pygolang: Accompany python-interpreter with gpython-interpreter to run gpython...

pygolang: Accompany python-interpreter with gpython-interpreter to run gpython instead of std python

With python-interpreter staying the default for pyprog, but possible to adjust.

We will need gpython-interpreter for ERP5 to use bstr+ustr as builting string types.

Remove [gpython] script in favour of gpython-interpreter since both provide the
same thing but via slightly different ways internally ([gpython] was generating
bin/gpython via setuptools and [gpython-interpreter] does it by hand with
user-visible result staying the same).

/cc @kazuhiko, @jerome

component/pygolang/buildout.cfg

@@ -8,7 +8,7 @@ extends =
 
 parts =
     pygolang
-    gpython
+    gpython-interpreter
 
 
 # pygolang is installed from git checkout
@@ -21,14 +21,6 @@ setup-eggs =
     setuptools-dso
     gevent
 
-# gpython program
-[gpython]
-recipe  = zc.recipe.egg:scripts
-eggs    = ${pygolang:egg}
-scripts = gpython
-# convenience for gpython users
-exe     = ${buildout:bin-directory}/gpython
-
 [pygolang-repository]
 recipe  = slapos.recipe.build:gitclone
 repository = https://lab.nexedi.com/nexedi/pygolang
@@ -63,6 +55,16 @@ scripts = ${:interpreter}
 exe     = ${buildout:bin-directory}/${:interpreter}
 
 
+# gpython-interpreter is like python-interpreter, but runs gpython instead of standard python.
+[gpython-interpreter]
+<= python-interpreter
+interpreter = gpython
+initialization =
+  from gpython import main
+  main()
+  sys.exit(0)
+
+
 # pyprog provides macro recipe to build python programs.
 #
 # Contrary to zc.recipe.egg:scripts it generates scripts that are run with
@@ -77,6 +79,13 @@ exe     = ${buildout:bin-directory}/${:interpreter}
 #   exe = ${buildout:bin-directory}/myprog
 #   entry = my.py.mod:main
 #   eggs = ...
+#
+# By default python interpreter defined in [python-interpreter] section is used
+# to run the program. The default can be adjusted as illustrated below:
+#
+#   [myprog]
+#   <= pyprog
+#   python-interpreter = gpython-interpreter  # set to name of the section that defines the interpreter
 [pyprog]
 recipe = slapos.recipe.build
 initialization =
@@ -88,6 +97,7 @@ init =
   entry  = options['entry']
   eggs   = options['eggs']
   pyinit = options['initialization']
+  pyinterpreter = options.get('python-interpreter', 'python-interpreter')
 
   options['depends'] += '$${.%s.pyprog:recipe}' % name
 
@@ -114,7 +124,7 @@ init =
 
   # .X.pyexe is python interpreter used by .X.pyprog
   [.%(name)s.pyexe]
-  <= python-interpreter
+  <= %(pyinterpreter)s
   eggs += %(__eggs)s
   interpreter = $${:_buildout_section_name_}
   """ % locals())