concretizer: add a rule to avoid cycles in the graph of dependencies

2 files changed, 9 insertions, 5 deletions

diff --git a/lib/spack/spack/solver/concretize.lp b/lib/spack/spack/solver/concretize.lp
index bf1d07a63d..9f8ab81161 100644
--- a/lib/spack/spack/solver/concretize.lp
+++ b/lib/spack/spack/solver/concretize.lp
@@ -111,6 +111,11 @@ needed(Dependency) :- needed(Package), depends_on(Package, Dependency).
 % real dependencies imply new nodes.
 node(Dependency) :- node(Package), depends_on(Package, Dependency).
 
+% Avoid cycles in the DAG
+path(Parent, Child) :- depends_on(Parent, Child).
+path(Parent, Descendant) :- path(Parent, A), depends_on(A, Descendant).
+:- path(A, B), path(B, A).
+
 % do not warn if generated program contains none of these.
 #defined depends_on/3.
 #defined declared_dependency/3.
diff --git a/lib/spack/spack/spec.py b/lib/spack/spack/spec.py
index 127091d8da..8a4fc12861 100644
--- a/lib/spack/spack/spec.py
+++ b/lib/spack/spack/spec.py
@@ -2372,11 +2372,10 @@ class Spec(object):
 
             patches = []
             for cond, dependency in pkg_deps[dspec.spec.name].items():
-                if dspec.parent.satisfies(cond, strict=True):
-                    for pcond, patch_list in dependency.patches.items():
-                        if dspec.spec.satisfies(pcond):
-                            for patch in patch_list:
-                                patches.append(patch)
+                for pcond, patch_list in dependency.patches.items():
+                    if (dspec.parent.satisfies(cond, strict=True)
+                            and dspec.spec.satisfies(pcond)):
+                        patches.extend(patch_list)
             if patches:
                 all_patches = spec_to_patches.setdefault(id(dspec.spec), [])
                 all_patches.extend(patches)