it seems that adding these two csproj options on macOS is what is causing the warnings:

<PublishSingleFile>true</PublishSingleFile>
<IncludeNativeLibrariesForSelfExtract>true</IncludeNativeLibrariesForSelfExtract>

Exceptions (if any)

Further technical details

• Include the output of dotnet --info

.NET SDK:
 Version:   7.0.100
 Commit:    e12b7af219

Runtime Environment:
 OS Name:     Mac OS X
 OS Version:  12.6
 OS Platform: Darwin
 RID:         osx.12-x64
 Base Path:   /usr/local/share/dotnet/sdk/7.0.100/

Host:
  Version:      7.0.0
  Architecture: x64
  Commit:       d099f075e4

.NET SDKs installed:
  5.0.302 [/usr/local/share/dotnet/sdk]
  6.0.402 [/usr/local/share/dotnet/sdk]
  7.0.100-rc.2.22477.23 [/usr/local/share/dotnet/sdk]
  7.0.100 [/usr/local/share/dotnet/sdk]

.NET runtimes installed:
  Microsoft.AspNetCore.App 5.0.8 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 6.0.10 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 7.0.0-rc.2.22476.2 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 7.0.0 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App]
  Microsoft.NETCore.App 5.0.8 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]
  Microsoft.NETCore.App 6.0.10 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]
  Microsoft.NETCore.App 7.0.0-rc.2.22472.3 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]
  Microsoft.NETCore.App 7.0.0 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]

Other architectures found:
  None

Environment variables:
  Not set

global.json file:
  Not found

• The IDE (VS / VS Code/ VS4Mac) you're running on, and its version

Visual Studio Code
Version: 1.74.1
Commit: 1ad8d514439d5077d2b0b7ee64d2ce82a9308e5a
Date: 2022-12-14T10:33:40.793Z (1 wk ago)
Electron: 19.1.8
Chromium: 102.0.5005.167
Node.js: 16.14.2
V8: 10.2.154.15-electron.0
OS: Darwin x64 21.6.0
Sandboxed: No

[vitek-karas]

Where does the error come from? What do you use to build the native code (as the error seems to be from the native side of things).

[vitek-karas]

Actually - looking at the failure some more... I guess this is at runtime right?

When you dotnet publish the output goes to something like /bin/Debug/net7.0/osx-x64/publish. The content of the bin/Debug/net7.0/osx-x64 directory is probably a semi-random collection of files needed to produce the final output. With single-file there should be no libSystem.Native.dylib file next to the executable (since its content is included in the executable).

[KTSnowy]

Actually - looking at the failure some more... I guess this is at runtime right?

This is when executing dotnet run inside a project with those two csproj options. Running dotnet publish and then running the executable doesn't display this error.

What do you use to build the native code (as the error seems to be from the native side of things).

The native PInvoke code we use in our project is built with Clang (on macOS) and is imported from a class library into the executable application. But it doesn't seem that the error is coming from the C code side of it.

With PublishSingleFile dotnet run will display it as part of its output before running the application. Without PublishSingleFile or when not using dotnet run it won't display it.

[Herz3h]

Same issue here with dotnet sdk 8.0, when I do dotnet publish executable works fine. If I do dotnet run it display same error:

objc[36476]: Class PlaceholderObject is implemented in both /my-project/WordGenerator/bin/Debug/net7.0/osx.13-arm64/WordGenerator (0x1027e1408) and /my-project/WordGenerator/bin/Debug/net7.0/osx.13-arm64/libSystem.Native.dylib (0x103fc8660). One of the two will be used. Which one is undefined.

[jakubmisek]

The same;

building console app using dotnet 7.0, osx-arm64:
dotnet build /p:PublishSingleFile=true /p:DebugType=portable /p:DebugSymbols=false /p:PublishReferencesDocumentationFiles=false

running the compiled executable produces the notice:
objc[57322]: Class PlaceholderObject is implemented in both /Users/jakub/Projects/peachpie-samples/console-application/bin/Debug/net7.0/osx-arm64/console-application (0x102c19408) and /Users/jakub/Projects/peachpie-samples/console-application/bin/Debug/net7.0/osx-arm64/libSystem.Native.dylib (0x1040f8660). One of the two will be used. Which one is undefined.