Merge pull request from justbur/imenu3

Improve imenu support
GitHub-reference: https://github.com/jwiegley/use-package/issues/356

diff --cc lisp/use-package/use-package.el
index bba24d923f5c55ab723090e8d5fd23d9b0d546fd,59f26158740902ed40673029d2a9025b79b886c5..d993ce645301a02afd459492e796f7935311c108
--- 1/lisp/use-package/use-package.el
--- 2/lisp/use-package/use-package.el
+++ b/lisp/use-package/use-package.el
@@@ -182,44 -176,18 +182,42 @@@ Must be set before loading use-package.
    :type 'boolean
    :group 'use-package)
  
 +(defcustom use-package-ensure-function 'use-package-ensure-elpa
 +  "Function that ensures a package is installed.
 +This function is called with one argument, the package name as a
 +symbol, by the `:ensure' keyword.
 +
 +The default value uses package.el to install the package."
 +  :type '(choice (const :tag "package.el" use-package-ensure-elpa)
 +                 (function :tag "Custom"))
 +  :group 'use-package)
 +
 +(defcustom use-package-defaults
 +  '((:config '(t) t)
 +    (:ensure use-package-always-ensure use-package-always-ensure)
 +    (:pin use-package-always-pin use-package-always-pin))
 +  "Alist of default values for `use-package' keywords.
 +Each entry in the alist is a list of three elements. The first
 +element is the `use-package' keyword and the second is a form
 +that can be evaluated to get the default value. The third element
 +is a form that can be evaluated to determine whether or not to
 +assign a default value; if it evaluates to nil, then the default
 +value is not assigned even if the keyword is not present in the
 +`use-package' form."
 +  :type '(repeat (list symbol sexp sexp)))
 +
  (when use-package-enable-imenu-support
-   ;; Not defined in Emacs 24
-   (defvar lisp-mode-symbol-regexp
-     "\\(?:\\sw\\|\\s_\\|\\\\.\\)+")
-   (add-to-list
-    'lisp-imenu-generic-expression
-    (list "Package"
-          (purecopy (concat "^\\s-*("
-                            (eval-when-compile
-                              (regexp-opt
-                               '("use-package" "require")
-                               t))
-                            "\\s-+\\(" lisp-mode-symbol-regexp "\\)"))
-          2)))
+   (eval-after-load 'lisp-mode
+     `(let ((sym-regexp (or (bound-and-true-p lisp-mode-symbol-regexp)
+                            "\\(?:\\sw\\|\\s_\\|\\\\.\\)+")))
+        (add-to-list
+         'lisp-imenu-generic-expression
+         (list "Packages"
+               (concat "^\\s-*("
+                       ,(eval-when-compile
+                          (regexp-opt '("use-package" "require") t))
+                       "\\s-+\\(" sym-regexp "\\)")
+               2)))))
  
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