bug#35718: 26.2; Functions in yank-handled-properties ALWAYS get called

bug#35718: 26.2; Functions in yank-handled-properties ALWAYS get called

[Xu Chunyang]

Hi,

I want to change how image is pasted (e.g., save the image to disk and
insert a markdown image link). When I play with yank-handled-properties:

    (add-to-list 'yank-handled-properties '(image . foo))
    
    (defun foo (image beg end)
      (message "=> %S %S %S" image beg end))

However, the function foo is always called even there is no image at
all. This is unexpected since the function should only be called when
the property 'image is found according to the documentation:

    When the `yank' command inserts text into the buffer, it scans the
    inserted text for stretches of text that have `eq' values of the text
    property PROP; for each such stretch of text, FUN is called with three
    arguments...

The function is called inside remove-yank-excluded-properties, however
FUN is always called no matter what PROP is:

    (while (< run-start end)
      (let ((value (get-text-property run-start prop))
            (run-end (next-single-property-change
                      run-start prop nil end)))
        (funcall fun value run-start run-end)
        (setq run-start run-end)))


--
In GNU Emacs 26.2 (build 1, x86_64-apple-darwin18.5.0, Carbon Version 158 AppKit 1671.4)
 of 2019-04-20 built on Chunyangs-MacBook-Air.local
Repository revision: d21490f428a6baf568ad0669425b4a7b39a6bd73
Windowing system distributor 'Apple Inc.', version 10.14.4

bug#35718: 26.2; Functions in yank-handled-properties ALWAYS get called

[Eli Zaretskii]

> From: Xu Chunyang <mail@xuchunyang.me>
> Date: Tue, 14 May 2019 01:02:11 +0800
> 
> I want to change how image is pasted (e.g., save the image to disk and
> insert a markdown image link). When I play with yank-handled-properties:
> 
>     (add-to-list 'yank-handled-properties '(image . foo))
>     
>     (defun foo (image beg end)
>       (message "=> %S %S %S" image beg end))
> 
> However, the function foo is always called even there is no image at
> all. This is unexpected since the function should only be called when
> the property 'image is found according to the documentation:
> 
>     When the `yank' command inserts text into the buffer, it scans the
>     inserted text for stretches of text that have `eq' values of the text
>     property PROP; for each such stretch of text, FUN is called with three
>     arguments...
> 
> The function is called inside remove-yank-excluded-properties, however
> FUN is always called no matter what PROP is:
> 
>     (while (< run-start end)
>       (let ((value (get-text-property run-start prop))
>             (run-end (next-single-property-change
>                       run-start prop nil end)))
>         (funcall fun value run-start run-end)
>         (setq run-start run-end)))

The above code actually calls the handler function whenever PROP's
value _changes_, not just where PROP is non-nil.  Not sure if this is
a bug or a feature; opinions welcome.

bug#35718: 26.2; Functions in yank-handled-properties ALWAYS get called

[Noam Postavsky]

>> However, the function foo is always called even there is no image at
>> all. This is unexpected since the function should only be called when
>> the property 'image is found according to the documentation:
>>
>>     When the `yank' command inserts text into the buffer, it scans the
>>     inserted text for stretches of text that have `eq' values of the text
>>     property PROP; for each such stretch of text, FUN is called with three
>>     arguments...
>> 
>> The function is called inside remove-yank-excluded-properties, however
>> FUN is always called no matter what PROP is:
>> 
>>     (while (< run-start end)
>>       (let ((value (get-text-property run-start prop))
>>             (run-end (next-single-property-change
>>                       run-start prop nil end)))
>>         (funcall fun value run-start run-end)
>>         (setq run-start run-end)))
>
> The above code actually calls the handler function whenever PROP's
> value _changes_, not just where PROP is non-nil.  Not sure if this is
> a bug or a feature; opinions welcome.

I think the question is more about whether we distinguish between an
absent property, and a property whose value is nil
(remove-yank-excluded-properties currently does not, which is what I
think this bug report is complaining about).  The manual doesn't say
either way, but text-property-any (and other property checking
functions) seem to treat them the same as well:

(text-property-any 0 2 'xxx nil (propertize "foo" 'xxx nil)) ;=> 0
(text-property-any 0 2 'xxx nil (propertize "foo" 'xxx t)) ;=> nil
(text-property-any 0 2 'xxx nil "foo") ;=> 0

bug#35718: 26.2; Functions in yank-handled-properties ALWAYS get called

[Lars Ingebrigtsen]

Noam Postavsky <npostavs@gmail.com> writes:

> I think the question is more about whether we distinguish between an
> absent property, and a property whose value is nil
> (remove-yank-excluded-properties currently does not, which is what I
> think this bug report is complaining about).  The manual doesn't say
> either way, but text-property-any (and other property checking
> functions) seem to treat them the same as well:
>
> (text-property-any 0 2 'xxx nil (propertize "foo" 'xxx nil)) ;=> 0
> (text-property-any 0 2 'xxx nil (propertize "foo" 'xxx t)) ;=> nil
> (text-property-any 0 2 'xxx nil "foo") ;=> 0

I think that we don't (in general) care about the difference of a nil
property and a missing property, so if I understand the snippet
correctly, this is basically working as intended, so I'm closing this
bug report.

If I misunderstood, please respond to the debbugs address and we'll
reopen.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no