Get rid of the --derivation flag

[Ericson2314]

Motivation

Since PR #7601, we've had enough flexibility in our types of installables that it is no longer needed. Almost. The only remaining issue is that drvPath has the wrong type of string for historical reasons, see #7910.

Context

Progress towards #7261

depends on #9216

Test plan

The test plan is taken by Robert's comment in #7910 (comment) describing how we could migrate Nixpkgs without a breaking change in Nix. The Nix testsuite has its own mkDerivation, and we so we do the same thing with it:

• drvPath is now overridden to not have the funky DrvDeep string context anymore.

• Tests that previously needed to builtins.unsafeDiscardOutputDependency a drvPath no don't.

• Tests that previous did not need to builtins.unsafeDiscardOutputDependency a drvPath now do.

Checklist for maintainers

Maintainers: tick if completed or explain if not relevant

• agreed on idea
• agreed on implementation strategy
• tests, as appropriate
  • functional tests - tests/**.sh
  • unit tests - src/*/tests
  • integration tests - tests/nixos/*
• documentation in the manual
• documentation in the internal API docs
• code and comments are self-explanatory
• commit message explains why the change was made
• new feature or incompatible change: updated release notes

Priorities

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[roberth]

depends on #8595

Idealistically yes, but for practicality, shouldn't we make the CLI do the expected thing for that weird string context, as a backcompat measure for older Nixpkgs?

[Ericson2314]

Hmm I dunno. I don't like how it wouldn't respect (at least my notion of) "referential transparency". I do admit it's not hard to do that, but I rather start with the cleaner thing, and only add the other if people absolutely demand it. Can always add it later, but can't remove it once added (and stable).

But maybe I am being unreasonable and I just dislike DrvDeep too much? If it warns in the DrvDeep case will that help remind people to switch to the new way of doing things? Or is that obnoxious noise when no on is empowered to e.g. change old Nixpkgs anyways?

[roberth]

I don't like how it wouldn't respect (at least my notion of) "referential transparency".

In what way is it violated?

If it warns in the DrvDeep case will that help remind people to switch to the new way of doing things?

A way to drive a wedge between those who need the old behavior of .drvPath and those who want a warning free Nixpkgs.
Ok, I'm exaggerating, but we should really make #8595 widely available before even considering this.

[dpulls]

🎉 All dependencies have been resolved !

[nixos-discourse]

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

https://discourse.nixos.org/t/2023-10-27-nix-team-meeting-minutes-98/34695/1

[fricklerhandwerk]

Discussed in Nix team meeting 2023-11-10:

• Idea: replace --derivation with .drvPath
  • Currently doesn't work because .drvPath has too big of a string context. And we can't really change that as that would be a breaking change
  • Plan: keep .drvPath the same for Nix, just change it in Nixpkgs
• @regnat: .drvPath is not a great interface. Something like .derivation would already be better
• @edolstra: the current --derivation flag is more discoverable
• @roberth: but --derivation only makes sense if the build plan is simple (no drvs-that-generate-drvs)
• @Ericson2314: Also, --derivation is global, not per-installable. So you can't mix-and-match

[nixos-discourse]

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

https://discourse.nixos.org/t/2023-11-10-nix-team-meeting-minutes-102/35379/1

[tomberek]

Did a review of use-cases via https://sourcegraph.com/search?q=context:global+nix.*--derivation&patternType=standard&sm=1&groupBy=repo to see if there are situations not covered by the proposal. The one that seems to be needed is nix path-info --derivaiton being used to obtain the build-time closure.

Top 4

• nix why-depends --derivation
• nix copy --derivation
• nix path-info --derivation
• nix-tree --derivation

[nixos-discourse]

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

https://discourse.nixos.org/t/2023-12-08-nix-team-meeting-minutes-110/36721/1