Add new package.el commands for recompilation

* doc/emacs/package.texi (Package Installation): Document them.

* lisp/emacs-lisp/package.el (package-recompile):
(package-recompile-all): New commands (bug#27253).

lisp/emacs-lisp/package.el

@@ -2422,6 +2422,34 @@ object."
    'force 'nosave)
   (package-install pkg 'dont-select))
 
+;;;###autoload
+(defun package-recompile (pkg)
+  "Byte-compile package PKG again.
+PKG should be either a symbol, the package name, or a `package-desc'
+object."
+  (interactive (list (intern (completing-read
+                              "Recompile package: "
+                              (mapcar #'symbol-name
+                                      (mapcar #'car package-alist))))))
+  (let ((pkg-desc (if (package-desc-p pkg)
+                      pkg
+                    (cadr (assq pkg package-alist)))))
+    ;; Delete the old .elc files to ensure that we don't inadvertently
+    ;; load them (in case they contain byte code/macros that are now
+    ;; invalid).
+    (dolist (elc (directory-files (package-desc-dir pkg-desc) t "\\.elc\\'"))
+      (delete-file elc))
+    (package--compile pkg-desc)))
+
+;;;###autoload
+(defun package-recompile-all ()
+  "Byte-compile all installed packages.
+This is meant to be used only in the case the byte-compiled files
+are invalid due to changed byte-code, macros or the like."
+  (interactive)
+  (pcase-dolist (`(_ ,pkg-desc) package-alist)
+    (package-recompile pkg-desc)))
+
 ;;;###autoload
 (defun package-autoremove ()
   "Remove packages that are no longer needed.