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|
{
runCommand, squashfsTools, closureInfo, lib, jq, writeText
}:
{
# The meta parameter is the contents of the `snap.yaml`, NOT the
# `snapcraft.yaml`.
#
# - `snap.yaml` is what is inside of the final Snap,
# - `snapcraft.yaml` is used by `snapcraft` to build snaps
#
# Since we skip the `snapcraft` tool, we skip the `snapcraft.yaml`
# file. For more information:
#
# https://docs.snapcraft.io/snap-format
#
# Note: unsquashfs'ing an existing snap from the store can be helpful
# for determining what you you're missing.
#
meta
}: let
snap_yaml = let
# Validate the snap's meta contains a name.
# Also: automatically set the `base` parameter and the layout for
# the `/nix` bind.
validate = { name, ... } @ args:
args // {
# Combine the provided arguments with the required options.
# base: built from https://github.com/NixOS/snapd-nix-base
# and published as The NixOS Foundation on the Snapcraft store.
base = "nix-base";
layout = (args.layout or {}) // {
# Bind mount the Snap's root nix directory to `/nix` in the
# execution environment's filesystem namespace.
"/nix".bind = "$SNAP/nix";
};
};
in writeText "snap.yaml"
(builtins.toJSON (validate meta));
# These are specifically required by snapd, so don't change them
# unless you've verified snapcraft / snapd can handle them. Best bet
# is to just mirror this list against how snapcraft creates images.
# from: https://github.com/snapcore/snapcraft/blob/b88e378148134383ffecf3658e3a940b67c9bcc9/snapcraft/internal/lifecycle/_packer.py#L96-L98
mksquashfs_args = [
"-noappend" "-comp" "xz" "-no-xattrs" "-no-fragments"
# Note: We want -all-root every time, since all the files are
# owned by root anyway. This is true for Nix, but not true for
# other builds.
# from: https://github.com/snapcore/snapcraft/blob/b88e378148134383ffecf3658e3a940b67c9bcc9/snapcraft/internal/lifecycle/_packer.py#L100
"-all-root"
];
in runCommand "squashfs.img" {
nativeBuildInputs = [ squashfsTools jq ];
closureInfo = closureInfo {
rootPaths = [ snap_yaml ];
};
} ''
root=$PWD/root
mkdir $root
(
# Put the snap.yaml in to `/meta/snap.yaml`, setting the version
# to the hash part of the store path
mkdir $root/meta
version=$(echo $out | cut -d/ -f4 | cut -d- -f1)
cat ${snap_yaml} | jq ". + { version: \"$version\" }" \
> $root/meta/snap.yaml
)
(
# Copy the store closure in to the root
mkdir -p $root/nix/store
cat $closureInfo/store-paths | xargs -I{} cp -r {} $root/nix/store/
)
# Generate the squashfs image.
mksquashfs $root $out \
${lib.concatStringsSep " " mksquashfs_args}
''
|