nixos/rfcs
1
0
Fork 0
mirror of https://github.com/NixOS/rfcs.git synced 2025-12-24 09:51:07 +01:00
Code Issues Projects Releases Packages Wiki Activity Actions

Revise to list-like syntax proposed by Synthetica9

Browse source 
The new syntax is

```
attrs.[ a b c ]
```

as sugar for

```
[ attrs.a attrs.b attrs.c ]
```
This commit is contained in:
Ryan Burns 2022-07-29 00:33:49 -07:00
parent 63ea2a18cc
commit f7730efee7
1 changed files with 7 additions and 37 deletions
Download patch file Download diff file Expand all files Collapse all files

44
rfcs/0110-inherit-as-list.md
View file

@ -11,7 +11,7 @@ related-issues: (will contain links to implementation PRs)
# Summary
[summary]: #summary
This RFC proposes a new Nix syntax `[ inherit (<attrset>) <attrnames>; ]`,
This RFC proposes a new Nix syntax `<attrset>.[ <attrnames> ]`,
which constructs a list from the values of an attrset.
The goal is to provide a similarly-terse but more principled alternative
@ -58,22 +58,16 @@ these drawbacks.
The proposed syntax is:
```
[ inherit (attrs) a b c; ]
[ inherit a b c; ]
attrs.[ a b c ]
```
These expressions are (respectively) syntactic sugar for:
This expression is syntactic sugar for:
```nix
[ attrs.a attrs.b attrs.c ]
[ a b c ]
```
The `inherit` keyword is intentionally reused so as to not add any new
keywords to the Nix grammar, and to evoke the similarities with the
existing attribute-based inherit syntax.
As the `inherit` keyword is currently a syntax error inside a list expression,
As the token `.` immediately preceding `[` is currently a syntax error,
a Nix interpreter which supports this new language feature will be compatible
with existing Nix code.
@ -90,38 +84,14 @@ third-party parsers/linters would also need to be updated.
This would be useful for many languages and frameworks in Nixpkgs which
extract packages from a package set argument.
For example, `python3.withPackages (ps: [ inherit (ps) ...; ])` will serve as a
For example, `python3.withPackages (ps: ps.[ ... ])` will serve as a
more fine-grained alternative to `python3.withPackages (ps: with ps; [ ... ])`.
This would apply similarly to `vim.withPlugins`, `lua.withPackages`, etc.
Certain list-typed `meta` fields could also make use of this feature, e.g.:
```
meta.licenses = [ inherit (lib.licenses) bsd3 mit; ];
meta.maintainers = [ inherit (lib.maintainers) johndoe janedoe; ];
```
List-inherits can be used multiple times in a list-expression, and intermingled
with ordinary list elements without needing to concatenate:
```
buildInputs = [
a b c /* ordinary list elements */
inherit (pkgsFoo) d e f;
g h i /* ordinary list elements */
inherit (pkgsBar) j k l;
];
```
The order of the elements is preserved inside of and between inherits,
so the previous is exactly equivalent to
```
buildInputs = [
a b c
pkgsFoo.d pkgsFoo.e pkgsFoo.f
g h i
pkgsBar.j pkgsBar.k pkgsBar.l
];
meta.licenses = lib.licenses.[ bsd3 mit ];
meta.maintainers = lib.maintainers.[ johndoe janedoe ];
```