Conditional builds falls back on Python2 if needed

Falls back to python2 when tested recipes are python3crystax compatible.
This is for instance the case on kivy#1428 where the recipes depend only on
python2, hence couldn't be automatically tested.

Also updated `vispy` recipe to handle the version string properly,
pin it and clean comments.
This recipe is a demo case scenario for the conditional build falling
back on python2 since `vispy` is not yet compatible with python3crystax.

Author: AndreMiras

ci/rebuild_updated_recipes.py

@@ -25,6 +25,8 @@
 """
 import sh
 import os
+from pythonforandroid.build import Context
+from pythonforandroid.graph import get_recipe_order_and_bootstrap
 from pythonforandroid.toolchain import current_directory
 from ci.constants import TargetPython, CORE_RECIPES, BROKEN_RECIPES
 
@@ -77,11 +79,21 @@ def main():
     target_python = TargetPython.python3crystax
     recipes = modified_recipes()
     print('recipes modified:', recipes)
-    broken_recipes = BROKEN_RECIPES[target_python]
-    recipes = recipes - (CORE_RECIPES | broken_recipes)
+    recipes -= CORE_RECIPES
     print('recipes to build:', recipes)
+    context = Context()
+    build_order, python_modules, bs = get_recipe_order_and_bootstrap(
+        context, recipes, None)
+    # fallback to python2 if default target is not compatible
+    if target_python.name not in build_order:
+        print('incompatible with {}'.format(target_python.name))
+        target_python = TargetPython.python2
+        print('falling back to {}'.format(target_python.name))
+    # removing the known broken recipe for the given target
+    broken_recipes = BROKEN_RECIPES[target_python]
+    recipes -= broken_recipes
+    print('recipes to build (no broken):', recipes)
     build(target_python, recipes)
-    print(recipes)
 
 
 if __name__ == '__main__':

pythonforandroid/recipes/vispy/__init__.py

@@ -1,18 +1,10 @@
-
 from pythonforandroid.recipe import PythonRecipe
 
 
 class VispyRecipe(PythonRecipe):
-    # version = 'v0.4.0'
-    version = 'master'
-    url = 'https://github.com/vispy/vispy/archive/{version}.tar.gz'
-    # version = 'campagnola-scenegraph-update'
-    # url = 'https://github.com/campagnola/vispy/archive/scenegraph-update.zip'
-    # version = '???'
-    # url = 'https://github.com/inclement/vispy/archive/Eric89GXL-arcball.zip'
-
+    version = '0.4.0'
+    url = 'https://github.com/vispy/vispy/archive/v{version}.tar.gz'
     depends = ['python2', 'numpy', 'pysdl2']
-
     patches = ['disable_freetype.patch',
                'disable_font_triage.patch',
                'use_es2.patch',