Chain-load user init.el instead of embedding it

Mostly to avoid sticking our copyright header on top of the user's
init.el.

init.el

@@ -0,0 +1,50 @@
+;;; init.el -*- lexical-binding: t; -*-
+
+;; Copyright 2024 Google LLC
+;;
+;; Licensed under the Apache License, Version 2.0 (the "License");
+;; you may not use this file except in compliance with the License.
+;; You may obtain a copy of the License at
+;;
+;;     http://www.apache.org/licenses/LICENSE-2.0
+;;
+;; Unless required by applicable law or agreed to in writing, software
+;; distributed under the License is distributed on an "AS IS" BASIS,
+;; WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+;; See the License for the specific language governing permissions and
+;; limitations under the License.
+
+;; Extra initialization code for nix-doom-emacs-unstraightened, run before the
+;; normal `init.el'.
+
+(defadvice! nix-doom-skip-core-packages (&rest _)
+  "HACK: don't install straight and core packages.
+
+`doom-initialize-core-packages' would no-op out if
+`straight-recipe-repositories' is set, but we do not want to set
+it. Just skip it entirely."
+  :override #'doom-initialize-core-packages
+  (doom-log "nix-doom-emacs-unstraightened overriding core package init")
+  ;; doom-initialize-core-packages normally registers recipes, which loads the
+  ;; build cache by side effect, which leaves straight--build-cache available
+  ;; afterwards. Doom assumes this cache is available, so force a load here.
+  (straight--load-build-cache))
+
+(after! doom-packages
+  (setq straight-base-dir unstraightened--straight-base-dir))
+
+;; TODO: remove if Doom accepts https://github.com/doomemacs/doomemacs/pull/7849
+(defadvice! nix-doom-configs-without-git (package)
+  "Override to use ripgrep instead of git."
+  :override #'doom--help-package-configs
+  (let ((default-directory doom-emacs-dir))
+    (split-string
+     (cdr (doom-call-process
+           "rg" "--no-heading" "--line-number" "--iglob" "!*.org"
+           (format "%s %s($| )"
+                   "(^;;;###package|\\(after!|\\(use-package!)"
+                   package)))
+     "\n" t)))
+
+;; Load the user's init.el.
+(load "@user-init@" nil 'nomessage)