Avoid marking more valid excuses as impossible.

Previously we could not reliably detect whether an excuse's dependency
from a source package to a binNMU was valid, as the excuse did not
contain sufficient information to determine the set of  architecture(s)
on which the dependency existed.

By modifying the representation of the dependency list in the excuse to
include an architecture list we can walk the relationships in reverse
in order to sanity-check the source -> binNMU dependency.

Signed-off-by: Adam D. Barratt <adam@adam-barratt.org.uk>

britney.py

@@ -1049,7 +1049,7 @@ class Britney:
                 # for the solving packages, update the excuse to add the dependencies
                 for p in packages:
                     if arch not in self.options.break_arches.split():
-                        excuse.add_dep(p)
+                        excuse.add_dep(p, arch)
                     else:
                         excuse.add_break_dep(p, arch)
 
@@ -1601,14 +1601,29 @@ class Britney:
             parts = e.name.split('/')
             for d in e.deps:
                 ok = False
+                # source -> source dependency; both packages must have
+                # valid excuses
                 if d in upgrade_me or d in unconsidered:
                     ok = True
                 # if the excuse is for a binNMU, also consider d/$arch as a
                 # valid excuse
-                if len(parts) == 2:
+                elif len(parts) == 2:
                     bd = '%s/%s' % (d, parts[1])
                     if bd in upgrade_me or bd in unconsidered:
                         ok = True
+                # if the excuse is for a source package, check each of the
+                # architectures on which the excuse lists a dependency on d,
+                # and consider the excuse valid if it is possible on each
+                # architecture
+                else:
+                    arch_ok = True
+                    for arch in e.deps[d]:
+                        bd = '%s/%s' % (d, arch)
+                        if bd not in upgrade_me and bd not in unconsidered:
+                            arch_ok = False
+                            break
+                    if arch_ok:
+                        ok = True
                 if not ok:
                     e.addhtml("Impossible dependency: %s -> %s" % (e.name, d))
         self.invalidate_excuses(upgrade_me, unconsidered)

excuse.py

@@ -53,7 +53,7 @@ class Excuse:
         self.dontinvalidate = 0
 
         self.invalid_deps = []
-        self.deps = []
+        self.deps = {}
         self.sane_deps = []
         self.break_deps = []
         self.unsat_deps = {}
@@ -85,9 +85,10 @@ class Excuse:
         """Set the urgency of upload of the package"""
         self.urgency = date
 
-    def add_dep(self, name):
+    def add_dep(self, name, arch):
         """Add a dependency"""
-        if name not in self.deps: self.deps.append(name)
+        if name not in self.deps: self.deps[name]=[]
+        self.deps[name].append(arch)
 
     def add_sane_dep(self, name):
         """Add a sane dependency"""