implement consult-help command which allows to search all documentation strings

consult.el

@@ -214,6 +214,9 @@ You may want to add a function which pulses the current line, e.g.,
 (defvar-local consult-imenu-history nil
   "Buffer-local history for the command `consult-imenu'.")
 
+(defvar consult-help-history nil
+  "History for the command `consult-help'.")
+
 (defvar consult-buffer-history nil
   "History for the command `consult-buffer'.")
 
@@ -786,6 +789,80 @@ This command obeys narrowing. Optionally INITIAL input can be provided."
    :category 'file
    :history 'file-name-history))
 
+(defun consult--help-candidates ()
+  "Return list of help candidates."
+  (message "Loading help...")
+  (let ((candidates))
+    (mapatoms
+     (lambda (sym)
+       (let ((str (symbol-name sym)))
+         (when (facep sym)
+           (push (consult--narrow-candidate ?a str (marginalia-annotate-face str)) candidates))
+         (when (and (fboundp 'cl-find-class) (cl-find-class sym))
+           (push (consult--narrow-candidate ?t str (marginalia-annotate-symbol str)) candidates))
+         (when (fboundp sym)
+           (cond
+            ((and (commandp sym) (where-is-internal sym nil t))
+             (push (consult--narrow-candidate ?b str (marginalia-annotate-symbol str)) candidates))
+            ((commandp sym)
+             (push (consult--narrow-candidate ?c str (marginalia-annotate-symbol str)) candidates))
+            ((macrop sym)
+             (push (consult--narrow-candidate ?m str (marginalia-annotate-symbol str)) candidates)))
+           (push (consult--narrow-candidate ?f str (marginalia-annotate-symbol str)) candidates))
+         (when (boundp sym)
+           (when (custom-variable-p sym)
+             (push (consult--narrow-candidate ?u str (marginalia-annotate-symbol str)) candidates))
+           (push (consult--narrow-candidate ?v str (marginalia-annotate-symbol str)) candidates)))))
+    ;; TODO better sorting, such that bindings or commands appear first?
+    (sort candidates #'string<)))
+
+(defvar consult--help-cache nil)
+
+;;;###autoload
+(defun consult-help (&optional initial)
+  "Open help.
+Optionally INITIAL input can be provided."
+  (interactive)
+  (minibuffer-with-setup-hook
+      (lambda ()
+        ;; TODO move this to consult-selectrum
+        (setq-local selectrum-refine-candidates-function #'selectrum-default-candidate-refine-function))
+    (when-let* ((selected (consult--read "Help: "
+                                    (or consult--help-cache
+                                        (setq consult--help-cache (consult--with-increased-gc (consult--help-candidates))))
+                                    :category 'consult-help
+                                    :require-match t
+                                    :initial initial
+                                    :sort nil
+                                    :narrow
+                                    '((?f . "Function")
+                                      (?c . "Command")
+                                      (?b . "Binding")
+                                      (?m . "Macro")
+                                      (?u . "Custom Variable")
+                                      (?v . "Variable")
+                                      (?a . "Face")
+                                      (?t . "CL Type"))
+                                    :history 'consult-help-history))
+           (name (intern-soft (replace-regexp-in-string "^[^ ]+ \\| .*" "" selected))))
+      (pcase (elt selected 0)
+        ;; lookup describe function via keybinding in order to support helpful
+        (?f (funcall (key-binding "\C-hf") name))
+        (?c (funcall (key-binding "\C-hf") name))
+        (?b (funcall (key-binding "\C-hf") name))
+        (?m (funcall (key-binding "\C-hf") name))
+        (?u (funcall (key-binding "\C-hv") name))
+        (?v (funcall (key-binding "\C-hv") name))
+        (?v (funcall (key-binding "\C-hv") name))
+        (?a (describe-face name))
+        (?t (funcall (key-binding "\C-ho") name))))))
+
+;;;###autoload
+(defun consult-help-symbol-at-point ()
+  "Open help for a symbol at point."
+  (interactive)
+  (consult-help (thing-at-point 'symbol)))
+
 ;;;###autoload
 (defun consult-recent-file ()
   "Find recent using `completing-read'."