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bug#50946: insert-file-contents can corrupt buffers. [Was: bug#50946: Em
From: |
Alan Mackenzie |
Subject: |
bug#50946: insert-file-contents can corrupt buffers. [Was: bug#50946: Emacs-28: Inadequate coding in hack-elisp-shorthands] |
Date: |
Sun, 3 Oct 2021 12:10:19 +0000 |
On Sat, Oct 02, 2021 at 18:00:38 +0300, Eli Zaretskii wrote:
> > Date: Sat, 2 Oct 2021 14:45:52 +0000
> > Cc: joaotavora@gmail.com, 50946@debbugs.gnu.org
> > From: Alan Mackenzie <acm@muc.de>
[ .... ]
> > Have you checked that things work if the first byte in your temporary
> > buffer isn't at the start of a character?
> I don't see why this matter, can you explain?
Yes, it does matter. Because....
Create a file utf8-chars.txt as follows. All the non-ascii characters
are 2-byte German UTF8 characters:
Yes, it does matter. Because....
Create a file ~/utf8-chars.txt as follows. All the non-ascii characters
are 2-byte German UTF8 characters. Only the Q is an ascii character.
There is a LF at the end:
ÄäÖöQÜüß
Now, in an empty buffer,
M-: (insert-file-contents "~/utf8-chars.txt" nil 3 15)
.. The first character of this buffer is now the Emacs encoding of the
raw byte 0xa4.
Now do
M-: (insert-file-contents "~/utf8-chars.txt" nil 0 3)
The entire buffer, apart from the Q and the LF, now consists of raw
bytes, and the buffer is now 16 characters long. (Is this a bug?).
Note that the Q is now further back from the end of the buffer than it
should be.
Using insert-file-contents-literally instead doesn't help.
So insert-file-contents corrupts the buffer when BEG or END is not at a
character boundary. This matters for hack-elisp-shorthands, because this
corruption could push the Local Variables: start further back than 3000
characters. Possibly other problems could happen, too.
My opinion, for what it's worth, is that using insert-file-contents in
hack-elisp-shorthands is a Bad Thing. Even if it is possible to get it
working rigorously, it is surely not worth the trouble. Why not simply
visit the file in a buffer, and check for buffer local variables in the
normal fashion?
#########################################################################
There are bugs in the documentation of insert-file-contents in the elisp
manual. It confuses bytes with characters, and it fails to mention the
need to keep BEG and END at character boundaries. I propose installing
the following patch to the release branch:
diff --git a/doc/lispref/files.texi b/doc/lispref/files.texi
index 2dc808e694..c344e18c2b 100644
--- a/doc/lispref/files.texi
+++ b/doc/lispref/files.texi
@@ -556,6 +556,9 @@ Reading from Files
If @var{beg} and @var{end} are non-@code{nil}, they should be numbers
that are byte offsets specifying the portion of the file to insert.
+Be careful to ensure that these byte positions are at character
+boundaries. Otherwise, Emacs's input functions will corrupt the
+buffer.
In this case, @var{visit} must be @code{nil}. For example,
@example
@@ -563,7 +566,7 @@ Reading from Files
@end example
@noindent
-inserts the first 500 characters of a file.
+inserts the characters coded by the first 500 bytes of a file.
If the argument @var{replace} is non-@code{nil}, it means to replace the
contents of the buffer (actually, just the accessible portion) with the
@@ -580,7 +583,8 @@ Reading from Files
This function works like @code{insert-file-contents} except that it
does not run @code{after-insert-file-functions}, and does not do
format decoding, character code conversion, automatic uncompression,
-and so on.
+and so on. @var{beg} and @var{end}, if non-@code{nil}, should be at
+character boundaries, as in @code{insert-file-contents}.
@end defun
If you want to pass a file name to another process so that another
The doc strings of insert-file-contents\(-literally\)? will also need to
be updated.
--
Alan Mackenzie (Nuremberg, Germany).
- bug#50946: Emacs-28: Inadequate coding in hack-elisp-shorthands, (continued)
- bug#50946: Emacs-28: Inadequate coding in hack-elisp-shorthands, João Távora, 2021/10/02
- bug#50946: Emacs-28: Inadequate coding in hack-elisp-shorthands, João Távora, 2021/10/02
- bug#50946: Emacs-28: Inadequate coding in hack-elisp-shorthands, Alan Mackenzie, 2021/10/02
- bug#50946: Emacs-28: Inadequate coding in hack-elisp-shorthands, Eli Zaretskii, 2021/10/02
- bug#50946: Emacs-28: Inadequate coding in hack-elisp-shorthands, Alan Mackenzie, 2021/10/02
- bug#50946: Emacs-28: Inadequate coding in hack-elisp-shorthands, Eli Zaretskii, 2021/10/02
- bug#50946: Emacs-28: Inadequate coding in hack-elisp-shorthands, Alan Mackenzie, 2021/10/02
- bug#50946: Emacs-28: Inadequate coding in hack-elisp-shorthands, Eli Zaretskii, 2021/10/02
- bug#50946: Emacs-28: Inadequate coding in hack-elisp-shorthands, Alan Mackenzie, 2021/10/02
- bug#50946: Emacs-28: Inadequate coding in hack-elisp-shorthands, Eli Zaretskii, 2021/10/03
- bug#50946: insert-file-contents can corrupt buffers. [Was: bug#50946: Emacs-28: Inadequate coding in hack-elisp-shorthands],
Alan Mackenzie <=
- bug#50946: insert-file-contents can corrupt buffers. [Was: bug#50946: Emacs-28: Inadequate coding in hack-elisp-shorthands], Eli Zaretskii, 2021/10/03
- bug#50946: insert-file-contents can corrupt buffers. [Was: bug#50946: Emacs-28: Inadequate coding in hack-elisp-shorthands], Alan Mackenzie, 2021/10/03
- bug#50946: insert-file-contents can corrupt buffers., Alan Mackenzie, 2021/10/03
- bug#50946: insert-file-contents can corrupt buffers., Eli Zaretskii, 2021/10/03
- bug#50946: insert-file-contents can corrupt buffers., Alan Mackenzie, 2021/10/03
- bug#50946: insert-file-contents can corrupt buffers., Eli Zaretskii, 2021/10/03
- bug#50946: insert-file-contents can corrupt buffers., Alan Mackenzie, 2021/10/03
- bug#50946: insert-file-contents can corrupt buffers. [Was: bug#50946: Emacs-28: Inadequate coding in hack-elisp-shorthands], João Távora, 2021/10/03
- bug#50946: insert-file-contents can corrupt buffers. [Was: bug#50946: Emacs-28: Inadequate coding in hack-elisp-shorthands], João Távora, 2021/10/03
- bug#50946: insert-file-contents can corrupt buffers. [Was: bug#50946: Emacs-28: Inadequate coding in hack-elisp-shorthands], Eli Zaretskii, 2021/10/03