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99 lines
3.1 KiB
Markdown
99 lines
3.1 KiB
Markdown
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R""(
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# Description
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`nix flake` provides subcommands for managing *flake
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registries*. Flake registries are a convenience feature that allows
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you to refer to flakes using symbolic identifiers such as `nixpkgs`,
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rather than full URLs such as `git://github.com/NixOS/nixpkgs`. You
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can use these identifiers on the command line (e.g. when you do `nix
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run nixpkgs#hello`) or in flake input specifications in `flake.nix`
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files. The latter are automatically resolved to full URLs and recorded
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in the flake's `flake.lock` file.
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In addition, the flake registry allows you to redirect arbitrary flake
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references (e.g. `github:NixOS/patchelf`) to another location, such as
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a local fork.
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There are multiple registries. These are, in order from lowest to
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highest precedence:
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* The global registry, which is a file downloaded from the URL
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specified by the setting `flake-registry`. It is cached locally and
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updated automatically when it's older than `tarball-ttl`
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seconds. The default global registry is kept in [a GitHub
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repository](https://github.com/NixOS/flake-registry).
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* The system registry, which is shared by all users. The default
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location is `/etc/nix/registry.json`. On NixOS, the system registry
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can be specified using the NixOS option `nix.registry`.
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* The user registry `~/.config/nix/registry.json`. This registry can
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be modified by commands such as `nix flake pin`.
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* Overrides specified on the command line using the option
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`--override-flake`.
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# Registry format
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A registry is a JSON file with the following format:
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```json
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{
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"version": 2,
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[
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{
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"from": {
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"type": "indirect",
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"id": "nixpkgs"
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},
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"to": {
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"type": "github",
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"owner": "NixOS",
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"repo": "nixpkgs"
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}
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},
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...
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]
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}
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```
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That is, it contains a list of objects with attributes `from` and
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`to`, both of which contain a flake reference in attribute
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representation. (For example, `{"type": "indirect", "id": "nixpkgs"}`
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is the attribute representation of `nixpkgs`, while `{"type":
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"github", "owner": "NixOS", "repo": "nixpkgs"}` is the attribute
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representation of `github:NixOS/nixpkgs`.)
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Given some flake reference *R*, a registry entry is used if its
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`from` flake reference *matches* *R*. *R* is then replaced by the
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*unification* of the `to` flake reference with *R*.
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# Matching
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The `from` flake reference in a registry entry *matches* some flake
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reference *R* if the attributes in `from` are the same as the
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attributes in `R`. For example:
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* `nixpkgs` matches with `nixpkgs`.
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* `nixpkgs` matches with `nixpkgs/nixos-20.09`.
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* `nixpkgs/nixos-20.09` does not match with `nixpkgs`.
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* `nixpkgs` does not match with `git://github.com/NixOS/patchelf`.
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# Unification
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The `to` flake reference in a registry entry is *unified* with some flake
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reference *R* by taking `to` and applying the `rev` and `ref`
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attributes from *R*, if specified. For example:
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* `github:NixOS/nixpkgs` unified with `nixpkgs` produces `github:NixOS/nixpkgs`.
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* `github:NixOS/nixpkgs` unified with `nixpkgs/nixos-20.09` produces `github:NixOS/nixpkgs/nixos-20.09`.
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* `github:NixOS/nixpkgs/master` unified with `nixpkgs/nixos-20.09` produces `github:NixOS/nixpkgs/nixos-20.09`.
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)""
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