:doc command unfolds partial applications even when definition has documentation

[leana8959]

Describe the bug

In the following snippet, :doc bar will explain foo instead of bar because bar is foo partially applied.

Steps To Reproduce

Save this to a file. In the repl, run :doc bar.

rec {
  /**
    foo
    */
  foo = _: _: {};
  
  /**
    bar
    */
  bar = foo {};
}

Expected behavior

Nix should not try to find the documentation of the underlying function. Or, alternatively, it should allow a pragma comment to specify whether it tries to find the documentation of the underlying function.

Metadata

nix-env (Nix) 2.34.8

Additional context

Checklist

• checked latest Nix manual (source)
• checked open bug issues and pull requests for possible duplicates
• reviewed the contributing guide

---

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[xokdvium]

Seems a bit hard to fix from a cursory glance.

The current implementation can only save doc comments for lambda expressions/primops and there isn't an easy way (that I can think of) to stuff documentation into partial application (be that of a lambda or a primop) due to the in-memory representation of those values.

[leana8959]

I just noticed two interesting phenomena:

• eta expanding the bar function in the example, nix was able to find the documentation.

  rec {
    /**
      foo
    */
    foo = _: _: { };
  
    /**
      bar
    */
    bar = meow: foo { } meow;
  }

  nix-repl> :doc bar
  Synopsis: bar = meow: ...
  
    bar
  
    /home/leana/r/NixOS/nixpkgs/test.nix:10
  

• fully applying foo will result to nix not being able to find the documentation.

  rec {
    /**
      foo
    */
    foo = _: _: { };
  
    /**
      bar
    */
    bar = foo { } { };
  }

  nix-repl> :doc bar
  error: value 'bar' does not have documentation