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Clarify the doc string of 'with-buffer-unmodified-if-unchanged'

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* lisp/emacs-lisp/subr-x.el (with-buffer-unmodified-if-unchanged):
Describe better what is meant by "buffer changes".  (Bug#4587)
This commit is contained in:
Eli Zaretskii
2022-05-04 11:46:01 +03:00
parent 19231f7db2
commit 69521ffcb0
1 changed files with 14 additions and 7 deletions
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21
lisp/emacs-lisp/subr-x.el
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@@ -417,16 +417,23 @@ this defaults to the current buffer."
process)))
(defmacro with-buffer-unmodified-if-unchanged (&rest body)
"Like `progn', but change buffer modification status only if buffer is changed.
That is, if the buffer is marked as unmodified before BODY, and
BODY does modifications that, in total, means that the buffer is
identical to the buffer before BODY, mark the buffer as
unmodified again. In other words, this won't change buffer
modification status:
"Like `progn', but change buffer-modified status only if buffer text changes.
If the buffer was unmodified before execution of BODY, and
buffer text after execution of BODY is identical to what it was
before, ensure that buffer is still marked unmodified afterwards.
For example, the following won't change the buffer's modification
status:
(with-buffer-unmodified-if-unchanged
(insert \"a\")
(delete-char -1))."
(delete-char -1))
Note that only changes in the raw byte sequence of the buffer text,
as stored in the internal representation, are monitored for the
purpose of detecting the lack of changes in buffer text. Any other
changes that are normally perceived as \"buffer modifications\", such
as changes in text properties, `buffer-file-coding-system', buffer
multibytenes, etc. -- will still cause the buffer to become modified."
(declare (debug t) (indent 0))
(let ((hash (gensym))
(buffer (gensym)))