forked from lix-project/lix
introduce lookup paths as a distinct language construct
so far they did not really have a name, and were at best referred to as "angle bracket syntax".
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@ -30,6 +30,7 @@
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- [Data Types](language/values.md)
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- [Language Constructs](language/constructs.md)
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- [String interpolation](language/string-interpolation.md)
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- [Lookup path](language/constructs/lookup-path.md)
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- [Operators](language/operators.md)
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- [Derivations](language/derivations.md)
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- [Advanced Attributes](language/advanced-attributes.md)
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27
doc/manual/src/language/constructs/lookup-path.md
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27
doc/manual/src/language/constructs/lookup-path.md
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# Lookup path
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> **Syntax**
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>
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> *lookup-path* = `<` *identifier* [ `/` *identifier* `]`... `>`
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A lookup path is an identifier with an optional path suffix that resolves to a [path value](@docroot@/language/values.md#type-path) if the identifier matches a search path entry.
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The value of a lookup path is determined by [`builtins.nixPath`](@docroot@/language/builtin-constants.md#builtins-nixPath).
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See [`builtins.findFile`](@docroot@/language/builtins.md#builtins-findFile) for details on lookup path resolution.
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> **Example**
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>
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> ```nix
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> <nixpkgs>
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>```
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>
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> /nix/var/nix/profiles/per-user/root/channels/nixpkgs
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> **Example**
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>
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> ```nix
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> <nixpkgs/nixos>
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>```
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>
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> /nix/var/nix/profiles/per-user/root/channels/nixpkgs/nixos
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@ -107,11 +107,6 @@
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e.g. `~/foo` would be equivalent to `/home/edolstra/foo` for a user
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whose home directory is `/home/edolstra`.
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Paths can also be specified between angle brackets, e.g.
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`<nixpkgs>`. This means that the directories listed in the
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environment variable `NIX_PATH` will be searched for the given file
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or directory name.
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When an [interpolated string][string interpolation] evaluates to a path, the path is first copied into the Nix store and the resulting string is the [store path] of the newly created [store object].
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[store path]: ../glossary.md#gloss-store-path
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@ -123,13 +118,15 @@
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For example, assume you used a file path in an interpolated string during a `nix repl` session.
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Later in the same session, after having changed the file contents, evaluating the interpolated string with the file path again might not return a new store path, since Nix might not re-read the file contents.
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Paths themselves, except those in angle brackets (`< >`), support [string interpolation].
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Paths support [string interpolation].
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At least one slash (`/`) must appear *before* any interpolated expression for the result to be recognized as a path.
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`a.${foo}/b.${bar}` is a syntactically valid division operation.
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`./a.${foo}/b.${bar}` is a path.
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[Lookup paths](./constructs/lookup-path.md) such as `<nixpkgs>` resolve to path values.
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- <a id="type-boolean" href="#type-boolean">Boolean</a>
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*Booleans* with values `true` and `false`.
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@ -1723,7 +1723,7 @@ static RegisterPrimOp primop_findFile(PrimOp {
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If the suffix is found inside that directory, then the entry is a match;
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the combined absolute path of the directory (now downloaded if need be) and the suffix is returned.
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The syntax
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[Lookup path](@docroot@/language/constructs/lookup-path.md) expressions can be [desugared](https://en.wikipedia.org/wiki/Syntactic_sugar) using this and [`builtins.nixPath`](@docroot@/language/builtin-constants.md#builtins-nixPath):
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```nix
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<nixpkgs>
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@ -4389,9 +4389,9 @@ void EvalState::createBaseEnv()
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addConstant("__nixPath", v, {
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.type = nList,
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.doc = R"(
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The search path used to resolve angle bracket path lookups.
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List of search path entries used to resolve [lookup paths](@docroot@/language/constructs/lookup-path.md).
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Angle bracket expressions can be
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Lookup path expressions can be
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[desugared](https://en.wikipedia.org/wiki/Syntactic_sugar)
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using this and
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[`builtins.findFile`](./builtins.html#builtins-findFile):
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