concretizer: treat conditional providers correctly (#20086)

refers #20040

This modification emits rules like:

provides_virtual("netlib-lapack","blas") :- variant_value("netlib-lapack","external-blas","False").

for packages that provide virtual dependencies conditionally instead
of a fact that doesn't account for the condition.

2 files changed, 18 insertions, 1 deletions

diff --git a/lib/spack/spack/solver/asp.py b/lib/spack/spack/solver/asp.py
index da24486c5c..022a57da50 100644
--- a/lib/spack/spack/solver/asp.py
+++ b/lib/spack/spack/solver/asp.py
@@ -1323,13 +1323,18 @@ class SpackSolverSetup(object):
             self.gen.fact(fn.virtual(vspec))
             all_providers = sorted(spack.repo.path.providers_for(vspec))
             for idx, provider in enumerate(all_providers):
-                self.gen.fact(fn.provides_virtual(provider.name, vspec))
+                provides_atom = fn.provides_virtual(provider.name, vspec)
                 possible_provider_fn = fn.possible_provider(
                     vspec, provider.name, idx
                 )
                 item = (idx, provider, possible_provider_fn)
                 self.providers_by_vspec_name[vspec].append(item)
                 clauses = self.spec_clauses(provider, body=True)
+                clauses_but_node = [c for c in clauses if c.name != 'node']
+                if clauses_but_node:
+                    self.gen.rule(provides_atom, AspAnd(*clauses_but_node))
+                else:
+                    self.gen.fact(provides_atom)
                 for clause in clauses:
                     self.gen.rule(clause, possible_provider_fn)
                 self.gen.newline()
diff --git a/lib/spack/spack/test/concretize.py b/lib/spack/spack/test/concretize.py
index 761641035f..b150d60426 100644
--- a/lib/spack/spack/test/concretize.py
+++ b/lib/spack/spack/test/concretize.py
@@ -883,3 +883,15 @@ class TestConcretize(object):
 
         # 'stuff' is provided by an external package, so check it's present
         assert 'externalvirtual' in s
+
+    @pytest.mark.regression('20040')
+    def test_conditional_provides_or_depends_on(self):
+        if spack.config.get('config:concretizer') == 'original':
+            pytest.xfail('Known failure of the original concretizer')
+
+        # Check that we can concretize correctly a spec that can either
+        # provide a virtual or depend on it based on the value of a variant
+        s = Spec('conditional-provider +disable-v1').concretized()
+        assert 'v1-provider' in s
+        assert s['v1'].name == 'v1-provider'
+        assert s['v2'].name == 'conditional-provider'