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lib/README.md
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       # Nixpkgs lib

     

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

     

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       ## Overview

     

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       The evaluation entry point for `lib` is [`default.nix`](default.nix).

     

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       This file evaluates to an attribute set containing two separate kinds of attributes:

     

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       - Sub-libraries:

     

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         Attribute sets grouping together similar functionality.

     

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         Each sub-library is defined in a separate file usually matching its attribute name.

     

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         Example: `lib.lists` is a sub-library containing list-related functionality such as `lib.lists.take` and `lib.lists.imap0`.

     

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         These are defined in the file [`lists.nix`](lists.nix).

     

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       - Aliases:

     

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

     

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

     

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

     

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       - [`minver.nix`](minver.nix): A string of the minimum version of Nix that is required to evaluate Nixpkgs.

     

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       - [`tests`](tests): Tests, see [Running tests](#running-tests)

     

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         - [`release.nix`](tests/release.nix): A derivation aggregating all tests

     

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         - [`misc.nix`](tests/misc.nix): Evaluation unit tests for most sub-libraries

     

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         - `*.sh`: Bash scripts that run tests for specific sub-libraries

     

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         - All other files in this directory exist to support the tests

     

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       - [`systems`](systems): The `lib.systems` sub-library, structured into a directory instead of a file due to its complexity

     

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       - [`path`](path): The `lib.path` sub-library, which includes tests as well as a document describing the design goals of `lib.path`

     

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       - All other files in this directory are sub-libraries

     

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       ### Module system

     

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       The [module system](https://nixos.org/manual/nixpkgs/#module-system) spans multiple sub-libraries:

     

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       - [`modules.nix`](modules.nix): `lib.modules` for the core functions and anything not relating to option definitions

     

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       - [`options.nix`](options.nix): `lib.options` for anything relating to option definitions

     

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       - [`types.nix`](types.nix): `lib.types` for module system types

     

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       ## Reference documentation

     

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       Reference documentation for library functions is written above each function as a multi-line comment.

     

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       These comments are processed using [nixdoc](https://github.com/nix-community/nixdoc) and [rendered in the Nixpkgs manual](https://nixos.org/manual/nixpkgs/stable/#chap-functions).

     

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       The nixdoc README describes the [comment format](https://github.com/nix-community/nixdoc#comment-format).

     

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       See the [chapter on contributing to the Nixpkgs manual](https://nixos.org/manual/nixpkgs/#chap-contributing) for how to build the manual.

     

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       ## Running tests

     

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       All library tests can be run by building the derivation in [`tests/release.nix`](tests/release.nix):

     

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       ```bash

     

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       nix-build tests/release.nix

     

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       ```

     

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

     

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       ```bash

     

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       # Run all evaluation unit tests in tests/misc.nix

     

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       # if the resulting list is empty, all tests passed

     

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       nix-instantiate --eval --strict tests/misc.nix

     

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       # Run the module system tests

     

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       tests/modules.sh

     

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       # Run the lib.sources tests

     

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       tests/sources.sh

     

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       # Run the lib.filesystem tests

     

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       tests/filesystem.sh

     

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       # Run the lib.path property tests

     

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       path/tests/prop.sh

     

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       ```