zeroinstall/injector/solver.py

   1 """
   2 Chooses a set of components to make a running program.
   3 """
   4
   5 # Copyright (C) 2009, Thomas Leonard
   6 # See the README file for details, or visit http://0install.net.
   7
   8 from zeroinstall import _
   9 import locale
  10 from logging import debug, warn, info
  11
  12 from zeroinstall.injector.reader import MissingLocalFeed
  13 from zeroinstall.injector import model, sat, selections, arch
  14
  15 class CommandInfo:
  16         def __init__(self, name, command, impl, arch):
  17                 self.name = name
  18                 self.command = command
  19                 self.impl = impl
  20                 self.arch = arch
  21
  22         def __repr__(self):
  23                 name = "%s_%s_%s_%s" % (self.impl.feed.get_name(), self.impl.get_version(), self.impl.arch, self.name)
  24                 return name.replace('-', '_').replace('.', '_')
  25
  26 class ImplInfo:
  27         is_dummy = False
  28
  29         def __init__(self, iface, impl, arch, dummy = False):
  30                 self.iface = iface
  31                 self.impl = impl
  32                 self.arch = arch
  33                 if dummy:
  34                         self.is_dummy = True
  35
  36         def __repr__(self):
  37                 name = "%s_%s_%s" % (self.impl.feed.get_name(), self.impl.get_version(), self.impl.arch)
  38                 return name.replace('-', '_').replace('.', '_')
  39
  40 class _DummyImpl(object):
  41         requires = []
  42         version = None
  43         arch = None
  44         commands = {}
  45
  46         def __repr__(self):
  47                 return "dummy"
  48
  49         feed = property(lambda self: self)
  50
  51         def get_version(self):
  52                 return "dummy"
  53
  54         def get_name(self):
  55                 return "dummy"
  56
  57 class _ForceImpl(model.Restriction):
  58         """Used by L{SATSolver.justify_decision}."""
  59
  60         def __init__(self, impl_id):
  61                 self.impl_id = impl_id
  62
  63         def meets_restriction(self, impl):
  64                 return impl.id == self.impl_id
  65
  66 class Solver(object):
  67         """Chooses a set of implementations to satisfy the requirements of a program and its user.
  68         Typical use:
  69          1. Create a Solver object and configure it
  70          2. Call L{solve}.
  71          3. If any of the returned feeds_used are stale or missing, you may like to start downloading them
  72          4. If it is 'ready' then you can download and run the chosen versions.
  73         @ivar selections: the chosen implementation of each interface
  74         @type selections: L{selections.Selections}
  75         @ivar requires: the selected dependencies for each chosen version
  76         @type requires: {L{model.Interface}: [L{model.Dependency}]}
  77         @ivar feeds_used: the feeds which contributed to the choice in L{selections}
  78         @type feeds_used: set(str)
  79         @ivar record_details: whether to record information about unselected implementations
  80         @type record_details: {L{Interface}: [(L{Implementation}, str)]}
  81         @ivar details: extra information, if record_details mode was used
  82         @type details: {str: [(Implementation, comment)]}
  83         """
  84         __slots__ = ['selections', 'requires', 'feeds_used', 'details', 'record_details', 'ready']
  85
  86         def __init__(self):
  87                 self.selections = self.requires = self.feeds_used = self.details = None
  88                 self.record_details = False
  89                 self.ready = False
  90
  91         def solve_for(self, requirements):
  92                 """Solve for given requirements.
  93                 @param requirements: the interface, architecture and command to solve for
  94                 @type requirements: L{requirements.Requirements}
  95                 @postcondition: self.ready, self.selections and self.feeds_used are updated
  96                 @since: 1.8"""
  97                 return self.solve(requirements.interface_uri, self.get_arch_for(requirements), requirements.command)
  98
  99         def solve(self, root_interface, root_arch, command_name = 'run'):
 100                 """Get the best implementation of root_interface and all of its dependencies.
 101                 @param root_interface: the URI of the program to be solved
 102                 @type root_interface: str
 103                 @param root_arch: the desired target architecture
 104                 @type root_arch: L{arch.Architecture}
 105                 @param command_name: which <command> element to select
 106                 @type command_name: str | None
 107                 @postcondition: self.ready, self.selections and self.feeds_used are updated"""
 108                 raise NotImplementedError("Abstract")
 109
 110         def get_arch_for(self, requirements, interface = None):
 111                 """Return the Architecture we would use when solving for this interface.
 112                 Normally, this architecture is constructed from the OS and CPU type in the requirements,
 113                 using the host platform's settings if these are not given.
 114                 If interface is the root, then we wrap this in a SourceArchitecture if looking
 115                 for source code and (for backwards compatibility) we enable use="testing" dependencies
 116                 if the command is "test".
 117                 @param requirements: the overall requirements for the solve
 118                 @type requirements: L{requirements.Requirements}
 119                 @param interface: the interface of interest
 120                 @type interface: L{model.Interface}
 121                 @return: the architecture that would be used
 122                 @rtype: L{architecture.Architecture}
 123                 @since: 1.9"""
 124                 root_arch = arch.get_architecture(requirements.os, requirements.cpu)
 125                 if interface is None or interface.uri == requirements.interface_uri:
 126                         if requirements.source:
 127                                 root_arch = arch.SourceArchitecture(root_arch)
 128                         if requirements.command == 'test':
 129                                 # This is for old feeds that have use='testing' instead of the newer
 130                                 # 'test' command for giving test-only dependencies.
 131                                 root_arch = arch.Architecture(root_arch.os_ranks, root_arch.machine_ranks)
 132                                 root_arch.use = frozenset([None, "testing"])
 133                         return root_arch
 134                 # Assume we use the same arch for all descendants
 135                 return root_arch.child_arch
 136
 137 class SATSolver(Solver):
 138         """Converts the problem to a set of pseudo-boolean constraints and uses a PB solver to solve them.
 139         @ivar langs: the preferred languages (e.g. ["es_ES", "en"]). Initialised to the current locale.
 140         @type langs: str"""
 141
 142         __slots__ = ['_failure_reason', 'config', 'extra_restrictions', '_lang_ranks', '_langs']
 143
 144         @property
 145         def iface_cache(self):
 146                 return self.config.iface_cache  # (deprecated; used by 0compile)
 147
 148         def __init__(self, config, extra_restrictions = None):
 149                 """
 150                 @param config: policy preferences (e.g. stability), the iface_cache and the stores to use
 151                 @type config: L{policy.Config}
 152                 @param extra_restrictions: extra restrictions on the chosen implementations
 153                 @type extra_restrictions: {L{model.Interface}: [L{model.Restriction}]}
 154                 """
 155                 Solver.__init__(self)
 156                 assert not isinstance(config, str), "API change!"
 157                 self.config = config
 158                 self.extra_restrictions = extra_restrictions or {}
 159
 160                 # By default, prefer the current locale's language first and English second
 161                 self.langs = [locale.getlocale()[0] or 'en', 'en']
 162
 163         def set_langs(self, langs):
 164                 """Set the preferred languages.
 165                 @param langs: languages (and regions), first choice first
 166                 @type langs: [str]
 167                 """
 168                 # _lang_ranks is a map from locale string to score (higher is better)
 169                 _lang_ranks = {}
 170                 score = 0
 171                 i = len(langs)
 172                 # (is there are duplicates, the first occurance takes precedence)
 173                 while i > 0:
 174                         i -= 1
 175                         lang = langs[i].replace('_', '-')
 176                         _lang_ranks[lang.split('-')[0]] = score
 177                         _lang_ranks[lang] = score + 1
 178                         score += 2
 179                 self._langs = langs
 180                 self._lang_ranks = _lang_ranks
 181
 182         langs = property(lambda self: self._langs, set_langs)
 183
 184         def get_rating(self, interface, impl, arch):
 185                 impl_langs = (impl.langs or 'en').split()
 186                 my_langs = self._lang_ranks
 187
 188                 stores = self.config.stores
 189                 is_available = impl.is_available(stores)
 190
 191                 # Stability
 192                 stab_policy = interface.stability_policy
 193                 if not stab_policy:
 194                         if self.config.help_with_testing: stab_policy = model.testing
 195                         else: stab_policy = model.stable
 196
 197                 stability = impl.get_stability()
 198                 if stability >= stab_policy:
 199                         stability_limited = model.preferred
 200                 else:
 201                         stability_limited = stability
 202
 203                 # Note: this list must match _ranking_component_reason above
 204                 return [
 205                         # Languages we understand come first
 206                         max(my_langs.get(l.split('-')[0], -1) for l in impl_langs),
 207
 208                         # Preferred versions come first
 209                         stability == model.preferred,
 210
 211                         # Prefer available implementations next if we have limited network access
 212                         self.config.network_use != model.network_full and is_available,
 213
 214                         # Packages that require admin access to install come last
 215                         not impl.requires_root_install,
 216
 217                         # Prefer more stable versions, but treat everything over stab_policy the same
 218                         # (so we prefer stable over testing if the policy is to prefer "stable", otherwise
 219                         # we don't care)
 220                         stability_limited,
 221
 222                         # Newer versions come before older ones (ignoring modifiers)
 223                         impl.version[0],
 224
 225                         # Prefer native packages if the main part of the versions are the same
 226                         impl.id.startswith('package:'),
 227
 228                         # Full version compare (after package check, since comparing modifiers between native and non-native
 229                         # packages doesn't make sense).
 230                         impl.version,
 231
 232                         # Get best OS
 233                         -arch.os_ranks.get(impl.os, 999),
 234
 235                         # Get best machine
 236                         -arch.machine_ranks.get(impl.machine, 999),
 237
 238                         # Slightly prefer languages specialised to our country
 239                         # (we know a and b have the same base language at this point)
 240                         max(my_langs.get(l, -1) for l in impl_langs),
 241
 242                         # Slightly prefer cached versions
 243                         is_available,
 244
 245                         # Order by ID so the order isn't random
 246                         impl.id
 247                 ]
 248
 249         def solve(self, root_interface, root_arch, command_name = 'run', closest_match = False):
 250                 # closest_match is used internally. It adds a lowest-ranked
 251                 # by valid implementation to every interface, so we can always
 252                 # select something. Useful for diagnostics.
 253
 254                 # The basic plan is this:
 255                 # 1. Scan the root interface and all dependencies recursively, building up a SAT problem.
 256                 # 2. Solve the SAT problem. Whenever there are multiple options, try the most preferred one first.
 257                 # 3. Create a Selections object from the results.
 258                 #
 259                 # All three involve recursively walking the tree in a similar way:
 260                 # 1) we follow every dependency of every implementation (order not important)
 261                 # 2) we follow every dependency of every selected implementation (better versions first)
 262                 # 3) we follow every dependency of every selected implementation (order doesn't matter)
 263                 #
 264                 # In all cases, a dependency may be on an <implementation> or on a specific <command>.
 265
 266                 # TODO: We need some way to figure out which feeds to include.
 267                 # Currently, we include any feed referenced from anywhere but
 268                 # this is probably too much. We could insert a dummy optimial
 269                 # implementation in stale/uncached feeds and see whether it
 270                 # selects that.
 271                 iface_cache = self.config.iface_cache
 272
 273                 problem = sat.SATProblem()
 274
 275                 impl_to_var = {}        # Impl -> sat var
 276                 self.feeds_used = set()
 277                 self.requires = {}
 278                 self.ready = False
 279                 self.details = self.record_details and {}
 280
 281                 self.selections = None
 282                 self._failure_reason = None
 283
 284                 ifaces_processed = set()
 285
 286                 machine_groups = arch.machine_groups
 287                 impls_for_machine_group = {0 : []}              # Machine group (e.g. "64") to [impl] in that group
 288                 for machine_group in machine_groups.values():
 289                         impls_for_machine_group[machine_group] = []
 290
 291                 impls_for_iface = {}    # Iface -> [impl]
 292
 293                 # For each interface, the group clause says we can't select two implementations of it at once.
 294                 # We use this map at the end to find out what was actually selected.
 295                 group_clause_for = {}   # Iface URI -> AtMostOneClause
 296                 group_clause_for_command = {}   # (Iface URI, command name) -> AtMostOneClause | bool
 297
 298                 # Return the dependencies of impl that we should consider.
 299                 # Skips dependencies if the use flag isn't what we need.
 300                 # (note: impl may also be a model.Command)
 301                 def deps_in_use(impl, arch):
 302                         for dep in impl.requires:
 303                                 use = dep.metadata.get("use", None)
 304                                 if use not in arch.use:
 305                                         continue
 306                                 yield dep
 307
 308                 # Must have already done add_iface on dependency.interface.
 309                 # If dependency is essential:
 310                 #   Add a clause so that if requiring_impl_var is True then an implementation
 311                 #   matching 'dependency' must also be selected.
 312                 # If dependency is optional:
 313                 #   Require that no incompatible version is selected.
 314                 # This ignores any 'command' required. Handle that separately.
 315                 def find_dependency_candidates(requiring_impl_var, dependency):
 316                         def meets_restrictions(candidate):
 317                                 for r in dependency.restrictions:
 318                                         if not r.meets_restriction(candidate):
 319                                                 #warn("%s rejected due to %s", candidate.get_version(), r)
 320                                                 return False
 321                                 return True
 322
 323                         essential = dependency.importance == model.Dependency.Essential
 324
 325                         dep_iface = iface_cache.get_interface(dependency.interface)
 326                         dep_union = [sat.neg(requiring_impl_var)]       # Either requiring_impl_var is False, or ...
 327                         for candidate in impls_for_iface[dep_iface]:
 328                                 if (candidate.__class__ is _DummyImpl) or meets_restrictions(candidate):
 329                                         if essential:
 330                                                 c_var = impl_to_var.get(candidate, None)
 331                                                 if c_var is not None:
 332                                                         dep_union.append(c_var)
 333                                                 # else we filtered that version out, so ignore it
 334                                 else:
 335                                         # Candidate doesn't meet our requirements
 336                                         # If the dependency is optional add a rule to make sure we don't
 337                                         # select this candidate.
 338                                         # (for essential dependencies this isn't necessary because we must
 339                                         # select a good version and we can't select two)
 340                                         if not essential:
 341                                                 c_var = impl_to_var.get(candidate, None)
 342                                                 if c_var is not None:
 343                                                         problem.add_clause(dep_union + [sat.neg(c_var)])
 344                                                 # else we filtered that version out, so ignore it
 345
 346                         if essential:
 347                                 problem.add_clause(dep_union)
 348
 349                 def is_unusable(impl, restrictions, arch):
 350                         """@return: whether this implementation is unusable.
 351                         @rtype: bool"""
 352                         return get_unusable_reason(impl, restrictions, arch) != None
 353
 354                 def get_unusable_reason(impl, restrictions, arch):
 355                         """
 356                         @param impl: Implementation to test.
 357                         @type restrictions: [L{model.Restriction}]
 358                         @return: The reason why this impl is unusable, or None if it's OK.
 359                         @rtype: str
 360                         @note: The restrictions are for the interface being requested, not the feed
 361                         of the implementation; they may be different when feeds are being used."""
 362                         for r in restrictions:
 363                                 if not r.meets_restriction(impl):
 364                                         return _("Incompatible with another selected implementation")
 365                         stability = impl.get_stability()
 366                         if stability <= model.buggy:
 367                                 return stability.name
 368                         if (self.config.network_use == model.network_offline or not impl.download_sources) and not impl.is_available(self.config.stores):
 369                                 if not impl.download_sources:
 370                                         return _("No retrieval methods")
 371                                 return _("Not cached and we are off-line")
 372                         if impl.os not in arch.os_ranks:
 373                                 return _("Unsupported OS")
 374                         if impl.machine not in arch.machine_ranks:
 375                                 if impl.machine == 'src':
 376                                         return _("Source code")
 377                                 elif 'src' in arch.machine_ranks:
 378                                         return _("Not source code")
 379                                 return _("Unsupported machine type")
 380                         return None
 381
 382                 def usable_feeds(iface, arch):
 383                         """Return all feeds for iface that support arch.
 384                         @rtype: generator(ZeroInstallFeed)"""
 385                         yield iface.uri
 386
 387                         for f in iface_cache.get_feed_imports(iface):
 388                                 # Note: when searching for src, None is not in machine_ranks
 389                                 if f.os in arch.os_ranks and \
 390                                    (f.machine is None or f.machine in arch.machine_ranks):
 391                                         yield f.uri
 392                                 else:
 393                                         debug(_("Skipping '%(feed)s'; unsupported architecture %(os)s-%(machine)s"),
 394                                                 {'feed': f, 'os': f.os, 'machine': f.machine})
 395
 396                 # If requiring_var is True then all of requirer's dependencies must be satisfied.
 397                 # requirer can be a <command> or an <implementation>
 398                 def process_dependencies(requiring_var, requirer, arch):
 399                         for d in deps_in_use(requirer, arch):
 400                                 debug(_("Considering command dependency %s"), d)
 401
 402                                 add_iface(d.interface, arch.child_arch)
 403
 404                                 for c in d.get_required_commands():
 405                                         # We depend on a specific command within the implementation.
 406                                         command_vars = add_command_iface(d.interface, arch.child_arch, c)
 407
 408                                         # If the parent command/impl is chosen, one of the candidate commands
 409                                         # must be too. If there aren't any, then this command is unselectable.
 410                                         problem.add_clause([sat.neg(requiring_var)] + command_vars)
 411
 412                                 # Must choose one version of d if impl is selected
 413                                 find_dependency_candidates(requiring_var, d)
 414
 415                 def add_iface(uri, arch):
 416                         """Name implementations from feed and assert that only one can be selected."""
 417                         if uri in ifaces_processed: return
 418                         ifaces_processed.add(uri)
 419
 420                         iface = iface_cache.get_interface(uri)
 421
 422                         impls = []
 423                         for f in usable_feeds(iface, arch):
 424                                 self.feeds_used.add(f)
 425                                 debug(_("Processing feed %s"), f)
 426
 427                                 try:
 428                                         feed = iface_cache.get_feed(f)
 429                                         if feed is None: continue
 430                                         #if feed.name and iface.uri != feed.url and iface.uri not in feed.feed_for:
 431                                         #       info(_("Missing <feed-for> for '%(uri)s' in '%(feed)s'"), {'uri': iface.uri, 'feed': f})
 432
 433                                         if feed.implementations:
 434                                                 impls.extend(feed.implementations.values())
 435
 436                                         distro_feed_url = feed.get_distro_feed()
 437                                         if distro_feed_url:
 438                                                 self.feeds_used.add(distro_feed_url)
 439                                                 distro_feed = iface_cache.get_feed(distro_feed_url)
 440                                                 if distro_feed.implementations:
 441                                                         impls.extend(distro_feed.implementations.values())
 442                                 except MissingLocalFeed as ex:
 443                                         warn(_("Missing local feed; if it's no longer required, remove it with:") +
 444                                                         '\n0install remove-feed ' + iface.uri + ' ' + f,
 445                                                 {'feed': f, 'interface': iface, 'exception': ex})
 446                                 except Exception as ex:
 447                                         warn(_("Failed to load feed %(feed)s for %(interface)s: %(exception)s"), {'feed': f, 'interface': iface, 'exception': ex})
 448                                         #raise
 449
 450                         impls.sort(key = lambda impl: self.get_rating(iface, impl, arch), reverse = True)
 451
 452                         impls_for_iface[iface] = filtered_impls = []
 453
 454                         my_extra_restrictions = self.extra_restrictions.get(iface, [])
 455
 456                         if self.record_details:
 457                                 self.details[iface] = [(impl, get_unusable_reason(impl, my_extra_restrictions, arch)) for impl in impls]
 458
 459                         var_names = []
 460                         for impl in impls:
 461                                 if is_unusable(impl, my_extra_restrictions, arch):
 462                                         continue
 463
 464                                 filtered_impls.append(impl)
 465
 466                                 assert impl not in impl_to_var
 467                                 v = problem.add_variable(ImplInfo(iface, impl, arch))
 468                                 impl_to_var[impl] = v
 469                                 var_names.append(v)
 470
 471                                 if impl.machine and impl.machine != 'src':
 472                                         impls_for_machine_group[machine_groups.get(impl.machine, 0)].append(v)
 473
 474                                 process_dependencies(v, impl, arch)
 475
 476                         if closest_match:
 477                                 dummy_impl = _DummyImpl()
 478                                 dummy_var = problem.add_variable(ImplInfo(iface, dummy_impl, arch, dummy = True))
 479                                 var_names.append(dummy_var)
 480                                 impl_to_var[dummy_impl] = dummy_var
 481                                 filtered_impls.append(dummy_impl)
 482
 483                         # Only one implementation of this interface can be selected
 484                         if uri == root_interface:
 485                                 if var_names:
 486                                         clause = problem.at_most_one(var_names)
 487                                         problem.add_clause(var_names)   # at least one
 488                                 else:
 489                                         problem.impossible()
 490                                         clause = False
 491                         elif var_names:
 492                                 clause = problem.at_most_one(var_names)
 493                         else:
 494                                 # Don't need to add to group_clause_for because we should
 495                                 # never get a possible selection involving this.
 496                                 return
 497
 498                         assert clause is not True
 499                         assert clause is not None
 500                         if clause is not False:
 501                                 group_clause_for[uri] = clause
 502
 503                 def add_command_iface(uri, arch, command_name):
 504                         """Add every <command> in interface 'uri' with this name.
 505                         Each one depends on the corresponding implementation and only
 506                         one can be selected. If closest_match is on, include a dummy
 507                         command that can always be selected."""
 508
 509                         # Check whether we've already processed this (interface,command) pair
 510                         existing = group_clause_for_command.get((uri, command_name), None)
 511                         if existing is not None:
 512                                 return existing.lits
 513
 514                         # First ensure that the interface itself has been processed
 515                         # We'll reuse the ordering of the implementations to order
 516                         # the commands too.
 517                         add_iface(uri, arch)
 518
 519                         iface = iface_cache.get_interface(uri)
 520                         filtered_impls = impls_for_iface[iface]
 521
 522                         var_names = []
 523                         for impl in filtered_impls:
 524                                 command = impl.commands.get(command_name, None)
 525                                 if not command:
 526                                         if not isinstance(impl, _DummyImpl):
 527                                                 # Mark implementation as unselectable
 528                                                 problem.add_clause([sat.neg(impl_to_var[impl])])
 529                                         continue
 530
 531                                 # We have a candidate <command>. Require that if it's selected
 532                                 # then we select the corresponding <implementation> too.
 533                                 command_var = problem.add_variable(CommandInfo(command_name, command, impl, arch))
 534                                 problem.add_clause([impl_to_var[impl], sat.neg(command_var)])
 535
 536                                 var_names.append(command_var)
 537
 538                                 process_dependencies(command_var, command, arch)
 539
 540                         # Tell the user why we couldn't use this version
 541                         if self.record_details:
 542                                 def new_reason(impl, old_reason):
 543                                         if command_name in impl.commands:
 544                                                 return old_reason
 545                                         return old_reason or (_('No %s command') % command_name)
 546                                 self.details[iface] = [(impl, new_reason(impl, reason)) for (impl, reason) in self.details[iface]]
 547
 548                         if closest_match:
 549                                 dummy_command = problem.add_variable(None)
 550                                 var_names.append(dummy_command)
 551
 552                         if var_names:
 553                                 # Can't select more than one of them.
 554                                 assert (uri, command_name) not in group_clause_for_command
 555                                 group_clause_for_command[(uri, command_name)] = problem.at_most_one(var_names)
 556
 557                         return var_names
 558
 559                 if command_name is None:
 560                         add_iface(root_interface, root_arch)
 561                 else:
 562                         commands = add_command_iface(root_interface, root_arch, command_name)
 563                         if len(commands) > int(closest_match):
 564                                 # (we have at least one non-dummy command)
 565                                 problem.add_clause(commands)            # At least one
 566                         else:
 567                                 # (note: might be because we haven't cached it yet)
 568                                 info("No %s <command> in %s", command_name, root_interface)
 569
 570                                 impls = impls_for_iface[iface_cache.get_interface(root_interface)]
 571                                 if impls == [] or (len(impls) == 1 and isinstance(impls[0], _DummyImpl)):
 572                                         # There were no candidates at all.
 573                                         if self.config.network_use == model.network_offline:
 574                                                 self._failure_reason = _("Interface '%s' has no usable implementations in the cache (and 0install is in off-line mode)") % root_interface
 575                                         else:
 576                                                 self._failure_reason = _("Interface '%s' has no usable implementations") % root_interface
 577                                 else:
 578                                         # We had some candidates implementations, but none for the command we need
 579                                         self._failure_reason = _("Interface '%s' cannot be executed directly; it is just a library "
 580                                                     "to be used by other programs (or missing '%s' command)") % (root_interface, command_name)
 581
 582                                 problem.impossible()
 583
 584                 # Require m<group> to be true if we select an implementation in that group
 585                 m_groups = []
 586                 for machine_group, impls in impls_for_machine_group.items():
 587                         m_group = 'm%d' % machine_group
 588                         group_var = problem.add_variable(m_group)
 589                         if impls:
 590                                 for impl in impls:
 591                                         problem.add_clause([group_var, sat.neg(impl)])
 592                         m_groups.append(group_var)
 593                 if m_groups:
 594                         m_groups_clause = problem.at_most_one(m_groups)
 595                 else:
 596                         m_groups_clause = None
 597
 598                 def decide():
 599                         """This is called by the SAT solver when it cannot simplify the problem further.
 600                         Our job is to find the most-optimal next selection to try.
 601                         Recurse through the current selections until we get to an interface with
 602                         no chosen version, then tell the solver to try the best version from that."""
 603
 604                         def find_undecided_dep(impl_or_command, arch):
 605                                 # Check for undecided dependencies of impl_or_command
 606                                 for dep in deps_in_use(impl_or_command, arch):
 607                                         # Restrictions don't express that we do or don't want the
 608                                         # dependency, so skip them here.
 609                                         if dep.importance == model.Dependency.Restricts: continue
 610
 611                                         for c in dep.get_required_commands():
 612                                                 dep_lit = find_undecided_command(dep.interface, c)
 613                                                 if dep_lit is not None:
 614                                                         return dep_lit
 615                                         dep_lit = find_undecided(dep.interface)
 616                                         if dep_lit is not None:
 617                                                 return dep_lit
 618                                 return None
 619
 620                         seen = set()
 621                         def find_undecided(uri):
 622                                 if uri in seen:
 623                                         return  # Break cycles
 624                                 seen.add(uri)
 625
 626                                 group = group_clause_for.get(uri, None)
 627
 628                                 if group is None:
 629                                         # (can be None if the selected impl has an optional dependency on
 630                                         # a feed with no implementations)
 631                                         return
 632
 633                                 #print "Group for %s = %s" % (uri, group)
 634                                 lit = group.current
 635                                 if lit is None:
 636                                         return group.best_undecided()
 637                                 # else there was only one choice anyway
 638
 639                                 # Check for undecided dependencies
 640                                 lit_info = problem.get_varinfo_for_lit(lit).obj
 641                                 return find_undecided_dep(lit_info.impl, lit_info.arch)
 642
 643                         def find_undecided_command(uri, name):
 644                                 if name is None: return find_undecided(uri)
 645
 646                                 group = group_clause_for_command[(uri, name)]
 647                                 lit = group.current
 648                                 if lit is None:
 649                                         return group.best_undecided()
 650                                 # else we've already chosen which <command> to use
 651
 652                                 # Check for undecided command-specific dependencies, and then for
 653                                 # implementation dependencies.
 654                                 lit_info = problem.get_varinfo_for_lit(lit).obj
 655                                 if lit_info is None:
 656                                         assert closest_match
 657                                         return None     # (a dummy command added for better diagnostics; has no dependencies)
 658                                 return find_undecided_dep(lit_info.command, lit_info.arch) or \
 659                                        find_undecided_dep(lit_info.impl, lit_info.arch)
 660
 661                         best = find_undecided_command(root_interface, command_name)
 662                         if best is not None:
 663                                 return best
 664
 665                         # If we're chosen everything we need, we can probably
 666                         # set everything else to False.
 667                         for group in list(group_clause_for.values()) + list(group_clause_for_command.values()) + [m_groups_clause]:
 668                                 if group.current is None:
 669                                         best = group.best_undecided()
 670                                         if best is not None:
 671                                                 return sat.neg(best)
 672
 673                         return None                     # Failed to find any valid combination
 674
 675                 ready = problem.run_solver(decide) is True
 676
 677                 if not ready and not closest_match:
 678                         # We failed while trying to do a real solve.
 679                         # Try a closest match solve to get a better
 680                         # error report for the user.
 681                         self.solve(root_interface, root_arch, command_name = command_name, closest_match = True)
 682                 else:
 683                         self.ready = ready and not closest_match
 684                         self.selections = selections.Selections(None)
 685                         self.selections.interface = root_interface
 686
 687                         sels = self.selections.selections
 688
 689                         commands_needed = []
 690
 691                         # Populate sels with the selected implementations.
 692                         # Also, note down all the commands we need.
 693                         for uri, group in group_clause_for.items():
 694                                 if group.current is not None:
 695                                         lit_info = problem.get_varinfo_for_lit(group.current).obj
 696                                         if lit_info.is_dummy:
 697                                                 sels[lit_info.iface.uri] = None
 698                                         else:
 699                                                 # We selected an implementation for interface 'uri'
 700                                                 impl = lit_info.impl
 701
 702                                                 for b in impl.bindings:
 703                                                         c = b.command
 704                                                         if c is not None:
 705                                                                 commands.append((uri, c))
 706
 707                                                 deps = self.requires[lit_info.iface] = []
 708                                                 for dep in deps_in_use(lit_info.impl, lit_info.arch):
 709                                                         deps.append(dep)
 710                                                         for c in dep.get_required_commands():
 711                                                                 commands_needed.append((dep.interface, c))
 712
 713                                                 sels[lit_info.iface.uri] = selections.ImplSelection(lit_info.iface.uri, impl, deps)
 714
 715                         # Now all all the commands in too.
 716                         def add_command(iface, name):
 717                                 sel = sels.get(iface, None)
 718                                 if sel:
 719                                         command = sel.impl.commands[name]
 720                                         if name in sel._used_commands:
 721                                                 return  # Already added
 722                                         sel._used_commands.add(name)
 723
 724                                         for dep in command.requires:
 725                                                 for dep_command_name in dep.get_required_commands():
 726                                                         add_command(dep.interface, dep_command_name)
 727
 728                                         # A <command> can depend on another <command> in the same interface
 729                                         # (e.g. the tests depending on the main program)
 730                                         for b in command.bindings:
 731                                                 c = b.command
 732                                                 if c is not None:
 733                                                         add_command(iface, c)
 734
 735                         for iface, command in commands_needed:
 736                                 add_command(iface, command)
 737
 738                         if command_name is not None:
 739                                 self.selections.command = command_name
 740                                 add_command(root_interface, command_name)
 741
 742         def get_failure_reason(self):
 743                 """Return an exception explaining why the solve failed."""
 744                 assert not self.ready
 745
 746                 if self._failure_reason:
 747                         return model.SafeException(self._failure_reason)
 748
 749                 return model.SafeException(_("Can't find all required implementations:") + '\n' +
 750                                 '\n'.join(["- %s -> %s" % (iface, self.selections[iface])
 751                                            for iface  in self.selections]))
 752
 753         def justify_decision(self, requirements, iface, impl):
 754                 """Run a solve with impl_id forced to be selected, and explain why it wasn't (or was)
 755                 selected in the normal case."""
 756                 assert isinstance(iface, model.Interface), iface
 757
 758                 restrictions = self.extra_restrictions.copy()
 759                 restrictions[iface] = restrictions.get(iface, []) + [_ForceImpl(impl.id)]
 760                 s = SATSolver(self.config, restrictions)
 761                 s.record_details = True
 762                 s.solve_for(requirements)
 763
 764                 wanted = "{iface} {version}".format(iface = iface.get_name(), version = impl.get_version())
 765
 766                 # Could a selection involving impl even be valid?
 767                 if not s.ready or iface.uri not in s.selections.selections:
 768                         reasons = s.details.get(iface, [])
 769                         for (rid, rstr) in reasons:
 770                                 if rid.id == impl.id and rstr is not None:
 771                                         return _("{wanted} cannot be used (regardless of other components): {reason}").format(
 772                                                         wanted = wanted,
 773                                                         reason = rstr)
 774
 775                         if not s.ready:
 776                                 return _("There is no possible selection using {wanted}.\n{reason}").format(
 777                                         wanted = wanted,
 778                                         reason = s.get_failure_reason())
 779
 780                 actual_selection = self.selections.get(iface, None)
 781                 if actual_selection is not None:
 782                         # Was impl actually selected anyway?
 783                         if actual_selection.id == impl.id:
 784                                 return _("{wanted} was selected as the preferred version.").format(wanted = wanted)
 785
 786                         # Was impl ranked below the selected version?
 787                         iface_arch = arch.get_architecture(requirements.os, requirements.cpu)
 788                         if requirements.source and iface.uri == requirements.interface_uri:
 789                                 iface_arch = arch.SourceArchitecture(iface_arch)
 790                         wanted_rating = self.get_rating(iface, impl, arch)
 791                         selected_rating = self.get_rating(iface, actual_selection, arch)
 792
 793                         if wanted_rating < selected_rating:
 794                                 _ranking_component_reason = [
 795                                         _("natural languages we understand are preferred"),
 796                                         _("preferred versions come first"),
 797                                         _("locally-available versions are preferred when network use is limited"),
 798                                         _("packages that don't require admin access to install are preferred"),
 799                                         _("more stable versions preferred"),
 800                                         _("newer versions are preferred"),
 801                                         _("native packages are preferred"),
 802                                         _("newer versions are preferred"),
 803                                         _("better OS match"),
 804                                         _("better CPU match"),
 805                                         _("better locale match"),
 806                                         _("is locally available"),
 807                                         _("better ID (tie-breaker)"),
 808                                 ]
 809
 810                                 actual = actual_selection.get_version()
 811                                 if impl.get_version() == actual:
 812                                         def detail(i):
 813                                                 if len(i.id) < 18:
 814                                                         return " (" + i.id + ")"
 815                                                 else:
 816                                                         return " (" + i.id[:16] + "...)"
 817
 818                                         wanted += detail(impl)
 819                                         actual += detail(actual_selection)
 820
 821                                 for i in range(len(wanted_rating)):
 822                                         if wanted_rating[i] < selected_rating[i]:
 823                                                 return _("{wanted} is ranked lower than {actual}: {why}").format(
 824                                                                 wanted = wanted,
 825                                                                 actual = actual,
 826                                                                 why = _ranking_component_reason[i])
 827
 828                 used_impl = iface.uri in s.selections.selections
 829
 830                 # Impl is selectable and ranked higher than the selected version. Selecting it would cause
 831                 # a problem elsewhere.
 832                 changes = []
 833                 for old_iface, old_sel in self.selections.selections.items():
 834                         if old_iface == iface.uri and used_impl: continue
 835                         new_sel = s.selections.selections.get(old_iface, None)
 836                         if new_sel is None:
 837                                 changes.append(_("{interface}: no longer used").format(interface = old_iface))
 838                         elif old_sel.version != new_sel.version:
 839                                 changes.append(_("{interface}: {old} to {new}").format(interface = old_iface, old = old_sel.version, new = new_sel.version))
 840                         elif old_sel.id != new_sel.id:
 841                                 changes.append(_("{interface}: {old} to {new}").format(interface = old_iface, old = old_sel.id, new = new_sel.id))
 842
 843                 if changes:
 844                         changes_text = '\n\n' + _('The changes would be:') + '\n\n' + '\n'.join(changes)
 845                 else:
 846                         changes_text = ''
 847
 848                 if used_impl:
 849                         return _("{wanted} is selectable, but using it would produce a less optimal solution overall.").format(wanted = wanted) + changes_text
 850                 else:
 851                         return _("If {wanted} were the only option, the best available solution wouldn't use it.").format(wanted = wanted) + changes_text
 852
 853 DefaultSolver = SATSolver