buildDotnetModule: cannot set argument installPath relative to $out

[UlyssesZh]

Describe the bug

The default value of the installPath argument to the buildDotnetModule function is $out/lib/${pname}. While the default value seems good, if you manually set it to $out/lib/${pname}, it will actually be interpreted as /build/source/$out/lib/${pname}, and the $out here is literal (it is a dir with a literal dollar sign in its name). This prevents setting anything relative to $out as installPath.

Steps To Reproduce

Steps to reproduce the behavior:

Take this hello world example (the postInstall line is for debugging purpose):

{
  fetchFromGitHub,
  buildDotnetModule,
  dotnetCorePackages,
} :

buildDotnetModule rec {
  pname = "hello-dotnet";
  version = "0.0.10";
  src = fetchFromGitHub {
    owner = "ofenloch";
    repo = "hello-world";
    rev = version;
    hash = "sha256-tjTeTxwBHIoaA41JplbEVgowiEgPslFVyDdEKkRjnY8=";
  };
  nugetDeps = ./deps.json;
  projectFile = "hello-world.csproj";
  dotnetInstallFlags = [ "-p:PublishSingleFile=false" ];
  executables = [ "hello-world" ];
  dotnet-runtime = dotnetCorePackages.runtime_6_0;
  postInstall = "ls";
  installPath = "$out/lib/${pname}"; # comment out this
}

If you comment out the installPath setting, it builds the package fine. The result structure is this:

$ tree result
result
├── bin
│   └── hello-world
└── lib
    └── hello-dotnet
        ├── hello-world
        ├── hello-world.deps.json
        ├── hello-world.dll
        ├── hello-world.pdb
        ├── hello-world.runtimeconfig.json
        ├── library.dll
        ├── library.pdb
        └── NLog.dll

4 directories, 9 files

However, if you set installPath, the result is like this:

$ tree result
result
└── bin
    └── hello-world

2 directories, 1 file

The files that should be installed in $out/lib/${pname} are not there. You can see from the build log that it is actually installed in a directory literally called $out:

Running phase: installPhase
Executing dotnetInstallHook
  hello-world -> /build/source/$out/lib/hello-dotnet/
'$out'          bin                  hello-world.sln   obj       test
 Dockerfile   data                   lib               scripts
 README.md    hello-world.csproj   nuget.config      src
Finished dotnetInstallHook

Expected behavior

Setting installPath = "$out/lib/${pname}"; shouldn't change the result of the build.

Screenshots

Additional context

Metadata

Notify maintainers

@NixOS/dotnet

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[aucub]

local -r dotnetInstallPath="${dotnetInstallPath-$out/lib/$pname}"

Because installPath is passed as dotnetInstallPath environment variable and not directly as part of the sh script. Will using placeholder meet your needs?

[UlyssesZh]

You mean have a placeholder in the script that gets replaced with a string passed as an argument to buildDotnetModule? I think that would work. Would this raise security concerns as script injection is possible?

[aucub]

As is often done.

installPath = "${placeholder "out"}/lib/${pname}";

Would this be correct?

[UlyssesZh]

Seems usable.