Make ido handle dynamically loading libs based on prefix

This patch enables describe-variable and describe-function to use ido
while also having the feature of automatically loading relevant libs
based on the prefix of the completion. This fixes issue #111

ido-completing-read+.el

@@ -145,6 +145,47 @@ https://github.com/DarwinAwardWinner/ido-ubiquitous/issues"
     (ido-cr+--debug-message "Falling back to `%s' because %s."
                             ido-cr+-fallback-function arg)))
 
+(defvar ido-cr+--predicate nil)
+;;; ido-cr+--update-help-prefixes needs to know the completion
+;;; predicate but ido discards that information
+
+(defun ido-cr+--update-help-prefixes ()
+  (let ((ido-cr+--old-load-history load-history))
+    (help--load-prefixes
+     (radix-tree-prefixes
+      (help-definition-prefixes)
+      (buffer-substring-no-properties (minibuffer-prompt-end) (point-max))))
+    ;; load new prefixes the same way as help--symbol-completion-table
+    ;; but without doing any completion
+    (unless (eq ido-cr+--old-load-history load-history)
+      ;; hackish way to see if help--load-prefixes loaded any new files
+      (with-no-warnings
+	;; ido dynamically binds ido-cur-list
+	(setq ido-cur-list (all-completions "" obarray ido-cr+--predicate))))))
+
+(defun ido-cr+--help-symbol-completion-minibuffer-hook ()
+  (remove-hook 'post-self-insert-hook
+	       #'ido-cr+--update-help-prefixes)
+  ;; prefixes are updated with each self-insert as necessary
+  (remove-hook 'ido-setup-hook
+	       #'ido-cr+--help-symbol-completion-ido-hook)
+  (remove-hook 'minibuffer-exit-hook
+	       #'ido-cr+--help-symbol-completion-minibuffer-hook)
+  (setq ido-cr+--predicate nil))
+
+(defun ido-cr+--help-symbol-completion-ido-hook ()
+  (add-hook 'post-self-insert-hook
+	    #'ido-cr+--update-help-prefixes)
+  (add-hook 'minibuffer-exit-hook
+	    #'ido-cr+--help-symbol-completion-minibuffer-hook))
+
+(defun ido-cr+--handle-help-symbol-completion (predicate)
+  ;; ido-setup-hook does all the setup for the prefix completion and
+  ;; minibuffer-exit-hook breaks it all down
+  (setq ido-cr+--predicate predicate)
+  (add-hook 'ido-setup-hook
+	    #'ido-cr+--help-symbol-completion-ido-hook))
+
 ;;;###autoload
 (defun ido-completing-read+ (prompt collection &optional predicate
                                     require-match initial-input
@@ -170,7 +211,14 @@ completion for them."
                     '("ido cannot handle non-nil INHERIT-INPUT-METHOD")))
            ((bound-and-true-p completion-extra-properties)
             (signal 'ido-cr+-fallback
-                    '("ido cannot handle non-nil `completion-extra-properties'")))
+                    '("ido cannot handle non-nil `completion-extra-properties'"))
+	   ((eq collection 'help--symbol-completion-table)
+	    ;; In newer Emacs help--symbol-completion-table loads libs
+	    ;; based on the prefix of the completion in
+	    ;; describe-variable and describe-function as the user
+	    ;; types. Detect and handle that case with ido.
+	    (ido-cr+--handle-help-symbol-completion predicate)
+	    (setq collection obarray))
            ((functionp collection)
             (signal 'ido-cr+-fallback
                     '("ido cannot handle COLLECTION being a function"))))

ido-ubiquitous.el

@@ -331,6 +331,7 @@ using overrides and disable it for everything else."
     (enable exact "find-tag")
     ;; https://github.com/DarwinAwardWinner/ido-ubiquitous/issues/89
     (enable prefix "etags-select-")
+    (enable regexp "\\`describe-\\(function\\|variable\\)\\'")
     ) ; Close paren on separate line for better VC diffs
   "Default value of `ido-ubiquitous-command-overrides'.
 
@@ -668,7 +669,8 @@ completion for them."
                         '("`ido-ubiquitous-active-state' is `disable'")))
               ;; Handle a collection that is a function: either expand
               ;; completion list now or fall back
-              (when (functionp collection)
+              (when (and (functionp collection)
+                         (not (eq collection 'help--symbol-completion-table)))
                 (if (or ido-ubiquitous-allow-on-functional-collection
                         (memq ido-ubiquitous-active-override
                               '(enable enable-old)))