feat(corfu): general move-to-minibuffer impl

We previously implemented only consult/vertico as a target for export,
now we have all of them. It was necessary to use case-by-case
conditions, unfortunately, because other UIs have subtle quirks that
prevent a single generalized approach to work.

Ivy is almost compliant, but it needs beg and end to not be markers.

Helm doesn't replace `completion-in-region-function`, it expects to go
around the default `completion--in-region`, so a small addition was made
to its module, because we weren't doing that. This was likely an
oversight due to the non-standard usage. This was fixed here because we
need it working for this feature.

Ido doesn't implement `completion-in-region` and its `completing-read`
is retricted to a list of strings as table, so it's treated the same as
absence of a framework, because it lacks the needed features.

modules/completion/corfu/README.org

@@ -144,12 +144,11 @@ regarding your state. In normal-like states, enter insert then start corfu; in
 visual-like states, perform [[help:evil-change][evil-change]] (which leaves you in insert state) then
 start corfu; in insert-like states, start corfu immediatelly.
 
-** Exporting to the minibuffer (requires [[doom-module::completion vertico]])
-When using the [[doom-module::completion vertico]] module, which pulls in the
-[[doom-package:consult]] package, the entries shown in the completion popup can be
-exported to a consult minibuffer, giving access to all the manipulations the
-Vertico suite allows. For instance, one could use this to export with
-[[doom-package:embark]] via [[kbd:][C-c C-l]] and get a buffer with all candidates.
+** Exporting to the minibuffer
+The entries shown in the completion popup can be exported to a ~completing-read~
+minibuffer, giving access to all the manipulations that suite allows. Using
+Vertico for instance, one could use this to export with [[doom-package:embark]] via
+[[kbd:][C-c C-l]] and get a buffer with all candidates.
 
 ** Manually call generic CAPFs
 Completion at point functions have the property that, when called interactively

modules/completion/corfu/autoload.el

@@ -10,12 +10,30 @@
 
 ;;;###autoload
 (defun +corfu-move-to-minibuffer ()
-  ;; Taken from corfu's README.
-  ;; TODO: extend this to other completion front-ends.
+  "Move the current list of candidates to your choice of minibuffer completion UI."
   (interactive)
-  (let ((completion-extra-properties corfu--extra)
-        (completion-cycle-threshold completion-cycling))
-    (apply #'consult-completion-in-region completion-in-region--data)))
+  (pcase completion-in-region--data
+    (`(,beg ,end ,table ,pred ,extras)
+     (let ((completion-extra-properties extras)
+           completion-cycle-threshold completion-cycling)
+       (cond ((and (modulep! :completion vertico)
+                   (fboundp #'consult-completion-in-region))
+              (consult-completion-in-region beg end table pred))
+             ((and (modulep! :completion ivy)
+                   (fboundp #'ivy-completion-in-region))
+              (ivy-completion-in-region (marker-position beg) (marker-position end) table pred))
+             ;; Helm is special and wants to _wrap_ `completion--in-region'
+             ;; instead of replacing it in `completion-in-region-function'.
+             ((and (modulep! :completion helm)
+                   (fboundp #'helm--completion-in-region)
+                   (advice-member-p #'helm--completion-in-region #'completion--in-region))
+              ;; Important: `completion-in-region-function' is set to corfu at
+              ;; this moment, so `completion-in-region' (single -) doesn't work.
+              (completion--in-region beg end table pred))
+             ;; Ido doesn't implement `completion-in-region', and its
+             ;; `completing-read' only accepts a plain list of strings as table,
+             ;; so there's not much we can do with it.
+             (t (error "No minibuffer completion UI available for moving to!")))))))
 
 ;;;###autoload
 (defun +corfu-smart-sep-toggle-escape ()

modules/completion/corfu/config.el

@@ -32,6 +32,8 @@
         tab-always-indent (if (modulep! +tng) 'complete tab-always-indent))
   (add-to-list 'completion-category-overrides `(lsp-capf (styles ,@completion-styles)))
 
+  (add-to-list 'corfu-continue-commands #'+corfu-move-to-minibuffer)
+
   (add-hook! 'minibuffer-setup-hook
     (defun +corfu-enable-in-minibuffer ()
       "Enable Corfu in the minibuffer if `completion-at-point' is bound."

modules/completion/helm/config.el

@@ -24,6 +24,7 @@ Can be negative.")
 (use-package! helm-mode
   :hook (doom-first-input . helm-mode)
   :config
+  (advice-add #'completion--in-region :around #'helm--completion-in-region)
   ;; helm is too heavy for `find-file-at-point'
   (add-to-list 'helm-completing-read-handlers-alist (cons #'find-file-at-point nil)))