gh-46927: Detect rl_change_environment with a configure probe

Guard the rl_change_environment assignment with HAVE_RL_CHANGE_ENVIRONMENT,
set by a configure link test, instead of the __APPLE__ macro.  This compiles
it out on any libedit build lacking the symbol, not just on macOS.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: 2 people

Modules/readline.c

@@ -1323,10 +1323,10 @@ setup_readline(readlinestate *mod_state)
     /* The name must be defined before initialization */
     rl_readline_name = "python";
 
-#if !defined(__APPLE__)
-    /* Prevent readline from changing environment variables such as LINES and
-     * COLUMNS.
-     */
+#ifdef HAVE_RL_CHANGE_ENVIRONMENT
+    /* Prevent readline from setting the LINES and COLUMNS environment
+     * variables: ncurses prefers them over an ioctl() query, so a stale value
+     * left after a resize breaks SIGWINCH / KEY_RESIZE handling (gh-46927). */
     rl_change_environment = 0;
 #endif
 

configure

@@ -6472,6 +6472,17 @@ AS_VAR_IF([with_readline], [no], [
       AC_DEFINE([HAVE_RL_RESIZE_TERMINAL], [1], [Define if you have readline 4.0])
     ])
 
+    # rl_change_environment is in readline 6.3, but not in editline
+    AC_CACHE_CHECK([for rl_change_environment in -l$LIBREADLINE], [ac_cv_readline_rl_change_environment], [
+      AC_LINK_IFELSE(
+        [AC_LANG_PROGRAM([readline_includes], [int x = rl_change_environment])],
+        [ac_cv_readline_rl_change_environment=yes], [ac_cv_readline_rl_change_environment=no]
+      )
+    ])
+    AS_VAR_IF([ac_cv_readline_rl_change_environment], [yes], [
+      AC_DEFINE([HAVE_RL_CHANGE_ENVIRONMENT], [1], [Define if you have readline 6.3])
+    ])
+
     # check for readline 4.2
     AC_CACHE_CHECK([for rl_completion_matches in -l$LIBREADLINE], [ac_cv_readline_rl_completion_matches], [
       AC_LINK_IFELSE(

configure.ac

@@ -1074,6 +1074,9 @@
 /* Define if you can turn off readline's signal handling. */
 #undef HAVE_RL_CATCH_SIGNAL
 
+/* Define if you have readline 6.3 */
+#undef HAVE_RL_CHANGE_ENVIRONMENT
+
 /* Define to 1 if the system has the type 'rl_compdisp_func_t'. */
 #undef HAVE_RL_COMPDISP_FUNC_T