general: add an adhoc test for checking mixin behaviour with namespace packages and __init__.py hack

also use that hack in my.fbmessenger

misc/check_legacy_init_py.py

@@ -59,7 +59,7 @@ check_warn('-c', 'from   my.fbmessenger import *')
 # note: dump_chat_history should really be deprecated, but it's a quick way to check we actually fell back to fbmessenger/export.py
 # NOTE: this is the most common legacy usecase
 check_warn('-c', 'from   my.fbmessenger import messages, dump_chat_history')
-check_warn('-m', 'my.core', 'query' , 'my.fbmessenger.messages')
+check_warn('-m', 'my.core', 'query' , 'my.fbmessenger.messages', '-o', 'pprint', '--limit=10')
 check_warn('-m', 'my.core', 'doctor', 'my.fbmessenger')
 
 # todo kinda annoying it doesn't work when executed as -c (but does as script!)
@@ -69,8 +69,14 @@ check_ok  ('-c', 'from   my.fbmessenger import export', run_as_cmd=False)
 check_ok  ('-c', 'import my.fbmessenger.export')
 check_ok  ('-c', 'from   my.fbmessenger.export import *')
 check_ok  ('-c', 'from my.fbmessenger.export import messages, dump_chat_history')
-check_ok  ('-m', 'my.core', 'query' , 'my.fbmessenger.export.messages')
+check_ok  ('-m', 'my.core', 'query' , 'my.fbmessenger.export.messages', '-o', 'pprint', '--limit=10')
 check_ok  ('-m', 'my.core', 'doctor', 'my.fbmessenger.export')
 
+# NOTE:
+# to check that overlays work, run something like
+# PYTHONPATH=misc/overlay_for_init_py_test/  hpi query my.fbmessenger.all.messages -s -o pprint --limit=10
+# you should see 1, 2, 3 from mixin.py
+# TODO would be nice to add an automated test for this
+
 # TODO with reddit, currently these don't work properly at all
 # only when imported from scripts etc?

misc/overlay_for_init_py_test/my/fbmessenger/all.py

@@ -0,0 +1,7 @@
+from my.fbmessenger import export
+from . import mixin
+
+
+def messages():
+    yield from mixin.messages()
+    yield from export.messages()

misc/overlay_for_init_py_test/my/fbmessenger/mixin.py

@@ -0,0 +1,2 @@
+def messages():
+    yield from ['1', '2', '3']

my/fbmessenger/__init__.py

@@ -57,3 +57,16 @@ REQUIRES = [
 
 # to prevent it from apprearing in modules list/doctor
 from ..core import __NOT_HPI_MODULE__
+
+###
+# this is to trick mypy into treating this as a proper namespace package
+# should only be used for backwards compatibility on packages that are convernted into namespace & all.py pattern
+# - https://www.python.org/dev/peps/pep-0382/#namespace-packages-today
+# - https://github.com/karlicoss/hpi_namespace_experiment
+# - discussion here https://memex.zulipchat.com/#narrow/stream/279601-hpi/topic/extending.20HPI/near/269946944
+from pkgutil import extend_path
+__path__ = extend_path(__path__, __name__)
+# 'this' source tree ends up first in the pythonpath when we extend_path()
+# so we need to move 'this' source tree towards the end to make sure we prioritize overlays
+__path__ = __path__[1:] + __path__[:1]
+###