master 637dde4aba: Don't always escape "." and "?" in `prin1'

[Lars Ingebrigtsen]

branch: master
commit 637dde4aba921435f78d0de769ad74c4f3230aa6
Author: Lars Ingebrigtsen <larsi@gnus.org>
Commit: Lars Ingebrigtsen <larsi@gnus.org>

    Don't always escape "." and "?" in `prin1'
    
    * src/print.c (print_object): Only escape "." and "?" when
    appearing as the first character in a symbol (bug#23130).
---
 etc/NEWS                | 16 ++++++++++++++++
 src/print.c             | 19 ++++++++++++-------
 test/src/print-tests.el |  8 ++++++++
 3 files changed, 36 insertions(+), 7 deletions(-)

diff --git a/etc/NEWS b/etc/NEWS
index b1aac3d6d0..d6b5da3902 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -1076,6 +1076,22 @@ Emacs buffers, like indentation and the like.  The new 
ert function
 
 * Incompatible Lisp Changes in Emacs 29.1
 
+---
+** 'prin1' doesn't always escape "." and "?" in symbols any more.
+Previously, symbols like 'foo.bar' would be printed by 'prin1' as
+"foo\.bar".  This now prints as "foo.bar" instead.  The Emacs Lisp
+reader interprets these strings as referring to the same symbol, so
+this is virtually always backwards-compatible, but there may
+theoretically be code out there that expects a specific printed
+representation.
+
+The same is the case with the "?" character: The 'foo?' symbol is now
+printed as "foo?" instead of "foo\?".
+
+If the "." and "?" characters are the first character in the symbol,
+they will still be escaped, so the '.foo' symbol is still printed as
+"\.foo" and the '?bar' symbol is still printed as "\?bar".
+
 +++
 ** Remapping 'mode-line' no longer works as expected.
 'mode-line' is now the parent face of the new 'mode-line-active' face,
diff --git a/src/print.c b/src/print.c
index 8cce8a1ad8..704fc278f2 100644
--- a/src/print.c
+++ b/src/print.c
@@ -2171,14 +2171,19 @@ print_object (Lisp_Object obj, Lisp_Object 
printcharfun, bool escapeflag)
        Lisp_Object name = SYMBOL_NAME (obj);
        ptrdiff_t size_byte = SBYTES (name);
 
-       /* Set CONFUSING if NAME looks like a number, calling
-          string_to_number for non-obvious cases.  */
        char *p = SSDATA (name);
        bool signedp = *p == '-' || *p == '+';
        ptrdiff_t len;
-       bool confusing = ((c_isdigit (p[signedp]) || p[signedp] == '.')
-                         && !NILP (string_to_number (p, 10, &len))
-                         && len == size_byte);
+       bool confusing =
+         /* Set CONFUSING if NAME looks like a number, calling
+            string_to_number for non-obvious cases.  */
+         ((c_isdigit (p[signedp]) || p[signedp] == '.')
+          && !NILP (string_to_number (p, 10, &len))
+          && len == size_byte)
+         /* We don't escape "." or "?" (unless they're the first
+            character in the symbol name).  */
+         || *p == '?'
+         || *p == '.';
 
        if (! NILP (Vprint_gensym)
            && !SYMBOL_INTERNED_IN_INITIAL_OBARRAY_P (obj))
@@ -2201,8 +2206,8 @@ print_object (Lisp_Object obj, Lisp_Object printcharfun, 
bool escapeflag)
              {
                if (c == '\"' || c == '\\' || c == '\''
                    || c == ';' || c == '#' || c == '(' || c == ')'
-                   || c == ',' || c == '.' || c == '`'
-                   || c == '[' || c == ']' || c == '?' || c <= 040
+                   || c == ',' || c == '`'
+                   || c == '[' || c == ']' || c <= 040
                    || c == NO_BREAK_SPACE
                    || confusing)
                  {
diff --git a/test/src/print-tests.el b/test/src/print-tests.el
index 1ef0caf1a4..0bae1959d1 100644
--- a/test/src/print-tests.el
+++ b/test/src/print-tests.el
@@ -417,5 +417,13 @@ otherwise, use a different charset."
            t)))
     (should (equal (prin1-to-string (make-marker)) ""))))
 
+(ert-deftest test-dots ()
+  (should (equal (prin1-to-string 'foo.bar) "foo.bar"))
+  (should (equal (prin1-to-string '.foo) "\\.foo"))
+  (should (equal (prin1-to-string '.foo.) "\\.foo."))
+  (should (equal (prin1-to-string 'bar?bar) "bar?bar"))
+  (should (equal (prin1-to-string '\?bar) "\\?bar"))
+  (should (equal (prin1-to-string '\?bar?) "\\?bar?")))
+
 (provide 'print-tests)
 ;;; print-tests.el ends here