From 2add3a1595f709bb071e2b775970038470b2fab2 Mon Sep 17 00:00:00 2001
From: Paul Eggert <address@hidden>
Date: Sat, 3 Feb 2018 20:30:48 -0800
Subject: [PATCH 3/4] prin1 etc. now escape more chars in symbols

Inspired by email from Aaron Ecay in:
https://lists.gnu.org/r/emacs-devel/2018-02/msg00125.html
* etc/NEWS: Mention this.
* src/print.c (print_object): Escape any character that is not
documented to not require escaping.
---
 etc/NEWS    |  7 +++++++
 src/print.c | 37 +++++++++++++++++++++++++++++++------
 2 files changed, 38 insertions(+), 6 deletions(-)

diff --git a/etc/NEWS b/etc/NEWS
index afd0fba..2a46002 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -87,6 +87,13 @@ regular expression was previously invalid, but is now accepted:
 
    x\{32768\}
 
+** 'print' and related functions now escape more chars in symbols.
+They now escape any symbol character that is outside the documented
+set of characters that do not need escaping.  For example, (print
+(intern "n\u0456l")) now outputs "n\іl" instead of "nіl", as a hint to
+the reader that the "і" is not the usual U+0069 LATIN SMALL LETTER I,
+but is instead U+0456 CYRILLIC SMALL LETTER BYELORUSSIAN-UKRAINIAN I.
+
 
 * Editing Changes in Emacs 27.1
 
diff --git a/src/print.c b/src/print.c
index d3eb49d..7eca36a 100644
--- a/src/print.c
+++ b/src/print.c
@@ -1959,12 +1959,37 @@ print_object (Lisp_Object obj, Lisp_Object printcharfun, bool escapeflag)
 
 	    if (escapeflag)
 	      {
-		if (c == '\"' || c == '\\' || c == '\''
-		    || c == ';' || c == '#' || c == '(' || c == ')'
-		    || c == ',' || c == '.' || c == '`'
-		    || c == '[' || c == ']' || c == '?' || c <= 040
-                    || confusing
-		    || (i == 1 && confusable_symbol_character_p (c)))
+		switch (c)
+		  {
+		    /* The Emacs Lisp manual lists these characters as
+		       not requiring escaping in symbols.  Although some
+		       other characters might also work, play it safe
+		       and escape all but these characters.  */
+		  case '!': case '$': case '%': case '&':
+		  case '*': case '-': case '+': case '/':
+		  case '0': case '1': case '2': case '3': case '4':
+		  case '5': case '6': case '7': case '8': case '9':
+		  case ':': case '<': case '=': case '>': case '@':
+		  case 'A': case 'B': case 'C': case 'D': case 'E': case 'F':
+		  case 'G': case 'H': case 'I': case 'J': case 'K': case 'L':
+		  case 'M': case 'N': case 'O': case 'P': case 'Q': case 'R':
+		  case 'S': case 'T': case 'U': case 'V': case 'W': case 'X':
+		  case 'Y': case 'Z':
+		  case '^': case '_':
+		  case 'a': case 'b': case 'c': case 'd': case 'e': case 'f':
+		  case 'g': case 'h': case 'i': case 'j': case 'k': case 'l':
+		  case 'm': case 'n': case 'o': case 'p': case 'q': case 'r':
+		  case 's': case 't': case 'u': case 'v': case 'w': case 'x':
+		  case 'y': case 'z':
+		  case '{': case '}': case '~':
+		    break;
+
+		  default:
+		    confusing = true;
+		    break;
+		  }
+
+		if (confusing)
 		  {
 		    printchar ('\\', printcharfun);
 		    confusing = false;
-- 
2.7.4