feat(eshell): add help command & lookup handler

Fix: #6867
Co-authored-by: aikrahguzar <aikrahguzar@users.noreply.github.com>

modules/term/eshell/autoload/commands.el

@@ -28,3 +28,6 @@ For folks with a habit of using \"emacs\" to open files, even in eshell."
   "Create a directory then cd into it."
   (make-directory dir t)
   (eshell/cd dir))
+
+;;;###autoload
+(defalias 'eshell/help #'+eshell-lookup-documentation)

modules/term/eshell/autoload/eshell.el

@@ -75,6 +75,21 @@
       (insert command)
       (eshell-send-input nil t))))
 
+;; Adapted from `esh-help-run-help'
+;;;###autoload
+(defun +eshell-lookup-documentation (cmd)
+  "Show help for CMD (a shell command or elisp function)."
+  (cond ((eshell-find-alias-function cmd)
+         (always (helpful-callable (eshell-find-alias-function cmd))))
+        ((and (or (and (string-match-p "^\\*." cmd)
+                       (cl-callf substring cmd 1))
+                  (eshell-search-path cmd))
+              (zerop (car (doom-call-process manual-program cmd))))
+         (always (display-buffer (man cmd))))
+        ((functionp (intern cmd))
+         (helpful-callable (intern cmd)) t)
+        ((user-error "Couldn't find man pages or elisp documentation for %S" cmd))))
+
 
 ;;
 ;;; Commands

modules/term/eshell/config.el

@@ -55,6 +55,9 @@ You should use `set-eshell-alias!' to change this.")
 ;;; Packages
 
 (after! eshell ; built-in
+  (set-lookup-handlers! 'eshell-mode
+    :documentation #'+eshell-lookup-documentation)
+
   (setq eshell-banner-message
         '(format "%s %s\n"
                  (propertize (format " %s " (string-trim (buffer-name)))