Fix #3796: env.resolve_references() crashes when non-document node given

CHANGES

@@ -28,6 +28,7 @@ Bugs fixed
 * #3772: 'str object' has no attribute 'filename'
 * #3763: got epubcheck validations error if epub_cover is set
 * #3779: 'ImportError' in sphinx.ext.autodoc due to broken 'sys.meta_path'
+* #3796: env.resolve_references() crashes when non-document node given
 
 Testing
 --------

sphinx/environment/__init__.py

@@ -943,10 +943,9 @@ class BuildEnvironment(object):
         try:
             # set env.docname during applying post-transforms
             self.temp_data['docname'] = docname
-            if hasattr(doctree, 'settings'):
-                doctree.settings.env = self
 
             transformer = SphinxTransformer(doctree)
+            transformer.set_environment(self)
             transformer.add_transforms(self.app.post_transforms)
             transformer.apply_transforms()
         finally:

sphinx/transforms/__init__.py

@@ -85,6 +85,9 @@ class SphinxTransformer(Transformer):
     def apply_transforms(self):
         # type: () -> None
         if isinstance(self.document, nodes.document):
+            if hasattr(self.document.settings, 'env') and self.env:
+                self.document.settings.env = self.env
+
             Transformer.apply_transforms(self)
         else:
             # wrap the target node by document node during transforming