- [`lib.path.hasStorePathPrefix`](https://nixos.org/manual/nixpkgs/unstable#function-library-lib.path.hasStorePathPrefix): Whether a [path](https://nixos.org/manual/nix/stable/language/values.html#type-path) has a [store path](https://nixos.org/manual/nix/stable/store/store-path.html#store-path) as a prefix.
- [`lib.filesystem.packagesFromDirectoryRecursive`](https://nixos.org/manual/nixpkgs/unstable#function-library-lib.filesystem.packagesFromDirectoryRecursive): Transform a directory tree containing package files suitable for `callPackage` into a matching nested attribute set of derivations.
- [`lib.fileset.toList`](https://nixos.org/manual/nixpkgs/unstable#function-library-lib.fileset.toList): The list of file paths contained in a given file set.
- [`lib.fileset.maybeMissing`](https://nixos.org/manual/nixpkgs/unstable#function-library-lib.fileset.maybeMissing): Create a file set from a path that may or may not exist.
- [`lib.derivations.optionalDrvAttr`](https://nixos.org/manual/nixpkgs/unstable#function-library-lib.derivations.optionalDrvAttr): Conditionally set a derivation attribute.
- [`lib.strings.makeIncludePath`](https://nixos.org/manual/nixpkgs/unstable#function-library-lib.strings.makeIncludePath): Construct an include search path (such as `C_INCLUDE_PATH`) containing the header files for a set of packages or paths.

Improvements:
- [`lib.fixedPoints.extends`](https://nixos.org/manual/nixpkgs/unstable#function-library-lib.fixedPoints.extends): Better documentation
- [`lib.customisation.makeScope`](https://nixos.org/manual/nixpkgs/unstable/#function-library-lib.customisation.makeScope): Better documentation
- [`lib.derivations.lazyDerivation`](https://nixos.org/manual/nixpkgs/unstable#function-library-lib.derivations.lazyDerivation): Now supports multiple outputs with an `outputs` argument
- [`lib.gvariant`](https://nixos.org/manual/nixpkgs/unstable#sec-functions-library-gvariant): Better error message for integers and attribute set values
- [`lib.filesets.gitTracked`](https://nixos.org/manual/nixpkgs/unstable#function-library-lib.fileset.gitTracked): Now works within store paths

Misc:
- The [`lib/` directory](https://github.com/NixOS/nixpkgs/tree/release-24.05/lib) is a self-contained flake now, including a working [`lib.trivial.version`](https://nixos.org/manual/nixpkgs/unstable/#function-library-lib.trivial.version) (but note that fetching a subtree by itself is not supported in Nix yet)
- [Various minor performance improvements](https://github.com/NixOS/nixpkgs/issues?q=author%3Aadisbladis+label%3A%226.topic%3A+lib%22+created%3A%3C2024-05-31+)

Module System:
- New types:
  - [`types.attrTag`](https://nixos.org/manual/nixos/unstable/#sec-option-types-sums): A tagged union type
  - `types.nonEmptyListOf`: A non-empty list
- Improved types:
  - `types.uniq`/`unique` now check the wrapped type

### Deprecations {#sec-release-24.05-lib-deprecations}

- [`lib.options.mdDoc`](https://nixos.org/manual/nixpkgs/unstable#function-library-lib.options.mdDoc) is obsolete and now emits a warning. The core ecosystem has completely migrated to markdown, so marking markdown as markdown is redundant.
- `lib.attrsets.zipWithNames` is now a deprecated alias of [`lib.attrsets.zipAttrsWithNames`](https://nixos.org/manual/nixpkgs/unstable/#function-library-lib.attrsets.zipAttrsWithNames)
- `lib.attrsets.cartesianProductOfSets` has been renamed to [`lib.attrsets.cartesianProduct`](https://nixos.org/manual/nixpkgs/unstable/#function-library-lib.attrsets.cartesianProduct)

### Internal {#sec-release-24.05-lib-internal}
- `lib` now has [Readme for contributing](https://github.com/NixOS/nixpkgs/tree/master/lib#readme).
- Some function's documentation is now written using the [accepted doc comment syntax](https://github.com/NixOS/rfcs/pull/145).
- `odoo` has been updated from `16.0.20231024` to `17.0.20240507`.