depot/third_party/nixpkgs/lib/README.md

Nixpkgs lib

This directory contains the implementation, documentation and tests for the Nixpkgs lib library.

Overview

The evaluation entry point for lib is default.nix. This file evaluates to an attribute set containing two separate kinds of attributes:

• Sub-libraries: Attribute sets grouping together similar functionality. Each sub-library is defined in a separate file usually matching its attribute name.

  Example: lib.lists is a sub-library containing list-related functionality such as lib.lists.take and lib.lists.imap0. These are defined in the file lists.nix.

• Aliases: Attributes that point to an attribute of the same name in some sub-library.

  Example: lib.take is an alias for lib.lists.take.

Most files in this directory are definitions of sub-libraries, but there are a few others:

• minver.nix: A string of the minimum version of Nix that is required to evaluate Nixpkgs.
• tests: Tests, see Running tests
  • release.nix: A derivation aggregating all tests
  • misc.nix: Evaluation unit tests for most sub-libraries
  • *.sh: Bash scripts that run tests for specific sub-libraries
  • All other files in this directory exist to support the tests
• systems: The lib.systems sub-library, structured into a directory instead of a file due to its complexity
• path: The lib.path sub-library, which includes tests as well as a document describing the design goals of lib.path
• All other files in this directory are sub-libraries

Module system

The module system spans multiple sub-libraries:

• modules.nix: lib.modules for the core functions and anything not relating to option definitions
• options.nix: lib.options for anything relating to option definitions
• types.nix: lib.types for module system types

Reference documentation

Reference documentation for library functions is written above each function as a multi-line comment. These comments are processed using nixdoc and rendered in the Nixpkgs manual. The nixdoc README describes the comment format.

See the chapter on contributing to the Nixpkgs manual for how to build the manual.

Running tests

All library tests can be run by building the derivation in tests/release.nix:

nix-build tests/release.nix

Some commands for quicker iteration over parts of the test suite are also available:

# Run all evaluation unit tests in tests/misc.nix
# if the resulting list is empty, all tests passed
nix-instantiate --eval --strict tests/misc.nix

# Run the module system tests
tests/modules.sh

# Run the lib.sources tests
tests/sources.sh

# Run the lib.filesystem tests
tests/filesystem.sh

# Run the lib.path property tests
path/tests/prop.sh