Don't apply shorthands to punctuation-only symbols (bug#51089)

This includes symbols used for arithmetic functions such as -, /=,
etc.  Using "-" or "/=" is still possible but doing so won't shadow
those functions.

* doc/lispref/symbols.texi (Shorthand, Exceptions): New
subsubsection.

* src/lread.c (read1): Exempt punctionation-only symbols from
oblookup_considering_shorthand.

* test/lisp/progmodes/elisp-mode-tests.el
(elisp-dont-shadow-punctuation-only-symbols): Tweak test.

1 files changed, 6 insertions, 1 deletions

diff --git a/src/lread.c b/src/lread.c
index 07580d11d13..128b46aefef 100644
--- a/src/lread.c
+++ b/src/lread.c
@@ -3805,7 +3805,12 @@ read1 (Lisp_Object readcharfun, int *pch, bool first_in_list)
               ptrdiff_t longhand_bytes = 0;
 
               Lisp_Object tem;
-              if (skip_shorthand)
+              if (skip_shorthand ||
+                  /* The following ASCII characters are used in the
+                     only "core" Emacs Lisp symbols that are
+                     exclusively comprised of 'symbol constituent'
+                     syntax. */
+                  strspn(read_buffer, "^*+-/<=>_|") >= nbytes)
                 tem = oblookup (obarray, read_buffer, nchars, nbytes);
               else
                 tem = oblookup_considering_shorthand (obarray, read_buffer,