Provide straight--build-cache

Add an (empty) straight.el build cache to the generated profile, and
load it when Doom calls `doom-initialize-core-packages` (which normally
does so by side effect).

Unfortunately requires adding to pre-init: Doom overrides
`straight-base-dir`, and we need to override that override.

Partially fixes package help.

build-helpers/build-profile-loader

@@ -3,13 +3,15 @@
 
 (defcli! build-profile-loader
   ((profile-name ("-n" form) "Profile name.")
-   (profile-directory ("-p" dir) "Profile data directory.")
+   (base-directory ("-b" dir) "Base directory (for profile and straight).")
    (profile-doom-dir ("-d" dir) "DOOMDIR"))
   "Write Doom's profile loader."
-  (let ((new-profiles `((,profile-name
-                         (user-emacs-directory . ,doom-emacs-dir)
-                         (doom-profile-data-dir . ,profile-directory)
-                         ("DOOMDIR" . ,profile-doom-dir)))))
+  (let* ((profile-directory (expand-file-name "profile/" base-directory))
+         (new-profiles `((,profile-name
+                          (user-emacs-directory . ,doom-emacs-dir)
+                          (doom-profile-data-dir . ,profile-directory)
+                          (unstraightened--straight-base-dir . ,base-directory)
+                          ("DOOMDIR" . ,profile-doom-dir)))))
     (doom-profiles-save new-profiles)))
 
 (run! "build-profile-loader" (cdr (member "--" argv)))

doom.nix

@@ -276,14 +276,14 @@ let
       # Required to avoid Doom erroring out at startup.
       nativeBuildInputs = [ git ];
     } ''
-    mkdir $out $out/loader $out/profile
+    mkdir $out $out/loader $out/profile $out/straight
     export DOOMPROFILELOADFILE=$out/loader/init.el
     export DOOMLOCALDIR=$(mktemp -d)
     # Prevent error on Emacs shutdown writing empty build cache.
     mkdir $DOOMLOCALDIR/straight
 
     ${runtimeShell} ${doomSource}/bin/doomscript ${./build-helpers/build-profile-loader} \
-      -n "${profileName}" -p "$out/profile" -d "${finalDoomDir}"
+      -n "${profileName}" -b "$out" -d "${finalDoomDir}"
 
     # With DOOMPROFILE set, doom-state-dir and friends are HOME-relative.
     export HOME=$(mktemp -d)

pre-init.el

@@ -9,7 +9,14 @@
 `straight-recipe-repositories' is set, but we do not want to set
 it. Just skip it entirely."
   :override #'doom-initialize-core-packages
-  (doom-log "Assuming straight was already initialized"))
+  (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))
 
 ;; nix-doom-emacs-unstraightened additions end here.
 ;; Original init.el follows.