The Nix Hour

Currently Playing: The Nix Hour #2 [overriding derivations, fixed-output derivations, sharing closures]

The Nix Hour is a weekly beginner-oriented improvised Q&A-style lecture on Nix, where you can bring your questions and we'll answer them with more context, examples, alternatives, tradeoffs and related topics. The Nix hour happens every week, is open to the public and is recorded and uploaded to the Tweag YouTube channel. For more info check out https://discourse.nixos.org/t/the-nix-hour-a-weekly-nix-qa-lecture-by-tweag/22767 This week we've covered these topics: 00:00 Intro 00:26 Question: How to override the source of a package 01:47 Difference between .override and .overrideAttrs 04:26 Updating derivation attributes 06:02 "or" operator precedence confusion 06:38 Back to overriding the source 07:18 Replacing "rec"s in mkDerivation with a function 10:15 Overriding the hash of a source 11:56 Demonstrating mkDerivation with a function 13:03 Trying to override the hash of a fetcher derivation directly 15:32 Nulling the hash to force a refetch 16:46 Trying to figure out why overriding the hash didn't work 18:51 Figuring it out: "sha256" is not a derivation attribute 20:45 We can't use override either 21:59 Overriding "outputHash" using "overrideAttrs" 22:47 Clarification about difference between similar problems 24:51 How overriding sha256 with overrideAttrs could work more nicely 26:58 Conclusion about source overriding 28:50 SRI hashes and the "hash" fetcher argument 31:09 "flat" file hashes 34:04 "recursive" NAR hashes 39:38 Conclusion "flat" vs "recursive" hashing 40:43 Why fetchFromGitHub uses "recursive" hashing 43:14 What changes is the NAR archive format sensitive to? 45:42 Sharing derivations using nix-store --export and --import and some other useful flags 52:40 Deleting store paths, nix-store --roots and garbage collection 54:41 Outro