Completely remove MetaElement

This dramatically affects the load process and removes one
hoop we had to jump through, which is the creation of the extra
intermediate MetaElement objects.

This allows us to more easily carry state discovered by the Loader
over to the Element constructor, as we need not add additional state
to the intermediate MetaElement for this. Instead we have the Element
initializer understand the LoadElement directly.

Summary of changes:

  * _loader/metaelement.py: Removed

  * _loader/loadelement.py: Added some attributes previously required on
    MetaElement

  * _loader/loader.py: Removed _collect_element() and collect_element_no_deps(),
    removing the process of Loader.load() which translates LoadElements into
    MetaElements completely.

  * _loader/init.py: Export LoadElement, Dependency and Symbol types, stop
    exporting MetaElement

  * _loader/metasource.py: Now take the 'first_pass' parameter as an argument

  * _artifactelement.py: Use a virtual LoadElement instead of a virtual
    MetaElement to instantiate the ArtifactElement objects.

  * _pluginfactory/elementfactory.py: Adjust to now take a LoadElement

  * _project.py: Adjust Project.create_element() to now take a LoadElement,
    and call the new Element._new_from_load_element() instead of the
    old Element._new_from_meta() function

  * element.py:

    - Now export Element._new_from_load_element() instead of Element._new_from_meta()

    - Adjust the constructor to do the LoadElement toplevel node parsing instead
      of expecting members on the MetaElement object

    - Added __load_sources() which parses out and creates MetaSource objects
      for the sake of instantiating the element's Source objects. Consequently
      this simplifies the scenario where workspaces are involved.

  * source.py: Adjusted to use the new `first_pass` parameter to MetaSource when
    creating a duplicate clone.

1 files changed, 2 insertions, 2 deletions

diff --git a/tests/internals/loader.py b/tests/internals/loader.py
index bdce428f0..2da01723b 100644
--- a/tests/internals/loader.py
+++ b/tests/internals/loader.py
@@ -5,7 +5,7 @@ import pytest
 from buildstream.exceptions import LoadErrorReason
 from buildstream._exceptions import LoadError
 from buildstream._project import Project
-from buildstream._loader import MetaElement
+from buildstream._loader import LoadElement
 
 from tests.testutils import dummy_context
 
@@ -30,7 +30,7 @@ def test_one_file(datafiles):
     with make_loader(basedir) as loader:
         element = loader.load(["elements/onefile.bst"])[0]
 
-        assert isinstance(element, MetaElement)
+        assert isinstance(element, LoadElement)
         assert element.kind == "pony"