Issue 6877: this patch makes it possible to link the readline extension

to the libedit emulation of the readline API on OSX 10.5 or later.

This also adds a minimal testsuite for readline to check that the
history manipuation functions have the same interface with both
C libraries.

Doc/library/readline.rst

@@ -14,6 +14,17 @@ made using  this module affect the behaviour of both the interpreter's
 interactive prompt  and the prompts offered by the :func:`raw_input` and
 :func:`input` built-in functions.
 
+..note::
+
+  On MacOS X the :mod:`readline` module can be implemented using
+  the ``libedit`` library instead of GNU readline.
+
+  The configuration file for ``libedit`` is different from that
+  of GNU readline. If you programmaticly load configuration strings
+  you can check for the text "libedit" in :const:`readline.__doc__`
+  to differentiate between GNU readline and libedit.
+
+
 The :mod:`readline` module defines the following functions:
 
 
@@ -181,7 +192,6 @@ The :mod:`readline` module defines the following functions:
 
    Append a line to the history buffer, as if it was the last line typed.
 
-
 .. seealso::
 
    Module :mod:`rlcompleter`

Lib/test/test_readline.py

@@ -0,0 +1,42 @@
+"""
+Very minimal unittests for parts of the readline module.
+
+These tests were added to check that the libedit emulation on OSX and
+the "real" readline have the same interface for history manipulation. That's
+why the tests cover only a small subset of the interface.
+"""
+import unittest
+from test.test_support import run_unittest
+
+import readline
+
+class TestHistoryManipulation (unittest.TestCase):
+    def testHistoryUpdates(self):
+        readline.clear_history()
+
+        readline.add_history("first line")
+        readline.add_history("second line")
+
+        self.assertEqual(readline.get_history_item(0), None)
+        self.assertEqual(readline.get_history_item(1), "first line")
+        self.assertEqual(readline.get_history_item(2), "second line")
+
+        readline.replace_history_item(0, "replaced line")
+        self.assertEqual(readline.get_history_item(0), None)
+        self.assertEqual(readline.get_history_item(1), "replaced line")
+        self.assertEqual(readline.get_history_item(2), "second line")
+
+        self.assertEqual(readline.get_current_history_length(), 2)
+
+        readline.remove_history_item(0)
+        self.assertEqual(readline.get_history_item(0), None)
+        self.assertEqual(readline.get_history_item(1), "second line")
+
+        self.assertEqual(readline.get_current_history_length(), 1)
+
+
+def test_main():
+    run_unittest(TestHistoryManipulation)
+
+if __name__ == "__main__":
+    test_main()

Misc/NEWS

@@ -1335,6 +1335,9 @@ C-API
 Extension Modules
 -----------------
 
+- Issue #6877: Make it possible to link the readline extension to libedit
+  on OSX.
+
 - Issue #6944: Fix a SystemError when socket.getnameinfo() was called
   with something other than a tuple as first argument.
 

Modules/readline.c

@@ -42,6 +42,25 @@ extern char **completion_matches(char *, CPFunction *);
 #endif
 #endif
 
+#ifdef __APPLE__
+/*
+ * It is possible to link the readline module to the readline
+ * emulation library of editline/libedit. 
+ * 
+ * On OSX this emulation library is not 100% API compatible
+ * with the "real" readline and cannot be detected at compile-time,
+ * hence we use a runtime check to detect if we're using libedit
+ *
+ * Currently there is one know API incompatibility: 
+ * - 'get_history' has a 1-based index with GNU readline, and a 0-based
+ *   index with libedit's emulation.
+ * - Note that replace_history and remove_history use a 0-based index
+ *   with both implementation.
+ */
+static int using_libedit_emulation = 0;
+static const char libedit_version_tag[] = "EditLine wrapper";
+#endif /* __APPLE__ */
+
 static void
 on_completion_display_matches_hook(char **matches,
 				   int num_matches, int max_length);
@@ -478,6 +497,29 @@ get_history_item(PyObject *self, PyObject *args)
 
 	if (!PyArg_ParseTuple(args, "i:index", &idx))
 		return NULL;
+#ifdef  __APPLE__
+	if (using_libedit_emulation) {
+		/* Libedit emulation uses 0-based indexes,
+		 * the real one uses 1-based indexes,
+		 * adjust the index to ensure that Python
+		 * code doesn't have to worry about the
+		 * difference.
+		 */
+		HISTORY_STATE *hist_st;
+		hist_st = history_get_history_state();
+
+		idx --;
+
+		/*
+		 * Apple's readline emulation crashes when
+		 * the index is out of range, therefore 
+		 * test for that and fail gracefully.
+		 */
+		if (idx < 0 || idx >= hist_st->length) {
+			Py_RETURN_NONE;
+		}
+	}
+#endif /* __APPLE__ */
 	if ((hist_ent = history_get(idx)))
 		return PyString_FromString(hist_ent->line);
 	else {
@@ -978,6 +1020,15 @@ call_readline(FILE *sys_stdin, FILE *sys_stdout, char *prompt)
 		char *line;
 		HISTORY_STATE *state = history_get_history_state();
 		if (state->length > 0)
+#ifdef __APPLE__
+			if (using_libedit_emulation) {
+				/* 
+				 * Libedit's emulation uses 0-based indexes,
+				 * the real readline uses 1-based indexes.
+				 */
+				line = history_get(state->length - 1)->line;
+			} else 
+#endif /* __APPLE__ */
 			line = history_get(state->length)->line;
 		else
 			line = "";
@@ -1011,16 +1062,35 @@ call_readline(FILE *sys_stdin, FILE *sys_stdout, char *prompt)
 PyDoc_STRVAR(doc_module,
 "Importing this module enables command line editing using GNU readline.");
 
+#ifdef __APPLE__
+PyDoc_STRVAR(doc_module_le,
+"Importing this module enables command line editing using libedit readline.");
+#endif /* __APPLE__ */
+
 PyMODINIT_FUNC
 initreadline(void)
 {
 	PyObject *m;
 
+#ifdef __APPLE__
+	if (strncmp(rl_library_version, libedit_version_tag, strlen(libedit_version_tag)) == 0) {
+		using_libedit_emulation = 1;
+	}
+
+	if (using_libedit_emulation) 
+		m = Py_InitModule4("readline", readline_methods, doc_module_le,
+			   (PyObject *)NULL, PYTHON_API_VERSION);
+	else
+
+#endif /* __APPLE__ */
+
 	m = Py_InitModule4("readline", readline_methods, doc_module,
 			   (PyObject *)NULL, PYTHON_API_VERSION);
 	if (m == NULL)
 		return;
 
+
+
 	PyOS_ReadlineFunctionPointer = call_readline;
 	setup_readline();
 }

setup.py

@@ -546,16 +546,16 @@ class PyBuildExt(build_ext):
 
         # readline
         do_readline = self.compiler_obj.find_library_file(lib_dirs, 'readline')
-        if platform == 'darwin': # and os.uname()[2] < '9.':
+        if platform == 'darwin':
-            # MacOSX 10.4 has a broken readline. Don't try to build
+            os_release = int(os.uname()[2].split('.')[0])
-            # the readline module unless the user has installed a fixed
+            if os_release < 9:
-            # readline package
+                # MacOSX 10.4 has a broken readline. Don't try to build
-            # FIXME: The readline emulation on 10.5 is better, but the
+                # the readline module unless the user has installed a fixed
-            # readline module doesn't compile out of the box.
+                # readline package
-            if find_file('readline/rlconf.h', inc_dirs, []) is None:
+                if find_file('readline/rlconf.h', inc_dirs, []) is None:
-                do_readline = False
+                    do_readline = False
         if do_readline:
-            if sys.platform == 'darwin':
+            if platform == 'darwin' and os_release < 9:
                 # In every directory on the search path search for a dynamic
                 # library and then a static library, instead of first looking
                 # for dynamic libraries on the entiry path.