error messages: compute connections between conditions

lib/spack/spack/solver/asp.py

@@ -1289,7 +1289,7 @@ def package_dependencies_rules(self, pkg):
                 if not deptypes:
                     continue
 
-                msg = "%s depends on %s" % (pkg.name, dep.spec.name)
+                msg = "%s depends on %s" % (pkg.name, dep.spec)
                 if cond != spack.spec.Spec():
                     msg += " when %s" % cond
 

lib/spack/spack/solver/concretize.lp

@@ -203,6 +203,28 @@ attr(Name, A1, A2, A3, A4) :- impose(ID), imposed_constraint(ID, Name, A1, A2, A
    not imposed_constraint(Hash, "node_flag", Package, FlagType, Flag),
    internal_error("imposed hash without imposing all flag values").
 
+% associated conditions by cause -> effect
+condition_cause(Effect, Cause) :-
+  condition_holds(Effect), condition_holds(Cause),
+  attr(Name, A1),
+  condition_requirement(Effect, Name, A1),
+  imposed_constraint(Cause, Name, A1).
+condition_cause(Effect, Cause) :-
+  condition_holds(Effect), condition_holds(Cause),
+  attr(Name, A1, A2),
+  condition_requirement(Effect, Name, A1, A2),
+  imposed_constraint(Cause, Name, A1, A2).
+condition_cause(Effect, Cause) :-
+  condition_holds(Effect), condition_holds(Cause),
+  attr(Name, A1, A2, A3),
+  condition_requirement(Effect, Name, A1, A2, A3),
+  imposed_constraint(Cause, Name, A1, A2, A3).
+condition_cause(Effect, Cause) :-
+  condition_holds(Effect), condition_holds(Cause),
+  attr(Name, A1, A2, A3, A4),
+  condition_requirement(Effect, Name, A1, A2, A3, A4),
+  imposed_constraint(Cause, Name, A1, A2, A3, A4).
+
 #defined condition/2.
 #defined condition_requirement/3.
 #defined condition_requirement/4.

lib/spack/spack/solver/display.lp

@@ -24,4 +24,8 @@
 #show error/5.
 #show error/6.
 
+% show cause -> effect data for errors
+#show condition_cause/2.
+#show condition/2.
+
 % debug