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This is needed to avoid this https://github.com/mesonbuild/meson/issues/13774 when we go back to making our subproject directory `src`.
54 lines
2.5 KiB
Markdown
54 lines
2.5 KiB
Markdown
## Default Nix expression
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The source for the [Nix expressions](@docroot@/glossary.md#gloss-nix-expression) used by [`nix-env`] by default:
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- `~/.nix-defexpr`
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- `$XDG_STATE_HOME/nix/defexpr` if [`use-xdg-base-directories`] is set to `true`.
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It is loaded as follows:
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- If the default expression is a file, it is loaded as a Nix expression.
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- If the default expression is a directory containing a `default.nix` file, that `default.nix` file is loaded as a Nix expression.
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- If the default expression is a directory without a `default.nix` file, then its contents (both files and subdirectories) are loaded as Nix expressions.
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The expressions are combined into a single attribute set, each expression under an attribute with the same name as the original file or subdirectory.
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Subdirectories without a `default.nix` file are traversed recursively in search of more Nix expressions, but the names of these intermediate directories are not added to the attribute paths of the default Nix expression.
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Then, the resulting expression is interpreted like this:
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- If the expression is an attribute set, it is used as the default Nix expression.
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- If the expression is a function, an empty set is passed as argument and the return value is used as the default Nix expression.
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> **Example**
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>
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> If the default expression contains two files, `foo.nix` and `bar.nix`, then the default Nix expression will be equivalent to
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>
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> ```nix
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> {
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> foo = import ~/.nix-defexpr/foo.nix;
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> bar = import ~/.nix-defexpr/bar.nix;
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> }
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> ```
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The file [`manifest.nix`](@docroot@/command-ref/files/manifest.nix.md) is always ignored.
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The command [`nix-channel`] places a symlink to the current user's [channels] in this directory, the [user channel link](#user-channel-link).
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This makes all subscribed channels available as attributes in the default expression.
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## User channel link
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A symlink that ensures that [`nix-env`] can find the current user's [channels]:
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- `~/.nix-defexpr/channels`
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- `$XDG_STATE_HOME/defexpr/channels` if [`use-xdg-base-directories`] is set to `true`.
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This symlink points to:
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- `$XDG_STATE_HOME/profiles/channels` for regular users
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- `$NIX_STATE_DIR/profiles/per-user/root/channels` for `root`
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In a multi-user installation, you may also have `~/.nix-defexpr/channels_root`, which links to the channels of the root user.
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[`nix-channel`]: @docroot@/command-ref/nix-channel.md
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[`nix-env`]: @docroot@/command-ref/nix-env.md
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[`use-xdg-base-directories`]: @docroot@/command-ref/conf-file.md#conf-use-xdg-base-directories
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[channels]: @docroot@/command-ref/files/channels.md
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