​​nixpkgs Merge Queue - Easy Mark Broken
​​​+nixpkgs Merge Queue - Overview​
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​​Summary

​​This provides an easy way to mark packages as broken. Currently it is very toilsome to mark a large number of packages broken. This is a significant burden on maintainers of highly depended-on packages such as common libraries and build tools.

​​Motivation

​​In the ​+nixpkgs Merge Queue - Breaking Change Policy​ it is expected that package owners will mark broken dependents as broken. Currently this is quite toilsome as it requires going from derivation path to the source file that declared it and updating the source.

​​Detailed design

​​The tool will take as an input a list of broken packages and then use builtins.unsafeGetAttrPos​ to identify an existing broken​ attr to update or append a broken = true​ attribute to the meta​ attrset.
​​
​​Proof of concept in bash below a production version would likely have the following improvements:
  • ​​Allow processing multiple packages at once to avoid continuously re-evaluating nixpkgs.
  • ​​Use a proper AST editor instead of regex​es.
​​
​​eval "$(nix eval '(let
​​        nixpkgs = import ./. {};
​​        lib = nixpkgs.lib;
​​        pkg = nixpkgs.ffmpeg;
​​
​​        generic-location = builtins.unsafeGetAttrPos "meta" pkg;
​​        meta-attrs = lib.mapAttrsToList (k: _: builtins.unsafeGetAttrPos k pkg.meta) pkg.meta;
​​        set-meta-attrs = builtins.filter (location:
​​                (location != null) &&
​​                (location.file != generic-location.file)
​​        ) meta-attrs;
​​
​​        broken = builtins.unsafeGetAttrPos "broken" pkg.meta;
​​        other = builtins.head set-meta-attrs;
​​in 
​​  if broken != null then
​​    "sed -i ''${broken.line} s/maintainers[[:space:]]*=[^;]+/broken = true/'' ${broken.file}"
​​  else
​​    "sed -Ei ''${other.line} s/^([[:space:]]*)(.*)/\0\n\1broken = true;/'' ${other.file}"
​​)')"

​​Examples and Interactions

​​curl https://nix-cache.s3.amazon-aws.com/logs/1234 | ./mark-broken.sh

​​Drawbacks

  • ​​This makes all derivations depend on a single, frequently changing file. This may make this solution unsuitable if smarter incremental evaluation support is added to nixpkgs CI.
  • ​​This approach will not work for all packages depending on how they are defined.
  • ​​This approach will over-mark packages where the meta attributes are shared across multiple different instances of the derivation.
  • ​​This can potentially be mitigated by setting a condition such as broken = name == "foo-1.2.3"​ instead of always setting to broken = true​.

​​Alternatives

​​Maintain Broken Information in a Separate File

​​This would allow getting more complete coverage by the tool. However it is expected that the
​​
​​See ​+nixpkgs Merge Queue - Easy Mark Broken v0​ 

​​Unresolved questions

  • ​​For what portion of packages will this approach work?
  • ​​Checking the number of packages that have a non-stdenv/generic/make-derivation.nix​ attr in meta should give us an approximation.