bug#40896: 27.0.91; Moving point fails sometimes in shell-command

bug#40896: 27.0.91; Moving point fails sometimes in shell-command

[Michael Albinus]

Hi,

`shell-command' shall move the point after the output of the command,
unless indicated otherwise by `shell-command-dont-erase-buffer'. This
works almost, but not always. I have extracted three test cases which fail.

--8<---------------cut here---------------start------------->8---
;; Erase if buffer is the current one, but
;; `shell-command-dont-erase-buffer' is set to `erase'.
;; Move point to `point-max'.
(let ((default-directory temporary-file-directory)
      (shell-command-dont-erase-buffer 'erase))
  (with-temp-buffer
    (insert "bar")
    (cl-assert (string-equal "bar" (buffer-string)))
    (cl-assert (= (point) (point-max)))
    (shell-command "echo baz" (current-buffer))
    (cl-assert (string-equal "baz\n" (buffer-string)))
    ;; Point is not moved after the inserted text.
    (cl-assert (= (point) (point-max)) 'show-args)))

;; Don't erase if the buffer is the current one and
;; `shell-command-dont-erase-buffer' is set to `end-last-out'.
;; Move point to `point-max'.
(let ((default-directory temporary-file-directory)
      (shell-command-dont-erase-buffer 'end-last-out))
  (with-temp-buffer
    (insert "bar")
    (cl-assert (string-equal "bar" (buffer-string)))
    (cl-assert (= (point) (point-max)))
    (shell-command "echo baz" (current-buffer))
    (cl-assert (string-equal "barbaz\n" (buffer-string)))
    ;; Point is not moved after the inserted text.
    (cl-assert (= (point) (point-max)) 'show-args)))

;; Don't erase if the buffer is the current one and
;; `shell-command-dont-erase-buffer' is set to a random value.
;; Move point to `point-max'.
(let ((default-directory temporary-file-directory)
      (shell-command-dont-erase-buffer 'random))
  (with-temp-buffer
    (insert "bar")
    (cl-assert (string-equal "bar" (buffer-string)))
    (cl-assert (= (point) (point-max)))
    (shell-command "echo baz" (current-buffer))
    (cl-assert (string-equal "barbaz\n" (buffer-string)))
    ;; Point is not moved after the inserted text.
    (cl-assert (= (point) (point-max)) 'show-args)))
--8<---------------cut here---------------end--------------->8---

If it is undecided where point will be in the first and third case, this
shall be documented at least.

Best regards, Michael.


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bug#40896: 27.0.91; Moving point fails sometimes in shell-command

[Eli Zaretskii]

> From: Michael Albinus <michael.albinus@gmx.de>
> Date: Mon, 27 Apr 2020 10:28:03 +0200
> Cc: Tino Calancha <tino.calancha@gmail.com>
> 
> `shell-command' shall move the point after the output of the command,
> unless indicated otherwise by `shell-command-dont-erase-buffer'.

Which part(s) of the documentation caused this interpretation?  AFAIK,
the truth is that the output is inserted at point (i.e. point is left
_before_ the output), unless indicated otherwise by
shell-command-dont-erase-buffer.  So if something we say tricks you to
think otherwise, we need to fix that text.

Thanks.

bug#40896: 27.0.91; Moving point fails sometimes in shell-command

[Michael Albinus]

Eli Zaretskii <eliz@gnu.org> writes:

Hi Eli,

>> `shell-command' shall move the point after the output of the command,
>> unless indicated otherwise by `shell-command-dont-erase-buffer'.
>
> Which part(s) of the documentation caused this interpretation?  AFAIK,
> the truth is that the output is inserted at point (i.e. point is left
> _before_ the output), unless indicated otherwise by
> shell-command-dont-erase-buffer.  So if something we say tricks you to
> think otherwise, we need to fix that text.

Hmm, maybe I have been biased with the Tramp behaviour. But still,
there's suspicious behaviour with shell-command:

--8<---------------cut here---------------start------------->8---
;; Don't erase if the buffer is not the current one and
;; `shell-command-dont-erase-buffer' is set to `save-point'.
;; Check point.
(let ((default-directory temporary-file-directory)
      (shell-command-dont-erase-buffer 'save-point)
      buffer point)
  (with-temp-buffer
    (setq buffer (current-buffer))
    (insert "foobar")
    (goto-char (- (point-max) 3))
    (setq point (point))
    (cl-assert (string-equal "foobar" (buffer-string)))
    (cl-assert (string-equal "foo" (buffer-substring (point-min) (point))))
    (cl-assert (string-equal "bar" (buffer-substring (point) (point-max))))
    (cl-assert (= (point) (- (point-max) 3)))
    (with-temp-buffer
      (shell-command "echo baz" buffer))
    ;; The shell command output should be inserted between "foo" and "bar".
    (cl-assert (string-equal "foobaz\nbar" (buffer-string)) 'show-args)
    (cl-assert (= point (point)) 'show-args)))

;; Don't erase if the buffer is not the current one and
;; `shell-command-dont-erase-buffer' is set to a non-nil value.
;; Point should be before shell command output.
(let ((default-directory temporary-file-directory)
      (shell-command-dont-erase-buffer 'random)
      buffer point)
  (with-temp-buffer
    (setq buffer (current-buffer))
    (insert "foobar")
    (setq point (point))
    (cl-assert (string-equal "foobar" (buffer-string)))
    (cl-assert (= (point) (point-max)))
    (with-temp-buffer
      (shell-command "echo baz" buffer))
    (cl-assert (string-equal "foobarbaz\n" (buffer-string)) 'show-args)
    ;; Point should be the same.
    (cl-assert (= point (point)) 'show-args)))
--8<---------------cut here---------------end--------------->8---

Unless I still misunderstand something, these cases should be checked. I
will work on Tramp when clarified.

> Thanks.

Best regards, Michael.

bug#40896: 27.0.91; Moving point fails sometimes in shell-command

[Eli Zaretskii]

> From: Michael Albinus <michael.albinus@gmx.de>
> Cc: 40896@debbugs.gnu.org,  tino.calancha@gmail.com
> Date: Mon, 27 Apr 2020 19:50:57 +0200
> 
> Hmm, maybe I have been biased with the Tramp behaviour. But still,
> there's suspicious behaviour with shell-command:

I think these also behave as intended.  In general, all the non-nil
values of shell-command-dont-erase-buffer are set up to accumulate
output of several consecutive commands.  Once again, perhaps the
documentation needs to be clarified.

bug#40896: 27.0.91; Moving point fails sometimes in shell-command

[Michael Albinus]

Eli Zaretskii <eliz@gnu.org> writes:

>> From: Michael Albinus <michael.albinus@gmx.de>
>> Cc: 40896@debbugs.gnu.org,  tino.calancha@gmail.com
>> Date: Mon, 27 Apr 2020 19:50:57 +0200
>> 
>> Hmm, maybe I have been biased with the Tramp behaviour. But still,
>> there's suspicious behaviour with shell-command:
>
> I think these also behave as intended.  In general, all the non-nil
> values of shell-command-dont-erase-buffer are set up to accumulate
> output of several consecutive commands.  Once again, perhaps the
> documentation needs to be clarified.

Whatever shell-command-dont-erase-buffer says, shell-command output in
non-interactive mode shall be inserted at point, possibly after erasing
the buffer first. The first example I gave shows that this doesn't happen:

--8<---------------cut here---------------start------------->8---
;; Don't erase if the buffer is not the current one and
;; `shell-command-dont-erase-buffer' is set to `save-point'.
;; Check point.
(let ((default-directory temporary-file-directory)
      (shell-command-dont-erase-buffer 'save-point)
      buffer point)
  (with-temp-buffer
    (setq buffer (current-buffer))
    (insert "foobar")
    (goto-char (- (point-max) 3))
    (setq point (point))
    (cl-assert (string-equal "foobar" (buffer-string)))
    (cl-assert (string-equal "foo" (buffer-substring (point-min) (point))))
    (cl-assert (string-equal "bar" (buffer-substring (point) (point-max))))
    (cl-assert (= (point) (- (point-max) 3)))
    (with-temp-buffer
      (shell-command "echo baz" buffer))
    ;; The shell command output should be inserted between "foo" and "bar".
    (cl-assert (string-equal "foobaz\nbar" (buffer-string)) 'show-args)
    (cl-assert (= point (point)) 'show-args)))
--8<---------------cut here---------------end--------------->8---

Note that in case the buffer the output has to be inserted in is the
current one, this test succeeds. You can achieve this be replacing
'(with-temp-buffer (shell-command "echo baz" buffer))' by
'(shell-command "echo baz" buffer)'. This is inconsistent, isn't it? And
I haven't found any indication, that in case the buffer is not the
current one, shell command is inserted at the end of the buffer instead
of being inserted at point.

The second test case I've shown indicates, that a random value of
shell-command-dont-erase-buffer (I use the symbol 'random' here) doesn't
behave as expected. The docstring of that user option is not clear to
me: could it be, that the special symbols 'beg-last-out', 'end-last-out'
and ‘save-point’ indicate only setting the point if the buffer is the
current one? Why that? It's inconsistent in my eyes.

Maybe all of this is irrelevant in real life. But I'm fighting with
Tramp, in order to let its shell-command implementation behave like in
the local case.

Best regards, Michael.

bug#40896: 27.0.91; Moving point fails sometimes in shell-command

[Michael Albinus]

Michael Albinus <michael.albinus@gmx.de> writes:

Hi Eli,

> Maybe all of this is irrelevant in real life. But I'm fighting with
> Tramp, in order to let its shell-command implementation behave like in
> the local case.

In order to understand the situation better, I have enhanced my test
code to cover all different values of shell-command-dont-erase-buffer,
and whether the OUTPUT-BUFFER argument of shell-command is the current
buffer, or not. Here's the code:

--8<---------------cut here---------------start------------->8---
(progn
  (message "   s-c-d-e-b current-buffer buffer-string point")
  (message "===============================================")

  (let ((default-directory temporary-file-directory)
	buffer)
    ;; These are the possible values of `shell-command-dont-erase-buffer'.
    ;; `random' is taken as non-nil value without special meaning.
    (dolist (shell-command-dont-erase-buffer
	     '(nil erase beg-last-out end-last-out save-point random))
      ;; `shell-command' might work over the current buffer, or not.
      (dolist (current '(t nil))
	(with-temp-buffer
	  ;; We insert the string "foobar" into an empty buffer.
	  ;; Point is set between "foo" and "bar".
	  (setq buffer (current-buffer))
	  (insert "foobar")
	  (goto-char (- (point) 3))

	  ;; Apply `shell-command'.  It shall output the string
	  ;; "bazz".  Messages in the *Messages* buffer are
	  ;; suppressed.
          (let (message-log-max)
	    (if current
		(shell-command "echo -n bazz" (current-buffer))
	      (with-temp-buffer (shell-command "echo -n bazz" buffer))))

	  ;; Print result.
	  (message
	   "%12s %14s %13s %5d"
	   shell-command-dont-erase-buffer current (buffer-string) (point))))
      (message "-----------------------------------------------"))))
--8<---------------cut here---------------end--------------->8---

In a temporary buffer, the string "foobar" is inserted. Point is set
between "foo" and "bar". Then, shell-command is called, which outputs
the string "bazz".

The result can be seen in the *Messages* buffer. Honestly, I cannot say
whether this is conform to the docstring of shell-command (I have read
it several times), because it describes too many cases, and it is not
always clear how the combination of the cases is meant. But at least, I
would say the results look inconsistent.

A first observation is, that the output is inserted at (point) if
OUTPUT-BUFFER is the current buffer, and it is appended at (point-max)
if OUTPUT-BUFFER is not the current buffer. The fact, that the output is
appended at the end of the buffer, isn't mentioned anywhere in the doc AFAICT.

Now, let's see the details:

--8<---------------cut here---------------start------------->8---
   s-c-d-e-b current-buffer buffer-string point
===============================================
         nil              t    foobazzbar     4
         nil            nil          bazz     5
--8<---------------cut here---------------end--------------->8---

shell-command-dont-erase-buffer is nil. In case OUTPUT-BUFFER is the
current one, "bazz" is inserted at (point), and (point) is
preserved. Fine. In case OUTPUT-BUFFER is not the current one, the
buffer is erased, which as OK. However, (point) is NOT preserved, but
moved to the end of the shell command output. That doesn't sound right.

--8<---------------cut here---------------start------------->8---
       erase              t          bazz     1
       erase            nil          bazz     5
--8<---------------cut here---------------end--------------->8---

shell-command-dont-erase-buffer is erase. In both cases of
OUTPUT-BUFFER, the buffer is erased (as expected), but again, in case
OUTPUT-BUFFER is not the current one, (point) is moved after the shell
command output.

--8<---------------cut here---------------start------------->8---
beg-last-out              t    foobazzbar     4
beg-last-out            nil    foobarbazz     7
--8<---------------cut here---------------end--------------->8---

shell-command-dont-erase-buffer is beg-last-out. Shell command output is
inserted in case OUTPUT-BUFFER is the current one, and it is appended
otherwise. (point) is moved in both cases to the begin of the shell
command output, which is consistent, but I don't still see why the
output is either inserted, or appended.

--8<---------------cut here---------------start------------->8---
end-last-out              t    foobazzbar     4
end-last-out            nil    foobazzbar    11
--8<---------------cut here---------------end--------------->8---

shell-command-dont-erase-buffer is end-last-out. In case OUTPUT-BUFFER
is the current one everything looks as expected. But in the other case,
OUTPUT-BUFFER is not the current buffer, the result is irritating. Shell
command is inserted in this case at (point), and (point) is not moved to the
end of the shell command output, but to the end of the buffer. Strange!

--8<---------------cut here---------------start------------->8---
  save-point              t    foobazzbar     4
  save-point            nil    foobarbazz     4
--8<---------------cut here---------------end--------------->8---

shell-command-dont-erase-buffer is save-point. And indeed, (point) is
saved in both cases. But again, shell command output is appended at the
end of the buffer, instead of being inserted at (point).

--8<---------------cut here---------------start------------->8---
      random              t    foobazzbar     4
      random            nil    foobazzbar    11
--8<---------------cut here---------------end--------------->8---

shell-command-dont-erase-buffer is random, which stands for a non-nil
value which has no special meaning. It behaves like end-last-out. I
don't know whether this is intended; if yes, it shall be documented.

Best regards, Michael.

bug#40896: 27.0.91; Moving point fails sometimes in shell-command

[Eli Zaretskii]

> From: Michael Albinus <michael.albinus@gmx.de>
> Cc: 40896@debbugs.gnu.org,  tino.calancha@gmail.com
> Date: Thu, 30 Apr 2020 15:45:38 +0200
> 
> In order to understand the situation better, I have enhanced my test
> code to cover all different values of shell-command-dont-erase-buffer,
> and whether the OUTPUT-BUFFER argument of shell-command is the current
> buffer, or not. Here's the code:

AFAIU, the use case of OUTPUT-BUFFER being different from the current
buffer is meant for the case where subsequent commands accumulate the
output in that buffer, which is why the output is appended in that
case.

Does what you see make more sense now?

bug#40896: 27.0.91; Moving point fails sometimes in shell-command

[Michael Albinus]

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Eli Zaretskii <eliz@gnu.org> writes:

Hi Eli,

>> In order to understand the situation better, I have enhanced my test
>> code to cover all different values of shell-command-dont-erase-buffer,
>> and whether the OUTPUT-BUFFER argument of shell-command is the current
>> buffer, or not. Here's the code:
>
> AFAIU, the use case of OUTPUT-BUFFER being different from the current
> buffer is meant for the case where subsequent commands accumulate the
> output in that buffer, which is why the output is appended in that
> case.
>
> Does what you see make more sense now?

Almost. But it is not documented. Maybe we shall apply the appended
patch. And if shell-command-dont-erase-buffer is end-last-out with
output buffer not being the current one, the behavior is simply
wrong, see my previous analysis. At least *this* case must be fixed.

Best regards, Michael.


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diff --git a/doc/emacs/misc.texi b/doc/emacs/misc.texi
index 47f195d0b2..ca3d52c36a 100644
--- a/doc/emacs/misc.texi
+++ b/doc/emacs/misc.texi
@@ -846,6 +846,9 @@ Single Shell
 shell-command output.
 @end table

+In case the output buffer is not the current buffer, shell command
+output is appended at the end of this buffer.
+
 @node Interactive Shell
 @subsection Interactive Subshell

diff --git a/lisp/simple.el b/lisp/simple.el
index ab277c4e11..2f0626d96e 100644
--- a/lisp/simple.el
+++ b/lisp/simple.el
@@ -3606,6 +3606,9 @@ shell-command
 interactively when the prefix argument is given), insert the
 output in current buffer after point leaving mark after it.  This
 cannot be done asynchronously.
+If OUTPUT-BUFFER is a buffer or buffer name different from the
+current buffer, append the output in this buffer instead of
+inserting it at point.

 The user option `shell-command-dont-erase-buffer', which see, controls
 whether the output buffer is erased and where to put point after

bug#40896: 27.0.91; Moving point fails sometimes in shell-command

[Lars Ingebrigtsen]

Michael Albinus <michael.albinus@gmx.de> writes:

> Almost. But it is not documented. Maybe we shall apply the appended
> patch. And if shell-command-dont-erase-buffer is end-last-out with
> output buffer not being the current one, the behavior is simply
> wrong, see my previous analysis. At least *this* case must be fixed.

I've now applied the proposed patch, with some slight alterations.

And the parameters to these shell functions are very, very confusing.
At this point, perhaps it'd be better to write some new functions in
this area that have less weird parameters.  But fixing end-last-out
would also be nice.

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