Refactor _load_support_matrix

In the Sphinx extension, split up the _load_support_matrix method, so
its easier to understand the additions for the feature_classification
table.

Change-Id: Ic3654017f63dda2c2505057b0063acbc6d5f83c2

doc/ext/support_matrix.py

@@ -141,9 +141,17 @@ class SupportMatrixDirective(rst.Directive):
         env.note_dependency(rel_fpath)
 
         matrix = SupportMatrix()
+        matrix.targets = self._get_targets(cfg)
+        matrix.features = self._get_features(cfg, matrix.targets)
 
+        return matrix
+
+    def _get_targets(self, cfg):
         # The 'targets' section is special - it lists all the
         # hypervisors that this file records data for
+
+        targets = {}
+
         for item in cfg.options("targets"):
             if not item.startswith("driver-impl-"):
                 continue
@@ -174,10 +182,16 @@ class SupportMatrixDirective(rst.Directive):
                 raise Exception("'%s' field is malformed in '[%s]' section" %
                                 (item, "DEFAULT"))
 
-            matrix.targets[key] = target
+            targets[key] = target
 
+        return targets
+
+    def _get_features(self, cfg, targets):
         # All sections except 'targets' describe some feature of
         # the Nova hypervisor driver implementation
+
+        features = []
+
         for section in cfg.sections():
             if section == "targets":
                 continue
@@ -225,7 +239,7 @@ class SupportMatrixDirective(rst.Directive):
                     continue
 
                 key = item[12:]
-                if key not in matrix.targets:
+                if key not in targets:
                     raise Exception(
                         "Driver impl '%s' in '[%s]' not declared" %
                         (item, section))
@@ -242,19 +256,19 @@ class SupportMatrixDirective(rst.Directive):
                 if cfg.has_option(section, noteskey):
                     notes = cfg.get(section, noteskey)
 
-                target = matrix.targets[key]
+                target = targets[key]
                 impl = SupportMatrixImplementation(status,
                                                    notes)
                 feature.implementations[target.key] = impl
 
-            for key in matrix.targets:
+            for key in targets:
                 if key not in feature.implementations:
                     raise Exception("'%s' missing in '[%s]' section" %
                                     (target.key, section))
 
-            matrix.features.append(feature)
+            features.append(feature)
 
-        return matrix
+        return features
 
     def _build_markup(self, matrix):
         """Constructs the docutils content for the support matrix