do not invoke wrapProgram directly, make a wrapProgramsHook

[worldofpeace]

Describe the bug Having all these setup-hooks like wrap{Python,{G,Qt}Apps}Hook that also wrap automatically has been a total pain. Intersecting any of these frameworks results in double (or more) wrapped files and it's just not a nice solution.

We should instead have none of these hooks do wrapping at all, just populate a shell array and forward it to makeWrapperArgs. After all these hooks run we run wrapProgramsHook which actually invokes wrapProgram on all paths mentioned in the array.

This idea was originally mentioned at https://discourse.nixos.org/t/wrappers-and-hooks-do-not-invoke-wrapprogram-directly/3551

[worldofpeace]

Added to the milestone because I can't imagine continuing without it.

[FRidh]

The hardest part here is that we want to set values per target. Using shell arrays means nested arrays. That does not seem like a very good idea to me. Therefore, I suggest using JSON directly. It's a pain for hooks written in bash, but long-term I think that's the best way forward. Together with structured attributes this seems like a good goal for 20.09.

[veprbl]

An alternative approach could be to teach the wrapProgram to detect an existing wrapper and amend it if needed.

[mkg20001]

Another idea would be to make the command just collect things into an array and then at the end execute all the changes in one hook?

[rnhmjoj]

Linking here #83321 for discussion.

[deliciouslytyped]

@veprbl wouldn't such a patching based approach likely be more complex than just generating things properly in the first place? - unless...you make the wrapper execute based on some sort of easy to modify description file.

Which is I guess the same as the JSON suggestion, just asking whether we should have that generated at Nix time or used at runtime.

We've run into some sort of classic compositionality problem here.

[veprbl]

@veprbl wouldn't such a patching based approach likely be more complex than just generating things properly in the first place?

From what I can tell, the proposed alternative is to set wrapper arguments via makeWrapperArgs for python, Qt and Gtk applications and use old style makeWrapper for the rest. And there will be some exceptions, because makeWrapperArgs is not very flexible. And, any mixing of makeWrapperArgs and makeWrapper or multiple application of makeWrapper will still produce a double wrapping. So, as you can see, in this case there is also quite a bit of complexity, and the worst part is that it is pushed onto the maintainers.

unless...you make the wrapper execute based on some sort of easy to modify description file.

Wrappers should not read or parse any descriptions to not hinder the runtime performance. But, yes, they will need to be generated from a machine-readable manifest.

[deliciouslytyped]

Why not change makeWrapper to also inspect the manifest?

(I guess I just like runtime/after-the-fact introspection; could we put the manifest in the nix-support directory anyway? (I think that's where this kind of stuff goes right?) Is it just me or have people been reluctant to expose more things in nix-support? It can't hurt to have the information in there anyway?)

[nixos-discourse]

This issue has been mentioned on NixOS Discourse. There might be relevant details there:

https://discourse.nixos.org/t/declarative-wrappers-another-idea/6661/1

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[turion]

What's the status on this? I didn't know about double-wrapping being problematic and recently double-wrapped a program (https://github.com/NixOS/nixpkgs/pull/163608). Would be nice to find out what the right resolution to this is.