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