autopkgtest: Extract some ("boring") loops into a function

When we convert legacy results in the autopkgtest-results.cache file,
we are only touching leaf results.  By moving the loops into a
function, we can remove 2-3 levels of ("redundant") nesting.  This in
turn makes it more clear what is relevant in the conversion.

This same also holds in save_state when we convert an Enum to a
string.

Signed-off-by: Niels Thykier <niels@thykier.net>

britney2/policies/autopkgtest.py

@@ -82,6 +82,12 @@ def added_pkgs_compared_to_target_suite(package_ids, target_suite, *, invert=Fal
     yield from (p for p in package_ids if p.package_name not in names_ignored)
 
 
+def all_leaf_results(test_results):
+    for trigger in test_results.values():
+        for arch in trigger.values():
+            yield from arch.values()
+
+
 class AutopkgtestPolicy(BasePolicy):
     """autopkgtest regression policy for source migrations
 
@@ -155,10 +161,8 @@ class AutopkgtestPolicy(BasePolicy):
         # read the cached results that we collected so far
         if os.path.exists(self.results_cache_file):
             with open(self.results_cache_file) as f:
-                results = json.load(f)
-                for trigger in results.values():
-                    for arch in trigger.values():
-                        for result in arch.values():
+                test_results = json.load(f)
+                for result in all_leaf_results(test_results):
                     try:
                         result[0] = Result[result[0]]
                     except KeyError:
@@ -175,7 +179,7 @@ class AutopkgtestPolicy(BasePolicy):
                             dummy = result[3]
                         except IndexError:
                             result.append(self._now)
-                self.test_results = results
+                self.test_results = test_results
             self.logger.info('Read previous results from %s', self.results_cache_file)
 
             # The cache can contain results against versions of packages that
@@ -305,13 +309,11 @@ class AutopkgtestPolicy(BasePolicy):
         # update the results on-disk cache, unless we are using a r/o shared one
         if not self.options.adt_shared_results_cache:
             self.logger.info('Updating results cache')
-            results = deepcopy(self.test_results)
-            for trigger in results.values():
-                for arch in trigger.values():
-                    for result in arch.values():
+            test_results = deepcopy(self.test_results)
+            for result in all_leaf_results(test_results):
                 result[0] = result[0].name
             with open(self.results_cache_file + '.new', 'w') as f:
-                json.dump(results, f, indent=2)
+                json.dump(test_results, f, indent=2)
             os.rename(self.results_cache_file + '.new', self.results_cache_file)
 
         # update the pending tests on-disk cache