golang: Fix print(_pystr)

On Python2 without .tp_print printing _pystr crashes as:

    pygolang$ ./golang/testprog/golang_test_str.py
    Traceback (most recent call last):
      File "./golang/testprog/golang_test_str.py", line 39, in <module>
        main()
      File "./golang/testprog/golang_test_str.py", line 34, in main
        print("print(qq(b)):", qq(sb))
    RuntimeError: print recursion

See added comments for details.

golang/_golang.pyx

@@ -914,6 +914,27 @@ cdef class _pyunicode(unicode):
         else:
             return pyb(self)
 
+# initialize .tp_print for _pystr so that this type could be printed.
+# If we don't - printing it will result in `RuntimeError: print recursion`
+# because str of this type never reaches real bytes or unicode.
+# Do it only on python2, because python3 does not use tp_print at all.
+# NOTE _pyunicode does not need this because on py2 str(_pyunicode) returns _pystr.
+IF PY2:
+    # NOTE Cython does not define tp_print for PyTypeObject - do it ourselves
+    from libc.stdio cimport FILE
+    cdef extern from "Python.h":
+        ctypedef int (*printfunc)(PyObject *, FILE *, int) except -1
+        ctypedef struct PyTypeObject:
+            printfunc tp_print
+        cdef PyTypeObject *Py_TYPE(object)
+
+    cdef int _pystr_tp_print(PyObject *obj, FILE *f, int nesting) except -1:
+        o = <bytes>obj
+        o = bytes(buffer(o))  # change tp_type to bytes instead of _pystr
+        return Py_TYPE(o).tp_print(<PyObject*>o, f, nesting)
+
+    Py_TYPE(_pystr()).tp_print = _pystr_tp_print
+
 
 # __pystr converts obj to str of current python:
 #

golang/golang_test.py

 # -*- coding: utf-8 -*-
-# Copyright (C) 2018-2021  Nexedi SA and Contributors.
+# Copyright (C) 2018-2022  Nexedi SA and Contributors.
 #                          Kirill Smelkov <kirr@nexedi.com>
 #
 # This program is free software: you can Use, Study, Modify and Redistribute
@@ -1784,6 +1784,15 @@ def test_strings():
     assert isinstance(_, unicode)
     assert u(_) is _
 
+# verify print for _pystr and _pyunicode
+def test_strings_print():
+    outok = readfile(dir_testprog + "/golang_test_str.txt")
+    retcode, stdout, stderr = _pyrun(["golang_test_str.py"],
+                                cwd=dir_testprog, stdout=PIPE, stderr=PIPE)
+    assert retcode == 0, (stdout, stderr)
+    assert stderr == b""
+    assertDoc(outok, stdout)
+
 
 def test_qq():
     # NOTE qq is also tested as part of strconv.quote

golang/pyx/build.py

@@ -246,9 +246,13 @@ def Extension(name, sources, **kw):
     # provide POSIX/PYPY/... defines to Cython
     POSIX = ('posix' in sys.builtin_module_names)
     PYPY  = (platform.python_implementation() == 'PyPy')
+    PY2   = (sys.version_info.major < 3)
+    PY3   = (not PY2)
     pyxenv = kw.get('cython_compile_time_env', {})
     pyxenv.setdefault('POSIX',  POSIX)
     pyxenv.setdefault('PYPY',   PYPY)
+    pyxenv.setdefault('PY2',    PY2)
+    pyxenv.setdefault('PY3',    PY3)
     gverhex = _gevent_version_hex()
     if gverhex is not None:
         pyxenv.setdefault('GEVENT_VERSION_HEX', gverhex)

golang/testprog/golang_test_str.py

+#!/usr/bin/env python
+# -*- coding: utf-8 -*-
+# Copyright (C) 2022  Nexedi SA and Contributors.
+#                     Kirill Smelkov <kirr@nexedi.com>
+#
+# This program is free software: you can Use, Study, Modify and Redistribute
+# it under the terms of the GNU General Public License version 3, or (at your
+# option) any later version, as published by the Free Software Foundation.
+#
+# You can also Link and Combine this program with other software covered by
+# the terms of any of the Free Software licenses or any of the Open Source
+# Initiative approved licenses and Convey the resulting work. Corresponding
+# source of such a combination shall include the source code for all other
+# software used.
+#
+# This program is distributed WITHOUT ANY WARRANTY; without even the implied
+# warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+#
+# See COPYING file for full licensing terms.
+# See https://www.nexedi.com/licensing for rationale and options.
+"""This program helps to verify _pystr and _pyunicode.
+
+It complements golang_test.test_strings.
+"""
+
+from __future__ import print_function, absolute_import
+
+from golang import b, u
+from golang.gcompat import qq
+
+def main():
+    sb = b("привет b")
+    su = u("привет u")
+    print("print(qq(b)):", qq(sb))
+    print("print(qq(u)):", qq(su))
+
+
+if __name__ == '__main__':
+    main()

golang/testprog/golang_test_str.txt

+print(qq(b)): "привет b"
+print(qq(u)): "привет u"