From 6ae48d6d28112d487ea09ca905814da47c2a26cf Mon Sep 17 00:00:00 2001
From: Philip Kaludercic <philipk@posteo.net>
Date: Tue, 15 Aug 2023 18:39:14 +0200
Subject: [PATCH] Add command to start Emacs with specific packages

* lisp/emacs-lisp/package.el (package--dependencies): Extend function
to handle and return package descriptors.
(package-isolate): Add new command.
* etc/NEWS: Announce new command.
---
 etc/NEWS                   |  6 ++++
 lisp/emacs-lisp/package.el | 57 ++++++++++++++++++++++++++++++++++----
 2 files changed, 57 insertions(+), 6 deletions(-)

diff --git a/etc/NEWS b/etc/NEWS
index 57f04609679..c374695a571 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -505,6 +505,12 @@ project, that you can quickly select using 'project-switch-project'
 When non-nil, package specifications with side-effects for building
 software will be used when building a package.
 
+---
+*** New command to start Emacs only with specific packages
+The command 'package-isolate' is equivalent to starting Emacs with the
+-Q flag and loading specific packages (and their dependencies)
+manually.
+
 ** Flymake
 
 +++
diff --git a/lisp/emacs-lisp/package.el b/lisp/emacs-lisp/package.el
index b3062d2608b..9e969ce1024 100644
--- a/lisp/emacs-lisp/package.el
+++ b/lisp/emacs-lisp/package.el
@@ -2330,12 +2330,26 @@ package-upgrade-all
       (mapc #'package-upgrade upgradeable))))
 
 (defun package--dependencies (pkg)
-  "Return a list of all dependencies PKG has.
-This is done recursively."
-  ;; Can we have circular dependencies?  Assume "nope".
-  (when-let* ((desc (cadr (assq pkg package-archive-contents)))
-              (deps (mapcar #'car (package-desc-reqs desc))))
-    (delete-dups (apply #'nconc deps (mapcar #'package--dependencies deps)))))
+  "Return a list of all recursive dependencies of PKG.
+If PKG is a package descriptor, the return value will consist of
+a list of package descriptors.  If PKG is a symbol, designating a
+package, the return value will be a list of symbols designating
+packages."
+  (when-let* ((desc (if (package-desc-p pkg) pkg
+                      (cadr (assq pkg package-archive-contents)))))
+    ;; Can we have circular dependencies?  Assume "nope".
+    (let ((all (named-let more ((pkg-desc desc))
+                 (let (deps)
+                   (dolist (req (package-desc-reqs pkg-desc))
+                     (setq deps (nconc
+                                 (catch 'found
+                                   (dolist (p (apply #'append (mapcar #'cdr (package--alist))))
+                                     (when (and (string= (car req) (package-desc-name p))
+                                                (version-list-<= (cadr req) (package-desc-version p)))
+                                       (throw 'found (more p)))))
+                                 deps)))
+                   (delete-dups (cons pkg-desc deps))))))
+      (remq pkg (mapcar (if (package-desc-p pkg) #'identity #'package-desc-name) all)))))
 
 (defun package-strip-rcs-id (str)
   "Strip RCS version ID from the version string STR.
@@ -2625,6 +2639,37 @@ package-autoremove
                   removable))
         (message "Nothing to autoremove")))))
 
+(defun package-isolate (packages)
+  "Start an uncustomised Emacs and only load a set of PACKAGES."
+  (interactive
+   (cl-loop for p in (cl-loop for p in (package--alist) append (cdr p))
+	    unless (package-built-in-p p)
+	    collect (cons (package-desc-full-name p) p) into table
+	    finally return
+	    (list (cl-loop for c in (completing-read-multiple
+                                     "Isolate packages: " table
+                                     nil t)
+		           collect (alist-get c table nil nil #'string=)))))
+  (let* ((name (concat "package-isolate-"
+                       (mapconcat #'package-desc-full-name packages ",")))
+         package-load-list)
+    (dolist (package (append packages (mapcan #'package--dependencies packages)))
+      (push (list (package-desc-name package)
+                  (package-version-join (package-desc-version package)))
+              package-load-list))
+    (apply #'start-process (concat "*" name "*") nil
+           (list (expand-file-name invocation-name invocation-directory)
+                 "--quick" "--debug-init"
+                 "--init-directory" (make-temp-file name t)
+                 (format "--eval=%S"
+                         `(progn
+                            (require 'warnings)
+                            (add-to-list 'warning-suppress-log-types 'initialization)
+                            (require 'package)
+                            (setq package-user-dir ,(expand-file-name package-user-dir)
+                                  package-load-list ',package-load-list)
+                            (package-initialize)))))))
+
 
 ;;;; Package description buffer.
 
-- 
2.39.2