Use Excuse.is_valid when iterating through checks and Policies

This gives Policies the opportunity to see if a previous check
(build/installability) or earlier policies already invalidated the update. This
allows writing policies that work on groups of packages, or skipping expensive
checks (such as triggering autopkgtests while the package is not built or
installable yet).

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

britney.py

@@ -1489,9 +1489,6 @@ class Britney(object):
         source_u.maintainer and excuse.set_maint(source_u.maintainer)
         source_u.section and excuse.set_section(source_u.section)
 
-        # the starting point is that we will update the candidate
-        update_candidate = True
-        
         # if the version in unstable is older, then stop here with a warning in the excuse and return False
         if source_t and apt_pkg.version_compare(source_u.version, source_t.version) < 0:
             excuse.addhtml("ALERT: %s is newer in testing (%s %s)" % (src, source_t.version, source_u.version))
@@ -1499,10 +1496,13 @@ class Britney(object):
             excuse.addreason("newerintesting")
             return False
 
+        # the starting point is that we will update the candidate
+        excuse.is_valid = True
+
         # check if the source package really exists or if it is a fake one
         if source_u.is_fakesrc:
             excuse.addhtml("%s source package doesn't exist" % (src))
-            update_candidate = False
+            excuse.is_valid = False
 
         # if there is a `remove' hint and the requested version is the same as the
         # version in testing, then stop here and return False
@@ -1512,7 +1512,7 @@ class Britney(object):
                 excuse.add_hint(hint)
                 excuse.addhtml("Removal request by %s" % (hint.user))
                 excuse.addhtml("Trying to remove package, not update it")
-                update_candidate = False
+                excuse.is_valid = False
 
         # check if there is a `block' or `block-udeb' hint for this package, or a `block-all source' hint
         blocked = {}
@@ -1566,7 +1566,7 @@ class Britney(object):
                 else:
                     excuse.addhtml("NEEDS APPROVAL BY RM")
                     excuse.addreason("block")
-                update_candidate = False
+                excuse.is_valid = False
 
         # at this point, we check the status of the builds on all the supported architectures
         # to catch the out-of-date ones
@@ -1612,9 +1612,9 @@ class Britney(object):
                         # we would not need to be forgiving at
                         # all. However, due to how arch:all packages
                         # are handled, we do run into occasionally.
-                        update_candidate = False
+                        excuse.is_valid = False
 
-            # if there are out-of-date packages, warn about them in the excuse and set update_candidate
+            # if there are out-of-date packages, warn about them in the excuse and set excuse.is_valid
             # to False to block the update; if the architecture where the package is out-of-date is
             # in the `outofsync_arches' list, then do not block the update
             if oodbins:
@@ -1642,22 +1642,22 @@ class Britney(object):
                         if self.options.ignore_cruft:
                             text = text + " (but ignoring cruft, so nevermind)"
                         else:
-                            update_candidate = False
+                            excuse.is_valid = False
                     else:
-                        update_candidate = False
+                        excuse.is_valid = False
                         excuse.missing_build_on_arch(arch)
 
                 excuse.addhtml(text)
 
-        # if the source package has no binaries, set update_candidate to False to block the update
+        # if the source package has no binaries, set is_valid to False to block the update
         if not source_u.binaries:
             excuse.addhtml("%s has no binaries on any arch" % src)
             excuse.addreason("no-binaries")
-            update_candidate = False
+            excuse.is_valid = False
 
         # if the suite is unstable, then we have to check the urgency and the minimum days of
         # permanence in unstable before updating testing; if the source package is too young,
-        # the check fails and we set update_candidate to False to block the update; consider
+        # the check fails and we set is_valid to False to block the update; consider
         # the age-days hint, if specified for the package
         policy_info = excuse.policy_info
         policy_verdict = PolicyVerdict.PASS
@@ -1668,7 +1668,7 @@ class Britney(object):
                     policy_verdict = v
 
         if policy_verdict.is_rejected:
-            update_candidate = False
+            excuse.is_valid = False
 
         if suite in ('pu', 'tpu') and source_t:
             # o-o-d(ish) checks for (t-)p-u
@@ -1699,7 +1699,7 @@ class Britney(object):
                     text = text + " (but %s isn't keeping up, so never mind)" % (arch)
                     excuse.missing_build_on_ood_arch(arch)
                 else:
-                    update_candidate = False
+                    excuse.is_valid = False
                     excuse.missing_build_on_arch(arch)
 
                 excuse.addhtml(text)
@@ -1708,17 +1708,13 @@ class Britney(object):
         forces = self.hints.search('force', package=src, version=source_u.version)
         if forces:
             excuse.dontinvalidate = True
-        if not update_candidate and forces:
+        if not excuse.is_valid and forces:
             excuse.addhtml("Should ignore, but forced by %s" % (forces[0].user))
             excuse.force()
-            update_candidate = True
-
-        # if the package can be updated, it is a valid candidate
-        if update_candidate:
             excuse.is_valid = True
 
         self.excuses[excuse.name] = excuse
-        return update_candidate
+        return excuse.is_valid
 
     def reversed_exc_deps(self):
         """Reverse the excuses dependencies