linux: further hack readline extension for libedit

We couldn't actually link the readline extension variation built
with libedit due to missing symbols.

This commit further hacks the build of this extension variant to
work with libedit.

With this change, PyOxidizer is able to link with the libedit
readline extension variant!

cpython-linux/build-cpython.sh

@@ -51,14 +51,53 @@ diff --git a/Lib/ctypes/__init__.py b/Lib/ctypes/__init__.py
  if _os.name == "nt":
 EOF
 
+# libedit on non-macOS requires various hacks because readline.c assumes
+# libedit is only used on macOS and its readline/libedit detection code
+# makes various assumptions about the macOS environment.
+#
+# USE_LIBEDIT comes from our static-modules file.
+#
+# TODO make upstream patches to readline.c to properly support libedit
+# on other platforms.
 cp Modules/readline.c Modules/readline-libedit.c
 
-# Python supports using libedit instead of readline. But Modules/readline.c
-# has all of this behind ``#ifdef __APPLE__`` instead of a more specific
-# feature flag. All occurrences of __APPLE__ in that file are related to
-# libedit. So we just replace the content. USE_LIBEDIT comes from our
-# static-modules file.
-# TODO make changes upstream to allow libedit to more easily be used
+# readline.c assumes that a modern readline API version has a free_history_entry().
+# but libedit does not. Change the #ifdef accordingly.
+#
+# Similarly, we invoke configure using readline, which sets
+# HAVE_RL_COMPLETION_SUPPRESS_APPEND improperly. So hack that. This is a bug
+# in our build system, as we should probably be invoking configure again when
+# using libedit.
+patch -p1 << EOF
+diff --git a/Modules/readline-libedit.c b/Modules/readline-libedit.c
+index 57335fe911..f3e83ff932 100644
+--- a/Modules/readline-libedit.c
++++ b/Modules/readline-libedit.c
+@@ -486,7 +486,7 @@ set the word delimiters for completion");
+
+ /* _py_free_history_entry: Utility function to free a history entry. */
+
+-#if defined(RL_READLINE_VERSION) && RL_READLINE_VERSION >= 0x0500
++#ifndef USE_LIBEDIT
+
+ /* Readline version >= 5.0 introduced a timestamp field into the history entry
+    structure; this needs to be freed to avoid a memory leak.  This version of
+@@ -1032,7 +1032,7 @@ flex_complete(const char *text, int start, int end)
+ #ifdef HAVE_RL_COMPLETION_APPEND_CHARACTER
+     rl_completion_append_character ='\0';
+ #endif
+-#ifdef HAVE_RL_COMPLETION_SUPPRESS_APPEND
++#ifndef USE_LIBEDIT
+     rl_completion_suppress_append = 0;
+ #endif
+
+
+EOF
+
+# Modules/readline.c has various libedit conditions behind an
+# ``#ifdef __APPLE__`` instead of a more specific feature flag. All
+# occurrences of __APPLE__ in that file are related to libedit. So we
+# just replace the content.
 sed -i s/__APPLE__/USE_LIBEDIT/g Modules/readline-libedit.c
 
 # Most bits look at CFLAGS. But setup.py only looks at CPPFLAGS.