3 files changed, 42 insertions, 1 deletions
diff --git a/lib/spack/spack/solver/asp.py b/lib/spack/spack/solver/asp.py
index 4a8a3fbbc5..c1c3cb33a9 100644
--- a/lib/spack/spack/solver/asp.py
+++ b/lib/spack/spack/solver/asp.py
@@ -1617,7 +1617,7 @@ class SpackSolverSetup(object):
             index = spack.binary_distribution.update_cache_and_get_specs()
             for spec in index:
                 self._facts_from_concrete_spec(spec, possible)
-        except spack.binary_distribution.FetchCacheError:
+        except (spack.binary_distribution.FetchCacheError, IndexError):
             # this is raised when no mirrors had indices.
             # TODO: update mirror configuration so it can indicate that the source cache
             # TODO: (or any mirror really) doesn't have binaries.
diff --git a/lib/spack/spack/solver/concretize.lp b/lib/spack/spack/solver/concretize.lp
index d0a8a8a308..8ad2a9a78a 100644
--- a/lib/spack/spack/solver/concretize.lp
+++ b/lib/spack/spack/solver/concretize.lp
@@ -8,6 +8,22 @@
 %=============================================================================
 
 %-----------------------------------------------------------------------------
+% 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).
+:- 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
 %-----------------------------------------------------------------------------
 
@@ -79,6 +95,11 @@ attr(Name, A1)         :- impose(ID), imposed_constraint(ID, Name, A1).
 attr(Name, A1, A2)     :- impose(ID), imposed_constraint(ID, Name, A1, A2).
 attr(Name, A1, A2, A3) :- impose(ID), imposed_constraint(ID, Name, A1, A2, A3).
 
+% we cannot have additional variant values when we are working with concrete specs
+:- node(Package), hash(Package, Hash),
+   variant_value(Package, Variant, Value),
+   not imposed_constraint(Hash, "variant_value", Package, Variant, Value).
+
 #defined condition/1.
 #defined condition_requirement/3.
 #defined condition_requirement/4.
diff --git a/lib/spack/spack/test/concretize.py b/lib/spack/spack/test/concretize.py
index bbe84b8a7e..54d886a55b 100644
--- a/lib/spack/spack/test/concretize.py
+++ b/lib/spack/spack/test/concretize.py
@@ -1324,3 +1324,23 @@ class TestConcretize(object):
                 if pkg.name == 'low-priority-provider':
                     continue
                 assert pkg not in s
+
+    @pytest.mark.regression('27237')
+    @pytest.mark.parametrize('spec_str,expect_installed', [
+        ('mpich', True),
+        ('mpich+debug', False),
+        ('mpich~debug', True)
+    ])
+    def test_concrete_specs_are_not_modified_on_reuse(
+            self, mutable_database, spec_str, expect_installed
+    ):
+        if spack.config.get('config:concretizer') == 'original':
+            pytest.skip('Original concretizer cannot reuse specs')
+
+        # Test the internal consistency of solve + DAG reconstruction
+        # when reused specs are added to the mix. This prevents things
+        # like additional constraints being added to concrete specs in
+        # the answer set produced by clingo.
+        s = spack.spec.Spec(spec_str).concretized(reuse=True)
+        assert s.package.installed is expect_installed
+        assert s.satisfies(spec_str, strict=True)