ci: rename update-scripts → ci

This changes how we think about this directory; it does not need to be
exclusively for scripts related to updates, but should be a place for
any scripts intended to be run by CI workflows.

This mindset should make it easier to develop and test the business
logic of workflows, without always needing to test "in production" on
the nixvim repo or a fork.

ci/version-info/default.nix

@@ -0,0 +1,42 @@
+{
+  lib,
+  callPackage,
+  writeShellApplication,
+  stdenv,
+}:
+let
+  mainInfo = callPackage ./main.nix { };
+  channelsURL = "https://raw.githubusercontent.com/NixOS/infra/refs/heads/main/channels.nix";
+in
+writeShellApplication {
+  name = "version-info";
+
+  runtimeEnv = {
+    NIX_CONFIG = ''
+      experimental-features = nix-command flakes pipe-operators
+    '';
+  };
+
+  text = ''
+    # Download channel info from NixOS/infra
+    curl ${channelsURL} | nix eval --file - --json > channels.json
+
+    # Use channels.nix to build channels.toml
+    nix build --impure \
+      --inputs-from ${toString ../..} \
+      --file ${./supported-versions.nix} \
+      --argstr system ${stdenv.hostPlatform.system} \
+      --arg-from-file channelsJSON channels.json \
+      --out-link channels.toml
+
+    (
+      echo "# DO NOT MODIFY!"
+      echo "# This file was generated by ${
+        lib.strings.removePrefix (toString ../.. + "/") (toString ./default.nix)
+      }"
+      cat ${mainInfo}
+      echo
+      cat channels.toml
+    ) > version-info.toml
+  '';
+}

ci/version-info/main.nix

@@ -0,0 +1,27 @@
+{
+  lib,
+  writers,
+}:
+let
+  inherit (builtins)
+    all
+    match
+    attrNames
+    ;
+  inherit (lib)
+    importJSON
+    ;
+
+  lockFile = importJSON ../../flake.lock;
+  nixpkgsLock =
+    # Assert there is only one nixpkgs node
+    assert all (node: match "nixpkgs_[0-9]+" node == null) (attrNames lockFile.nodes);
+    lockFile.nodes.nixpkgs.original;
+
+  info = {
+    inherit (lib.trivial) release;
+    nixpkgs_rev = lib.trivial.revisionWithDefault (throw "nixpkgs revision not available");
+    unstable = lib.strings.hasSuffix "-unstable" nixpkgsLock.ref;
+  };
+in
+writers.writeTOML "version-info.toml" info

ci/version-info/supported-versions.nix

@@ -0,0 +1,62 @@
+{
+  system ? builtins.currentSystem,
+  pkgs ? import <nixpkgs> { inherit system; },
+  lib ? import <nixpkgs/lib>,
+  channelsJSON ? throw "Neither `channels` or `channelsJSON` provided",
+  channels ? builtins.fromJSON channelsJSON,
+}:
+let
+  # Pick out supported stable channels
+  supported = [
+    "beta"
+    "stable"
+    "deprecated"
+  ];
+
+  stable_versions =
+    channels.channels
+    |> builtins.mapAttrs (channel: entry: entry // { inherit channel; })
+    |> builtins.attrValues
+    |> builtins.filter (entry: entry.variant or null == "primary")
+    |> builtins.filter (entry: builtins.elem entry.status supported)
+    |> builtins.map (entry: {
+      name = entry.channel |> builtins.match "nixos-(.+)" |> builtins.head;
+      value = {
+        inherit (entry) channel status;
+        # Currently, Nixvim stable branches match NixOS channel names
+        branch = entry.channel;
+      };
+    })
+    |> builtins.listToAttrs;
+
+  newest_stable =
+    stable_versions |> builtins.attrNames |> builtins.sort (a: b: a > b) |> builtins.head;
+
+  bumpYear = y: toString (lib.toIntBase10 y + 1);
+  bumpMonth =
+    m:
+    assert m == "05" || m == "11";
+    if m == "05" then "11" else "05";
+
+  unstable =
+    newest_stable
+    |> builtins.match "(.+)[.](.+)"
+    |> (v: {
+      y = builtins.elemAt v 0;
+      m = builtins.elemAt v 1;
+    })
+    |> (v: {
+      y = if v.m == "11" then bumpYear v.y else v.y;
+      m = bumpMonth v.m;
+    })
+    |> (v: "${v.y}.${v.m}");
+in
+pkgs.writers.writeTOML "channels.toml" {
+  versions = stable_versions // {
+    ${unstable} = {
+      branch = "main";
+      channel = "nixpkgs-unstable";
+      status = "rolling";
+    };
+  };
+}