Switch to default completion UI

Mostly to avoid icomplete jank (bug#40152).

Inspired by:
<https://www.scss.tcd.ie/~sulimanm/posts/default-emacs-completion.html>

Rationale for the customizations:

C-M- chord for navigation   Because I found myself missing C-n/C-p in
                            a couple of situations.

auto-help 'visible          The feedback is not as immediate as
                            icomplete, but it's good enough.  Tried
                            'always, but there's a sit-for somewhere
                            that causes a weird pause if you happen to
                            RET before bringing up completions.

auto-select 'second-tab     M-v?  M-g M-c??

show-help nil               "Click on a selection to select it" 😏

format 'one-column          Where have you been all my life.

max-height 10               More often than not I'm typing something
                            inspired by the content from another
                            buffer, so limit how much
                            context *Completions* can hide.

auto-choose                 icomplete never clobbered the minibuffer
                            until I asked it to (with e.g. C-M-i).
                            Since C-u M-RET is a thing, keep
                            candidates off the minibuffer unless I
                            pull them in, in case I change my mind and
                            start typing something entirely different
                            from the currently highlighted candidate.

1 files changed, 29 insertions, 7 deletions

diff --git a/.emacs b/.emacs
index af613f3..4d3ab5c 100644
--- a/.emacs
+++ b/.emacs
@@ -742,13 +742,6 @@
    (my/list-update erc-track-exclude-types
      '("JOIN" "PART" "QUIT"))))
 
-(use-package icomplete
-  :config
-  (setq icomplete-scroll t)
-  :custom
-  (icomplete-mode t)
-  (icomplete-vertical-mode t))
-
 (use-package isearch
   :delight "🔍"
   :custom
@@ -778,12 +771,41 @@
   (markdown-header-scaling t)
   (markdown-indent-on-enter 'indent-and-new-item))
 
+;; Gripes:
+;; - underused keys: C-M-i, C-j
+;; - (minibuffer-)choose-completion ignore completion-no-auto-exit
+;;   when the candidate is a directory: the candidate is inserted in
+;;   the minibuffer and the user does *not* exit the minibuffer.
+;;
+;; In minibuffer:
+;; - TAB            complete, or show/update completions
+;; - TAB²           jump to completions
+;; - C-M-n, C-M-p   highlight candidate (without changing minibuffer)
+;; - RET, C-j       accept minibuffer input
+;; - M-RET          accept highlighted candidate
+;; - C-u M-RET      insert highlighted candidate (without accepting)
+;;
+;; In completions:
+;; - n, TAB, p      highlight candidate (without changing minibuffer)
+;; - RET            accept highlighted candidate
+;; - C-u RET        insert highlighted candidate in minibuffer (without accepting)
+;; - C-g, q         back to minibuffer
 (use-package minibuffer
   :config
   (setq completion-ignore-case t)
+  (define-key completion-in-region-mode-map (kbd "C-M-n") 'minibuffer-next-completion)
+  (define-key completion-in-region-mode-map (kbd "C-M-p") 'minibuffer-previous-completion)
+  (define-key minibuffer-mode-map (kbd "C-M-n") 'minibuffer-next-completion)
+  (define-key minibuffer-mode-map (kbd "C-M-p") 'minibuffer-previous-completion)
   :custom
+  (completion-auto-help 'visible)
+  (completion-auto-select 'second-tab)
+  (completion-show-help nil)
   (completions-detailed t)
+  (completions-format 'one-column)
   (completions-group t)
+  (completions-max-height 10)
+  (minibuffer-completion-auto-choose nil)
   (read-buffer-completion-ignore-case t)
   (read-file-name-completion-ignore-case t))