fixup Spec parsing in error messages

add message to variant conditionals

lib/spack/spack/cmd/solve.py

@@ -136,13 +136,13 @@ def solve(parser, args):
             )
 
             fmt = "  @K{%%-8d}  %%-%ds%%9s  %%7s" % maxlen
-            for i, (idx, build_idx, name) in enumerate(result.criteria, 1):
+            for i, (installed_cost, build_cost, name) in enumerate(result.criteria, 1):
                 color.cprint(
                     fmt % (
                         i,
                         name,
-                        "-" if build_idx is None else opt[idx],
-                        opt[idx] if build_idx is None else opt[build_idx],
+                        "-" if build_cost is None else installed_cost,
+                        installed_cost if build_cost is None else build_cost,
                     )
                 )
             print()

lib/spack/spack/error.py

@@ -10,9 +10,9 @@
 
 import llnl.util.tty as tty
 
-#: whether we should write stack traces or short error messages
+#: at what level we should write stack traces or short error messages
 #: this is module-scoped because it needs to be set very early
-debug = False
+debug = 0
 
 
 class SpackError(Exception):

lib/spack/spack/main.py

@@ -375,13 +375,6 @@ def make_argument_parser(**kwargs):
     # stat names in groups of 7, for nice wrapping.
     stat_lines = list(zip(*(iter(stat_names),) * 7))
 
-    # help message for --show-cores
-    show_cores_help = 'provide additional information on concretization failures\n'
-    show_cores_help += 'off (default): show only the violated rule\n'
-    show_cores_help += 'full: show raw unsat cores from clingo\n'
-    show_cores_help += 'minimized: show subset-minimal unsat cores '
-    show_cores_help += '(Warning: this may take hours for some specs)'
-
     parser.add_argument(
         '-h', '--help',
         dest='help', action='store_const', const='short', default=None,
@@ -405,9 +398,6 @@ def make_argument_parser(**kwargs):
         '-d', '--debug', action='count', default=0,
         help="write out debug messages "
              "(more d's for more verbosity: -d, -dd, -ddd, etc.)")
-    parser.add_argument(
-        '--show-cores', choices=["off", "full", "minimized"], default="off",
-        help=show_cores_help)
     parser.add_argument(
         '--timestamp', action='store_true',
         help="Add a timestamp to tty output")
@@ -490,18 +480,11 @@ def setup_main_options(args):
     # errors raised by spack.config.
 
     if args.debug:
-        spack.error.debug = True
+        spack.error.debug = args.debug
         spack.util.debug.register_interrupt_handler()
         spack.config.set('config:debug', True, scope='command_line')
         spack.util.environment.tracing_enabled = True
 
-    if args.show_cores != "off":
-        # minimize_cores defaults to true, turn it off if we're showing full core
-        # but don't want to wait to minimize it.
-        spack.solver.asp.full_cores = True
-        if args.show_cores == 'full':
-            spack.solver.asp.minimize_cores = False
-
     if args.timestamp:
         tty.set_timestamp(True)
 

lib/spack/spack/solver/asp.py

@@ -9,6 +9,7 @@
 import itertools
 import os
 import pprint
+import re
 import types
 import warnings
 
@@ -55,14 +56,6 @@
 parse_files = None
 
 
-#: whether we should write ASP unsat cores quickly in debug mode when the cores
-#: may be very large or take the time (sometimes hours) to minimize them
-minimize_cores = True
-
-#: whether we should include all facts in the unsat cores or only error messages
-full_cores = False
-
-
 # backward compatibility functions for clingo ASTs
 def ast_getter(*names):
     def getter(node):
@@ -114,7 +107,7 @@ def getter(node):
 
 
 def build_criteria_names(costs, tuples):
-    """Construct an ordered mapping from criteria names to indices in the cost list."""
+    """Construct an ordered mapping from criteria names to costs."""
     # pull optimization criteria names out of the solution
     priorities_names = []
 
@@ -141,7 +134,10 @@ def build_criteria_names(costs, tuples):
     # sort the criteria by priority
     priorities_names = sorted(priorities_names, reverse=True)
 
-    assert len(priorities_names) == len(costs), "Wrong number of optimization criteria!"
+    # We only have opt-criterion values for non-error types
+    # error type criteria are excluded (they come first)
+    error_criteria = len(costs) - len(priorities_names)
+    costs = costs[error_criteria:]
 
     # split list into three parts: build criteria, fixed criteria, non-build criteria
     num_criteria = len(priorities_names)
@@ -154,12 +150,12 @@ def build_criteria_names(costs, tuples):
     # mapping from priority to index in cost list
     indices = dict((p, i) for i, (p, n) in enumerate(priorities_names))
 
-    # make a list that has each name with its build and non-build priority
+    # make a list that has each name with its build and non-build costs
     criteria = [
-        (p - fixed_priority_offset + num_build, None, name) for p, name in fixed
+        (costs[p - fixed_priority_offset + num_build], None, name) for p, name in fixed
     ]
     for (i, name), (b, _) in zip(installed, build):
-        criteria.append((indices[i], indices[b], name))
+        criteria.append((costs[indices[i]], costs[indices[b]], name))
 
     return criteria
 
@@ -331,9 +327,6 @@ def format_core(self, core):
         core_symbols = []
         for atom in core:
             sym = symbols[atom]
-            if sym.name in ("rule", "error"):
-                # these are special symbols we use to get messages in the core
-                sym = sym.arguments[0].string
             core_symbols.append(sym)
 
         return sorted(str(symbol) for symbol in core_symbols)
@@ -392,7 +385,7 @@ def raise_if_unsat(self):
         """
         Raise an appropriate error if the result is unsatisfiable.
 
-        The error is a UnsatisfiableSpecError, and includes the minimized cores
+        The error is an InternalConcretizerError, and includes the minimized cores
         resulting from the solve, formatted to be human readable.
         """
         if self.satisfiable:
@@ -402,12 +395,8 @@ def raise_if_unsat(self):
         if len(constraints) == 1:
             constraints = constraints[0]
 
-        if minimize_cores:
-            conflicts = self.format_minimal_cores()
-        else:
-            conflicts = self.format_cores()
-
-        raise UnsatisfiableSpecError(constraints, conflicts=conflicts)
+        conflicts = self.format_minimal_cores()
+        raise InternalConcretizerError(constraints, conflicts=conflicts)
 
     @property
     def specs(self):
@@ -507,13 +496,11 @@ def h2(self, name):
     def newline(self):
         self.out.write('\n')
 
-    def fact(self, head, assumption=False):
+    def fact(self, head):
         """ASP fact (a rule without a body).
 
         Arguments:
             head (AspFunction): ASP function to generate as fact
-            assumption (bool): If True and using cores, use this fact as a
-                choice point in ASP and include it in unsatisfiable cores
         """
         symbol = head.symbol() if hasattr(head, 'symbol') else head
 
@@ -521,10 +508,9 @@ def fact(self, head, assumption=False):
 
         atom = self.backend.add_atom(symbol)
 
-        # with `--show-cores=full or --show-cores=minimized, make all facts
-        # choices/assumptions, otherwise only if assumption=True
-        choice = self.cores and (full_cores or assumption)
-
+        # Only functions relevant for constructing bug reports for bad error messages
+        # are assumptions, and only when using cores.
+        choice = self.cores and symbol.name == 'internal_error'
         self.backend.add_rule([atom], [], choice=choice)
         if choice:
             self.assumptions.append(atom)
@@ -582,9 +568,10 @@ def visit(node):
                     for term in node.body:
                         if ast_type(term) == ASTType.Literal:
                             if ast_type(term.atom) == ASTType.SymbolicAtom:
-                                if ast_sym(term.atom).name == "error":
+                                name = ast_sym(term.atom).name
+                                if name == 'internal_error':
                                     arg = ast_sym(ast_sym(term.atom).arguments[0])
-                                    self.fact(fn.error(arg.string), assumption=True)
+                                    self.fact(AspFunction(name)(arg.string))
 
             path = os.path.join(parent_dir, 'concretize.lp')
             parse_files([path], visit)
@@ -737,7 +724,7 @@ def spec_versions(self, spec):
 
         # record all version constraints for later
         self.version_constraints.add((spec.name, spec.versions))
-        return [fn.version_satisfies(spec.name, spec.versions)]
+        return [fn.node_version_satisfies(spec.name, spec.versions)]
 
     def target_ranges(self, spec, single_target_fn):
         target = spec.architecture.target
@@ -750,13 +737,24 @@ def target_ranges(self, spec, single_target_fn):
         return [fn.node_target_satisfies(spec.name, target)]
 
     def conflict_rules(self, pkg):
+        default_msg = "{0} '{1}' conflicts with '{2}'"
+        no_constraint_msg = "{0} conflicts with '{1}'"
         for trigger, constraints in pkg.conflicts.items():
-            trigger_id = self.condition(spack.spec.Spec(trigger), name=pkg.name)
-            self.gen.fact(fn.conflict_trigger(trigger_id))
+            trigger_msg = "conflict trigger %s" % str(trigger)
+            trigger_id = self.condition(
+                spack.spec.Spec(trigger), name=pkg.name, msg=trigger_msg)
 
-            for constraint, _ in constraints:
-                constraint_id = self.condition(constraint, name=pkg.name)
-                self.gen.fact(fn.conflict(pkg.name, trigger_id, constraint_id))
+            for constraint, conflict_msg in constraints:
+                if conflict_msg is None:
+                    if constraint == spack.spec.Spec():
+                        conflict_msg = no_constraint_msg.format(pkg.name, trigger)
+                    else:
+                        conflict_msg = default_msg.format(pkg.name, trigger, constraint)
+                constraint_msg = "conflict constraint %s" % str(constraint)
+                constraint_id = self.condition(
+                    constraint, name=pkg.name, msg=constraint_msg)
+                self.gen.fact(
+                    fn.conflict(pkg.name, trigger_id, constraint_id, conflict_msg))
                 self.gen.newline()
 
     def available_compilers(self):
@@ -840,9 +838,18 @@ def pkg_rules(self, pkg, tests):
         for name, entry in sorted(pkg.variants.items()):
             variant, when = entry
 
-            for w in when:
-                cond_id = self.condition(w, name=pkg.name)
-                self.gen.fact(fn.variant_condition(cond_id, pkg.name, name))
+            if spack.spec.Spec() in when:
+                # unconditional variant
+                self.gen.fact(fn.variant(pkg.name, name))
+            else:
+                # conditional variant
+                for w in when:
+                    msg = "%s has variant %s" % (pkg.name, name)
+                    if str(w):
+                        msg += " when %s" % w
+
+                    cond_id = self.condition(w, name=pkg.name, msg=msg)
+                    self.gen.fact(fn.variant_condition(cond_id, pkg.name, name))
 
             single_value = not variant.multi
             if single_value:
@@ -885,7 +892,9 @@ def pkg_rules(self, pkg, tests):
                     imposed = spack.spec.Spec(value.when)
                     imposed.name = pkg.name
                     self.condition(
-                        required_spec=required, imposed_spec=imposed, name=pkg.name
+                        required_spec=required, imposed_spec=imposed, name=pkg.name,
+                        msg="%s variant %s value %s when %s" % (
+                            pkg.name, name, value, when)
                     )
 
             if variant.sticky:
@@ -913,7 +922,7 @@ def pkg_rules(self, pkg, tests):
             )
         )
 
-    def condition(self, required_spec, imposed_spec=None, name=None):
+    def condition(self, required_spec, imposed_spec=None, name=None, msg=None):
         """Generate facts for a dependency or virtual provider condition.
 
         Arguments:
@@ -922,7 +931,7 @@ def condition(self, required_spec, imposed_spec=None, name=None):
                 are imposed when this condition is triggered
             name (str or None): name for `required_spec` (required if
                 required_spec is anonymous, ignored if not)
-
+            msg (str or None): description of the condition
         Returns:
             int: id of the condition created by this function
         """
@@ -931,7 +940,7 @@ def condition(self, required_spec, imposed_spec=None, name=None):
         assert named_cond.name, "must provide name for anonymous condtions!"
 
         condition_id = next(self._condition_id_counter)
-        self.gen.fact(fn.condition(condition_id))
+        self.gen.fact(fn.condition(condition_id, msg))
 
         # requirements trigger the condition
         requirements = self.spec_clauses(
@@ -963,7 +972,8 @@ def package_provider_rules(self, pkg):
 
         for provided, whens in pkg.provided.items():
             for when in whens:
-                condition_id = self.condition(when, provided, pkg.name)
+                msg = '%s provides %s when %s' % (pkg.name, provided, when)
+                condition_id = self.condition(when, provided, pkg.name, msg)
                 self.gen.fact(fn.provider_condition(
                     condition_id, when.name, provided.name
                 ))
@@ -987,7 +997,11 @@ def package_dependencies_rules(self, pkg):
                 if not deptypes:
                     continue
 
-                condition_id = self.condition(cond, dep.spec, pkg.name)
+                msg = '%s depends on %s' % (pkg.name, dep.spec.name)
+                if cond != spack.spec.Spec():
+                    msg += ' when %s' % cond
+
+                condition_id = self.condition(cond, dep.spec, pkg.name, msg)
                 self.gen.fact(fn.dependency_condition(
                     condition_id, pkg.name, dep.spec.name
                 ))
@@ -1067,7 +1081,8 @@ def external_packages(self):
 
             # Declare external conditions with a local index into packages.yaml
             for local_idx, spec in enumerate(external_specs):
-                condition_id = self.condition(spec)
+                msg = '%s available as external when satisfying %s' % (spec.name, spec)
+                condition_id = self.condition(spec, msg=msg)
                 self.gen.fact(
                     fn.possible_external(condition_id, pkg_name, local_idx)
                 )
@@ -1920,6 +1935,17 @@ def node_os(self, pkg, os):
     def node_target(self, pkg, target):
         self._arch(pkg).target = target
 
+    def error(self, priority, msg, *args):
+        msg = msg.format(*args)
+
+        # For variant formatting, we sometimes have to construct specs
+        # to format values properly. Find/replace all occurances of
+        # Spec(...) with the string representation of the spec mentioned
+        specs_to_construct = re.findall(r'Spec\(([^)]*)\)', msg)
+        for spec_str in specs_to_construct:
+            msg = msg.replace('Spec(%s)' % spec_str, str(spack.spec.Spec(spec_str)))
+        raise UnsatisfiableSpecError(msg)
+
     def variant_value(self, pkg, name, value):
         # FIXME: is there a way not to special case 'dev_path' everywhere?
         if name == 'dev_path':
@@ -2042,15 +2068,27 @@ def deprecated(self, pkg, version):
         msg = 'using "{0}@{1}" which is a deprecated version'
         tty.warn(msg.format(pkg, version))
 
+    @staticmethod
+    def sort_fn(function_tuple):
+        name = function_tuple[0]
+        if name == 'error':
+            priority = function_tuple[1][0]
+            return (-4, priority)
+        elif name == 'hash':
+            return (-3, 0)
+        elif name == 'node':
+            return (-2, 0)
+        elif name == 'node_compiler':
+            return (-1, 0)
+        else:
+            return (0, 0)
+
     def build_specs(self, function_tuples):
         # Functions don't seem to be in particular order in output.  Sort
         # them here so that directives that build objects (like node and
         # node_compiler) are called in the right order.
-        function_tuples.sort(key=lambda f: {
-            "hash": -3,
-            "node": -2,
-            "node_compiler": -1,
-        }.get(f[0], 0))
+        self.function_tuples = function_tuples
+        self.function_tuples.sort(key=self.sort_fn)
 
         self._specs = {}
         for name, args in function_tuples:
@@ -2058,7 +2096,6 @@ def build_specs(self, function_tuples):
                 continue
 
             action = getattr(self, name, None)
-
             # print out unknown actions so we can display them for debugging
             if not action:
                 msg = "%s(%s)" % (name, ", ".join(str(a) for a in args))
@@ -2068,16 +2105,18 @@ def build_specs(self, function_tuples):
             assert action and callable(action)
 
             # ignore predicates on virtual packages, as they're used for
-            # solving but don't construct anything
-            pkg = args[0]
-            if spack.repo.path.is_virtual(pkg):
-                continue
+            # solving but don't construct anything. Do not ignore error
+            # predicates on virtual packages.
+            if name != 'error':
+                pkg = args[0]
+                if spack.repo.path.is_virtual(pkg):
+                    continue
 
-            # if we've already gotten a concrete spec for this pkg,
-            # do not bother calling actions on it.
-            spec = self._specs.get(pkg)
-            if spec and spec.concrete:
-                continue
+                # if we've already gotten a concrete spec for this pkg,
+                # do not bother calling actions on it.
+                spec = self._specs.get(pkg)
+                if spec and spec.concrete:
+                    continue
 
             action(*args)
 
@@ -2201,25 +2240,27 @@ def solve(
 
 
 class UnsatisfiableSpecError(spack.error.UnsatisfiableSpecError):
+    """
+    Subclass for new constructor signature for new concretizer
+    """
+    def __init__(self, msg):
+        super(spack.error.UnsatisfiableSpecError, self).__init__(msg)
+        self.provided = None
+        self.required = None
+        self.constraint_type = None
+
+
+class InternalConcretizerError(spack.error.UnsatisfiableSpecError):
     """
     Subclass for new constructor signature for new concretizer
     """
     def __init__(self, provided, conflicts):
         indented = ['  %s\n' % conflict for conflict in conflicts]
-        conflict_msg = ''.join(indented)
-        issue = 'conflicts' if full_cores else 'errors'
-        msg = '%s is unsatisfiable, %s are:\n%s' % (provided, issue, conflict_msg)
-
-        newline_indent = '\n    '
-        if not full_cores:
-            msg += newline_indent + 'To see full clingo unsat cores, '
-            msg += 're-run with `spack --show-cores=full`'
-        if not minimize_cores or not full_cores:
-            # not solver.minimalize_cores and not solver.full_cores impossible
-            msg += newline_indent + 'For full, subset-minimal unsat cores, '
-            msg += 're-run with `spack --show-cores=minimized'
-            msg += newline_indent
-            msg += 'Warning: This may take (up to) hours for some specs'
+        error_msg = ''.join(indented)
+        msg = 'Spack concretizer internal error. Please submit a bug report'
+        msg += '\n    Please include the command, environment if applicable,'
+        msg += '\n    and the following error message.'
+        msg = '\n        %s is unsatisfiable, errors are:\n%s' % (provided, error_msg)
 
         super(spack.error.UnsatisfiableSpecError, self).__init__(msg)
 

lib/spack/spack/solver/concretize.lp

@@ -7,22 +7,6 @@
 % This logic program implements Spack's concretizer
 %=============================================================================
 
-%-----------------------------------------------------------------------------
-% Generic constraints on nodes
-%-----------------------------------------------------------------------------
-
-% each node must have a single version
-:- not 1 { version(Package, _) } 1, node(Package).
-
-% each node must have a single platform, os and target
-:- not 1 { node_platform(Package, _) } 1, node(Package), error("A node must have exactly one platform").
-:- not 1 { node_os(Package, _) } 1, node(Package).
-:- not 1 { node_target(Package, _) } 1, node(Package).
-
-% each node has a single compiler associated with it
-:- not 1 { node_compiler(Package, _) } 1, node(Package).
-:- not 1 { node_compiler_version(Package, _, _) } 1, node(Package).
-
 %-----------------------------------------------------------------------------
 % Version semantics
 %-----------------------------------------------------------------------------
@@ -35,7 +19,7 @@ version_declared(Package, Version, Weight) :- version_declared(Package, Version,
 :- version_declared(Package, Version, Weight, Origin1),
    version_declared(Package, Version, Weight, Origin2),
    Origin1 < Origin2,
-   error("Internal error: two versions with identical weights").
+   internal_error("Two versions with identical weights").
 
 % We cannot use a version declared for an installed package if we end up building it
 :- version_declared(Package, Version, Weight, "installed"),
@@ -48,11 +32,27 @@ version_declared(Package, Version) :- version_declared(Package, Version, _).
 
 % If something is a package, it has only one version and that must be a
 % declared version.
-1 { version(Package, Version) : version_declared(Package, Version) } 1
- :- node(Package), error("Each node must have exactly one version").
+% We allow clingo to choose any version(s), and infer an error if there
+% is not precisely one version chosen. Error facts are heavily optimized
+% against to ensure they cannot be inferred when a non-error solution is
+% possible
+{ version(Package, Version) : version_declared(Package, Version) }
+ :- node(Package).
+error(2, "No version for '{0}' satisfies '@{1}' and '@{2}'", Package, Version1, Version2)
+  :- node(Package),
+     version(Package, Version1),
+     version(Package, Version2),
+     Version1 < Version2.  % see[1]
 
-% A virtual package may have or not a version, but never has more than one
-:- virtual_node(Package), 2 { version(Package, _) }.
+error(2, "No versions available for package '{0}'", Package)
+  :- node(Package), not version(Package, _).
+
+% A virtual package may or may not have a version, but never has more than one
+error(2, "No version for '{0}' satisfies '@{1}' and '@{2}'", Virtual, Version1, Version2)
+  :- virtual_node(Virtual),
+     version(Virtual, Version1),
+     version(Virtual, Version2),
+     Version1 < Version2. % see[1]
 
 % If we select a deprecated version, mark the package as deprecated
 deprecated(Package, Version) :- version(Package, Version), deprecated_version(Package, Version).
@@ -61,14 +61,27 @@ possible_version_weight(Package, Weight)
  :- version(Package, Version),
     version_declared(Package, Version, Weight).
 
-1 { version_weight(Package, Weight) : possible_version_weight(Package, Weight) } 1 :- node(Package), error("Internal error: Package version must have a unique weight").
+version_weight(Package, Weight)
+  :- version(Package, Version),
+     node(Package),
+     Weight = #min{W : version_declared(Package, Version, W)}.
 
-% version_satisfies implies that exactly one of the satisfying versions
+% node_version_satisfies implies that exactly one of the satisfying versions
 % is the package's version, and vice versa.
-1 { version(Package, Version) : version_satisfies(Package, Constraint, Version) } 1
-  :- version_satisfies(Package, Constraint),
-     error("no version satisfies the given constraints").
-version_satisfies(Package, Constraint)
+% While this choice rule appears redundant with the initial choice rule for
+% versions, virtual nodes with version constraints require this rule to be
+% able to choose versions
+{ version(Package, Version) : version_satisfies(Package, Constraint, Version) }
+  :- node_version_satisfies(Package, Constraint).
+
+% More specific error message if the version cannot satisfy some constraint
+% Otherwise covered by `no_version_error` and `versions_conflict_error`.
+error(1, "No valid version for '{0}' satisfies '@{1}'", Package, Constraint)
+  :- node_version_satisfies(Package, Constraint),
+     C = #count{ Version : version(Package, Version), version_satisfies(Package, Constraint, Version)},
+     C < 1.
+
+node_version_satisfies(Package, Constraint)
   :- version(Package, Version), version_satisfies(Package, Constraint, Version).
 
 #defined version_satisfies/3.
@@ -87,7 +100,7 @@ version_satisfies(Package, Constraint)
 % conditions are specified with `condition_requirement` and hold when
 % corresponding spec attributes hold.
 condition_holds(ID) :-
-  condition(ID);
+  condition(ID, _);
   attr(Name, A1)         : condition_requirement(ID, Name, A1);
   attr(Name, A1, A2)     : condition_requirement(ID, Name, A1, A2);
   attr(Name, A1, A2, A3) : condition_requirement(ID, Name, A1, A2, A3).
@@ -106,7 +119,7 @@ attr(Name, A1, A2, A3) :- impose(ID), imposed_constraint(ID, Name, A1, A2, A3).
    variant_value(Package, Variant, Value),
    not imposed_constraint(Hash, "variant_value", Package, Variant, Value).
 
-#defined condition/1.
+#defined condition/2.
 #defined condition_requirement/3.
 #defined condition_requirement/4.
 #defined condition_requirement/5.
@@ -133,9 +146,7 @@ depends_on(Package, Dependency) :- depends_on(Package, Dependency, _).
 dependency_holds(Package, Dependency, Type) :-
   dependency_condition(ID, Package, Dependency),
   dependency_type(ID, Type),
-  condition_holds(ID),
-  build(Package),
-  not external(Package).
+  condition_holds(ID).
 
 % We cut off dependencies of externals (as we don't really know them).
 % Don't impose constraints on dependencies that don't exist.
@@ -161,17 +172,18 @@ node(Dependency) :- node(Package), depends_on(Package, Dependency).
 % dependencies) and get a two-node unconnected graph
 needed(Package) :- root(Package).
 needed(Dependency) :- needed(Package), depends_on(Package, Dependency).
-:- node(Package), not needed(Package),
-   error("All dependencies must be reachable from root").
+error(1, "'{0}' is not a valid dependency for any package in the DAG", Package)
+  :- node(Package),
+     not needed(Package).
 
 % Avoid cycles in the DAG
 % some combinations of conditional dependencies can result in cycles;
 % this ensures that we solve around them
 path(Parent, Child) :- depends_on(Parent, Child).
 path(Parent, Descendant) :- path(Parent, A), depends_on(A, Descendant).
-:- path(A, B), path(B, A), error("Cyclic dependencies are not allowed").
-
-#defined error/1.
+error(2, "Cyclic dependency detected between '{0}' and '{1}'\n    Consider changing variants to avoid the cycle", A, B)
+  :- path(A, B),
+     path(B, A).
 
 #defined dependency_type/2.
 #defined dependency_condition/3.
@@ -179,14 +191,13 @@ path(Parent, Descendant) :- path(Parent, A), depends_on(A, Descendant).
 %-----------------------------------------------------------------------------
 % Conflicts
 %-----------------------------------------------------------------------------
-:- node(Package),
-   conflict(Package, TriggerID, ConstraintID),
+error(0, Msg) :- node(Package),
+   conflict(Package, TriggerID, ConstraintID, Msg),
    condition_holds(TriggerID),
    condition_holds(ConstraintID),
-   not external(Package),  % ignore conflicts for externals
-   error("A conflict was triggered").
+   not external(Package).  % ignore conflicts for externals
 
-#defined conflict/3.
+#defined conflict/4.
 
 %-----------------------------------------------------------------------------
 % Virtual dependencies
@@ -206,8 +217,17 @@ virtual_node(Virtual)
 
 % If there's a virtual node, we must select one and only one provider.
 % The provider must be selected among the possible providers.
-1 { provider(Package, Virtual) : possible_provider(Package, Virtual) } 1
-  :- virtual_node(Virtual), error("Virtual packages must be satisfied by a unique provider").
+{ provider(Package, Virtual) : possible_provider(Package, Virtual) }
+  :- virtual_node(Virtual).
+error(2, "Cannot find valid provider for virtual {0}", Virtual)
+  :- virtual_node(Virtual),
+     P = #count{ Package : provider(Package, Virtual)},
+     P < 1.
+error(2, "Spec cannot include multiple providers for virtual '{0}'\n    Requested '{1}' and '{2}'", Virtual, P1, P2)
+  :- virtual_node(Virtual),
+     provider(P1, Virtual),
+     provider(P2, Virtual),
+     P1 < P2.
 
 % virtual roots imply virtual nodes, and that one provider is a root
 virtual_node(Virtual) :- virtual_root(Virtual).
@@ -232,7 +252,7 @@ virtual_condition_holds(Provider, Virtual) :-
 % A package cannot be the actual provider for a virtual if it does not
 % fulfill the conditions to provide that virtual
 :- provider(Package, Virtual), not virtual_condition_holds(Package, Virtual),
-   error("Internal error: virtual when provides not respected").
+   internal_error("Virtual when provides not respected").
 
 #defined possible_provider/2.
 
@@ -245,7 +265,7 @@ virtual_condition_holds(Provider, Virtual) :-
 % we select the weight, among the possible ones, that minimizes the overall objective function.
 1 { provider_weight(Dependency, Virtual, Weight, Reason) :
     possible_provider_weight(Dependency, Virtual, Weight, Reason) } 1
- :- provider(Dependency, Virtual), error("Internal error: package provider weights must be unique").
+ :- provider(Dependency, Virtual), internal_error("Package provider weights must be unique").
 
 % Get rid or the reason for enabling the possible weight (useful for debugging)
 provider_weight(Dependency, Virtual, Weight) :- provider_weight(Dependency, Virtual, Weight, _).
@@ -291,7 +311,7 @@ node(Package)                          :- attr("node", Package).
 virtual_node(Virtual)                  :- attr("virtual_node", Virtual).
 hash(Package, Hash)                    :- attr("hash", Package, Hash).
 version(Package, Version)              :- attr("version", Package, Version).
-version_satisfies(Package, Constraint) :- attr("version_satisfies", Package, Constraint).
+node_version_satisfies(Package, Constraint) :- attr("node_version_satisfies", Package, Constraint).
 node_platform(Package, Platform)       :- attr("node_platform", Package, Platform).
 node_os(Package, OS)                   :- attr("node_os", Package, OS).
 node_target(Package, Target)           :- attr("node_target", Package, Target).
@@ -310,7 +330,7 @@ attr("node", Package)                          :- node(Package).
 attr("virtual_node", Virtual)                  :- virtual_node(Virtual).
 attr("hash", Package, Hash)                    :- hash(Package, Hash).
 attr("version", Package, Version)              :- version(Package, Version).
-attr("version_satisfies", Package, Constraint) :- version_satisfies(Package, Constraint).
+attr("node_version_satisfies", Package, Constraint) :- node_version_satisfies(Package, Constraint).
 attr("node_platform", Package, Platform)       :- node_platform(Package, Platform).
 attr("node_os", Package, OS)                   :- node_os(Package, OS).
 attr("node_target", Package, Target)           :- node_target(Package, Target).
@@ -338,7 +358,7 @@ attr("node_compiler_version_satisfies", Package, Compiler, Version)
 #defined external_only/1.
 #defined pkg_provider_preference/4.
 #defined default_provider_preference/3.
-#defined version_satisfies/2.
+#defined node_version_satisfies/2.
 #defined node_compiler_version_satisfies/3.
 #defined root/1.
 
@@ -347,9 +367,17 @@ attr("node_compiler_version_satisfies", Package, Compiler, Version)
 %-----------------------------------------------------------------------------
 
 % if a package is external its version must be one of the external versions
-1 { external_version(Package, Version, Weight):
-    version_declared(Package, Version, Weight, "external") } 1
-    :- external(Package), error("External package version does not satisfy external spec").
+{ external_version(Package, Version, Weight):
+    version_declared(Package, Version, Weight, "external") }
+    :- external(Package).
+error(2, "Attempted to use external for '{0}' which does not satisfy any configured external spec", Package)
+  :- external(Package),
+     not external_version(Package, _, _).
+error(2, "Attempted to use external for '{0}' which does not satisfy any configured external spec", Package)
+  :- external(Package),
+     external_version(Package, Version1, Weight1),
+     external_version(Package, Version2, Weight2),
+     (Version1, Weight1) < (Version2, Weight2). % see[1]
 
 version_weight(Package, Weight) :- external_version(Package, Version, Weight).
 version(Package, Version) :- external_version(Package, Version, Weight).
@@ -369,7 +397,7 @@ external(Package) :- external_spec_selected(Package, _).
    version_weight(Package, Weight),
    version_declared(Package, Version, Weight, "external"),
    not external(Package),
-   error("Internal error: external weight used for internal spec").
+   internal_error("External weight used for internal spec").
 
 % determine if an external spec has been selected
 external_spec_selected(Package, LocalIndex) :-
@@ -381,8 +409,9 @@ external_conditions_hold(Package, LocalIndex) :-
 
 % it cannot happen that a spec is external, but none of the external specs
 % conditions hold.
-:- external(Package), not external_conditions_hold(Package, _),
-   error("External package does not satisfy external spec").
+error(2, "Attempted to use external for '{0}' which does not satisfy any configured external spec", Package)
+ :- external(Package),
+    not external_conditions_hold(Package, _).
 
 #defined possible_external/3.
 #defined external_spec_index/3.
@@ -399,16 +428,16 @@ variant(Package, Variant) :- variant_condition(ID, Package, Variant),
                              condition_holds(ID).
 
 % a variant cannot be set if it is not a variant on the package
-:- variant_set(Package, Variant),
-   not variant(Package, Variant),
-   build(Package),
-   error("Unsatisfied conditional variants cannot be set").
+error(2, "Cannot set variant '{0}' for package '{1}' because the variant condition cannot be satisfied for the given spec", Package, Variant)
+  :- variant_set(Package, Variant),
+     not variant(Package, Variant),
+     build(Package).
 
 % a variant cannot take on a value if it is not a variant of the package
-:- variant_value(Package, Variant, _),
-   not variant(Package, Variant),
-   build(Package),
-   error("Unsatisfied conditional variants cannot take on a variant value").
+error(2, "Cannot set variant '{0}' for package '{1}' because the variant condition cannot be satisfied for the given spec", Package, Variant)
+  :- variant_value(Package, Variant, _),
+     not variant(Package, Variant),
+     build(Package).
 
 % if a variant is sticky and not set its value is the default value
 variant_value(Package, Variant, Value) :-
@@ -418,27 +447,30 @@ variant_value(Package, Variant, Value) :-
   variant_default_value(Package, Variant, Value),
   build(Package).
 
-% one variant value for single-valued variants.
-1 {
+% at most one variant value for single-valued variants.
+{
   variant_value(Package, Variant, Value)
   : variant_possible_value(Package, Variant, Value)
-} 1
- :- node(Package),
-    variant(Package, Variant),
-    variant_single_value(Package, Variant),
-    build(Package),
-    error("Single valued variants must have a single value").
-
-% at least one variant value for multi-valued variants.
-1 {
- variant_value(Package, Variant, Value)
- : variant_possible_value(Package, Variant, Value)
 }
  :- node(Package),
     variant(Package, Variant),
-    not variant_single_value(Package, Variant),
-    build(Package),
-    error("Internal error: All variants must have a value").
+    build(Package).
+
+
+error(2, "'{0}' required multiple values for single-valued variant '{1}'\n    Requested 'Spec({1}={2})' and 'Spec({1}={3})'", Package, Variant, Value1, Value2)
+  :- node(Package),
+     variant(Package, Variant),
+     variant_single_value(Package, Variant),
+     build(Package),
+     variant_value(Package, Variant, Value1),
+     variant_value(Package, Variant, Value2),
+     Value1 < Value2. % see[1]
+error(2, "No valid value for variant '{1}' of package '{0}'", Package, Variant)
+  :- node(Package),
+     variant(Package, Variant),
+     build(Package),
+     C = #count{ Value : variant_value(Package, Variant, Value) },
+     C < 1.
 
 % if a variant is set to anything, it is considered 'set'.
 variant_set(Package, Variant) :- variant_set(Package, Variant, _).
@@ -446,21 +478,21 @@ variant_set(Package, Variant) :- variant_set(Package, Variant, _).
 % A variant cannot have a value that is not also a possible value
 % This only applies to packages we need to build -- concrete packages may
 % have been built w/different variants from older/different package versions.
-:- variant_value(Package, Variant, Value),
-   not variant_possible_value(Package, Variant, Value),
-   build(Package),
-   error("Variant set to invalid value").
+error(1, "'Spec({1}={2})' is not a valid value for '{0}' variant '{1}'", Package, Variant, Value)
+ :- variant_value(Package, Variant, Value),
+    not variant_possible_value(Package, Variant, Value),
+    build(Package).
 
 % Some multi valued variants accept multiple values from disjoint sets.
 % Ensure that we respect that constraint and we don't pick values from more
 % than one set at once
-:- variant_value(Package, Variant, Value1),
-   variant_value(Package, Variant, Value2),
-   variant_value_from_disjoint_sets(Package, Variant, Value1, Set1),
-   variant_value_from_disjoint_sets(Package, Variant, Value2, Set2),
-   Set1 < Set2,
-   build(Package),
-   error("Variant values selected from multiple disjoint sets").
+error(2, "{0} variant '{1}' cannot have values '{2}' and '{3}' as they come from disjoing value sets", Package, Variant, Value1, Value2)
+  :- variant_value(Package, Variant, Value1),
+     variant_value(Package, Variant, Value2),
+     variant_value_from_disjoint_sets(Package, Variant, Value1, Set1),
+     variant_value_from_disjoint_sets(Package, Variant, Value2, Set2),
+     Set1 < Set2, % see[1]
+     build(Package).
 
 % variant_set is an explicitly set variant value. If it's not 'set',
 % we revert to the default value. If it is set, we force the set value
@@ -518,12 +550,11 @@ variant_default_value(Package, Variant, Value) :- variant_default_value_from_cli
 
 % Treat 'none' in a special way - it cannot be combined with other
 % values even if the variant is multi-valued
-:- 2 {
-     variant_value(Package, Variant, Value) : variant_possible_value(Package, Variant, Value)
-   },
-   variant_value(Package, Variant, "none"),
-   build(Package),
-   error("Variant value 'none' cannot be combined with any other value").
+error(2, "{0} variant '{1}' cannot have values '{2}' and 'none'", Package, Variant, Value)
+ :- variant_value(Package, Variant, Value),
+    variant_value(Package, Variant, "none"),
+    Value != "none",
+    build(Package).
 
 % patches and dev_path are special variants -- they don't have to be
 % declared in the package, so we just allow them to spring into existence
@@ -567,6 +598,18 @@ node_platform(Package, Platform)
 % platform is set if set to anything
 node_platform_set(Package) :- node_platform_set(Package, _).
 
+% each node must have a single platform
+error(2, "No valid platform found for {0}", Package)
+  :- node(Package),
+     C = #count{ Platform : node_platform(Package, Platform)},
+     C < 1.
+
+error(2, "Cannot concretize {0} with multiple platforms\n    Requested 'platform={1}' and 'platform={2}'", Package, Platform1, Platform2)
+  :- node(Package),
+     node_platform(Package, Platform1),
+     node_platform(Package, Platform2),
+     Platform1 < Platform2. % see[1]
+
 #defined node_platform_set/2.  % avoid warnings
 
 %-----------------------------------------------------------------------------
@@ -576,20 +619,32 @@ node_platform_set(Package) :- node_platform_set(Package, _).
 os(OS) :- os(OS, _).
 
 % one os per node
-1 { node_os(Package, OS) : os(OS) } 1 :-
-   node(Package), error("Each node must have exactly one OS").
+{ node_os(Package, OS) : os(OS) } :- node(Package).
+
+error(2, "Cannot find valid operating system for '{0}'", Package)
+  :- node(Package),
+     C = #count{ OS : node_os(Package, OS)},
+     C < 1.
+
+error(2, "Cannot concretize {0} with multiple operating systems\n    Requested 'os={1}' and 'os={2}'", Package, OS1, OS2)
+  :- node(Package),
+     node_os(Package, OS1),
+     node_os(Package, OS2),
+     OS1 < OS2. %see [1]
 
 % can't have a non-buildable OS on a node we need to build
-:- build(Package), node_os(Package, OS), not buildable_os(OS),
-   error("No available OS can be built for").
+error(2, "Cannot concretize '{0} os={1}'. Operating system '{1}' is not buildable", Package, OS)
+ :- build(Package),
+    node_os(Package, OS),
+    not buildable_os(OS).
 
 % can't have dependencies on incompatible OS's
-:- depends_on(Package, Dependency),
-   node_os(Package, PackageOS),
-   node_os(Dependency, DependencyOS),
-   not os_compatible(PackageOS, DependencyOS),
-   build(Package),
-   error("Dependencies must have compatible OS's with their dependents").
+error(2, "{0} and dependency {1} have incompatible operating systems 'os={2}' and 'os={3}'", Package, Dependency, PackageOS, DependencyOS)
+  :- depends_on(Package, Dependency),
+     node_os(Package, PackageOS),
+     node_os(Dependency, DependencyOS),
+     not os_compatible(PackageOS, DependencyOS),
+     build(Package).
 
 % give OS choice weights according to os declarations
 node_os_weight(Package, Weight)
@@ -621,14 +676,24 @@ node_os(Package, OS) :- node_os_set(Package, OS), node(Package).
 %-----------------------------------------------------------------------------
 
 % Each node has only one target chosen among the known targets
-1 { node_target(Package, Target) : target(Target) } 1 :- node(Package), error("Each node must have exactly one target").
+{ node_target(Package, Target) : target(Target) } :- node(Package).
+
+error(2, "Cannot find valid target for '{0}'", Package)
+  :- node(Package),
+     C = #count{Target : node_target(Package, Target)},
+     C < 1.
+
+error(2, "Cannot concretize '{0}' with multiple targets\n    Requested 'target={1}' and 'target={2}'", Package, Target1, Target2)
+  :- node(Package),
+     node_target(Package, Target1),
+     node_target(Package, Target2),
+     Target1 < Target2. % see[1]
 
 % If a node must satisfy a target constraint, enforce it
-:- node_target(Package, Target),
-   node_target_satisfies(Package, Constraint),
-   not target_satisfies(Constraint, Target),
-   error("Node targets must satisfy node target constraints").
-
+error(1, "'{0} target={1}' cannot satisfy constraint 'target={2}'", Package, Target, Constraint)
+  :- node_target(Package, Target),
+     node_target_satisfies(Package, Constraint),
+     not target_satisfies(Constraint, Target).
 
 % If a node has a target and the target satisfies a constraint, then the target
 % associated with the node satisfies the same constraint
@@ -636,10 +701,10 @@ node_target_satisfies(Package, Constraint)
   :- node_target(Package, Target), target_satisfies(Constraint, Target).
 
 % If a node has a target, all of its dependencies must be compatible with that target
-:- depends_on(Package, Dependency),
-   node_target(Package, Target),
-   not node_target_compatible(Dependency, Target),
-   error("Dependency node targets must be compatible with dependent targets").
+error(2, "Cannot find compatible targets for {0} and {1}", Package, Dependency)
+  :- depends_on(Package, Dependency),
+     node_target(Package, Target),
+     not node_target_compatible(Dependency, Target).
 
 % Intermediate step for performance reasons
 % When the integrity constraint above was formulated including this logic
@@ -680,12 +745,12 @@ target_weight(Target, Package, Weight)
   :- package_target_weight(Target, Package, Weight).
 
 % can't use targets on node if the compiler for the node doesn't support them
-:- node_target(Package, Target),
-   not compiler_supports_target(Compiler, Version, Target),
-   node_compiler(Package, Compiler),
-   node_compiler_version(Package, Compiler, Version),
-   build(Package),
-   error("No satisfying compiler available is compatible with a satisfying target").
+error(2, "{0} compiler '{2}@{3}' incompatible with 'target={1}'", Package, Target, Compiler, Version)
+  :- node_target(Package, Target),
+     not compiler_supports_target(Compiler, Version, Target),
+     node_compiler(Package, Compiler),
+     node_compiler_version(Package, Compiler, Version),
+     build(Package).
 
 % if a target is set explicitly, respect it
 node_target(Package, Target)
@@ -712,8 +777,10 @@ node_target_mismatch(Parent, Dependency)
      not node_target_match(Parent, Dependency).
 
 % disallow reusing concrete specs that don't have a compatible target
-:- node(Package), node_target(Package, Target), not target(Target),
-   error("No satisfying package's target is compatible with this machine").
+error(2, "'{0} target={1}' is not compatible with this machine", Package, Target)
+  :- node(Package),
+     node_target(Package, Target),
+     not target(Target).
 
 #defined node_target_set/2.
 #defined package_target_weight/3.
@@ -725,10 +792,19 @@ compiler(Compiler) :- compiler_version(Compiler, _).
 
 % There must be only one compiler set per built node. The compiler
 % is chosen among available versions.
-1 { node_compiler_version(Package, Compiler, Version) : compiler_version(Compiler, Version) } 1 :-
+{ node_compiler_version(Package, Compiler, Version) : compiler_version(Compiler, Version) } :-
     node(Package),
-    build(Package),
-    error("Each node must have exactly one compiler").
+    build(Package).
+
+error(2, "No valid compiler version found for '{0}'", Package)
+  :- node(Package),
+     C = #count{ Version : node_compiler_version(Package, _, Version)},
+     C < 1.
+error(2, "'{0}' compiler constraints '%{1}@{2}' and '%{3}@{4}' are incompatible", Package, Compiler1, Version1, Compiler2, Version2)
+  :- node(Package),
+     node_compiler_version(Package, Compiler1, Version1),
+     node_compiler_version(Package, Compiler2, Version2),
+     (Compiler1, Version1) < (Compiler2, Version2). % see[1]
 
 % Sometimes we just need to know the compiler and not the version
 node_compiler(Package, Compiler) :- node_compiler_version(Package, Compiler, _).
@@ -737,14 +813,22 @@ node_compiler(Package, Compiler) :- node_compiler_version(Package, Compiler, _).
 :- node_compiler(Package, Compiler1),
    node_compiler_version(Package, Compiler2, _),
    Compiler1 != Compiler2,
-   error("Internal error: mismatch between selected compiler and compiler version").
+   internal_error("Mismatch between selected compiler and compiler version").
+
+% If the compiler of a node cannot be satisfied, raise
+error(1, "No valid compiler for {0} satisfies '%{1}'", Package, Compiler)
+  :- node(Package),
+     node_compiler_version_satisfies(Package, Compiler, ":"),
+     C = #count{ Version : node_compiler_version(Package, Compiler, Version), compiler_version_satisfies(Compiler, ":", Version) },
+     C < 1.
 
 % If the compiler of a node must satisfy a constraint, then its version
 % must be chosen among the ones that satisfy said constraint
-1 { node_compiler_version(Package, Compiler, Version)
-    : compiler_version_satisfies(Compiler, Constraint, Version) } 1 :-
-    node_compiler_version_satisfies(Package, Compiler, Constraint),
-    error("Internal error: node compiler version mismatch").
+error(2, "No valid version for '{0}' compiler '{1}' satisfies '@{2}'", Package, Compiler, Constraint)
+  :- node(Package),
+     node_compiler_version_satisfies(Package, Compiler, Constraint),
+     C = #count{ Version : node_compiler_version(Package, Compiler, Version), compiler_version_satisfies(Compiler, Constraint, Version) },
+     C < 1.
 
 % If the node is associated with a compiler and the compiler satisfy a constraint, then
 % the compiler associated with the node satisfy the same constraint
@@ -762,11 +846,12 @@ node_compiler_version(Package, Compiler, Version) :- node_compiler_version_set(P
 % Cannot select a compiler if it is not supported on the OS
 % Compilers that are explicitly marked as allowed
 % are excluded from this check
-:- node_compiler_version(Package, Compiler, Version), node_os(Package, OS),
-   not compiler_supports_os(Compiler, Version, OS),
-   not allow_compiler(Compiler, Version),
-   build(Package),
-   error("No satisfying compiler available is compatible with a satisfying os").
+error(2, "{0} compiler '%{1}@{2}' incompatible with 'os={3}'", Package, Compiler, Version, OS)
+  :- node_compiler_version(Package, Compiler, Version),
+     node_os(Package, OS),
+     not compiler_supports_os(Compiler, Version, OS),
+     not allow_compiler(Compiler, Version),
+     build(Package).
 
 % If a package and one of its dependencies don't have the
 % same compiler there's a mismatch.
@@ -859,7 +944,7 @@ no_flags(Package, FlagType)
 %-----------------------------------------------------------------------------
 % the solver is free to choose at most one installed hash for each package
 { hash(Package, Hash) : installed_hash(Package, Hash) } 1
- :- node(Package), error("Internal error: package must resolve to at most one hash").
+ :- node(Package), internal_error("Package must resolve to at most one hash").
 
 % you can't choose an installed hash for a dev spec
 :- hash(Package, Hash), variant_value(Package, "dev_path", _).
@@ -909,6 +994,23 @@ build_priority(Package, 0)   :- node(Package), not optimize_for_reuse().
 
 #defined installed_hash/2.
 
+%-----------------------------------------------------------------
+% Optimization to avoid errors
+%-----------------------------------------------------------------
+% Some errors are handled as rules instead of constraints because
+% it allows us to explain why something failed. Here we optimize
+% HEAVILY against the facts generated by those rules.
+#minimize{ 0@1000: #true}.
+#minimize{ 0@1001: #true}.
+#minimize{ 0@1002: #true}.
+
+#minimize{ 1000@1000+Priority,Msg: error(Priority, Msg) }.
+#minimize{ 1000@1000+Priority,Msg,Arg1: error(Priority, Msg, Arg1) }.
+#minimize{ 1000@1000+Priority,Msg,Arg1,Arg2: error(Priority, Msg, Arg1, Arg2) }.
+#minimize{ 1000@1000+Priority,Msg,Arg1,Arg2,Arg3: error(Priority, Msg, Arg1, Arg2, Arg3) }.
+#minimize{ 1000@1000+Priority,Msg,Arg1,Arg2,Arg3,Arg4: error(Priority, Msg, Arg1, Arg2, Arg3, Arg4) }.
+#minimize{ 1000@1000+Priority,Msg,Arg1,Arg2,Arg3,Arg4,Arg5: error(Priority, Msg, Arg1, Arg2, Arg3, Arg4, Arg5) }.
+
 %-----------------------------------------------------------------------------
 % How to optimize the spec (high to low priority)
 %-----------------------------------------------------------------------------
@@ -1088,3 +1190,11 @@ opt_criterion(1, "non-preferred targets").
 #heuristic variant_value(Package, Variant, Value) : variant_default_value(Package, Variant, Value), node(Package). [10, true]
 #heuristic provider(Package, Virtual) : possible_provider_weight(Package, Virtual, 0, _), virtual_node(Virtual). [10, true]
 #heuristic node(Package) : possible_provider_weight(Package, Virtual, 0, _), virtual_node(Virtual). [10, true]
+
+%-----------
+% Notes
+%-----------
+
+% [1] Clingo ensures a total ordering among all atoms. We rely on that total ordering
+%     to reduce symmetry in the solution by checking `<` instead of `!=` in symmetric
+%     cases. These choices are made without loss of generality.

lib/spack/spack/solver/display.lp

@@ -34,3 +34,13 @@
 
 % deprecated packages
 #show deprecated/2.
+
+% error types
+#show error/2.
+#show error/3.
+#show error/4.
+#show error/5.
+#show error/6.
+#show error/7.
+
+% debug

lib/spack/spack/test/cmd/install.py

@@ -532,7 +532,7 @@ def test_cdash_report_concretization_error(tmpdir, mock_fetch, install_mockery,
             # new or the old concretizer
             expected_messages = (
                 'Conflicts in concretized spec',
-                'A conflict was triggered',
+                'conflicts with',
             )
             assert any(x in content for x in expected_messages)
 

lib/spack/spack/test/concretize.py

@@ -638,14 +638,11 @@ def test_conflicts_show_cores(self, conflict_spec, monkeypatch):
         if spack.config.get('config:concretizer') == 'original':
             pytest.skip('Testing debug statements specific to new concretizer')
 
-        monkeypatch.setattr(spack.solver.asp, 'full_cores', True)
-        monkeypatch.setattr(spack.solver.asp, 'minimize_cores', False)
-
         s = Spec(conflict_spec)
         with pytest.raises(spack.error.SpackError) as e:
             s.concretize()
 
-        assert "conflict_trigger(" in e.value.message
+        assert "conflict" in e.value.message
 
     def test_conflict_in_all_directives_true(self):
         s = Spec('when-directives-true')

share/spack/spack-completion.bash

@@ -335,7 +335,7 @@ _spacktivate() {
 _spack() {
     if $list_options
     then
-        SPACK_COMPREPLY="-h --help -H --all-help --color -c --config -C --config-scope -d --debug --show-cores --timestamp --pdb -e --env -D --env-dir -E --no-env --use-env-repo -k --insecure -l --enable-locks -L --disable-locks -m --mock -b --bootstrap -p --profile --sorted-profile --lines -v --verbose --stacktrace -V --version --print-shell-vars"
+        SPACK_COMPREPLY="-h --help -H --all-help --color -c --config -C --config-scope -d --debug --timestamp --pdb -e --env -D --env-dir -E --no-env --use-env-repo -k --insecure -l --enable-locks -L --disable-locks -m --mock -b --bootstrap -p --profile --sorted-profile --lines -v --verbose --stacktrace -V --version --print-shell-vars"
     else
         SPACK_COMPREPLY="activate add analyze arch audit blame bootstrap build-env buildcache cd checksum ci clean clone commands compiler compilers concretize config containerize create deactivate debug dependencies dependents deprecate dev-build develop diff docs edit env extensions external fetch find gc gpg graph help info install license list load location log-parse maintainers make-installer mark mirror module monitor patch pkg providers pydoc python reindex remove rm repo resource restage solve spec stage style tags test test-env tutorial undevelop uninstall unit-test unload url verify versions view"
     fi