ASP-based solver: fix for unsplittable providers (#40859)

Some providers must provide virtuals "together", i.e.
if they provide one virtual of a set, they must be the
providers also of the others.

There was a bug though, where we were not checking if
the other virtuals in the set were needed at all in
the DAG.

This commit fixes the bug.

lib/spack/spack/solver/concretize.lp

@@ -492,7 +492,9 @@ error(100, "Package '{0}' needs to provide both '{1}' and '{2}' together, but pr
    pkg_fact(Package, provided_together(ID, SetID, Virtual2)),
    Virtual1 != Virtual2,
    attr("virtual_on_incoming_edges", node(X, Package), Virtual1),
-   not attr("virtual_on_incoming_edges", node(X, Package), Virtual2).
+   not attr("virtual_on_incoming_edges", node(X, Package), Virtual2),
+   attr("virtual_node", node(_, Virtual1)),
+   attr("virtual_node", node(_, Virtual2)).
 
 % if a package depends on a virtual, it's not external and we have a
 % provider for that virtual then it depends on the provider

lib/spack/spack/test/concretize.py

@@ -2360,3 +2360,16 @@ def test_condition_triggered_by_edge_property(
 
         for not_expected in expected_not_satisfies:
             assert not s.satisfies(not_expected), str(not_expected)
+
+    def test_virtuals_provided_together_but_only_one_required_in_dag(self):
+        """Tests that we can use a provider that provides more than one virtual together,
+        and is providing only one, iff the others are not needed in the DAG.
+
+        o blas-only-client
+        | [virtual=blas]
+        o openblas (provides blas and lapack together)
+
+        """
+        s = Spec("blas-only-client ^openblas").concretized()
+        assert s.satisfies("^[virtuals=blas] openblas")
+        assert not s.satisfies("^[virtuals=blas,lapack] openblas")

var/spack/repos/edges.test/packages/blas-only-client/package.py

@@ -0,0 +1,19 @@
+# Copyright 2013-2023 Lawrence Livermore National Security, LLC and other
+# Spack Project Developers. See the top-level COPYRIGHT file for details.
+#
+# SPDX-License-Identifier: (Apache-2.0 OR MIT)
+
+from spack.package import *
+
+
+class BlasOnlyClient(Package):
+    """This package depends on the 'blas' virtual only, but should be able to use also provider
+    that provide e.g. 'blas' together with 'lapack'.
+    """
+
+    homepage = "http://www.openblas.net"
+    url = "http://github.com/xianyi/OpenBLAS/archive/v0.2.15.tar.gz"
+
+    version("0.2.16", md5="b1190f3d3471685f17cfd1ec1d252ac9")
+
+    depends_on("blas")

var/spack/repos/edges.test/packages/openblas/package.py

@@ -0,0 +1,22 @@
+# Copyright 2013-2023 Lawrence Livermore National Security, LLC and other
+# Spack Project Developers. See the top-level COPYRIGHT file for details.
+#
+# SPDX-License-Identifier: (Apache-2.0 OR MIT)
+
+from spack.package import *
+
+
+class Openblas(Package):
+    """This package provides two virtuals together, so if one is chosen the other
+    must be used too if needed.
+    """
+
+    homepage = "http://www.openblas.net"
+    url = "http://github.com/xianyi/OpenBLAS/archive/v0.2.15.tar.gz"
+
+    version("0.2.16", md5="b1190f3d3471685f17cfd1ec1d252ac9")
+    version("0.2.15", md5="b1190f3d3471685f17cfd1ec1d252ac9")
+    version("0.2.14", md5="b1190f3d3471685f17cfd1ec1d252ac9")
+    version("0.2.13", md5="b1190f3d3471685f17cfd1ec1d252ac9")
+
+    provides("blas", "lapack")