ASP-based solver: don't sort when defining variant possible values (#29013)

fixes #28260

Since we iterate over different variants from many packages, the variant 
values may have types which are not comparable, which causes errors 
at runtime. This is not a real issue though, since we don't need the facts
to be ordered. Thus, to avoid needless sorting, the sorted function has 
been removed and a comment has been added to tip any developer that
might need to inspect these clauses for debugging to add back sorting 
on the first two items only.

It's kind of difficult to add a test for this, since the error depends on 
whether Python sorting algorithm ever needs to compare the third 
value of a tuple being ordered.

1 files changed, 3 insertions, 2 deletions

diff --git a/lib/spack/spack/solver/asp.py b/lib/spack/spack/solver/asp.py
index 0df83191a4..dfd2111453 100644
--- a/lib/spack/spack/solver/asp.py
+++ b/lib/spack/spack/solver/asp.py
@@ -1617,8 +1617,9 @@ class SpackSolverSetup(object):
 
         """
         # Tell the concretizer about possible values from specs we saw in
-        # spec_clauses()
-        for pkg, variant, value in sorted(self.variant_values_from_specs):
+        # spec_clauses(). We might want to order these facts by pkg and name
+        # if we are debugging.
+        for pkg, variant, value in self.variant_values_from_specs:
             self.gen.fact(fn.variant_possible_value(pkg, variant, value))
 
     def _facts_from_concrete_spec(self, spec, possible):