bug#21644: 24.4; completing-read acts differently on functional collection

bug#21644: 24.4; completing-read acts differently on functional collection

[Ryan C. Thompson]

I've discovered that completing-read works differently if COLLECTION is 
a function than if it is a list, even if the function represents exactly 
the same set of completions as the list. For example, we can define a 
function to convert any collection to an equivalent function using a 
closure:

(setq lexical-binding t)
(defun collection-as-function (collection)
   "Return a function equivalent to COLLECTION.

The returned function will work equivalently to COLLECTION when
passed to `all-completions' and `try-completion'."
   (if (functionp collection)
       collection
     ;; Capture collection in a closure
     (lambda (string pred all)
       (funcall (if all #'all-completions #'try-completion)
                string collection pred))))
collection-as-function

(completing-read "Prompt: " '("blue" "yellow" "green") nil t)
(completing-read "Prompt: " (collection-as-function '("blue" "yellow" 
"green")) nil t)

Try typing "g" followed by RET for both of the above. In the first case 
(collection is a list), it returns "green". In the second case 
(collection is a function), it returns just "g". This is reproducible in 
emacs -Q.


In GNU Emacs 24.4.1 (x86_64-pc-linux-gnu, X toolkit, Xaw3d scroll bars)
of 2015-03-21 on kissel, modified by Debian
Windowing system distributor `The X.Org Foundation', version 11.0.11701000
System Description: Ubuntu 15.04

Configured using:
`configure --build x86_64-linux-gnu --prefix=/usr
--sharedstatedir=/var/lib --libexecdir=/usr/lib
--localstatedir=/var/lib --infodir=/usr/share/info
--mandir=/usr/share/man --with-pop=yes
--enable-locallisppath=/etc/emacs24:/etc/emacs:/usr/local/share/emacs/24.4/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/24.4/site-lisp:/usr/share/emacs/site-lisp 

--build x86_64-linux-gnu --prefix=/usr --sharedstatedir=/var/lib
--libexecdir=/usr/lib --localstatedir=/var/lib
--infodir=/usr/share/info --mandir=/usr/share/man --with-pop=yes
--enable-locallisppath=/etc/emacs24:/etc/emacs:/usr/local/share/emacs/24.4/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/24.4/site-lisp:/usr/share/emacs/site-lisp 

--with-x=yes --with-x-toolkit=lucid --with-toolkit-scroll-bars
--without-gconf --without-gsettings 'CFLAGS=-g -O2
-fstack-protector-strong -Wformat -Werror=format-security -Wall'
CPPFLAGS=-D_FORTIFY_SOURCE=2 'LDFLAGS=-Wl,-Bsymbolic-functions
-Wl,-z,relro''

Important settings:
value of $LC_COLLATE: en_US.UTF-8
value of $LC_CTYPE: en_US.UTF-8
value of $LC_MESSAGES: en_US.UTF-8
value of $LANG: en_US.UTF-8
value of $XMODIFIERS: @im=ibus
locale-coding-system: utf-8-unix

Major mode: Emacs-Lisp

Minor modes in effect:
recentf-mode: t
ws-butler-global-mode: t
ws-butler-mode: t
winner-mode: t
sml-modeline-mode: t
savehist-mode: t
minibuffer-electric-default-mode: t
minibuffer-depth-indicate-mode: t
ido-yes-or-no-mode: t
icomplete-mode: t
global-undo-tree-mode: t
undo-tree-mode: t
global-pointback-mode: t
pointback-mode: t
global-hl-line-mode: t
global-anzu-mode: t
anzu-mode: t
desktop-save-mode: t
delete-selection-mode: t
auto-dim-other-buffers-mode: t
git-wip-mode: t
ido-complete-space-or-hyphen-mode: t
pretty-symbols-mode: t
diff-auto-refine-mode: t
global-git-commit-mode: t
lexbind-mode: t
highlight-defined-mode: t
global-git-gutter-mode: t
git-gutter-mode: t
ido-everywhere: t
shell-dirtrack-mode: t
eldoc-mode: t
autopair-global-mode: t
autopair-mode: t
show-paren-mode: t
global-auto-complete-mode: t
auto-complete-mode: t
adjust-parens-mode: t
override-global-mode: t
tooltip-mode: t
electric-indent-mode: t
mouse-wheel-mode: t
file-name-shadow-mode: t
global-font-lock-mode: t
font-lock-mode: t
blink-cursor-mode: t
auto-composition-mode: t
auto-encryption-mode: t
auto-compression-mode: t
line-number-mode: t
transient-mark-mode: t

Recent input:
C-_ C-x C-e <down> <up> <left> C-x C-e g <tab> <backspace>
<backspace> <backspace> <backspace> <backspace> g <return>
C-a <tab> C-M-S-f M-w C-e <return> <return> C-y <C-left>
<C-left> <C-left> <C-left> <C-left> <C-left> <C-right>
<right> <C-S-left> <C-S-left> <C-S-left> <S-left> <backspace>
C-e <left> <left> <left> <left> <left> <backspace>
C-e C-j g <return> M-x i d o - u <tab> b <tab> - m
o <return> <left> C-_ C-j g <return> C-_ <up> <up>
<tab> <tab> C-a <tab> C-M-S-f M-w <down> <return> C-y
C-j g <return> <down> <down> C-e C-j g <return> <down-mouse-1>
<mouse-1> ( u n e <backspace> l e s s SPC ( f u n c
t i o n <backspace> <backspace> <backspace> <backspace>
<backspace> <backspace> <backspace> <backspace> <backspace>
<backspace> <backspace> <backspace> <backspace> <backspace>
<backspace> <backspace> <backspace> C-x C-s <down-mouse-4>
<mouse-4> <double-down-mouse-4> <double-mouse-4> <triple-down-mouse-4>
<triple-mouse-4> <triple-down-mouse-4> <triple-mouse-4>
<triple-down-mouse-4> <triple-mouse-4> <down-mouse-1>
<mouse-1> C-a <C-S-down> <C-S-down> M-w <C-S-up> <S-up>
<S-up> M-w <help-echo> <help-echo> <down-mouse-1> <mouse-1>
<down-mouse-1> <mouse-1> C-a <up> <up> <down> <C-S-down>
<C-S-down> M-w <help-echo> <help-echo> <help-echo>
<help-echo> <help-echo> <help-echo> <down-mouse-1>
<mouse-1> C-a <C-S-down> <C-S-down> <up> <down> C-_
C-_ C-_ C-a <C-S-down> <C-S-down> M-w <down-mouse-1>
<mouse-1> M-x r e p o r t <return> <down> <up> <down>
<down> <up> <up> M-x <return> M-x r e p o r t - e m
a c s <tab> <return> c o m p l e t i n g - r e a d
SPC a c t s SPC d i f f e r e n t l y SPC o n SPC f
u n c t i o n a l SPC c o l l e c t i o n <return>
M-x r e p o r C-g C-g C-x k <return> <return> M-x r
e p o r - v i a - m a i l <return>

Recent messages:
Checking 261 files in /usr/share/emacs/24.4/lisp/gnus...
Checking 57 files in /usr/share/emacs/24.4/lisp/eshell...
Checking 70 files in /usr/share/emacs/24.4/lisp/erc...
Checking 48 files in /usr/share/emacs/24.4/lisp/emulation...
Checking 151 files in /usr/share/emacs/24.4/lisp/emacs-lisp...
Checking 24 files in /usr/share/emacs/24.4/lisp/cedet...
Checking 57 files in /usr/share/emacs/24.4/lisp/calendar...
Checking 87 files in /usr/share/emacs/24.4/lisp/calc...
Checking 95 files in /usr/share/emacs/24.4/lisp/obsolete...
Checking for load-path shadows...done
Quit [2 times]

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bug#21644: 24.4; completing-read acts differently on functional collection

[Oleh Krehel]

[-- Attachment #1: Type: text/plain, Size: 532 bytes --]

> Try typing "g" followed by RET for both of the above. In the first
> case (collection is a list), it returns "green". In the second case
> (collection is a function), it returns just "g". This is reproducible
> in emacs -Q.

I can reproduce this as well, although "TAB RET" works where "RET"
doesn't. I attach a patch with a fix. If someone can check it I can push
it. The patch doesn't solve all the intricacies of
`completion-ignore-case' that were mentioned in that function's
comments, just this specific use case.

    Oleh


[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #2: 0001-lisp-minibuffer.el-completion-complete-and-exit-Fix-.patch --]
[-- Type: text/x-diff, Size: 6224 bytes --]

From 6eca5cbbe328bc035fff41d33b47f03ac5b6ca81 Mon Sep 17 00:00:00 2001
From: Oleh Krehel <ohwoeowho@gmail.com>
Date: Thu, 8 Oct 2015 12:05:20 +0200
Subject: [PATCH] lisp/minibuffer.el (completion--complete-and-exit): Fix
 (bug#21644)

When `test-completion' returns a string and `completion-ignore-case'
is nil, the result was not used at all and only the minibuffer text
was returned. This change makes it use that returned string.
---
 lisp/minibuffer.el | 96 ++++++++++++++++++++++++++++--------------------------
 1 file changed, 49 insertions(+), 47 deletions(-)

diff --git a/lisp/minibuffer.el b/lisp/minibuffer.el
index 2814d02..f684164 100644
--- a/lisp/minibuffer.el
+++ b/lisp/minibuffer.el
@@ -1342,56 +1342,58 @@ completion-complete-and-exit
        (_ nil)))))
 
 (defun completion--complete-and-exit (beg end
-                                          exit-function completion-function)
+                                      exit-function completion-function)
   "Exit from `require-match' minibuffer.
 COMPLETION-FUNCTION is called if the current buffer's content does not
 appear to be a match."
-    (cond
-     ;; Allow user to specify null string
-   ((= beg end) (funcall exit-function))
-     ((test-completion (buffer-substring beg end)
-                       minibuffer-completion-table
-                       minibuffer-completion-predicate)
-      ;; FIXME: completion-ignore-case has various slightly
-      ;; incompatible meanings.  E.g. it can reflect whether the user
-      ;; wants completion to pay attention to case, or whether the
-      ;; string will be used in a context where case is significant.
-      ;; E.g. usually try-completion should obey the first, whereas
-      ;; test-completion should obey the second.
-      (when completion-ignore-case
-        ;; Fixup case of the field, if necessary.
-        (let* ((string (buffer-substring beg end))
-               (compl (try-completion
-                       string
-                       minibuffer-completion-table
-                       minibuffer-completion-predicate)))
-          (when (and (stringp compl) (not (equal string compl))
-                     ;; If it weren't for this piece of paranoia, I'd replace
-                     ;; the whole thing with a call to do-completion.
-                     ;; This is important, e.g. when the current minibuffer's
-                     ;; content is a directory which only contains a single
-                     ;; file, so `try-completion' actually completes to
-                     ;; that file.
-                     (= (length string) (length compl)))
-            (completion--replace beg end compl))))
-      (funcall exit-function))
-
-     ((memq minibuffer-completion-confirm '(confirm confirm-after-completion))
-      ;; The user is permitted to exit with an input that's rejected
-      ;; by test-completion, after confirming her choice.
-      (if (or (eq last-command this-command)
-              ;; For `confirm-after-completion' we only ask for confirmation
-              ;; if trying to exit immediately after typing TAB (this
-              ;; catches most minibuffer typos).
-              (and (eq minibuffer-completion-confirm 'confirm-after-completion)
-                   (not (memq last-command minibuffer-confirm-exit-commands))))
-        (funcall exit-function)
-        (minibuffer-message "Confirm")
-        nil))
-
-     (t
-      ;; Call do-completion, but ignore errors.
-      (funcall completion-function))))
+  (cond
+    ;; Allow user to specify null string
+    ((= beg end) (funcall exit-function))
+    ((test-completion (buffer-substring beg end)
+                      minibuffer-completion-table
+                      minibuffer-completion-predicate)
+     (let* ((string (buffer-substring beg end))
+            (compl (try-completion
+                    string
+                    minibuffer-completion-table
+                    minibuffer-completion-predicate)))
+       (when (and (stringp compl)
+                  (or (not completion-ignore-case)
+                      ;; FIXME: completion-ignore-case has various slightly
+                      ;; incompatible meanings.  E.g. it can reflect whether the user
+                      ;; wants completion to pay attention to case, or whether the
+                      ;; string will be used in a context where case is significant.
+                      ;; E.g. usually try-completion should obey the first, whereas
+                      ;; test-completion should obey the second.d
+
+                      ;; Fixup case of the field, if necessary.
+                      (and (not (equal string compl))
+                           ;; If it weren't for this piece of paranoia, I'd replace
+                           ;; the whole thing with a call to do-completion.
+                           ;; This is important, e.g. when the current minibuffer's
+                           ;; content is a directory which only contains a single
+                           ;; file, so `try-completion' actually completes to
+                           ;; that file.
+                           (= (length string) (length compl)))))
+         (completion--replace beg end compl)))
+     (funcall exit-function))
+
+    ((memq minibuffer-completion-confirm '(confirm confirm-after-completion))
+     ;; The user is permitted to exit with an input that's rejected
+     ;; by test-completion, after confirming her choice.
+     (if (or (eq last-command this-command)
+             ;; For `confirm-after-completion' we only ask for confirmation
+             ;; if trying to exit immediately after typing TAB (this
+             ;; catches most minibuffer typos).
+             (and (eq minibuffer-completion-confirm 'confirm-after-completion)
+                  (not (memq last-command minibuffer-confirm-exit-commands))))
+         (funcall exit-function)
+       (minibuffer-message "Confirm")
+       nil))
+
+    (t
+     ;; Call do-completion, but ignore errors.
+     (funcall completion-function))))
 
 (defun completion--try-word-completion (string table predicate point md)
   (let ((comp (completion-try-completion string table predicate point md)))
-- 
2.6.1

bug#21644: 24.4; completing-read acts differently on functional collection

[Dmitry Gutov]

On 10/08/2015 01:13 PM, Oleh Krehel wrote:

> I can reproduce this as well, although "TAB RET" works where "RET"
> doesn't. I attach a patch with a fix. If someone can check it I can push
> it. The patch doesn't solve all the intricacies of
> `completion-ignore-case' that were mentioned in that function's
> comments, just this specific use case.

Is there really a bug here?

The example code didn't handle `test-completion' (the case when ALL 
would be `lambda').

With this definition, the behavior is the same in either case:

(defun collection-as-function (collection)
   "Return a function equivalent to COLLECTION.

The returned function will work equivalently to COLLECTION when
passed to `all-completions' and `try-completion'."
   (if (functionp collection)
       collection
     ;; Capture collection in a closure
     (lambda (string pred all)
       (funcall
        (cond
         ((eq all 't)
          #'all-completions)
         ((eq all 'lambda)
          #'test-completion)
         (t
          #'try-completion))
        string collection pred))))

bug#21644: 24.4; completing-read acts differently on functional collection

[Ryan]

On 10/12/15 6:23 PM, Dmitry Gutov wrote:
> On 10/08/2015 01:13 PM, Oleh Krehel wrote:
>
>> I can reproduce this as well, although "TAB RET" works where "RET"
>> doesn't. I attach a patch with a fix. If someone can check it I can push
>> it. The patch doesn't solve all the intricacies of
>> `completion-ignore-case' that were mentioned in that function's
>> comments, just this specific use case.
>
> Is there really a bug here?
>
> The example code didn't handle `test-completion' (the case when ALL 
> would be `lambda').
>
> With this definition, the behavior is the same in either case:
>
> (defun collection-as-function (collection)
>   "Return a function equivalent to COLLECTION.
>
> The returned function will work equivalently to COLLECTION when
> passed to `all-completions' and `try-completion'."
>   (if (functionp collection)
>       collection
>     ;; Capture collection in a closure
>     (lambda (string pred all)
>       (funcall
>        (cond
>         ((eq all 't)
>          #'all-completions)
>         ((eq all 'lambda)
>          #'test-completion)
>         (t
>          #'try-completion))
>        string collection pred))))
>
>
I wasn't aware of `test-completion'. I was going based on the docstring 
for `completing-read', which only mentions `try-completion' and 
`all-completions'. Is there any other documentation I should have consulted?

bug#21644: 24.4; completing-read acts differently on functional collection

[Dmitry Gutov]

On 10/13/2015 04:34 AM, Ryan wrote:

> I wasn't aware of `test-completion'. I was going based on the docstring
> for `completing-read', which only mentions `try-completion' and
> `all-completions'.

Maybe it should mention test-completion as well. 
completion-table-with-predicate does.

> Is there any other documentation I should have
> consulted?

(info "(elisp) Programmed Completion") or
(info "(elisp) Basic Completion"), probably.

bug#21644: 24.4; completing-read acts differently on functional collection

[Ryan C. Thompson]

On 10/12/2015 07:27 PM, Dmitry Gutov wrote:
> On 10/13/2015 04:34 AM, Ryan wrote:
>
>> I wasn't aware of `test-completion'. I was going based on the docstring
>> for `completing-read', which only mentions `try-completion' and
>> `all-completions'.
>
> Maybe it should mention test-completion as well. 
> completion-table-with-predicate does.
>
>> Is there any other documentation I should have
>> consulted?
>
> (info "(elisp) Programmed Completion") or
> (info "(elisp) Basic Completion"), probably.
Maybe the `completing-read' docstring should link to these info nodes.

bug#21644: 24.4; completing-read acts differently on functional collection

[Dmitry Gutov]

On 10/13/2015 09:59 PM, Ryan C. Thompson wrote:

>> (info "(elisp) Programmed Completion") or
>> (info "(elisp) Basic Completion"), probably.
> Maybe the `completing-read' docstring should link to these info nodes.

This seems like it should suffice. Do you agree?

diff --git a/src/minibuf.c b/src/minibuf.c
index 4e5c17d..2cde8b0 100644
--- a/src/minibuf.c
+++ b/src/minibuf.c
@@ -1595,7 +1595,7 @@ PROMPT is a string to prompt with; normally it 
ends in a colon and a space.
  COLLECTION can be a list of strings, an alist, an obarray or a hash table.
  COLLECTION can also be a function to do the completion itself.
  PREDICATE limits completion to a subset of COLLECTION.
-See `try-completion' and `all-completions' for more details
+See Info node `(elisp)Basic Completion' for more details
   on completion, COLLECTION, and PREDICATE.

  REQUIRE-MATCH can take the following values:

bug#21644: 24.4; completing-read acts differently on functional collection

[Ryan]

On 10/14/15 10:12 PM, Dmitry Gutov wrote:
> On 10/13/2015 09:59 PM, Ryan C. Thompson wrote:
>
>>> (info "(elisp) Programmed Completion") or
>>> (info "(elisp) Basic Completion"), probably.
>> Maybe the `completing-read' docstring should link to these info nodes.
>
> This seems like it should suffice. Do you agree?
>
> diff --git a/src/minibuf.c b/src/minibuf.c
> index 4e5c17d..2cde8b0 100644
> --- a/src/minibuf.c
> +++ b/src/minibuf.c
> @@ -1595,7 +1595,7 @@ PROMPT is a string to prompt with; normally it 
> ends in a colon and a space.
>  COLLECTION can be a list of strings, an alist, an obarray or a hash 
> table.
>  COLLECTION can also be a function to do the completion itself.
>  PREDICATE limits completion to a subset of COLLECTION.
> -See `try-completion' and `all-completions' for more details
> +See Info node `(elisp)Basic Completion' for more details
>   on completion, COLLECTION, and PREDICATE.
>
>  REQUIRE-MATCH can take the following values:
>
Yes, I think that should be fine. That would have certainly solved the 
problem in my case, since I would have known to implement the 
`test-completion' case.

bug#21644: 24.4; completing-read acts differently on functional collection

[Dmitry Gutov]

On 10/15/2015 08:17 AM, Ryan wrote:

> Yes, I think that should be fine. That would have certainly solved the
> problem in my case, since I would have known to implement the
> `test-completion' case.

Good, installed.

bug#21644: 24.4; completing-read acts differently on functional collection

[Drew Adams]

> >> (info "(elisp) Programmed Completion") or
> >> (info "(elisp) Basic Completion"), probably.
> > Maybe the `completing-read' docstring should link to these info nodes.
> 
> This seems like it should suffice. Do you agree?
> +See Info node `(elisp)Basic Completion' for more details
>    on completion, COLLECTION, and PREDICATE.

Yes and no, IMO.  `Basic Completion' certainly provides
some information about "completion, COLLECTION, and
PREDICATE."  But for 3 other functions, not explicitly
for `completing-read' - it is not even mentioned there.

To understand COLLECTION for `completing-read', that node
not the best place to go.

As was suggested earlier (see above), node `Programmed
Completion' is where we should send someone for information
about a function-valued COLLECTION argument.

It doesn't hurt to send them to both nodes or to only
their parent, `Completion'.  But it is not clear to me
that someone trying to use `completing-read' with a
function-valued COLLECTION will understand what is
needed just from `Basic Completion'.

Especially since the `completing-read' doc string
mentions only `all-completions' and `try-completion',
not `test-completion' (which is OK): Someone going to
`Basic Completion' to find out more about parameter
COLLECTION for  `completing-read' is likely to miss
the description of COLLECTION for `test-completion'
or to think that it is not relevant.

A priori, there is nothing that necessarily connects
the COLLECTION parameter of `completing-read' with
the COLLECTION parameters of those 3 more-basic
functions, or even that connects those 3 COLLECTION
parameters.  That is, just giving them the same
name is not sufficient to specify that they are the
same.

Just saying to go see `Basic Completion' for info
about COLLECTION etc. _suggests_ that there is a
connection, but, again, that doesn't mean that
someone will see the relevance of `test-completion'
here.

bug#21644: 24.4; completing-read acts differently on functional collection

[Dmitry Gutov]

On 10/15/2015 06:01 PM, Drew Adams wrote:

> Yes and no, IMO.  `Basic Completion' certainly provides
> some information about "completion, COLLECTION, and
> PREDICATE."  But for 3 other functions, not explicitly
> for `completing-read' - it is not even mentioned there.

What's not mentioned? Basic Completion mentions the three key functions.

> As was suggested earlier (see above), node `Programmed
> Completion' is where we should send someone for information
> about a function-valued COLLECTION argument.

Basic Completion references Programmed Completion, twice.

On the other hand, Programmed Completion assumes that the collection is 
a function from the outset. This is not necessarily true in completing-read.

bug#21644: 24.4; completing-read acts differently on functional collection

[Drew Adams]

> > Yes and no, IMO.  `Basic Completion' certainly provides
> > some information about "completion, COLLECTION, and
> > PREDICATE."  But for 3 other functions, not explicitly
> > for `completing-read' - it is not even mentioned there.
> 
> What's not mentioned? Basic Completion mentions the three key functions.

Please reread what I wrote.  I said that `completing-read' is
not mentioned in node `Basic Completion'.  And it is not.

> > As was suggested earlier (see above), node `Programmed
> > Completion' is where we should send someone for information
> > about a function-valued COLLECTION argument.
> 
> Basic Completion references Programmed Completion, twice.

So what?

If the bug is that a user will not know the details for a
function-valued COLLECTION argument to `completing-read' then the
right place to send a reader for __that information__ is node
`Programmed Completion'.  That is specifically the purpose of
that node.  And that is the _only_ place that info is provided.

> On the other hand, Programmed Completion assumes that the collection is
> a function from the outset. This is not necessarily true in completing-read.

No one said that that is true.  This bug is about that particular
case.

The point is that mention of a function-valued COLLECTION in the
doc string should get readers to `Programmed Completion'.

Read what I said.  I did not say that we should send users to
`P. C.' for general info about COLLECTION.  I said:

  `Programmed Completion' is where we should send someone for
  information about a function-valued COLLECTION argument.
                      ^^^^^^^^^^^^^^^
And I said, regarding general info about COLLECTION:

  It doesn't hurt to send them to both nodes or to only
  their parent, `Completion'.

What is inadequate for the function-valued COLLECTION case, is
to send readers __only__ to `Basic Completion'.  Especially with
no indication that they need to consult not only `all-completions'
and `try-completion' there, but also `test-completion'.

That's the missing info, if you send them only to `B. C.': no
info that `test-completion' is relevant to the function-valued
COLLECTION case for `completing-read'.

bug#21644: 24.4; completing-read acts differently on functional collection

[Dmitry Gutov]

On 10/15/2015 07:47 PM, Drew Adams wrote:

> Please reread what I wrote.  I said that `completing-read' is
> not mentioned in node `Basic Completion'.  And it is not.

I see, thanks. But if you want me to read your writings in whole, you 
should really try to write more concisely.

>> Basic Completion references Programmed Completion, twice.
>
> So what?

If if they want to find out about function-value COLLECTION, they'll go 
there. On the other hand, we say that the node in question has 
information about completion, collection and predicate. That includes 
the case when the collection is not a function.

> If the bug is that a user will not know the details for a
> function-valued COLLECTION argument to `completing-read' then the
> right place to send a reader for __that information__ is node
> `Programmed Completion'.

_This_ bug was about that. That doesn't mean we should fix it by 
introducing another bug.

> And I said, regarding general info about COLLECTION:
>
>    It doesn't hurt to send them to both nodes or to only
>    their parent, `Completion'.

I think that asking the user to read the whole Completion section is too 
much. Basic Completion already contains the necessary information, or 
links to it. If the user wants the overview, they can navigate to the 
parent node just as easily.

bug#21644: 24.4; completing-read acts differently on functional collection

[Drew Adams]

> > If the bug is that a user will not know the details for a
> > function-valued COLLECTION argument to `completing-read' then the
> > right place to send a reader for __that information__ is node
> > `Programmed Completion'.
> 
> _This_ bug was about that. That doesn't mean we should fix it by
> introducing another bug.

No one has said anything that would introduce another bug.
It's about fixing this bug, by getting users to the information
about function-valued COLLECTION.  And that info is in node
`Programmed Completion'.

No one has said that users should not consult `Basic Completion'
for info about `all-completions', `try-completion', and
`test-completion'.

> > And I said, regarding general info about COLLECTION:
> >    It doesn't hurt to send them to both nodes or to only
> >    their parent, `Completion'.
> 
> I think that asking the user to read the whole Completion section is too
> much. 

No one is asking users to read the whole `Completion' section.
That is the section that covers all of the info about
`completing-read', _if_ you insist on pointing to only one section.

If you send them to only one section then a section that talks
only about the low-level functions `*-completion[s]' is not the
right destination.

Again: "It doesn't hurt to send them to both nodes".

> Basic Completion already contains the necessary information,

No, it does not.  It says *nothing* about `completing-read'.
Doesn't even mention it.

> or links to it.

As does `Completion'.

Really what should be done is to link from the `completing-read'
doc string only to node `Minibuffer Completion', which is the
node that documents `completing-read'.

But that node should document COLLECTION (it does not), and that
doc of COLLECTION should point to node `Programmed Completion'
for details about function-valued COLLECTION.

It is a bug (IMHO) that the node that documents `completing-read'
does not specify parameter COLLECTION - which is arguably the
*most important* parameter.

Fix that bug and link to node `Minibuffer Completion' from the
doc string, and you will have fixed this bug as well.

bug#21644: 24.4; completing-read acts differently on functional collection

[Dmitry Gutov]

On 10/15/2015 11:28 PM, Drew Adams wrote:

> No one has said anything that would introduce another bug.
> It's about fixing this bug, by getting users to the information
> about function-valued COLLECTION.  And that info is in node
> `Programmed Completion'.
>
> No one has said that users should not consult `Basic Completion'
> for info about `all-completions', `try-completion', and
> `test-completion'.

The current sentence that refers to the Info node would become wrong. 
But I suppose an alternative wording might escape that problem.

Patch welcome.

> No one is asking users to read the whole `Completion' section.
> That is the section that covers all of the info about
> `completing-read', _if_ you insist on pointing to only one section.

If you link to Completion as a whole, the user might not know better 
than to read it all.

> Really what should be done is to link from the `completing-read'
> doc string only to node `Minibuffer Completion', which is the
> node that documents `completing-read'.

I don't know about that: that page basically re-tells the docstring of 
completing-read. Sending to it from that docstring seems redundant.

> It is a bug (IMHO) that the node that documents `completing-read'
> does not specify parameter COLLECTION - which is arguably the
> *most important* parameter.

You're probably right. Please send a patch.

bug#21644: 24.4; completing-read acts differently on functional collection

[Eli Zaretskii]

> From: Dmitry Gutov <dgutov@yandex.ru>
> Date: Fri, 16 Oct 2015 00:07:40 +0300
> Cc: 21644@debbugs.gnu.org
> 
> On 10/15/2015 11:28 PM, Drew Adams wrote:
> 
> > No one has said anything that would introduce another bug.
> > It's about fixing this bug, by getting users to the information
> > about function-valued COLLECTION.  And that info is in node
> > `Programmed Completion'.
> >
> > No one has said that users should not consult `Basic Completion'
> > for info about `all-completions', `try-completion', and
> > `test-completion'.
> 
> The current sentence that refers to the Info node would become wrong. 
> But I suppose an alternative wording might escape that problem.
> 
> Patch welcome.

Done.

> > Really what should be done is to link from the `completing-read'
> > doc string only to node `Minibuffer Completion', which is the
> > node that documents `completing-read'.
> 
> I don't know about that: that page basically re-tells the docstring of 
> completing-read. Sending to it from that docstring seems redundant.

I agree.

> > It is a bug (IMHO) that the node that documents `completing-read'
> > does not specify parameter COLLECTION - which is arguably the
> > *most important* parameter.
> 
> You're probably right. Please send a patch.

Done.

I also re-added the references to the completion functions into the
doc string of completing-read (and added 2 more functions to that
list).  While referencing the manual is good, especially for complex
topics, I feel that the absolute minimum of usage information,
including the arguments with which callbacks can be called, should be
available from the doc strings.

bug#21644: 24.4; completing-read acts differently on functional collection

[Dmitry Gutov]

On 10/16/2015 12:45 PM, Eli Zaretskii wrote:

> I also re-added the references to the completion functions into the
> doc string of completing-read (and added 2 more functions to that
> list).  While referencing the manual is good, especially for complex
> topics, I feel that the absolute minimum of usage information,
> including the arguments with which callbacks can be called, should be
> available from the doc strings.

All right.

That's a bit too verbose for my taste, but I'm not going to argue.

bug#21644: 24.4; completing-read acts differently on functional collection

[Eli Zaretskii]

Btw, the completion--unquote argument to COMPLETION is not documented
-- is that on purpose?

bug#21644: 24.4; completing-read acts differently on functional collection

[Dmitry Gutov]

On 10/16/2015 12:46 PM, Eli Zaretskii wrote:
> Btw, the completion--unquote argument to COMPLETION is not documented
> -- is that on purpose?

Cc'ing Stefan.

bug#21644: 24.4; completing-read acts differently on functional collection

[Stefan Monnier]

> Btw, the completion--unquote argument to COMPLETION is not documented
> -- is that on purpose?

Yes.  It's only used internally by completion-table-with-quoting.
[ Admittedly, it's used in other places as well, but only after
  checking for the presence of the completion--unquote-requote property
  which is set by completion-table-with-quoting.  ]


        Stefan

bug#21644: 24.4; completing-read acts differently on functional collection

[Eli Zaretskii]

> From: Stefan Monnier <monnier@iro.umontreal.ca>
> Cc: Dmitry Gutov <dgutov@yandex.ru>,  21644@debbugs.gnu.org,  rct@thompsonclan.org,  drew.adams@oracle.com,  ohwoeowho@gmail.com
> Date: Fri, 16 Oct 2015 09:12:36 -0400
> 
> > Btw, the completion--unquote argument to COMPLETION is not documented
> > -- is that on purpose?
> 
> Yes.  It's only used internally by completion-table-with-quoting.

So no user COLLECTION callback will ever be called with it?

bug#21644: 24.4; completing-read acts differently on functional collection

[Stefan Monnier]

>> > Btw, the completion--unquote argument to COMPLETION is not documented
>> > -- is that on purpose?
>> Yes.  It's only used internally by completion-table-with-quoting.
> So no user COLLECTION callback will ever be called with it?

That's the intention, yes,


        Stefan

bug#21644: 24.4; completing-read acts differently on functional collection

[Stefan Monnier]

>> (if (functionp collection)
>> collection
>> ;; Capture collection in a closure
>> (lambda (string pred all)
>> (funcall
>> (cond
>> ((eq all 't)
>> #'all-completions)
>> ((eq all 'lambda)
>> #'test-completion)
>> (t
>> #'try-completion))
>> string collection pred))))
> I wasn't aware of `test-completion'. I was going based on the docstring for
> `completing-read', which only mentions `try-completion' and
> `all-completions'. Is there any other documentation I should have consulted?

Don't write the code above.  Use complete-with-action (or
completion-table-dynamic if that fits your need) which should handle all
the possible values of `all', including the new ones we'll introduce in
Emacs-27.


        Stefan

bug#21644: 24.4; completing-read acts differently on functional collection

[Drew Adams]

> > > It is a bug (IMHO) that the node that documents `completing-read'
> > > does not specify parameter COLLECTION - which is arguably the
> > > *most important* parameter.
> 
> Done.
> I also re-added the references to the completion functions into the
> doc string of completing-read (and added 2 more functions to that
> list).  While referencing the manual is good, especially for complex
> topics, I feel that the absolute minimum of usage information,
> including the arguments with which callbacks can be called, should be
> available from the doc strings.

Great.  Thx.