Re: [PATCH] `completing-read`: Add `group-function` support to completion metadata (REVISED PATCH VERSION 6)

[Daniel Mendler <mail@daniel-mendler.de>]

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On 5/11/21 9:59 PM, Eli Zaretskii wrote:
>> The snippet which I just sent is a proposal. Up to now there has been a
>> bit of back and forth of how the grouping feature is best implemented.
>> Under these circumstances it does not make sense to send a fully
>> polished patch each time. But by now the discussion seems to have
>> somehow concluded, or at least I interpret that there is some agreement
>> between the participants of the discussion which was mostly Juri,
>> Stefan, Dmitry and myself.
> 
> Then please consider my humble request to make this user-friendlier by
> offering simple Lisp values, not just functions.  You and me can grasp
> 'identity or 'ignore with no trouble, but I'm not talking about you or
> me, or anyone else of the respected group mentioned above.  This
> feature is not just for us.

I attached the updated patches, the variable `completions-group-sort`
allows the more user friendly values nil and 'alphabetical. I hope it is
more acceptable in this form.

Daniel

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From c9e4e53a5edd6eb00a562c554d402a5bc5e288a1 Mon Sep 17 00:00:00 2001
From: Daniel Mendler <mail@daniel-mendler.de>
Date: Sun, 25 Apr 2021 13:07:29 +0200
Subject: [PATCH 1/5] (completing-read): Add `group-function` to completion
 metadata

A completion table can specify a `group-function` in its metadata.
The group function takes two arguments, a completion candidate and a
transform argument. The group function is used to group the candidates
after sorting and to enhance the completion UI with group titles.

If the transform argument is nil, the function must return the title
of the group to which the completion candidate belongs. The function
may also return nil in case the candidate does not belong to a group.

Otherwise the function must return the transformed candidate. The
transformation allows for example to remove a part of the candidate,
which is then displayed in the title.

The grouping functionality guarded by the variable `completions-group`
and turned off by default for the *Completions* buffer.

The specific form of the `group-function` has been chosen in order to
allow allocation-free grouping. This is important for completion UIs,
which continously update the displayed set of candidates (Icomplete,
Vertico, Ivy, etc.). Only when the transform argument is non-nil the
candidate transformation is performed, which may involve a string
allocation as for example in `xref--completing-read-group`.

The function `xref-show-definitions-completing-read` makes use of the
`group-function`, by moving the file name prefix to the title. If
grouping is enabled, the *Completions* are displayed as
"linenum:summary" instead of "file:linenum:summary". This way the
*Completions* buffer resembles the *Occur* buffer.

* doc/lispref/minibuf.texi: Add documentation.

* lisp/minibuffer.el (completion-metadata): Describe `group-function`
in the docstring.
(completions-group): Add guard variable, by default off.
(completions-group-format): Add format string for group titles.
(completions-group-title): Add face for group titles.
(completions-group-separator): Add face for group separator.
(minibuffer--group-by): New grouping function.
(minibuffer-completion-help): Use it.
(display-completion-list): Add optional GROUP-FUN argument.
(completion--insert-strings): Add optional GROUP-FUN argument. Insert
group titles if `completions-format` is `one-column`. Transform each
candidate with the GROUP-FUN. Attach the untransformed candidate to
the property `completion--string`.

* lisp/simple.el (choose-completion): Retrieve the untransformed
completion candidate from the property `completion--string`.

* lisp/progmodes/xref.el:
(xref--completing-read-group): New grouping function.
(xref-show-definitions-completing-read): Use it.
---
 doc/lispref/minibuf.texi |  10 ++++
 lisp/minibuffer.el       | 123 ++++++++++++++++++++++++++++++++-------
 lisp/progmodes/xref.el   |  18 ++++--
 lisp/simple.el           |  11 ++--
 4 files changed, 131 insertions(+), 31 deletions(-)

diff --git a/doc/lispref/minibuf.texi b/doc/lispref/minibuf.texi
index 145eee8f06..aa57c2bda0 100644
--- a/doc/lispref/minibuf.texi
+++ b/doc/lispref/minibuf.texi
@@ -1943,6 +1943,16 @@ Programmed Completion
 a suffix displayed after the completion string.  This function
 takes priority over @code{annotation-function}.
 
+@item group-function
+The value should be a function for grouping the completion candidates.
+The function must take two arguments, @var{completion}, which is a
+completion candidate and @var{transform}, which is a boolean flag.  If
+@var{transform} is @code{nil}, the function must return a group title,
+to which the candidate belongs. The returned title can also
+@code{nil}.  Otherwise the function must return the transformed
+candidate. The transformation can for example remove a redundant
+prefix, which is displayed in the group title instead.
+
 @item display-sort-function
 The value should be a function for sorting completions.  The function
 should take one argument, a list of completion strings, and return a
diff --git a/lisp/minibuffer.el b/lisp/minibuffer.el
index caf06ec710..e21a699dae 100644
--- a/lisp/minibuffer.el
+++ b/lisp/minibuffer.el
@@ -126,6 +126,13 @@ completion-metadata
    three-element lists: completion, its prefix and suffix.  This
    function takes priority over `annotation-function' when both are
    provided, so only this function is used.
+- `group-function': function for grouping the completion candidates.
+   Takes two arguments: a completion candidate (COMPLETION) and a
+   boolean flag (TRANSFORM).  If TRANSFORM is nil, the function
+   returns a group title, to which the candidate belongs.  The
+   returned title may be nil.  Otherwise the function returns the
+   transformed candidate.  The transformation can remove a redundant
+   prefix, which is displayed in the group title instead.
 - `display-sort-function': function to sort entries in *Completions*.
    Takes one argument (COMPLETIONS) and should return a new list
    of completions.  Can operate destructively.
@@ -1138,6 +1145,30 @@ completion-cycle-threshold
   :version "24.1"
   :type completion--cycling-threshold-type)
 
+(defcustom completions-group nil
+  "Enable grouping of completion candidates in the *Completions* buffer.
+See also `completions-group-format'."
+  :type 'boolean
+  :version "28.1")
+
+(defcustom completions-group-format
+  (concat
+   (propertize "    " 'face 'completions-group-separator)
+   (propertize " %s " 'face 'completions-group-title)
+   (propertize " " 'face 'completions-group-separator
+               'display '(space :align-to right)))
+  "Format string used for the group title."
+  :type 'string
+  :version "28.1")
+
+(defface completions-group-title '((t :inherit shadow :slant italic))
+  "Face used for the title text of the candidate group headlines."
+  :version "28.1")
+
+(defface completions-group-separator '((t :inherit shadow :strike-through t))
+  "Face used for the separator lines of the candidate groups."
+  :version "28.1")
+
 (defun completion--cycle-threshold (metadata)
   (let* ((cat (completion-metadata-get metadata 'category))
          (over (completion--category-override cat 'cycle)))
@@ -1401,6 +1432,17 @@ minibuffer--sort-preprocess-history
                      (substring c base-size)))
                  hist)))))
 
+(defun minibuffer--group-by (fun elems)
+  "Group ELEMS by FUN."
+  (let ((groups))
+    (dolist (cand elems)
+      (let* ((key (funcall fun cand nil))
+             (group (assoc key groups)))
+        (if group
+            (setcdr group (cons cand (cdr group)))
+          (push (list key cand) groups))))
+    (mapcan (lambda (x) (nreverse (cdr x))) (nreverse groups))))
+
 (defun completion-all-sorted-completions (&optional start end)
   (or completion-all-sorted-completions
       (let* ((start (or start (minibuffer-prompt-end)))
@@ -1747,11 +1789,17 @@ completions-detailed
   :type 'boolean
   :version "28.1")
 
-(defun completion--insert-strings (strings)
+;; TODO: Split up this function in one function per `completions-format'.
+;; TODO: Add group title support for horizontal and vertical format.
+(defun completion--insert-strings (strings &optional group-fun)
   "Insert a list of STRINGS into the current buffer.
-Uses columns to keep the listing readable but compact.
-It also eliminates runs of equal strings."
+Uses columns to keep the listing readable but compact.  It also
+eliminates runs of equal strings.  GROUP-FUN is a `group-function'
+used for grouping the completion."
   (when (consp strings)
+    ;; FIXME: Currently grouping is enabled only for the 'one-column format.
+    (unless (eq completions-format 'one-column)
+      (setq group-fun nil))
     (let* ((length (apply #'max
 			  (mapcar (lambda (s)
 				    (if (consp s)
@@ -1768,6 +1816,7 @@ completion--insert-strings
 		     (max 1 (/ (length strings) 2))))
 	   (colwidth (/ wwidth columns))
            (column 0)
+           (last-title nil)
 	   (rows (/ (length strings) columns))
 	   (row 0)
            (first t)
@@ -1780,6 +1829,13 @@ completion--insert-strings
       ;; The insertion should be "sensible" no matter what choices were made
       ;; for the parameters above.
       (dolist (str strings)
+        ;; Add group titles.
+        (when group-fun
+          (let ((title (funcall group-fun (if (consp str) (car str) str) nil)))
+            (unless (equal title last-title)
+              (when title
+                (insert (format completions-group-format title) "\n"))
+              (setq last-title title))))
 	(unless (equal laststring str) ; Remove (consecutive) duplicates.
 	  (setq laststring str)
           ;; FIXME: `string-width' doesn't pay attention to
@@ -1825,8 +1881,15 @@ completion--insert-strings
 		  nil))))
             (setq first nil)
             (if (not (consp str))
-                (put-text-property (point) (progn (insert str) (point))
-                                   'mouse-face 'highlight)
+                (add-text-properties
+                 (point)
+                 (progn
+                   (insert
+                    (if group-fun
+                        (funcall group-fun str 'transform)
+                      str))
+                   (point))
+                 `(mouse-face highlight completion--string ,str))
               ;; If `str' is a list that has 2 elements,
               ;; then the second element is a suffix annotation.
               ;; If `str' has 3 elements, then the second element
@@ -1837,8 +1900,15 @@ completion--insert-strings
                   (let ((beg (point))
                         (end (progn (insert prefix) (point))))
                     (put-text-property beg end 'mouse-face nil)))
-                (put-text-property (point) (progn (insert (car str)) (point))
-                                   'mouse-face 'highlight)
+                (add-text-properties
+                 (point)
+                 (progn
+                   (insert
+                    (if group-fun
+                         (funcall group-fun (car str) 'transform)
+                      (car str)))
+                   (point))
+                 `(mouse-face highlight completion--string ,(car str)))
                 (let ((beg (point))
                       (end (progn (insert suffix) (point))))
                   (put-text-property beg end 'mouse-face nil)
@@ -1923,7 +1993,7 @@ completion-hilit-commonality
         completions)
        base-size))))
 
-(defun display-completion-list (completions &optional common-substring)
+(defun display-completion-list (completions &optional common-substring group-fun)
   "Display the list of completions, COMPLETIONS, using `standard-output'.
 Each element may be just a symbol or string
 or may be a list of two strings to be printed as if concatenated.
@@ -1933,7 +2003,8 @@ display-completion-list
 The actual completion alternatives, as inserted, are given `mouse-face'
 properties of `highlight'.
 At the end, this runs the normal hook `completion-setup-hook'.
-It can find the completion buffer in `standard-output'."
+It can find the completion buffer in `standard-output'.
+GROUP-FUN is a `group-function' used for grouping the completion."
   (declare (advertised-calling-convention (completions) "24.4"))
   (if common-substring
       (setq completions (completion-hilit-commonality
@@ -1946,7 +2017,7 @@ display-completion-list
 	(let ((standard-output (current-buffer))
 	      (completion-setup-hook nil))
           (with-suppressed-warnings ((callargs display-completion-list))
-	    (display-completion-list completions common-substring)))
+	    (display-completion-list completions common-substring group-fun)))
 	(princ (buffer-string)))
 
     (with-current-buffer standard-output
@@ -1954,7 +2025,7 @@ display-completion-list
       (if (null completions)
           (insert "There are no possible completions of what you have typed.")
         (insert "Possible completions are:\n")
-        (completion--insert-strings completions))))
+        (completion--insert-strings completions group-fun))))
 
   (run-hooks 'completion-setup-hook)
   nil)
@@ -2067,6 +2138,9 @@ minibuffer-completion-help
              (aff-fun (or (completion-metadata-get all-md 'affixation-function)
                           (plist-get completion-extra-properties
                                      :affixation-function)))
+             (sort-fun (completion-metadata-get all-md 'display-sort-function))
+             (group-fun (and completions-group
+                             (completion-metadata-get all-md 'group-function)))
              (mainbuf (current-buffer))
              ;; If the *Completions* buffer is shown in a new
              ;; window, mark it as softly-dedicated, so bury-buffer in
@@ -2098,15 +2172,22 @@ minibuffer-completion-help
                       ;; Remove the base-size tail because `sort' requires a properly
                       ;; nil-terminated list.
                       (when last (setcdr last nil))
-                      (setq completions
-                            ;; FIXME: This function is for the output of all-completions,
-                            ;; not completion-all-completions.  Often it's the same, but
-                            ;; not always.
-                            (let ((sort-fun (completion-metadata-get
-                                             all-md 'display-sort-function)))
-                              (if sort-fun
-                                  (funcall sort-fun completions)
-                                (sort completions 'string-lessp))))
+
+                      ;; Sort first using the `display-sort-function'.
+                      ;; FIXME: This function is for the output of
+                      ;; all-completions, not
+                      ;; completion-all-completions.  Often it's the
+                      ;; same, but not always.
+                      (setq completions (if sort-fun
+                                            (funcall sort-fun completions)
+                                          (sort completions 'string-lessp)))
+
+                      ;; After sorting, group the candidates using the
+                      ;; `group-function'.
+                      (when group-fun
+                        (setq completions
+                              (minibuffer--group-by group-fun completions)))
+
                       (cond
                        (aff-fun
                         (setq completions
@@ -2152,7 +2233,7 @@ minibuffer-completion-help
                                                      (if (eq (car bounds) (length result))
                                                          'exact 'finished)))))))
 
-                      (display-completion-list completions)))))
+                      (display-completion-list completions nil group-fun)))))
           nil)))
     nil))
 
diff --git a/lisp/progmodes/xref.el b/lisp/progmodes/xref.el
index 7fc7181acc..2a4fb2c417 100644
--- a/lisp/progmodes/xref.el
+++ b/lisp/progmodes/xref.el
@@ -1044,6 +1044,12 @@ xref-show-definitions-buffer-at-bottom
 (define-obsolete-function-alias 'xref--show-defs-buffer-at-bottom
   #'xref-show-definitions-buffer-at-bottom "28.1")
 
+(defun xref--completing-read-group (cand transform)
+  "Return group title of candidate CAND or TRANSFORM the candidate."
+  (if transform
+      (substring cand (1+ (next-single-property-change 0 'xref--group cand)))
+    (get-text-property 0 'xref--group cand)))
+
 (defun xref-show-definitions-completing-read (fetcher alist)
   "Let the user choose the target definition with completion.
 
@@ -1072,10 +1078,12 @@ xref-show-definitions-completing-read
                                     (format #("%d:" 0 2 (face xref-line-number))
                                             line)
                                   ""))
+                               (group-prefix
+                                (substring group group-prefix-length))
                                (group-fmt
-                                (propertize
-                                 (substring group group-prefix-length)
-                                 'face 'xref-file-header))
+                                (propertize group-prefix
+                                            'face 'xref-file-header
+                                            'xref--group group-prefix))
                                (candidate
                                 (format "%s:%s%s" group-fmt line-fmt summary)))
                           (push (cons candidate xref) xref-alist-with-line-info)))))
@@ -1087,7 +1095,9 @@ xref-show-definitions-completing-read
                          (lambda (string pred action)
                            (cond
                             ((eq action 'metadata)
-                             '(metadata . ((category . xref-location))))
+                             `(metadata
+                               . ((category . xref-location)
+                                  (group-function . ,#'xref--completing-read-group))))
                             (t
                              (complete-with-action action collection string pred)))))
                         (def (caar collection)))
diff --git a/lisp/simple.el b/lisp/simple.el
index b4e34f1e4c..fe7ff0333f 100644
--- a/lisp/simple.el
+++ b/lisp/simple.el
@@ -8876,18 +8876,17 @@ choose-completion
           (choice
            (save-excursion
              (goto-char (posn-point (event-start event)))
-             (let (beg end)
+             (let (beg)
                (cond
                 ((and (not (eobp)) (get-text-property (point) 'mouse-face))
-                 (setq end (point) beg (1+ (point))))
+                 (setq beg (1+ (point))))
                 ((and (not (bobp))
                       (get-text-property (1- (point)) 'mouse-face))
-                 (setq end (1- (point)) beg (point)))
+                 (setq beg (point)))
                 (t (error "No completion here")))
                (setq beg (previous-single-property-change beg 'mouse-face))
-               (setq end (or (next-single-property-change end 'mouse-face)
-                             (point-max)))
-               (buffer-substring-no-properties beg end)))))
+               (substring-no-properties
+                (get-text-property beg 'completion--string))))))
 
       (unless (buffer-live-p buffer)
         (error "Destination buffer is dead"))
-- 
2.20.1


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From 6a95ba7952b8f265453f987e0cdf1eaa026b2694 Mon Sep 17 00:00:00 2001
From: Daniel Mendler <mail@daniel-mendler.de>
Date: Fri, 30 Apr 2021 08:40:59 +0200
Subject: [PATCH 2/5] (completion--insert-strings): Split function; Full group
 title support

Split `completion--insert-strings` into a function per completions
format in order to increase readability and extensibility. This change
eases the addition of more formats. Add support for group titles to
the vertical and horizontal format.

* minibuffer.el (completion--insert): Add new function.
(completion--insert-vertical, completion--insert-horizontal,
completion--insert-one-column): Extract new function from
`completion--insert-strings`. Use `completion--insert`.
(completion--insert-strings): Use new insertion functions.
---
 lisp/minibuffer.el | 269 ++++++++++++++++++++++++++-------------------
 1 file changed, 154 insertions(+), 115 deletions(-)

diff --git a/lisp/minibuffer.el b/lisp/minibuffer.el
index e21a699dae..cf1a4350bd 100644
--- a/lisp/minibuffer.el
+++ b/lisp/minibuffer.el
@@ -1789,21 +1789,16 @@ completions-detailed
   :type 'boolean
   :version "28.1")
 
-;; TODO: Split up this function in one function per `completions-format'.
-;; TODO: Add group title support for horizontal and vertical format.
 (defun completion--insert-strings (strings &optional group-fun)
   "Insert a list of STRINGS into the current buffer.
 Uses columns to keep the listing readable but compact.  It also
 eliminates runs of equal strings.  GROUP-FUN is a `group-function'
 used for grouping the completion."
   (when (consp strings)
-    ;; FIXME: Currently grouping is enabled only for the 'one-column format.
-    (unless (eq completions-format 'one-column)
-      (setq group-fun nil))
     (let* ((length (apply #'max
 			  (mapcar (lambda (s)
 				    (if (consp s)
-					(apply #'+ (mapcar #'string-width s))
+				        (apply #'+ (mapcar #'string-width s))
 				      (string-width s)))
 				  strings)))
 	   (window (get-buffer-window (current-buffer) 0))
@@ -1814,126 +1809,170 @@ completion--insert-strings
 		     ;; Don't allocate more columns than we can fill.
 		     ;; Windows can't show less than 3 lines anyway.
 		     (max 1 (/ (length strings) 2))))
-	   (colwidth (/ wwidth columns))
-           (column 0)
-           (last-title nil)
-	   (rows (/ (length strings) columns))
-	   (row 0)
-           (first t)
-	   (laststring nil))
+	   (colwidth (/ wwidth columns)))
       (unless (or tab-stop-list (null completion-tab-width)
                   (zerop (mod colwidth completion-tab-width)))
         ;; Align to tab positions for the case
         ;; when the caller uses tabs inside prefix.
         (setq colwidth (- colwidth (mod colwidth completion-tab-width))))
-      ;; The insertion should be "sensible" no matter what choices were made
-      ;; for the parameters above.
-      (dolist (str strings)
-        ;; Add group titles.
+      (funcall (intern (format "completion--insert-%s" completions-format))
+               strings group-fun length wwidth colwidth columns))))
+
+(defun completion--insert-horizontal (strings group-fun
+                                              length wwidth
+                                              colwidth _columns)
+  (let ((column 0)
+        (first t)
+	(last-title nil)
+        (last-string nil))
+    (dolist (str strings)
+      (unless (equal last-string str) ; Remove (consecutive) duplicates.
+	(setq last-string str)
         (when group-fun
           (let ((title (funcall group-fun (if (consp str) (car str) str) nil)))
             (unless (equal title last-title)
+              (setq last-title title)
               (when title
-                (insert (format completions-group-format title) "\n"))
-              (setq last-title title))))
-	(unless (equal laststring str) ; Remove (consecutive) duplicates.
-	  (setq laststring str)
+                (insert (if first "" "\n") (format completions-group-format title) "\n")
+                (setq column 0
+                      first t)))))
+	(unless first
           ;; FIXME: `string-width' doesn't pay attention to
           ;; `display' properties.
-          (let ((length (if (consp str)
-                            (apply #'+ (mapcar #'string-width str))
-                          (string-width str))))
-            (cond
-             ((eq completions-format 'one-column)
-              ;; Nothing special
-              )
-	     ((eq completions-format 'vertical)
-	      ;; Vertical format
-	      (when (> row rows)
-		(forward-line (- -1 rows))
-		(setq row 0 column (+ column colwidth)))
-	      (when (> column 0)
-		(end-of-line)
-		(while (> (current-column) column)
-		  (if (eobp)
-		      (insert "\n")
-		    (forward-line 1)
-		    (end-of-line)))
-		(insert " \t")
-		(set-text-properties (1- (point)) (point)
-				     `(display (space :align-to ,column)))))
-	     (t
-	      ;; Horizontal format
-	      (unless first
-		(if (< wwidth (+ (max colwidth length) column))
-		    ;; No space for `str' at point, move to next line.
-		    (progn (insert "\n") (setq column 0))
-		  (insert " \t")
-		  ;; Leave the space unpropertized so that in the case we're
-		  ;; already past the goal column, there is still
-		  ;; a space displayed.
-		  (set-text-properties (1- (point)) (point)
-				       ;; We can set tab-width using
-				       ;; completion-tab-width, but
-				       ;; the caller can prefer using
-				       ;; \t to align prefixes.
-				       `(display (space :align-to ,column)))
-		  nil))))
-            (setq first nil)
-            (if (not (consp str))
-                (add-text-properties
-                 (point)
-                 (progn
-                   (insert
-                    (if group-fun
-                        (funcall group-fun str 'transform)
-                      str))
-                   (point))
-                 `(mouse-face highlight completion--string ,str))
-              ;; If `str' is a list that has 2 elements,
-              ;; then the second element is a suffix annotation.
-              ;; If `str' has 3 elements, then the second element
-              ;; is a prefix, and the third element is a suffix.
-              (let* ((prefix (when (nth 2 str) (nth 1 str)))
-                     (suffix (or (nth 2 str) (nth 1 str))))
-                (when prefix
-                  (let ((beg (point))
-                        (end (progn (insert prefix) (point))))
-                    (put-text-property beg end 'mouse-face nil)))
-                (add-text-properties
-                 (point)
-                 (progn
-                   (insert
-                    (if group-fun
-                         (funcall group-fun (car str) 'transform)
-                      (car str)))
-                   (point))
-                 `(mouse-face highlight completion--string ,(car str)))
-                (let ((beg (point))
-                      (end (progn (insert suffix) (point))))
-                  (put-text-property beg end 'mouse-face nil)
-                  ;; Put the predefined face only when suffix
-                  ;; is added via annotation-function without prefix,
-                  ;; and when the caller doesn't use own face.
-                  (unless (or prefix (text-property-not-all
-                                      0 (length suffix) 'face nil suffix))
-                    (font-lock-prepend-text-property
-                     beg end 'face 'completions-annotations)))))
-	    (cond
-             ((eq completions-format 'one-column)
-              (insert "\n"))
-	     ((eq completions-format 'vertical)
-	      ;; Vertical format
-	      (if (> column 0)
-		  (forward-line)
-		(insert "\n"))
-	      (setq row (1+ row)))
-	     (t
-	      ;; Horizontal format
-	      ;; Next column to align to.
-	      (setq column (+ column
-			      ;; Round up to a whole number of columns.
-			      (* colwidth (ceiling length colwidth))))))))))))
+	  (if (< wwidth (+ column (max colwidth
+                                       (if (consp str)
+                                           (apply #'+ (mapcar #'string-width str))
+                                         (string-width str)))))
+	      ;; No space for `str' at point, move to next line.
+	      (progn (insert "\n") (setq column 0))
+	    (insert " \t")
+	    ;; Leave the space unpropertized so that in the case we're
+	    ;; already past the goal column, there is still
+	    ;; a space displayed.
+	    (set-text-properties (1- (point)) (point)
+				 ;; We can set tab-width using
+				 ;; completion-tab-width, but
+				 ;; the caller can prefer using
+				 ;; \t to align prefixes.
+				 `(display (space :align-to ,column)))
+	    nil))
+        (setq first nil)
+        (completion--insert str group-fun)
+	;; Next column to align to.
+	(setq column (+ column
+			;; Round up to a whole number of columns.
+			(* colwidth (ceiling length colwidth))))))))
+
+(defun completion--insert-vertical (strings group-fun
+                                            _length _wwidth
+                                            colwidth columns)
+  (let ((column 0)
+        (rows (/ (length strings) columns))
+	(row 0)
+	(last-title nil)
+	(last-string nil)
+        (start-point (point))
+        (next 0) (pos 0))
+    (dolist (str strings)
+      (unless (equal last-string str) ; Remove (consecutive) duplicates.
+	(setq last-string str)
+	(when (> row rows)
+	  (goto-char start-point)
+	  (setq row 0 column (+ column colwidth)))
+        (when group-fun
+          (let ((title (funcall group-fun (if (consp str) (car str) str) nil)))
+            (unless (equal title last-title)
+              (setq last-title title)
+              (when title
+                ;; Align before title insertion
+	        (when (> column 0)
+	          (end-of-line)
+	          (while (> (current-column) column)
+	            (if (eobp)
+		        (insert "\n")
+	              (forward-line 1)
+	              (end-of-line)))
+	          (insert " \t")
+	          (set-text-properties (1- (point)) (point)
+			               `(display (space :align-to ,column))))
+                (let* ((fmt completions-group-format)
+                       (len (length fmt)))
+                  ;; Adjust display space for columns
+                  (when (equal (get-text-property (- len 1) 'display fmt) '(space :align-to right))
+                    (setq fmt (substring fmt))
+                    (put-text-property (- len 1) len
+                                       'display
+                                       `(space :align-to ,(+ colwidth column -1))
+                                       fmt))
+                  (insert (format fmt title)))
+                ;; Align after title insertion
+	        (if (> column 0)
+	            (forward-line)
+	          (insert "\n"))))))
+        ;; Align before candidate insertion
+	(when (> column 0)
+	  (end-of-line)
+	  (while (> (current-column) column)
+	    (if (eobp)
+		(insert "\n")
+	      (forward-line 1)
+	      (end-of-line)))
+	  (insert " \t")
+	  (set-text-properties (1- (point)) (point)
+			       `(display (space :align-to ,column))))
+        (completion--insert str group-fun)
+        ;; Align after candidate insertion
+	(if (> column 0)
+	    (forward-line)
+	  (insert "\n"))
+	(setq row (1+ row))))))
+
+(defun completion--insert-one-column (strings group-fun &rest _)
+  (let ((last-title nil) (last-string nil))
+    (dolist (str strings)
+      (unless (equal last-string str) ; Remove (consecutive) duplicates.
+	(setq last-string str)
+        (when group-fun
+          (let ((title (funcall group-fun (if (consp str) (car str) str) nil)))
+            (unless (equal title last-title)
+              (setq last-title title)
+              (when title
+                (insert (format completions-group-format title) "\n")))))
+        (completion--insert str group-fun)
+        (insert "\n")))))
+
+(defun completion--insert (str group-fun)
+  (if (not (consp str))
+      (add-text-properties
+       (point)
+       (progn
+         (insert
+          (if group-fun
+              (funcall group-fun str 'transform)
+            str))
+         (point))
+       `(mouse-face highlight completion--string ,str))
+    ;; If `str' is a list that has 2 elements,
+    ;; then the second element is a suffix annotation.
+    ;; If `str' has 3 elements, then the second element
+    ;; is a prefix, and the third element is a suffix.
+    (let* ((prefix (when (nth 2 str) (nth 1 str)))
+           (suffix (or (nth 2 str) (nth 1 str))))
+      (when prefix
+        (let ((beg (point))
+              (end (progn (insert prefix) (point))))
+          (put-text-property beg end 'mouse-face nil)))
+      (completion--insert (car str) group-fun)
+      (let ((beg (point))
+            (end (progn (insert suffix) (point))))
+        (put-text-property beg end 'mouse-face nil)
+        ;; Put the predefined face only when suffix
+        ;; is added via annotation-function without prefix,
+        ;; and when the caller doesn't use own face.
+        (unless (or prefix (text-property-not-all
+                            0 (length suffix) 'face nil suffix))
+          (font-lock-prepend-text-property
+           beg end 'face 'completions-annotations))))))
 
 (defvar completion-setup-hook nil
   "Normal hook run at the end of setting up a completion list buffer.
-- 
2.20.1


[-- Attachment #4: 0003-minibuffer-completion-help-Do-not-check-completions-.patch --]
[-- Type: text/x-diff, Size: 1378 bytes --]

From 75f98611ca5aee1706762bbe5dbd9c347ea19d7d Mon Sep 17 00:00:00 2001
From: Daniel Mendler <mail@daniel-mendler.de>
Date: Sun, 2 May 2021 15:50:08 +0200
Subject: [PATCH 3/5] (minibuffer-completion-help): Do not check
 `completions-group` centrally

The guard variable `completions-group` should be checked in each
completion table individually. The guard variable
`completions-detailed` variable is used in the same way.

* minibuffer.el (minibuffer-completion-help): Remove check of
  `completions-group`.
---
 lisp/minibuffer.el | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/lisp/minibuffer.el b/lisp/minibuffer.el
index cf1a4350bd..b743b2bd40 100644
--- a/lisp/minibuffer.el
+++ b/lisp/minibuffer.el
@@ -2178,8 +2178,7 @@ minibuffer-completion-help
                           (plist-get completion-extra-properties
                                      :affixation-function)))
              (sort-fun (completion-metadata-get all-md 'display-sort-function))
-             (group-fun (and completions-group
-                             (completion-metadata-get all-md 'group-function)))
+             (group-fun (completion-metadata-get all-md 'group-function))
              (mainbuf (current-buffer))
              ;; If the *Completions* buffer is shown in a new
              ;; window, mark it as softly-dedicated, so bury-buffer in
-- 
2.20.1


[-- Attachment #5: 0004-completion-insert-vertical-Separate-groups-completel.patch --]
[-- Type: text/x-diff, Size: 5061 bytes --]

From 7768f1142f5af9d58229884c8365dd921c2d65c9 Mon Sep 17 00:00:00 2001
From: Daniel Mendler <mail@daniel-mendler.de>
Date: Sun, 2 May 2021 16:19:42 +0200
Subject: [PATCH 4/5] (completion--insert-vertical): Separate groups completely

Insert the candidates vertically within the groups, but keep the
groups completely separate using the full width group separators.

* minibuffer.el (completion--insert-vertical): Adjust grouping.
---
 lisp/minibuffer.el | 108 ++++++++++++++++++++-------------------------
 1 file changed, 48 insertions(+), 60 deletions(-)

diff --git a/lisp/minibuffer.el b/lisp/minibuffer.el
index b743b2bd40..73a38a8137 100644
--- a/lisp/minibuffer.el
+++ b/lisp/minibuffer.el
@@ -1866,66 +1866,54 @@ completion--insert-horizontal
 (defun completion--insert-vertical (strings group-fun
                                             _length _wwidth
                                             colwidth columns)
-  (let ((column 0)
-        (rows (/ (length strings) columns))
-	(row 0)
-	(last-title nil)
-	(last-string nil)
-        (start-point (point))
-        (next 0) (pos 0))
-    (dolist (str strings)
-      (unless (equal last-string str) ; Remove (consecutive) duplicates.
-	(setq last-string str)
-	(when (> row rows)
-	  (goto-char start-point)
-	  (setq row 0 column (+ column colwidth)))
-        (when group-fun
-          (let ((title (funcall group-fun (if (consp str) (car str) str) nil)))
-            (unless (equal title last-title)
-              (setq last-title title)
-              (when title
-                ;; Align before title insertion
-	        (when (> column 0)
-	          (end-of-line)
-	          (while (> (current-column) column)
-	            (if (eobp)
-		        (insert "\n")
-	              (forward-line 1)
-	              (end-of-line)))
-	          (insert " \t")
-	          (set-text-properties (1- (point)) (point)
-			               `(display (space :align-to ,column))))
-                (let* ((fmt completions-group-format)
-                       (len (length fmt)))
-                  ;; Adjust display space for columns
-                  (when (equal (get-text-property (- len 1) 'display fmt) '(space :align-to right))
-                    (setq fmt (substring fmt))
-                    (put-text-property (- len 1) len
-                                       'display
-                                       `(space :align-to ,(+ colwidth column -1))
-                                       fmt))
-                  (insert (format fmt title)))
-                ;; Align after title insertion
-	        (if (> column 0)
-	            (forward-line)
-	          (insert "\n"))))))
-        ;; Align before candidate insertion
-	(when (> column 0)
-	  (end-of-line)
-	  (while (> (current-column) column)
-	    (if (eobp)
-		(insert "\n")
-	      (forward-line 1)
-	      (end-of-line)))
-	  (insert " \t")
-	  (set-text-properties (1- (point)) (point)
-			       `(display (space :align-to ,column))))
-        (completion--insert str group-fun)
-        ;; Align after candidate insertion
-	(if (> column 0)
-	    (forward-line)
-	  (insert "\n"))
-	(setq row (1+ row))))))
+  (while strings
+    (let ((group nil)
+          (column 0)
+	  (row 0)
+          (rows)
+          (last-string nil))
+      (if group-fun
+          (let* ((str (car strings))
+                 (title (funcall group-fun (if (consp str) (car str) str) nil)))
+            (while (and strings
+                        (equal title (funcall group-fun
+                                              (if (consp (car strings))
+                                                  (car (car strings))
+                                                (car strings))
+                                              nil)))
+              (push (car strings) group)
+              (pop strings))
+            (setq group (nreverse group)))
+        (setq group strings
+              strings nil))
+      (setq rows (/ (length group) columns))
+      (when group-fun
+        (let* ((str (car group))
+               (title (funcall group-fun (if (consp str) (car str) str) nil)))
+          (when title
+            (goto-char (point-max))
+            (insert (format completions-group-format title) "\n"))))
+      (dolist (str group)
+        (unless (equal last-string str) ; Remove (consecutive) duplicates.
+	  (setq last-string str)
+	  (when (> row rows)
+            (forward-line (- -1 rows))
+	    (setq row 0 column (+ column colwidth)))
+	  (when (> column 0)
+	    (end-of-line)
+	    (while (> (current-column) column)
+	      (if (eobp)
+		  (insert "\n")
+	        (forward-line 1)
+	        (end-of-line)))
+	    (insert " \t")
+	    (set-text-properties (1- (point)) (point)
+			         `(display (space :align-to ,column))))
+          (completion--insert str group-fun)
+	  (if (> column 0)
+	      (forward-line)
+	    (insert "\n"))
+	  (setq row (1+ row)))))))
 
 (defun completion--insert-one-column (strings group-fun &rest _)
   (let ((last-title nil) (last-string nil))
-- 
2.20.1


[-- Attachment #6: 0005-minibuffer-completion-help-Add-group-sorting.patch --]
[-- Type: text/x-diff, Size: 3633 bytes --]

From 5fc173f155e1fb9caae2675d0d4f9667a5d99a45 Mon Sep 17 00:00:00 2001
From: Daniel Mendler <mail@daniel-mendler.de>
Date: Tue, 11 May 2021 09:08:05 +0200
Subject: [PATCH 5/5] (minibuffer-completion-help): Add group sorting

Sorting the groups as returned by the `group-function` of the
completion table depending on the value of `completions-group-sort`.
By default `completions-group-sort` is set to nil, the value
`alphabetical` is offered for alphabetical sorting. Furthermore custom
sorting functions can be used.

* lisp/minibuffer.el (completions-group-sort): New variable.
(minibuffer--group-by): Add SORT-FUN argument.
(minibuffer-completion-help): Pass `completions-group-sort`
to `minibuffer--group-by`.
---
 lisp/minibuffer.el | 37 ++++++++++++++++++++++++++++++++-----
 1 file changed, 32 insertions(+), 5 deletions(-)

diff --git a/lisp/minibuffer.el b/lisp/minibuffer.el
index 73a38a8137..fd94718497 100644
--- a/lisp/minibuffer.el
+++ b/lisp/minibuffer.el
@@ -1151,6 +1151,18 @@ completions-group
   :type 'boolean
   :version "28.1")
 
+(defcustom completions-group-sort nil
+  "Sort groups in the *Completions* buffer.
+
+The value can either be nil to disable sorting, `alphabetical' for
+alphabetical sorting or a custom sorting function. The sorting
+function takes and returns an alist of groups, where each element is a
+pair of a group title string and a list of group candidate strings."
+  :type '(choice (const nil :tag "No sorting")
+                 (const alphabetical :tag "Alphabetical sorting")
+                 function)
+  :version "28.1")
+
 (defcustom completions-group-format
   (concat
    (propertize "    " 'face 'completions-group-separator)
@@ -1432,16 +1444,21 @@ minibuffer--sort-preprocess-history
                      (substring c base-size)))
                  hist)))))
 
-(defun minibuffer--group-by (fun elems)
-  "Group ELEMS by FUN."
+(defun minibuffer--group-by (group-fun sort-fun elems)
+  "Group ELEMS by GROUP-FUN and sort using SORT-FUN."
   (let ((groups))
     (dolist (cand elems)
-      (let* ((key (funcall fun cand nil))
+      (let* ((key (funcall group-fun cand nil))
              (group (assoc key groups)))
         (if group
             (setcdr group (cons cand (cdr group)))
           (push (list key cand) groups))))
-    (mapcan (lambda (x) (nreverse (cdr x))) (nreverse groups))))
+    (setq groups (nreverse groups)
+          groups (mapc (lambda (x)
+                         (setcdr x (nreverse (cdr x))))
+                       groups)
+          groups (funcall sort-fun groups))
+    (mapcan #'cdr groups)))
 
 (defun completion-all-sorted-completions (&optional start end)
   (or completion-all-sorted-completions
@@ -2212,7 +2229,17 @@ minibuffer-completion-help
                       ;; `group-function'.
                       (when group-fun
                         (setq completions
-                              (minibuffer--group-by group-fun completions)))
+                              (minibuffer--group-by
+                               group-fun
+                               (pcase completions-group-sort
+                                 ('nil #'identity)
+                                 ('alphabetical
+                                  (lambda (groups)
+                                    (sort groups
+                                          (lambda (x y)
+                                            (string< (car x) (car y))))))
+                                 (_ completions-group-sort))
+                               completions)))
 
                       (cond
                        (aff-fun
-- 
2.20.1