Propagate variant across nodes that don't have that variant (#38512)

Before this PR, variant were not propagated to leaf nodes that could accept 
the propagated value, if some intermediate node couldn't accept it.

This PR fixes that issue by marking nodes as "candidate" for propagation
and by setting the variant only if it can be accepted by the node.

Co-authored-by: Massimiliano Culpo <massimiliano.culpo@gmail.com>

5 files changed, 104 insertions, 0 deletions

diff --git a/var/spack/repos/builtin.mock/packages/adios2/package.py b/var/spack/repos/builtin.mock/packages/adios2/package.py
new file mode 100644
index 0000000000..fb2f43ea0e
--- /dev/null
+++ b/var/spack/repos/builtin.mock/packages/adios2/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 Adios2(Package):
+    """This packagae has the variants shared and
+    bzip2, both defaulted to True"""
+
+    homepage = "https://example.com"
+    url = "https://example.com/adios2.tar.gz"
+
+    version("2.9.1", sha256="ddfa32c14494250ee8a48ef1c97a1bf6442c15484bbbd4669228a0f90242f4f9")
+
+    variant("shared", default=True, description="Build shared libraries")
+    variant("bzip2", default=True, description="Enable BZip2 compression")
+
+    depends_on("bzip2")
diff --git a/var/spack/repos/builtin.mock/packages/ascent/package.py b/var/spack/repos/builtin.mock/packages/ascent/package.py
new file mode 100644
index 0000000000..9a8db472dc
--- /dev/null
+++ b/var/spack/repos/builtin.mock/packages/ascent/package.py
@@ -0,0 +1,21 @@
+# 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 Ascent(Package):
+    """This packagae has the variants shared, defaulted
+    to True and adios2 defaulted to False"""
+
+    homepage = "https://github.com/Alpine-DAV/ascent"
+    url = "http://www.example.com/ascent-1.0.tar.gz"
+
+    version("0.9.2", sha256="44cd954aa5db478ab40042cd54fd6fcedf25000c3bb510ca23fcff8090531b91")
+
+    variant("adios2", default=False, description="Build Adios2 filter support")
+    variant("shared", default=True, description="Build Ascent as shared libs")
+
+    depends_on("adios2", when="+adios2")
diff --git a/var/spack/repos/builtin.mock/packages/bzip2/package.py b/var/spack/repos/builtin.mock/packages/bzip2/package.py
new file mode 100644
index 0000000000..326533ac5e
--- /dev/null
+++ b/var/spack/repos/builtin.mock/packages/bzip2/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 Bzip2(Package):
+    """This packagae has the variants shared
+    defaulted to True"""
+
+    homepage = "https://example.com"
+    url = "https://example.com/bzip2-1.0.8tar.gz"
+
+    version("1.0.8", sha256="ab5a03176ee106d3f0fa90e381da478ddae405918153cca248e682cd0c4a2269")
+
+    variant("shared", default=True, description="Enables the build of shared libraries.")
diff --git a/var/spack/repos/builtin.mock/packages/dependency-foo-bar/package.py b/var/spack/repos/builtin.mock/packages/dependency-foo-bar/package.py
new file mode 100644
index 0000000000..21e67f8a61
--- /dev/null
+++ b/var/spack/repos/builtin.mock/packages/dependency-foo-bar/package.py
@@ -0,0 +1,20 @@
+# 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 DependencyFooBar(Package):
+    """This package has a variant "bar", which is False by default, and
+    variant "foo" which is True by default.
+    """
+
+    homepage = "http://www.example.com"
+    url = "http://www.example.com/dependency-foo-bar-1.0.tar.gz"
+
+    version("1.0", md5="1234567890abcdefg1234567890098765")
+
+    variant("foo", default=True, description="")
+    variant("bar", default=False, description="")
diff --git a/var/spack/repos/builtin.mock/packages/parent-foo-bar/package.py b/var/spack/repos/builtin.mock/packages/parent-foo-bar/package.py
new file mode 100644
index 0000000000..14516566a9
--- /dev/null
+++ b/var/spack/repos/builtin.mock/packages/parent-foo-bar/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 ParentFooBar(Package):
+    """This package has a variant "bar", which is True by default, and depends on another
+    package which has the same variant defaulting to False.
+    """
+
+    homepage = "http://www.example.com"
+    url = "http://www.example.com/parent-foo-bar-1.0.tar.gz"
+
+    version("1.0", md5="abcdefg0123456789abcdefghfedcba0")
+
+    variant("foo", default=True, description="")
+    variant("bar", default=True, description="")
+
+    depends_on("dependency-foo-bar")