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.

Add convenient utility to read whole file and return its content
similarly to Go. The code is taken from wendelin.core:

https://lab.nexedi.com/nexedi/wendelin.core/blob/wendelin.core-2.0.alpha1-18-g38dde766/wcfs/client/wcfs_misc.cpp#L246-281

Provide os/signal package that can be used to setup signal delivery to nogil
channels. This way for user code signal handling becomes regular handling of a
signalling channel instead of being something special or limited to only-main
python thread. The rationale for why we need it is explained below:

There are several problems with regular python's stdlib signal module:

1. Python2 does not call signal handler from under blocked lock.acquire.
   This means that if the main thread is blocked waiting on a semaphore,
   signal delivery will be delayed indefinitely, similarly to e.g. problem
   described in nxdtest!14 (comment 147527)
   where raising KeyboardInterrupt is delayed after SIGINT for many,
   potentially unbounded, seconds until ~semaphore wait finishes.

   Note that Python3 does not have this problem wrt stdlib locks and
   semaphores, but read below for the next point.

2. all pygolang communication operations (channels send/recv, sync.Mutex,
   sync.RWMutex, sync.Sema, sync.WaitGroup, sync.WorkGroup, ...) run with
   GIL released, but if blocked do not handle EINTR and do not schedule
   python signal handler to run (on main thread).

   Even if we could theoretically adjust this behaviour of pygolang at python
   level to match Python3, there are also C++ and pyx/nogil worlds. And we want gil
   and nogil worlds to interoperate (see https://pypi.org/project/pygolang/#cython-nogil-api),
   so that e.g. if completely nogil code happens to run on the main thread,
   signal handling is still possible, even if that signal handling was setup at
   python level.

With signals delivered to nogil channels both nogil world and python
world can setup signal handlers and to be notified of them irregardles
of whether main python thread is currently blocked in nogil wait or not.

/reviewed-on !17

To convert an object to str of current python.
It will be handy to use __pystr when implementing __str__ methods.

/reviewed-on nexedi/pygolang!17

Provide C++ package "os" with File, Pipe, etc similarly to what is
provided on Go side. The package works through IO methods provided by
runtimes.

We need IO facility because os/signal package will need to use
pipe in cooperative IO mode in its receiving-loop goroutine.

os.h and os.cpp are based on drafts from wendelin.core:

https://lab.nexedi.com/nexedi/wendelin.core/blob/wendelin.core-2.0.alpha1-18-g38dde766/wcfs/client/wcfs_misc.h
https://lab.nexedi.com/nexedi/wendelin.core/blob/wendelin.core-2.0.alpha1-18-g38dde766/wcfs/client/wcfs_misc.cpp

/reviewed-on !17

Else as https://github.com/python-greenlet/greenlet/pull/285
demonstrates there can be segmentation faults and crashes due to
exceptions from one greenlet propagating to C stack of another greenlet.

No test here. I've tried to do it, but with gevent (contrary to plain
greenlets), spawning new task only schedules corresponding greenlet to
run in the end of current event loop cycle instead of switching to
created greenlet immediately. With this delaying, it was hard for me to
develop corresponding test in a reasonable time.

Hopefully having the test I've done for greenlet itself + hereby
protection is good enough.

/reviewed-on nexedi/pygolang!17

This package provides special kind of atomic that is automatically reset
to zero after fork in child. This kind of atomic will be used in os
package to implement IO that does not deadlock in Close after fork.

/reviewed-on nexedi/pygolang!17

This package provides wrappers to OS system calls.
Minimal functionality that will be used to implement os and os/signal pacakges.

/reviewed-on nexedi/pygolang!17

Package os will need to access runtime operations to implement IO.

/reviewed-on nexedi/pygolang!17

We will soon need to use common functionality(*) from both runtimes and
other packages. The "other packages" are all C++ and it is handy to keep
common functionality in C++ as well. While we could also maintain
`extern "C"` interface, it duplicates the work. Let's switch everything
to C++ to ease further maintenance.

(*) e.g. package internal/syscall from both runtimes and from package os.

/reviewed-on !17

Without defined std::hash it is not possible to use channels as keys in
dict or set. We will be using set<chan> in os/signal package
implementation.

/reviewed-on nexedi/pygolang!17

I forgot to include it in ad00be70 (libgolang: Introduce runtimes).

/reviewed-on !17

/reviewed-on !17

    $ check-manifest
    lists of files in version control and sdist do not match!
    missing from sdist:
      .nxdtest

/reviewed-on nexedi/pygolang!17

See https://foss.heptapod.net/pypy/pypy/-/issues/3610 for stdin case.
-m started to behave as CPython.

On py3 'ps1' and b'ps1' are different keys and it was failing on PyPy3 as follows:

            # -i after stdin (also tests interactive mode as -i forces interactive even on non-tty)
            d = {
                b'hellopy': b(hellopy),
                b'ps1':     b'' # cpython emits prompt to stderr
            }
            if is_pypy and not is_gpython:
                d['ps1'] = b'>>>> ' # native pypy emits prompt to stdout and >>>> instead of >>>
            _ = pyout(['-i'], stdin=b'import hello\n', cwd=testdata)
    >       assert _ == b"%(ps1)shello\nworld\n['']\n%(ps1)s"           % d
    E       assert b">>>> hello\...\n['']\n>>>> " == b"hello\nworld\n['']\n"
    E         At index 0 diff: b'>' != b'h'
    E         Full diff:
    E         - b"hello\nworld\n['']\n"
    E         + b">>>> hello\nworld\n['']\n>>>> "
    E         ?   +++++                    +++++

    gpython/gpython_test.py:200: AssertionError

Fix it.
Amends e205dbf6 (gpython: Implement -i (interactive inspect after program run) + promised interactive-mode tests)

When _BaseCtx is setting up cancel propagation it locks a parent,
checks for parent.err != nil, and, if it is, calls
ctx._cancel(parent.err) _with_ _holding_ parent.mu. Since _cancel
internally also goes through parents and locks them, this was deadlocking
on the second call to parent.mu.lock().

-> Fix it by calling ctx._cancel(err) in the constructor outside of
parent lock.

The bug was there from the beginning - from e9567c7b (context: New
package that mirrors Go's context).

/trusted-by @jerome
/reviewed-on nexedi/pygolang!16

- _propagateCancel is used only in _BaseCtx constructor -> inline it
  there. Being run in the constructor makes it clear that this code
  works on new _BaseCtx object with empty set of children.

- since _cancelFrom interacts with the code moved from _propagateCancel,
  also move it to be close to cancel propagation setup.

No functional changes, just plain code movement.

/trusted-by @jerome
/reviewed-on nexedi/pygolang!16

The function that verifies "no exception/panic" case was prepared but not called at all.
This oversight was there from 5146eb0b "Add support for defer & recover".

/reviewed-by @jerome
/reviewed-on nexedi/pygolang!15

Because else sys.modules['__main__'] points to the module of gpython
itself, not user program. This difference can be important when e.g.
user defines classes in main module and tries to pickle them. Such
pickling will fail if gpython is not careful to run user's code in its
own main.

Without this patch added test fails as

      File "check_main.py", line 51, in <module>
        main()
      File "check_main.py", line 39, in main
        assert hasattr(mainmod, 'MyUniqueClassXYZ'),        dir(mainmod)
    AssertionError: ['__builtins__', '__doc__', '__file__', '__name__', '__package__', 'main']

The problem was discovered while trying to run test program from
https://github.com/zopefoundation/ZEO/issues/166 :

    $ gpython zopenrace-zeo.py
    Traceback (most recent call last):
      File "/home/kirr/tmp/trashme/Z/py2.venv/bin/gpython", line 8, in <module>
        sys.exit(main())
      File "/home/kirr/tmp/trashme/Z/py2.venv/lib/python2.7/site-packages/gpython/__init__.py", line 395, in main
        pymain(argv, init)
      File "/home/kirr/tmp/trashme/Z/py2.venv/lib/python2.7/site-packages/gpython/__init__.py", line 266, in pymain
        run()
      File "/home/kirr/tmp/trashme/Z/py2.venv/lib/python2.7/site-packages/gpython/__init__.py", line 172, in run
        _execfile(filepath, g)
      File "/home/kirr/tmp/trashme/Z/py2.venv/lib/python2.7/site-packages/gpython/__init__.py", line 275, in _execfile
        six.exec_(code, globals, locals)
      File "/home/kirr/tmp/trashme/Z/py2.venv/lib/python2.7/site-packages/six.py", line 719, in exec_
        exec("""exec _code_ in _globs_, _locs_""")
      File "<string>", line 1, in <module>
      File "zopenrace-zeo.py", line 205, in <module>
        main()
      File "zopenrace-zeo.py", line 190, in main
        init()
      File "zopenrace-zeo.py", line 126, in init
        transaction.commit()
      File "/home/kirr/tmp/trashme/Z/py2.venv/lib/python2.7/site-packages/transaction/_manager.py", line 257, in commit
        return self.manager.commit()
      File "/home/kirr/tmp/trashme/Z/py2.venv/lib/python2.7/site-packages/transaction/_manager.py", line 134, in commit
        return self.get().commit()
      File "/home/kirr/tmp/trashme/Z/py2.venv/lib/python2.7/site-packages/transaction/_transaction.py", line 282, in commit
        reraise(t, v, tb)
      File "/home/kirr/tmp/trashme/Z/py2.venv/lib/python2.7/site-packages/transaction/_transaction.py", line 273, in commit
        self._commitResources()
      File "/home/kirr/tmp/trashme/Z/py2.venv/lib/python2.7/site-packages/transaction/_transaction.py", line 456, in _commitResources
        reraise(t, v, tb)
      File "/home/kirr/tmp/trashme/Z/py2.venv/lib/python2.7/site-packages/transaction/_transaction.py", line 430, in _commitResources
        rm.commit(self)
      File "/home/kirr/tmp/trashme/Z/py2.venv/lib/python2.7/site-packages/ZODB/Connection.py", line 497, in commit
        self._commit(transaction)
      File "/home/kirr/tmp/trashme/Z/py2.venv/lib/python2.7/site-packages/ZODB/Connection.py", line 546, in _commit
        self._store_objects(ObjectWriter(obj), transaction)
      File "/home/kirr/tmp/trashme/Z/py2.venv/lib/python2.7/site-packages/ZODB/Connection.py", line 578, in _store_objects
        p = writer.serialize(obj)  # This calls __getstate__ of obj
      File "/home/kirr/tmp/trashme/Z/py2.venv/lib/python2.7/site-packages/ZODB/serialize.py", line 430, in serialize
        return self._dump(meta, obj.__getstate__())
      File "/home/kirr/tmp/trashme/Z/py2.venv/lib/python2.7/site-packages/ZODB/serialize.py", line 439, in _dump
        self._p.dump(state)
    PicklingError: Can't pickle <class '__main__.PInt'>: attribute lookup __main__.PInt failed

/reviewed-by @jerome
/reviewed-on nexedi/pygolang!15

To match python behaviour:

    $ python >/dev/null
    Python 2.7.18 (default, Apr 20 2020, 20:30:41)
    [GCC 9.3.0] on linux2
    Type "help", "copyright", "credits" or "license" for more information.
    >>> 1+1			# NOTE the prompt (printed to stderr)

    $ python 2>/dev/null
    >>> 1+1			# NOTE the prompt (printed to stdout)

Tests pending.

/reviewed-by @jerome
/reviewed-on nexedi/pygolang!15

Not through interactive console, because it was printing prompts, while
`python <prog.py` does not emit anything:

    $ cat prog.py
    print 'Hello World'

    $ python <prog.py
    Hello World

    $ gpython <prog.py
    Python 2.7.18 (default, Apr 20 2020, 20:30:41)
    [GCC 9.3.0] [GPython 0.0.8] [gevent 20.9.0] on linux2
    Type "help", "copyright", "credits" or "license" for more information.
    (InteractiveConsole)
    Hello World

After the patch gpython output is the same as of python:

    $ gpython <prog.py
    Hello World

Test coverage for interactive mode is pending.
We'll add them soon in a follow-up patch after implementing -i.

For _interact - by this patch logic - we should be dropping custom
raw_input, since now _interact is called only when sys.stdin is tty.
But we'll soon be invoking _interact when stdin is not a tty (for
`gpython -i <prog.py`), so leave that logic in place as is.

/reviewed-by @jerome
/reviewed-on nexedi/pygolang!15

We will soon need this to be run from several places when implementing
support for -i.

/reviewed-by @jerome
/reviewed-on nexedi/pygolang!15

setuptools_dso 2 started to emit those autogenerated files.
See https://github.com/mdavidsaver/setuptools_dso/pull/15 for details.

Those are quote codes that Go strconv.Quote might produce. And even
though Python does not use them when quoting, it too handles those quote
codes when decoding:

    In [1]: '\r'
    Out[1]: '\r'

    In [2]: '\a\b\v\f'
    Out[2]: '\x07\x08\x0b\x0c'

https://github.com/python/cpython/blob/2.7.18-0-g8d21aa21f2c/Objects/stringobject.c#L677-L688

-> Teach strconv.unquote + friends to handle them as well.

/reviewed-by @jerome
/reviewed-on !14

https://bugs.python.org/issue20443

This broke test_defer_excchain_dump because
testprog/golang_test_defer_excchain.txt is prepared with output where
`python file` shows that file name in traceback as it was specified on
the command line, e.g.

    .../pygolang/golang/testprog$ python golang_test_defer_excchain.py
    Traceback (most recent call last):
      File ".../pygolang/golang/__init__.py", line 103, in _
        return f(*argv, **kw)
      File "golang_test_defer_excchain.py", line 42, in main
        raise RuntimeError("err")
    RuntimeError: err

while with py39 it became

    .../pygolang/golang/testprog$ python golang_test_defer_excchain.py
    Traceback (most recent call last):
      File ".../pygolang/golang/__init__.py", line 103, in _
        return f(*argv, **kw)
      File ".../pygolang/golang/testprog/golang_test_defer_excchain.py", line 42, in main
        raise RuntimeError("err")
    RuntimeError: err

(notice the difference related to "line 42")

-> Fix it:

- amend the test to conditionally prefix golang_test_defer_excchain.py
  in expected output with PYGOLANG/golang/testprog/ if it is Python >= 3.9.
- amend `gpython file` to match behaviour of underlying `python file`,
  so that the test passes unconditionally whether it is run by python or
  gpython.

--------

@jerome also says (nexedi/pygolang!13 (comment 122826)):

FYI, buildout (and many zope packages) essentially use doctests for
testing and they had to deal with similar differences in output.
`zope.testing` comes with a doctest checker named "renormalizing" which
normalize output with regular expressions, see for example setup of some
buildout test [here](https://github.com/buildout/buildout/blob/db3d6e2fbf5d7ff2cc4b2507253c7a221cfc3e32/src/zc/buildout/tests.py#L3615-L3651).
We definitely don't need this here for the moment, but maybe one day it
can be useful.

/reviewed-on nexedi/pygolang!13

Debian testing recently switched default python3 to be python3.9.
Let's make sure pygolang works with that python version.
Currently some tests fail - this will be addressed in the next patch.

/reviewed-on nexedi/pygolang!13

So that it becomes possible to write

    with WorkGroup(ctx) as wg:
        wg.go(f1)
        wg.go(f2)

instead of

    wg = WorkGroup(ctx)
    defer(wg.wait)
    wg.go(f1)
    wg.go(f2)

or

    wg = WorkGroup(ctx)
    wg.go(f1)
    wg.go(f2)
    wg.wait()

This is sometimes handy and is referred to as "structured concurrency"
in Python world.

sync.Sema, sync.Mutex, sync.RWMutex already support "with".
sync.WaitGroup is imho too low-level, but we might consider adding
"with" support for it in the future as well.

In general pygolang way is to use defer instead of plugging all classes
with __enter__/__exit__ "with" support, but for small well-known class of
concurrency-related things its seems "with" support is worth it:

- having "with" for sync.Mutex+co allows it to be used as a drop-in
  replacement instead of threading.Lock+co, and
- having "with" for sync.WorkGroup - the most commonly-used tool to
  spawn jobs and wait for their completion - makes it on-par with
  "structured concurrency".

/reviewed-on nexedi/pygolang!12

WorkGroup methods work on PyWorkGroup, not on PyWaitGroup.
This probably used to work because Cython ignores (?) provided type of self?

/reviewed-on !12

Similarly to test_pymain_syspath we cannot run this test on SlapOS because with
buildout raw underlying python interpreter does not have access to eggs with
which gpython script was generated.

See 0fa9d6e7 and 92bb5bcc for details.

Without this patch running pygolang tests fails on SlapOS as shown below:

    (pygolang-env) slapuser34@vifibcloud-rapidspace-hosting-007:~/srv/runner/software/44fe7dd3f13ecd100894c6368a35c055/parts/pygolang-dev$ gpython -m pytest -vsx -k relpath
    ================================================= test session starts ==================================================
    platform linux2 -- Python 2.7.18, pytest-4.6.11, py-1.9.0, pluggy-0.13.1 -- /srv/slapgrid/slappart34/srv/runner/software/44fe7dd3f13ecd100894c6368a35c055/bin/gpython
    cachedir: .pytest_cache
    rootdir: /srv/slapgrid/slappart34/srv/runner/software/44fe7dd3f13ecd100894c6368a35c055/parts/pygolang-dev
    collected 115 items / 114 deselected / 1 selected

    gpython/gpython_test.py::test_pymain_run_via_relpath Traceback (most recent call last):
      File "./__init__.py", line 511, in <module>
        main()
      File "./__init__.py", line 395, in main
        pymain(argv, init)
      File "./__init__.py", line 217, in pymain
        init()
      File "./__init__.py", line 364, in init
        import gevent
    ImportError: No module named gevent
    FAILED

    ======================================================= FAILURES =======================================================
    _____________________________________________ test_pymain_run_via_relpath ______________________________________________

        @gpython_only
        def test_pymain_run_via_relpath():
            argv = ['-c',  'import sys; print(sys.version)']
            out1 = pyout(                    argv, pyexe=sys.executable)
    >       out2 = pyout(['./__init__.py'] + argv, pyexe=sys._gpy_underlying_executable, cwd=here)

    gpython/gpython_test.py:301:
    _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
    golang/golang_test.py:1842: in pyout
        return pyrun(argv, stdin=stdin, stdout=stdout, stderr=stderr, **kw)
    _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

    argv = ['./__init__.py', '-c', 'import sys; print(sys.version)'], stdin = None, stdout = '', stderr = None
    kw = {'cwd': '/srv/slapgrid/slappart34/srv/runner/software/44fe7dd3f13ecd100894c6368a35c055/parts/pygolang-dev/gpython', 'pyexe': '/srv/slapgrid/slappart34/srv//runner//shared/python2.7/44578f5389723084b136574c34bc8023/bin/python2.7'}
    retcode = 1

        def pyrun(argv, stdin=None, stdout=None, stderr=None, **kw):
            retcode, stdout, stderr = _pyrun(argv, stdin=stdin, stdout=stdout, stderr=stderr, **kw)
            if retcode:
    >           raise RuntimeError(' '.join(argv) + '\n' + (stderr and str(stderr) or '(failed)'))
    E           RuntimeError: ./__init__.py -c import sys; print(sys.version)
    E           (failed)

    golang/golang_test.py:1836: RuntimeError
    ======================================= 1 failed, 114 deselected in 0.73 seconds =======================================

Fixes 076cdd8f (gpython: Fix crash when invoked as e.g. ./bin/gpython).

/reviewed-on !11

PyPy changed home from bitbucket to foss.heptapod recently[1]. The old
links on bitbucket no longer works. -> Update bitbucket links to their
correspondents on foss.heptapod.net .

[1] https://morepypy.blogspot.com/2020/02/pypy-and-cffi-have-moved-to-heptapod.html

PyPy2 implements -OO differently compared to CPython and it breaks zope.interfaces
at import time: https://foss.heptapod.net/pypy/pypy/-/issues/3356.

- Teach gpython and pymain about `-`;
- Teach gpython and pymain about -O;
- Teach pymain to always set sys.executable, so that subprocess and multiprocessing work correctly out of the box;
- Fix ./bin/gpython crash;
- Rewrite options parsing via incremental getopt-like thing.

This changes are motivated by nexedi/slapos!862 (comment 121470) and nexedi/slapos!862 (comment 121600).

/reviewed-by @jerome
/reviewed-on nexedi/pygolang!10

Reported by @jerome here:
nexedi/slapos!862 (comment 121738)

Let's teach gpython and pymain about -O because buildout calls `python -O`
to byte-compile python sources in optimized mode:

nexedi/slapos!862 (comment 121470)

When seeing -O, we take the approach to reexecute underlying python with
-O, so that e.g.

	gpython -O file.py

becomes executed as

	python -O gpython file.py

This ensures correctness. The same approach could be used to implement
support for e.g. -S and other low-level options.

An earlier attempt to implement -O without reexecution can be seen at

nexedi/pygolang!7

together with list of problems that arise via that way.

Original idea to reexecute itself come from @jerome.