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".
This commit is contained in:
Valentin Gagarin 2023-10-07 03:10:20 +02:00
parent 61720d0035
commit f00a5eb11b
4 changed files with 34 additions and 9 deletions

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@ -30,6 +30,7 @@
- [Data Types](language/values.md)
- [Language Constructs](language/constructs.md)
- [String interpolation](language/string-interpolation.md)
- [Lookup path](language/constructs/lookup-path.md)
- [Operators](language/operators.md)
- [Derivations](language/derivations.md)
- [Advanced Attributes](language/advanced-attributes.md)

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@ -0,0 +1,27 @@
# Lookup path
> **Syntax**
>
> *lookup-path* = `<` *identifier* [ `/` *identifier* `]`... `>`
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.
The value of a lookup path is determined by [`builtins.nixPath`](@docroot@/language/builtin-constants.md#builtins-nixPath).
See [`builtins.findFile`](@docroot@/language/builtins.md#builtins-findFile) for details on lookup path resolution.
> **Example**
>
> ```nix
> <nixpkgs>
>```
>
> /nix/var/nix/profiles/per-user/root/channels/nixpkgs
> **Example**
>
> ```nix
> <nixpkgs/nixos>
>```
>
> /nix/var/nix/profiles/per-user/root/channels/nixpkgs/nixos

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@ -107,11 +107,6 @@
e.g. `~/foo` would be equivalent to `/home/edolstra/foo` for a user
whose home directory is `/home/edolstra`.
Paths can also be specified between angle brackets, e.g.
`<nixpkgs>`. This means that the directories listed in the
environment variable `NIX_PATH` will be searched for the given file
or directory name.
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].
[store path]: ../glossary.md#gloss-store-path
@ -123,13 +118,15 @@
For example, assume you used a file path in an interpolated string during a `nix repl` session.
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.
Paths themselves, except those in angle brackets (`< >`), support [string interpolation].
Paths support [string interpolation].
At least one slash (`/`) must appear *before* any interpolated expression for the result to be recognized as a path.
`a.${foo}/b.${bar}` is a syntactically valid division operation.
`./a.${foo}/b.${bar}` is a path.
[Lookup paths](./constructs/lookup-path.md) such as `<nixpkgs>` resolve to path values.
- <a id="type-boolean" href="#type-boolean">Boolean</a>
*Booleans* with values `true` and `false`.

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@ -1723,7 +1723,7 @@ static RegisterPrimOp primop_findFile(PrimOp {
If the suffix is found inside that directory, then the entry is a match;
the combined absolute path of the directory (now downloaded if need be) and the suffix is returned.
The syntax
[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):
```nix
<nixpkgs>
@ -4389,9 +4389,9 @@ void EvalState::createBaseEnv()
addConstant("__nixPath", v, {
.type = nList,
.doc = R"(
The search path used to resolve angle bracket path lookups.
List of search path entries used to resolve [lookup paths](@docroot@/language/constructs/lookup-path.md).
Angle bracket expressions can be
Lookup path expressions can be
[desugared](https://en.wikipedia.org/wiki/Syntactic_sugar)
using this and
[`builtins.findFile`](./builtins.html#builtins-findFile):