concretizer: use clingo json output instead of text

Clingo actually has an option to output JSON -- use that instead of
parsing the raw otuput ourselves.

This also allows us to pick the best answer -- modify the parser to
*only* construct a spec for that one rather than building all of them
like we did before.

lib/spack/spack/cmd/solve.py

@@ -22,7 +22,7 @@
 level = 'long'
 
 #: output options
-dump_options = ('asp', 'warnings', 'output', 'solutions')
+dump_options = ('asp', 'output', 'solutions')
 
 
 def setup_parser(subparser):
@@ -87,6 +87,8 @@ def solve(parser, args):
 
     # dump generated ASP program
     result = asp.solve(specs, dump=dump, models=models)
+    if dump == ['asp']:
+        return
 
     # die if no solution was found
     # TODO: we need to be able to provide better error messages than this
@@ -95,8 +97,15 @@ def solve(parser, args):
 
     # dump the solutions as concretized specs
     if 'solutions' in dump:
-        for i, answer in enumerate(result.answers):
-            tty.msg("Answer %d" % (i + 1))
+        best = min(result.answers)
+        assert best[1] == result.answers[-1][1]
+
+        opt, i, answer = best
+        tty.msg(
+            "%d Answers. Best optimization %s:" % (i + 1, opt)
+        )
+
+        # iterate over roots from command line
         for spec in specs:
             answer_spec = answer[spec.name]
             if args.yaml:

lib/spack/spack/solver/asp.py

@@ -6,6 +6,7 @@
 from __future__ import print_function
 
 import collections
+import json
 import pkgutil
 import re
 import sys
@@ -503,36 +504,13 @@ def depends_on(self, pkg, dep):
         self._specs[pkg]._add_dependency(
             self._specs[dep], ('link', 'run'))
 
-    def parse(self, stream, result):
-        for line in stream:
-            match = re.match(r'SATISFIABLE', line)
-            if match:
-                result.satisfiable = True
-                continue
-
-            match = re.match(r'OPTIMUM FOUND', line)
-            if match:
-                result.satisfiable = True
-                continue
-
-            match = re.match(r'UNSATISFIABLE', line)
-            if match:
-                result.satisfiable = False
-                continue
-
-            match = re.match(r'Answer: (\d+)', line)
-            if not match:
-                continue
-
-            answer_number = int(match.group(1))
-            assert answer_number == len(result.answers) + 1
-
-            answer = next(stream)
-            tty.debug("Answer: %d" % answer_number, answer)
+    def call_actions_for_functions(self, function_strings):
+        function_re = re.compile(r'(\w+)\(([^)]*)\)')
 
         # parse functions out of ASP output
         functions = []
-            for m in re.finditer(r'(\w+)\(([^)]*)\)', answer):
+        for string in function_strings:
+            m = function_re.match(string)
             name, arg_string = m.groups()
             args = re.split(r'\s*,\s*', arg_string)
             args = [s.strip('"') if s.startswith('"') else int(s)
@@ -553,14 +531,33 @@ def parse(self, stream, result):
             assert action and callable(action)
             action(*args)
 
-            result.answers.append(self._specs)
+    def parse_json(self, data, result):
+        if data["Result"] == "UNSATISFIABLE":
+            result.satisfiable = False
+            return
 
+        result.satisfiable = True
+        if data["Result"] == "OPTIMUM FOUND":
+            result.optimal = True
+
+        nmodels = data["Models"]["Number"]
+        best_model_number = nmodels - 1
+        best_model = data["Call"][0]["Witnesses"][best_model_number]
+        opt = list(best_model["Costs"])
+
+        functions = best_model["Value"]
+
+        self.call_actions_for_functions(functions)
+        result.answers.append((opt, best_model_number, self._specs))
 
 class Result(object):
     def __init__(self, asp):
         self.asp = asp
         self.satisfiable = None
+        self.optimal = None
         self.warnings = None
+
+        # specs ordered by optimization level
         self.answers = []
 
 
@@ -625,12 +622,18 @@ def colorize(string):
         if 'asp' in dump:
             if sys.stdout.isatty():
                 tty.msg('ASP program:')
+
+            if dump == ['asp']:
+                print(result.asp)
+                return
+            else:
                 colorize(result.asp)
 
         with tempfile.TemporaryFile("w+") as output:
             with tempfile.TemporaryFile() as warnings:
                 clingo(
-                    '--models=%d' % models,
+                    '--models=0',
+                    '--outf=2',
                     input=program,
                     output=output,
                     error=warnings,
@@ -640,7 +643,6 @@ def colorize(string):
                 result.warnings = warnings.read().decode("utf-8")
 
                 # dump any warnings generated by the solver
-                if 'warnings' in dump:
                 if result.warnings:
                     if sys.stdout.isatty():
                         tty.msg('Clingo gave the following warnings:')
@@ -651,14 +653,19 @@ def colorize(string):
 
                 output.seek(0)
                 result.output = output.read()
+                data = json.loads(result.output)
 
                 # dump the raw output of the solver
                 if 'output' in dump:
                     if sys.stdout.isatty():
                         tty.msg('Clingo output:')
-                    colorize(result.output)
+
+                    print(result.output)
+
+                    if 'solutions' not in dump:
+                        return
 
                 output.seek(0)
-                parser.parse(output, result)
+                parser.parse_json(data, result)
 
     return result