From: Stefan Monnier via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>
To: Eli Zaretskii <eliz@gnu.org>
Cc: 65051@debbugs.gnu.org, acm@muc.de
Subject: bug#65051: internal_equal manipulates symbols with position without checking symbols-with-pos-enabled.
Date: Sat, 12 Aug 2023 14:46:24 -0400 [thread overview]
Message-ID: <jwv1qg8rteb.fsf-monnier+emacs@gnu.org> (raw)
In-Reply-To: <83msywg5a0.fsf@gnu.org> (Eli Zaretskii's message of "Sat, 12 Aug 2023 09:10:15 +0300")
Thanks,
Stefan
diff --git a/doc/lispref/symbols.texi b/doc/lispref/symbols.texi
index 34db0caf3a8..d2e397faf80 100644
--- a/doc/lispref/symbols.texi
+++ b/doc/lispref/symbols.texi
@@ -782,11 +782,16 @@ Symbols with Position
@cindex symbol with position
@cindex bare symbol
-A @dfn{symbol with position} is a symbol, the @dfn{bare symbol},
-together with an unsigned integer called the @dfn{position}. These
-objects are intended for use by the byte compiler, which records in
-them the position of each symbol occurrence and uses those positions
-in warning and error messages.
+A @dfn{symbol with position} is a pair of a symbol, the @dfn{bare
+symbol}, together with an unsigned integer called the @dfn{position}.
+Symbol with position cannot themselves have entries in obarrays
+(contrary to their bare symbols; @pxref{Creating Symbols}).
+
+Symbols with position are for the use of the byte compiler, which
+records in them the position of each symbol occurrence and uses those
+positions in warning and error messages. They shouldn't normally be
+used otherwise. Doing so can cause unexpected results with basic
+Emacs functions such as @code{eq} and @code{equal}.
The printed representation of a symbol with position uses the hash
notation outlined in @ref{Printed Representation}. It looks like
@@ -798,11 +803,21 @@ Symbols with Position
For most purposes, when the flag variable
@code{symbols-with-pos-enabled} is non-@code{nil}, symbols with
-positions behave just as bare symbols do. For example, @samp{(eq
-#<symbol foo at 12345> foo)} has a value @code{t} when that variable
-is set (but @code{nil} when it isn't set). Most of the time in Emacs this
-variable is @code{nil}, but the byte compiler binds it to @code{t}
-when it runs.
+position behave just as their bare symbols would. For example,
+@samp{(eq #<symbol foo at 12345> foo)} has a value @code{t} when the
+variable is set; likewise, @code{equal} will treat a symbol with
+position argument as its bare symbol.
+
+When @code{symbols-with-pos-enabled} is @code{nil}, any symbols with
+position continue to exist, but do not always behave as symbols.
+Most importantly @code{eq} only returns @code{t} when given truly
+identical arguments, for performance reasons. @code{equal} on the
+other hand continues to treat a symbol with
+position argument as its bare symbol.
+
+Most of the time in Emacs @code{symbols-with-pos-enabled} is
+@code{nil}, but the byte compiler and the native compiler bind it to
+@code{t} when they run.
Typically, symbols with position are created by the byte compiler
calling the reader function @code{read-positioning-symbols}
diff --git a/src/fns.c b/src/fns.c
index ac30670b3ac..fde4ef6b08b 100644
--- a/src/fns.c
+++ b/src/fns.c
@@ -5166,7 +5166,7 @@ sxhash_obj (Lisp_Object obj, int depth)
hash = sxhash_combine (hash, sxhash_obj (XOVERLAY (obj)->plist, depth));
return SXHASH_REDUCE (hash);
}
- else if (symbols_with_pos_enabled && pvec_type == PVEC_SYMBOL_WITH_POS)
+ else if (pvec_type == PVEC_SYMBOL_WITH_POS)
return sxhash_obj (XSYMBOL_WITH_POS (obj)->sym, depth + 1);
else
/* Others are 'equal' if they are 'eq', so take their
next prev parent reply other threads:[~2023-08-12 18:46 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-08-04 14:00 bug#65051: internal_equal manipulates symbols with position without checking symbols-with-pos-enabled Alan Mackenzie
2023-08-04 14:32 ` Eli Zaretskii
2023-08-04 14:59 ` Alan Mackenzie
2023-08-04 15:27 ` Eli Zaretskii
2023-08-04 17:06 ` Alan Mackenzie
2023-08-04 18:01 ` Eli Zaretskii
2023-08-05 10:45 ` Alan Mackenzie
2023-08-05 10:57 ` Eli Zaretskii
2023-08-05 11:52 ` Alan Mackenzie
2023-08-05 12:13 ` Eli Zaretskii
2023-08-05 13:04 ` Alan Mackenzie
2023-08-05 13:13 ` Eli Zaretskii
2023-08-13 16:14 ` Alan Mackenzie
2023-08-05 14:40 ` Mattias Engdegård
2023-08-05 16:59 ` Alan Mackenzie
2023-08-05 17:02 ` Mattias Engdegård
2023-08-05 21:07 ` Alan Mackenzie
2023-08-06 13:37 ` Mattias Engdegård
2023-08-06 15:02 ` Alan Mackenzie
2023-08-07 8:58 ` Mattias Engdegård
2023-08-07 9:44 ` Alan Mackenzie
2023-08-09 18:45 ` Mattias Engdegård
2023-08-07 3:30 ` Stefan Monnier via Bug reports for GNU Emacs, the Swiss army knife of text editors
2023-08-07 9:20 ` Alan Mackenzie
2023-08-08 2:56 ` Stefan Monnier via Bug reports for GNU Emacs, the Swiss army knife of text editors
2023-08-08 15:33 ` Alan Mackenzie
2023-08-10 3:28 ` Stefan Monnier via Bug reports for GNU Emacs, the Swiss army knife of text editors
2023-08-10 9:14 ` Alan Mackenzie
2023-08-10 14:28 ` Stefan Monnier via Bug reports for GNU Emacs, the Swiss army knife of text editors
2023-08-10 18:35 ` Alan Mackenzie
2023-08-12 5:36 ` Stefan Monnier via Bug reports for GNU Emacs, the Swiss army knife of text editors
2023-08-12 6:10 ` Eli Zaretskii
2023-08-12 18:46 ` Stefan Monnier via Bug reports for GNU Emacs, the Swiss army knife of text editors [this message]
2023-08-12 19:10 ` Eli Zaretskii
2023-08-13 15:27 ` Alan Mackenzie
2023-08-12 10:41 ` Alan Mackenzie
2023-08-12 18:07 ` Stefan Monnier via Bug reports for GNU Emacs, the Swiss army knife of text editors
2023-08-13 13:52 ` Alan Mackenzie
2023-08-12 21:59 ` Alan Mackenzie
2023-08-11 0:51 ` Dmitry Gutov
2023-08-11 10:42 ` Alan Mackenzie
2023-08-11 11:18 ` Dmitry Gutov
2023-08-11 12:05 ` Alan Mackenzie
2023-08-11 13:19 ` Dmitry Gutov
2023-08-11 14:04 ` Alan Mackenzie
2023-08-11 18:15 ` Dmitry Gutov
[not found] ` <handler.65051.B.169115764532326.ack@debbugs.gnu.org>
2023-09-04 12:57 ` bug#65051: Acknowledgement (internal_equal manipulates symbols with position without checking symbols-with-pos-enabled.) Alan Mackenzie
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