bitbake: event: Add event for deferred inherits

Now that deferred inherits are extension specific, we can pass this
list to an event, which our metadata can use to set class overrides
earlier (as an example).

There are limitations to this, the list of classes is unexpanded and
recursive classes are not visible. There isn't much that can be done
about this, the ones we are interested in would usually be visible
at the top level (such as class extensions).

(Bitbake rev: 205d461c05fc7b4a7c81039af3bc3fd71cbb982c)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/lib/bb/parse/ast.py

@@ -471,6 +471,9 @@ def finalize(fn, d, variant = None):
         if d.getVar("_FAILPARSINGERRORHANDLED", False) == True:
             raise bb.BBHandledException()
 
+        inherits = [x[0] for x in (d.getVar('__BBDEFINHERITS', False) or [('',)])]
+        bb.event.fire(bb.event.RecipePreDeferredInherits(fn, inherits), d)
+
         while True:
             inherits = d.getVar('__BBDEFINHERITS', False) or []
             if not inherits: