💥 Remove :feature category

:feature was a "catch-all" category. Many of its modules fit better in
other categories, so they've been moved:

- feature/debugger -> tools/debugger
- feature/evil -> editor/evil
- feature/eval -> tools/eval
- feature/lookup -> tools/lookup
- feature/snippets -> editor/snippets
- feature/file-templates -> editor/file-templates
- feature/workspaces -> ui/workspaces

More potential changes in the future:

- A new :term category for terminal emulation modules (eshell, term and
  vterm).
- A new :os category for modules dedicated to os-specific functionality.
  The :tools macos module would fit here, but so would modules for nixos
  and arch.
- A new :services category for web-service integration, like wakatime,
  twitter, elfeed, gist and pastebin services.

modules/tools/lookup/autoload/docsets.el

@@ -0,0 +1,100 @@
+;;; tools/lookup/autoload/docsets.el -*- lexical-binding: t; -*-
+;;;###if (featurep! +docsets)
+
+(defvar +lookup-docset-alist nil
+  "An alist mapping major and minor modes to lists of Dash docsets.
+
+Entries are added by `set-docsets!' and used by `+lookup-docsets-for-buffer' to
+assemble a list of installed & active docsets.")
+
+;;;###autodef
+(defun set-docsets! (modes &rest docsets)
+  "Registers a list of DOCSETS for MODES.
+
+MODES can be one major mode, or a list thereof.
+
+DOCSETS can be strings, each representing a dash docset, or a vector with the
+structure [DOCSET FORM]. If FORM evaluates to nil, the DOCSET is omitted. If it
+is non-nil, (format DOCSET FORM) is used as the docset.
+
+The first element in DOCSETS can be :add or :remove, making it easy for users to
+add to or remove default docsets from modes.
+
+DOCSETS can also contain sublists, which will be flattened.
+
+Example:
+
+  (set-docsets! '(js2-mode rjsx-mode) \"JavaScript\"
+    [\"React\" (eq major-mode 'rjsx-mode)]
+    [\"TypeScript\" (bound-and-true-p tide-mode)])
+
+Used by `+lookup/in-docsets' and `+lookup/documentation'."
+  (declare (indent defun))
+  (dolist (mode (doom-enlist modes))
+    (if (null docsets)
+        (setq +lookup-docset-alist
+              (delq (assq mode +lookup-docset-alist)
+                    +lookup-docset-alist))
+      (let ((action  (if (keywordp (car docsets)) (pop docsets)))
+            (docsets (mapcan #'doom-enlist docsets))) ; flatten list
+        (setf (alist-get mode +lookup-docset-alist)
+              (pcase action
+                (:add    (append docsets (alist-get mode +lookup-docset-alist)))
+                (:remove (cl-set-difference (alist-get mode +lookup-docset-alist) docsets))
+                (_ docsets)))))))
+
+
+;;
+;; Library
+
+;;;###autoload
+(defun +lookup-docsets-for-buffer ()
+  "Return list of installed & selected docsets for the current major mode.
+
+This list is built from `+lookup-docset-alist'."
+  (cl-loop for docset in (cdr (assq major-mode +lookup-docset-alist))
+           when (or (stringp docset)
+                    (and (vectorp docset)
+                         (eval (aref docset 1) t)))
+           collect docset))
+
+;;;###autoload
+(defun +lookup-docset-installed-p (docset)
+  "Return t if DOCSET is installed."
+  (let ((path (helm-dash-docsets-path)))
+    (file-directory-p
+     (expand-file-name (format "%s.docset" docset)
+                       path))))
+
+;;;###autoload
+(autoload 'helm-dash-installed-docsets "helm-dash")
+
+;;;###autoload
+(autoload 'helm-dash-docset-installed-p "helm-dash")
+
+
+;;
+;; Commands
+
+;;;###autoload
+(defalias '+lookup/install-docset #'helm-dash-install-docset)
+
+(defvar counsel-dash-docsets)
+(defvar helm-dash-docsets)
+;;;###autoload
+(defun +lookup/in-docsets (&optional query docsets)
+  "Lookup QUERY in dash DOCSETS.
+
+QUERY is a string and docsets in an array of strings, each a name of a Dash
+docset. Requires either helm or ivy.
+
+Use `+lookup/install-docset' to install docsets."
+  (interactive)
+  (let* ((counsel-dash-docsets (or docsets (+lookup-docsets-for-buffer)))
+         (helm-dash-docsets counsel-dash-docsets)
+         (query (or query (+lookup--symbol-or-region) "")))
+    (cond ((featurep! :completion helm)
+           (helm-dash query))
+          ((featurep! :completion ivy)
+           (counsel-dash query))
+          ((user-error "No dash backend is installed, enable ivy or helm.")))))