repos: Form the basic chroots and cache them

This way, we'll take into account the dependencies
on the packages from the base environment when
sorting the package set topologically.

repos_cmp/repos.py

@@ -32,6 +32,11 @@ class Dependency(collections.namedtuple(
                         | rpm.RPMSENSE_GREATER
                         | rpm.RPMSENSE_LESS)
 
+    @classmethod
+    def from_names(cls, names):
+        for name in names:
+            yield cls(name, 0, None)
+
     @classmethod
     def from_header(cls, header, kind):
         tp, tf, tv = cls.HEADER_TRIPLETS[kind]
@@ -162,9 +167,20 @@ class Chroot:
         return any(p.is_provide_for(dep)
                    for p in self.provides.get(dep.name, ()))
 
+    def copy(self):
+        copy = Chroot()
+        copy.provides = self.provides.copy()
+        copy.binaries = self.binaries.copy()
+        return copy
+
 
 # consider this repository components by default
 DEFAULT_COMPONENTS = ('classic', 'checkinstall')
+PKG_INIT_LIST = tuple(Dependency.from_names(
+    (b'setup',  b'filesystem',  b'rpm', b'fakeroot')))
+PKG_BUILD_LIST = tuple(Dependency.from_names(
+    (b'basesystem', b'rpm-build', b'kernel-headers-common',
+     b'sisyphus_check', b'time')))
 
 
 class Repository:
@@ -177,6 +193,9 @@ class Repository:
         self.reverse_prov = {}  # name -> [(provide, binary)]
         self.addon = None
         self.reverse_prov_addon = {}
+        self.base_chroot = None
+        self.build_chroot = None
+
         self.update_indexes()
 
     def copy(self, new_name):
@@ -198,6 +217,10 @@ class Repository:
     def update_indexes(self):
         self.reverse_prov = self._reverse_provides_index(self.binaries)
         self.reverse_prov_addon = self._reverse_provides_index(self.addon)
+        self.base_chroot = None
+        self.build_chroot = None
+        self.base_chroot = self.chroot_for(PKG_INIT_LIST, build=False)
+        self.build_chroot = self.chroot_for(PKG_BUILD_LIST, build=False)
 
     @classmethod
     def load(cls, repo_name, path, arch, components=DEFAULT_COMPONENTS):
@@ -271,10 +294,18 @@ class Repository:
             del self.binaries[name]
         self.update_indexes()
 
-    def chroot_for(self, requires, prefer=()):
-        stack = list(reversed(list(requires)))
-        chroot = Chroot()
+    def chroot_for(self, requires, prefer=(), build=True):
+        prefer = list(prefer)
+        # rudimentary pkgpriorities
+        prefer.append(b'altlinux-release-sisyphus')
 
+        base_chroot = self.build_chroot if build else self.base_chroot
+        if base_chroot is not None:
+            chroot = base_chroot.copy()
+        else:
+            chroot = Chroot()
+
+        stack = list(reversed(list(requires)))
         while stack:
             dep = stack.pop()
             if chroot.is_provided(dep):