Deprecated aliases should be annotated somehow to be obvious in nix search output

[lilyball]

Describe the bug
nixpkgs has a bunch of deprecated aliases for packages. These are alternative paths that contain the exact same derivation as a normal path.

This can be rather confusing when searching for packages with nix search as the aliases aren't marked in any fashion, leading to output like

* nixpkgs.youtube-dl (youtube-dl)
  Command-line tool to download videos from YouTube.com and other sites

* nixpkgs.youtubeDL (youtube-dl)
  Command-line tool to download videos from YouTube.com and other sites

There's no way to tell from this output which path you should use.

This issue was motivated by my friend who just installed Nix and one of his very first questions was "why are there duplicate packages?"

To Reproduce
Steps to reproduce the behavior:

1. nix search 'youtube-?dl'

Expected behavior
It should include nixpkgs.youtube-dl, but it either shouldn't include nixpkgs.youtubeDL, or it should include it but marked as a deprecated alias.

Additional context
An obvious way we could handle this in nixpkgs is to modify the deprecated aliases such that the meta.description is prefixed with something like (Deprecated alias) .

In a more ideal world, these packages would be annotated specifically as aliases and nix search would be modified to do something with these, such as hide them by default but include a command-line flag to show aliases (perhaps even including a footer like "(12 deprecated compatibility aliases hidden; use --show-aliases to show)").

Or we could just hide them from nix search outright; if you know the attribute path for an alias you could find it with nix-env -qaA but if you're not already using the alias then you shouldn't start. This would require some way for nixpkgs to know that we're building the cache for nix search so it can skip them, which could possibly be accomplished by having nix search set a particular env var (NIX_SEARCH=1) and using builtins.getEnv to read it.

Metadata

• system: "x86_64-darwin"
• host os: Darwin 18.7.0, macOS 10.14.6
• multi-user?: no
• sandbox: no
• version: nix-env (Nix) 2.2.2
• channels(eridius): "nixpkgs-19.09pre186574.88d9f776091"
• nixpkgs: /Users/eridius/.nix-defexpr/channels/nixpkgs

[matthewbauer]

Ideally we could just hide the aliases completely, see NixOS/nix#2113

[lilyball]

I still care about this.

[lilyball]

I still care about this.

[stale]

I marked this as stale due to inactivity. → More info

[lilyball]

I still care about this. Also, I suspect this should be labeled as 0.kind: enhancement instead.

Edit: Oh neat, I have permissions to change labels.

[stale]

I marked this as stale due to inactivity. → More info