STATUS: beta
When using nix within a project, developers often use src = ./.;
for a
project like this:
{ stdenv }:
stdenv.mkDerivation {
name = "my-project";
src = ./.;
}
This works but has an issue; on each build, nix will copy the whole project
source code into the /nix/store. Including the .git
folder and any temporary
files left over by the editor.
The main workaround is to use either builtins.fetchGit ./.
or one of the
many gitignore filter projects but this is not precise enough. If the
project README changes, it should not rebuild the project. If the nix code
changes, it should not rebuild the project.
This project is a small library that makes it easy to filter in and out what files should go into a nix derivation.
nix-filter works best for projects where the files needed for a build are easy
to match. Using it with only an exclude
argument will likely not reduce the
reasons for rebuilds by a lot. Here's an Example:
{ stdenv, nix-filter }:
stdenv.mkDerivation {
name = "my-project";
src = nix-filter {
root = ./.;
# If no include is passed, it will include all the paths.
include = [
# Include the "src" path relative to the root.
"src"
# Include this specific path. The path must be under the root.
./package.json
# Include all files with the .js extension
(nix-filter.matchExt "js")
];
# Works like include, but the reverse.
exclude = [
./main.js
];
};
}
Import this folder. Eg:
let
nix-filter = import ./path/to/nix-filter;
in
# ...
The top-level is a functor that takes:
root
of typepath
: pointing to the root of the source to add to the /nix/store.name
of typestring
(optional): the name of the derivation (defaults to "source")include
of typelist(string|path|matcher)
(optional): a list of patterns to include (defaults to all).exclude
of typelist(string|path|matcher)
(optional): a list of patterns to exclude (defaults to none).
The include
and exclude
take a matcher, and automatically convert the string
and path
types to a matcher.
The matcher is a function that takes a path
and type
and returns true
if
the pattern matches.
The flake usage is like this:
{
inputs = {
nixpkgs.url = "github:nixos/nixpkgs/nixos-22.11";
nix-filter.url = "github:numtide/nix-filter";
};
outputs = { self, nixpkgs, nix-filter }:
let
pkgs = nixpkgs.legacyPackages.x86_64-linux;
# Avoid calling it nix-filter as it may result in an infinite recursion
filter = nix-filter.lib;
# ....
in
{
# ...
};
}
The functor also contains a number of matchers:
nix-filter.matchExt
:ext
-> returns a function that matches the given file extension.nix-filter.inDirectory
:directory
-> returns a function that matches a directory and any path inside of it.nix-filter.isDirectory
: matches all paths that are directories
and
:a -> b -> c
combines the result of two matchers into a new matcher.or_
:a -> b -> c
combines the result of two matchers into a new matcher.
NOTE: or
is a keyword in nix, which is why we use a variation here.
REMINDER: both, include
& exlude
already XOR elements, so or_
is
not useful at the top level.
This solution uses builtins.path { path, name, filter ? path: type: true }
under the hood, which ships with Nix.
While traversing the filesystem, starting from path
, it will call filter
on each file and folder recursively. If the filter
returns false
then the
file or folder is ignored. If a folder is ignored, it won't recurse into it
anymore.
Because of that, it makes it difficult to implement recursive glob matchers.
Something like **/*.js
would necessarily have to add every folder, to be
able to traverse them. And those empty folders will end-up in the output.
If we want to control rebuild, it's important to have a fixed set of folders.
One possibility is to use a two-pass system, where first all the folders are being added, and then the empty ones are being filtered out. But all of this happens at Nix evaluation time. Nix evaluation is already slow enough like that.
That's why nix-filter is asking the users to explicitly list all the folders
that they want to include
, and using only an exclude
is not recommended.
Add more matchers.
- nixpkgs'
lib.cleanSourceWith
. - All the git-based solutions. See https://github.com/hercules-ci/gitignore.nix#comparison
Copyright (c) 2021 Numtide under the MIT.