From afcb6d0bc7abcdbca6b18d020deeff24d1ad197f Mon Sep 17 00:00:00 2001
From: Alan Mackenzie <acm@muc.de>
Date: Mon, 4 Sep 2023 12:51:24 +0000
Subject: [PATCH] Correct the handling of symbols with position in equal
* src/fns.c (internal_equal): Only regard symbols with position
as their symbols when symbols-with-pos-enabled is non-nil.
* doc/lispref/symbols.texi (Symbols with Position): Expand the
description of symbols with position, in particular the way
they work with eq and equal.
* doc/lispref/objects.texi (Equality Predicates): Describe how
eq and equal handle symbols with position.
* test/src/fns-tests.el (fns-tests-equal-symbols-with-position):
New tests for symbols with position.
---
doc/lispref/objects.texi | 11 +++++++++++
doc/lispref/symbols.texi | 40 +++++++++++++++++++++++++++-------------
src/fns.c | 20 ++++++++++++++------
test/src/fns-tests.el | 20 ++++++++++++++++++++
4 files changed, 72 insertions(+), 19 deletions(-)
diff --git a/doc/lispref/objects.texi b/doc/lispref/objects.texi
index ad079e0d63a..784d59720ed 100644
--- a/doc/lispref/objects.texi
+++ b/doc/lispref/objects.texi
@@ -2206,6 +2206,10 @@ and the same non-fixnum numeric type, then they might or might not be
the same object, and @code{eq} returns @code{t} or @code{nil}
depending on whether the Lisp interpreter created one object or two.
+If @var{object1} or @var{object2} is a symbol with position, @code{eq}
+regards it as its bare symbol when @code{symbols-with-pos-enabled} is
+non-@code{nil} (@pxref{Symbols with Position}).
+
@example
@group
(eq 'foo 'foo)
@@ -2363,6 +2367,13 @@ same sequence of character codes and all these codes are in the range
The @code{equal} function recursively compares the contents of objects
if they are integers, strings, markers, vectors, bool-vectors,
byte-code function objects, char-tables, records, or font objects.
+
+If @var{object1} or @var{object2} is a symbol with position,
+@code{equal} regards it as its bare symbol when
+@code{symbols-with-pos-enabled} is non-@code{nil}. Otherwise
+@code{equal} compares two symbols with position by recursively
+comparing their components. @xref{Symbols with Position}.
+
Other objects are considered @code{equal} only if they are @code{eq}.
For example, two distinct buffers are never considered @code{equal},
even if their textual contents are the same.
diff --git a/doc/lispref/symbols.texi b/doc/lispref/symbols.texi
index 34db0caf3a8..1f3b677d7fb 100644
--- a/doc/lispref/symbols.texi
+++ b/doc/lispref/symbols.texi
@@ -783,10 +783,15 @@ Symbol forms whose names start with @samp{#_} are not transformed.
@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.
+together with an unsigned integer called the @dfn{position}. Symbols
+with position don't themselves have entries in the obarray (though
+their bare symbols do; @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 +803,20 @@ the compiled Lisp file.
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.
+positions 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 behave as symbols, or have the
+other useful properties outlined in the previous paragraph. @code{eq}
+returns @code{t} when given identical arguments, and @code{equal}
+returns @code{t} when given arguments with @code{equal} components.
+
+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}
@@ -810,17 +824,17 @@ calling the reader function @code{read-positioning-symbols}
@code{position-symbol}.
@defvar symbols-with-pos-enabled
-When this variable is non-@code{nil}, symbols with position behave
+When this variable is non-@code{nil}, a symbol with position behaves
like the contained bare symbol. Emacs runs a little more slowly in
this case.
@end defvar
@defvar print-symbols-bare
-When bound to non-@code{nil}, the Lisp printer prints only the bare symbol of
-a symbol with position, ignoring the position.
+When bound to non-@code{nil}, the Lisp printer prints only the bare
+symbol of a symbol with position, ignoring the position.
@end defvar
-@defun symbol-with-pos-p symbol.
+@defun symbol-with-pos-p symbol
This function returns @code{t} if @var{symbol} is a symbol with
position, @code{nil} otherwise.
@end defun
diff --git a/src/fns.c b/src/fns.c
index ae9969a5432..bd1d63a58c4 100644
--- a/src/fns.c
+++ b/src/fns.c
@@ -2774,10 +2774,13 @@ internal_equal (Lisp_Object o1, Lisp_Object o2, enum equal_kind equal_kind,
/* A symbol with position compares the contained symbol, and is
`equal' to the corresponding ordinary symbol. */
- if (SYMBOL_WITH_POS_P (o1))
- o1 = SYMBOL_WITH_POS_SYM (o1);
- if (SYMBOL_WITH_POS_P (o2))
- o2 = SYMBOL_WITH_POS_SYM (o2);
+ if (symbols_with_pos_enabled)
+ {
+ if (SYMBOL_WITH_POS_P (o1))
+ o1 = SYMBOL_WITH_POS_SYM (o1);
+ if (SYMBOL_WITH_POS_P (o2))
+ o2 = SYMBOL_WITH_POS_SYM (o2);
+ }
if (BASE_EQ (o1, o2))
return true;
@@ -2825,8 +2828,8 @@ internal_equal (Lisp_Object o1, Lisp_Object o2, enum equal_kind equal_kind,
if (ASIZE (o2) != size)
return false;
- /* Compare bignums, overlays, markers, and boolvectors
- specially, by comparing their values. */
+ /* Compare bignums, overlays, markers, boolvectors, and
+ symbols with position specially, by comparing their values. */
if (BIGNUMP (o1))
return mpz_cmp (*xbignum_val (o1), *xbignum_val (o2)) == 0;
if (OVERLAYP (o1))
@@ -2858,6 +2861,11 @@ internal_equal (Lisp_Object o1, Lisp_Object o2, enum equal_kind equal_kind,
if (TS_NODEP (o1))
return treesit_node_eq (o1, o2);
#endif
+ if (SYMBOL_WITH_POS_P(o1)) /* symbols_with_pos_enabled is false. */
+ return (BASE_EQ (XSYMBOL_WITH_POS (o1)->sym,
+ XSYMBOL_WITH_POS (o2)->sym)
+ && BASE_EQ (XSYMBOL_WITH_POS (o1)->pos,
+ XSYMBOL_WITH_POS (o2)->pos));
/* Aside from them, only true vectors, char-tables, compiled
functions, and fonts (font-spec, font-entity, font-object)
diff --git a/test/src/fns-tests.el b/test/src/fns-tests.el
index 79ae4393f40..9c09e4f0c33 100644
--- a/test/src/fns-tests.el
+++ b/test/src/fns-tests.el
@@ -98,6 +98,26 @@
(should-not (equal-including-properties #("a" 0 1 (k "v"))
#("b" 0 1 (k "v")))))
+(ert-deftest fns-tests-equal-symbols-with-position ()
+ "Test `eq' and `equal' on symbols with position."
+ (let ((foo1 (position-symbol 'foo 42))
+ (foo2 (position-symbol 'foo 666))
+ (foo3 (position-symbol 'foo 42)))
+ (let (symbols-with-pos-enabled)
+ (should (eq foo1 foo1))
+ (should (equal foo1 foo1))
+ (should-not (eq foo1 foo2))
+ (should-not (equal foo1 foo2))
+ (should-not (eq foo1 foo3))
+ (should (equal foo1 foo3)))
+ (let ((symbols-with-pos-enabled t))
+ (should (eq foo1 foo1))
+ (should (equal foo1 foo1))
+ (should (eq foo1 foo2))
+ (should (equal foo1 foo2))
+ (should (eq foo1 foo3))
+ (should (equal foo1 foo3)))))
+
(ert-deftest fns-tests-reverse ()
(should-error (reverse))
(should-error (reverse 1))
--
2.39.5