Configuration: allow users to enforce hard spec constraints (#27987)

Spack doesn't have an easy way to say something like "If I build
package X, then I *need* version Y":

* If you specify something on the command line, then you ensure
  that the constraints are applied, but the package is always built
* Likewise if you `spack add X...`` to your environment, the
  constraints are guaranteed to hold, but the environment always
  builds the package
* You can add preferences to packages.yaml, but these are not
  guaranteed to hold (Spack can choose other settings)

This commit adds a 'require' subsection to packages.yaml: the
specs added there are guaranteed to hold. The commit includes
documentation for the feature.

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

7 files changed, 545 insertions, 75 deletions

diff --git a/lib/spack/docs/build_settings.rst b/lib/spack/docs/build_settings.rst
index 568b92aac3..c306536c51 100644
--- a/lib/spack/docs/build_settings.rst
+++ b/lib/spack/docs/build_settings.rst
@@ -339,6 +339,72 @@ concretization rules.  A provider lists a value that packages may
 ``depend_on`` (e.g, MPI) and a list of rules for fulfilling that
 dependency.
 
+.. _package-requirements:
+
+--------------------
+Package Requirements
+--------------------
+
+You can use the configuration to force the concretizer to choose
+specific properties for packages when building them. Like preferences,
+these are only applied when the package is required by some other
+request (e.g. if the package is needed as a dependency of a
+request to ``spack install``).
+
+An example of where this is useful is if you have a package that
+is normally built as a dependency but only under certain circumstances
+(e.g. only when a variant on a dependent is active): you can make
+sure that it always builds the way you want it to; this distinguishes
+package configuration requirements from constraints that you add to
+``spack install`` or to environments (in those cases, the associated
+packages are always built).
+
+The following is an example of how to enforce package properties in
+``packages.yaml``:
+
+.. code-block:: yaml
+
+   packages:
+     libfabric:
+       require: "@1.13.2"
+     openmpi:
+       require:
+       - any_of: ["~cuda", "gcc"]
+     mpich:
+      require:
+      - one_of: ["+cuda", "+rocm"]
+
+Requirements are expressed using Spec syntax (the same as what is provided
+to ``spack install``). In the simplest case, you can specify attributes
+that you always want the package to have by providing a single spec to
+``require``; in the above example, ``libfabric`` will always build
+with version 1.13.2.
+
+You can provide a more-relaxed constraint and allow the concretizer to
+choose between a set of options using ``any_of`` or ``one_of``:
+
+* ``any_of`` is a list of specs. One of those specs must be satisfied
+  and it is also allowed for the concretized spec to match more than one.
+  In the above example, that means you could build ``openmpi+cuda%gcc``,
+  ``openmpi~cuda%clang`` or ``openmpi~cuda%gcc`` (in the last case,
+  note that both specs in the ``any_of`` for ``openmpi`` are
+  satisfied).
+* ``one_of`` is also a list of specs, and the final concretized spec
+  must match exactly one of them.  In the above example, that means
+  you could build ``mpich+cuda`` or ``mpich+rocm`` but not
+  ``mpich+cuda+rocm`` (note the current package definition for
+  ``mpich`` already includes a conflict, so this is redundant but
+  still demonstrates the concept).
+
+Other notes about ``requires``:
+
+* You can only specify requirements for specific packages: you cannot
+  add ``requires`` under ``all``.
+* You cannot specify requirements for virtual packages (e.g. you can
+  specify requirements for ``openmpi`` but not ``mpi``).
+* For ``any_of`` and ``one_of``, the order of specs indicates a
+  preference: items that appear earlier in the list are preferred
+  (note that these preferences can be ignored in favor of others).
 
 .. _package_permissions:
 
diff --git a/lib/spack/spack/schema/packages.py b/lib/spack/spack/schema/packages.py
index 87d489028e..92fe9e0ba8 100644
--- a/lib/spack/spack/schema/packages.py
+++ b/lib/spack/spack/schema/packages.py
@@ -21,6 +21,29 @@ properties = {
                 "default": {},
                 "additionalProperties": False,
                 "properties": {
+                    "require": {
+                        "oneOf": [
+                            # 'require' can be a list of requirement_groups.
+                            # each requirement group is a list of one or more
+                            # specs. Either at least one or exactly one spec
+                            # in the group must be satisfied (depending on
+                            # whether you use "any_of" or "one_of",
+                            # repectively)
+                            {
+                                "type": "array",
+                                "items": {
+                                    "type": "object",
+                                    "properties": {
+                                        "one_of": {"type": "array"},
+                                        "any_of": {"type": "array"},
+                                    },
+                                },
+                            },
+                            # Shorthand for a single requirement group with
+                            # one member
+                            {"type": "string"},
+                        ]
+                    },
                     "version": {
                         "type": "array",
                         "default": [],
diff --git a/lib/spack/spack/solver/asp.py b/lib/spack/spack/solver/asp.py
index c28e6f459a..080e21ca5f 100644
--- a/lib/spack/spack/solver/asp.py
+++ b/lib/spack/spack/solver/asp.py
@@ -927,6 +927,30 @@ class SpackSolverSetup(object):
                 fn.node_compiler_preference(pkg.name, cspec.name, cspec.version, -i * 100)
             )
 
+    def package_requirement_rules(self, pkg):
+        pkg_name = pkg.name
+        config = spack.config.get("packages")
+        requirements = config.get(pkg_name, {}).get("require", [])
+        if isinstance(requirements, string_types):
+            rules = [(pkg_name, "one_of", [requirements])]
+        else:
+            rules = []
+            for requirement in requirements:
+                for policy in ("one_of", "any_of"):
+                    if policy in requirement:
+                        rules.append((pkg_name, policy, requirement[policy]))
+
+        for requirement_grp_id, (pkg_name, policy, requirement_grp) in enumerate(rules):
+            self.gen.fact(fn.requirement_group(pkg_name, requirement_grp_id))
+            self.gen.fact(fn.requirement_policy(pkg_name, requirement_grp_id, policy))
+            for requirement_weight, spec_str in enumerate(requirement_grp):
+                spec = spack.spec.Spec(spec_str)
+                if not spec.name:
+                    spec.name = pkg_name
+                member_id = self.condition(spec, imposed_spec=spec, name=pkg_name)
+                self.gen.fact(fn.requirement_group_member(member_id, pkg_name, requirement_grp_id))
+                self.gen.fact(fn.requirement_has_weight(member_id, requirement_weight))
+
     def pkg_rules(self, pkg, tests):
         pkg = packagize(pkg)
 
@@ -1017,6 +1041,8 @@ class SpackSolverSetup(object):
             lambda v, p, i: self.gen.fact(fn.pkg_provider_preference(pkg.name, v, p, i)),
         )
 
+        self.package_requirement_rules(pkg)
+
     def condition(self, required_spec, imposed_spec=None, name=None, msg=None):
         """Generate facts for a dependency or virtual provider condition.
 
diff --git a/lib/spack/spack/solver/concretize.lp b/lib/spack/spack/solver/concretize.lp
index 8ed6b1b6bb..3a497c1d3b 100644
--- a/lib/spack/spack/solver/concretize.lp
+++ b/lib/spack/spack/solver/concretize.lp
@@ -501,6 +501,49 @@ error(2, "Attempted to use external for '{0}' which does not satisfy any configu
 #defined external_spec_condition/5.
 
 %-----------------------------------------------------------------------------
+% Config required semantics
+%-----------------------------------------------------------------------------
+
+requirement_group_satisfied(Package, X) :-
+  1 { condition_holds(Y) : requirement_group_member(Y, Package, X) } 1,
+  node(Package),
+  requirement_policy(Package, X, "one_of"),
+  requirement_group(Package, X).
+
+requirement_weight(Package, W) :-
+  condition_holds(Y),
+  requirement_has_weight(Y, W),
+  requirement_group_member(Y, Package, X),
+  requirement_policy(Package, X, "one_of"),
+  requirement_group_satisfied(Package, X).
+
+requirement_group_satisfied(Package, X) :-
+  1 { condition_holds(Y) : requirement_group_member(Y, Package, X) } ,
+  node(Package),
+  requirement_policy(Package, X, "any_of"),
+  requirement_group(Package, X).
+
+requirement_weight(Package, W) :-
+  W = #min {
+    Z : requirement_has_weight(Y, Z), condition_holds(Y), requirement_group_member(Y, Package, X);
+    % We need this to avoid an annoying warning during the solve
+    %   concretize.lp:1151:5-11: info: tuple ignored:
+    %   #sup@73
+    10000
+  },
+  requirement_policy(Package, X, "any_of"),
+  requirement_group_satisfied(Package, X).
+
+error(2, "Cannot satisfy requirement group for package '{0}'", Package) :-
+  node(Package),
+  requirement_group(Package, X),
+  not requirement_group_satisfied(Package, X).
+
+#defined requirement_group/2.
+#defined requirement_group_member/3.
+#defined requirement_has_weight/2.
+
+%-----------------------------------------------------------------------------
 % Variant semantics
 %-----------------------------------------------------------------------------
 % a variant is a variant of a package if it is a variant under some condition
@@ -898,8 +941,7 @@ error(2, "No valid version for '{0}' compiler '{1}' satisfies '@{2}'", Package,
 % the compiler associated with the node satisfy the same constraint
 node_compiler_version_satisfies(Package, Compiler, Constraint)
   :- node_compiler_version(Package, Compiler, Version),
-     compiler_version_satisfies(Compiler, Constraint, Version),
-     build(Package).
+     compiler_version_satisfies(Compiler, Constraint, Version).
 
 #defined compiler_version_satisfies/3.
 
@@ -1092,12 +1134,24 @@ opt_criterion(100, "number of packages to build (vs. reuse)").
 #minimize { 1@100,Package : build(Package), optimize_for_reuse() }.
 #defined optimize_for_reuse/0.
 
+% A condition group specifies one or more specs that must be satisfied.
+% Specs declared first are preferred, so we assign increasing weights and
+% minimize the weights.
+opt_criterion(75, "requirement weight").
+#minimize{ 0@275: #true }.
+#minimize{ 0@75: #true }.
+#minimize {
+    Weight@75+Priority
+    : requirement_weight(Package, Weight),
+      build_priority(Package, Priority)
+}.
+
 % Minimize the number of deprecated versions being used
-opt_criterion(15, "deprecated versions used").
-#minimize{ 0@215: #true }.
-#minimize{ 0@15: #true }.
+opt_criterion(73, "deprecated versions used").
+#minimize{ 0@273: #true }.
+#minimize{ 0@73: #true }.
 #minimize{
-    1@15+Priority,Package
+    1@73+Priority,Package
     : deprecated(Package, _),
       build_priority(Package, Priority)
 }.
@@ -1106,51 +1160,51 @@ opt_criterion(15, "deprecated versions used").
 % 1. Version weight
 % 2. Number of variants with a non default value, if not set
 % for the root(Package)
-opt_criterion(14, "version weight").
-#minimize{ 0@214: #true }.
-#minimize{ 0@14: #true }.
+opt_criterion(70, "version weight").
+#minimize{ 0@270: #true }.
+#minimize{ 0@70: #true }.
 #minimize {
-    Weight@14+Priority
+    Weight@70+Priority
     : root(Package),version_weight(Package, Weight),
       build_priority(Package, Priority)
 }.
 
-opt_criterion(13, "number of non-default variants (roots)").
-#minimize{ 0@213: #true }.
-#minimize{ 0@13: #true }.
+opt_criterion(65, "number of non-default variants (roots)").
+#minimize{ 0@265: #true }.
+#minimize{ 0@65: #true }.
 #minimize {
-    1@13+Priority,Package,Variant,Value
+    1@65+Priority,Package,Variant,Value
     : variant_not_default(Package, Variant, Value),
       root(Package),
       build_priority(Package, Priority)
 }.
 
-opt_criterion(12, "preferred providers for roots").
-#minimize{ 0@212 : #true }.
-#minimize{ 0@12: #true }.
+opt_criterion(60, "preferred providers for roots").
+#minimize{ 0@260: #true }.
+#minimize{ 0@60: #true }.
 #minimize{
-    Weight@12+Priority,Provider,Virtual
+    Weight@60+Priority,Provider,Virtual
     : provider_weight(Provider, Virtual, Weight),
       root(Provider),
       build_priority(Provider, Priority)
 }.
 
-opt_criterion(11, "default values of variants not being used (roots)").
-#minimize{ 0@211: #true }.
-#minimize{ 0@11: #true }.
+opt_criterion(55, "default values of variants not being used (roots)").
+#minimize{ 0@255: #true }.
+#minimize{ 0@55: #true }.
 #minimize{
-    1@11+Priority,Package,Variant,Value
+    1@55+Priority,Package,Variant,Value
     : variant_default_not_used(Package, Variant, Value),
       root(Package),
       build_priority(Package, Priority)
 }.
 
 % Try to use default variants or variants that have been set
-opt_criterion(10, "number of non-default variants (non-roots)").
-#minimize{ 0@210: #true }.
-#minimize{ 0@10: #true }.
+opt_criterion(50, "number of non-default variants (non-roots)").
+#minimize{ 0@250: #true }.
+#minimize{ 0@50: #true }.
 #minimize {
-    1@10+Priority,Package,Variant,Value
+    1@50+Priority,Package,Variant,Value
     : variant_not_default(Package, Variant, Value),
       not root(Package),
       build_priority(Package, Priority)
@@ -1158,91 +1212,91 @@ opt_criterion(10, "number of non-default variants (non-roots)").
 
 % Minimize the weights of the providers, i.e. use as much as
 % possible the most preferred providers
-opt_criterion(9, "preferred providers (non-roots)").
-#minimize{ 0@209: #true }.
-#minimize{ 0@9: #true }.
+opt_criterion(45, "preferred providers (non-roots)").
+#minimize{ 0@245: #true }.
+#minimize{ 0@45: #true }.
 #minimize{
-    Weight@9+Priority,Provider,Virtual
+    Weight@45+Priority,Provider,Virtual
     : provider_weight(Provider, Virtual, Weight), not root(Provider),
       build_priority(Provider, Priority)
 }.
 
 % Try to minimize the number of compiler mismatches in the DAG.
-opt_criterion(8, "compiler mismatches").
-#minimize{ 0@208: #true }.
-#minimize{ 0@8: #true }.
+opt_criterion(40, "compiler mismatches").
+#minimize{ 0@240: #true }.
+#minimize{ 0@40: #true }.
 #minimize{
-    1@8+Priority,Package,Dependency
+    1@40+Priority,Package,Dependency
     : compiler_mismatch(Package, Dependency),
       build_priority(Package, Priority)
 }.
 
 % Try to minimize the number of compiler mismatches in the DAG.
-opt_criterion(7, "OS mismatches").
-#minimize{ 0@207: #true }.
-#minimize{ 0@7: #true }.
+opt_criterion(35, "OS mismatches").
+#minimize{ 0@235: #true }.
+#minimize{ 0@35: #true }.
 #minimize{
-    1@7+Priority,Package,Dependency
+    1@35+Priority,Package,Dependency
     : node_os_mismatch(Package, Dependency),
       build_priority(Package, Priority)
 }.
 
-opt_criterion(6, "non-preferred OS's").
-#minimize{ 0@206: #true }.
-#minimize{ 0@6: #true }.
+opt_criterion(30, "non-preferred OS's").
+#minimize{ 0@230: #true }.
+#minimize{ 0@30: #true }.
 #minimize{
-    Weight@6+Priority,Package
+    Weight@30+Priority,Package
     : node_os_weight(Package, Weight),
       build_priority(Package, Priority)
 }.
 
 % Choose more recent versions for nodes
-opt_criterion(5, "version badness").
-#minimize{ 0@205: #true }.
-#minimize{ 0@5: #true }.
+opt_criterion(25, "version badness").
+#minimize{ 0@225: #true }.
+#minimize{ 0@25: #true }.
 #minimize{
-    Weight@5+Priority,Package
+    Weight@25+Priority,Package
     : version_weight(Package, Weight),
       build_priority(Package, Priority)
 }.
 
 % Try to use all the default values of variants
-opt_criterion(4, "default values of variants not being used (non-roots)").
-#minimize{ 0@204: #true }.
-#minimize{ 0@4: #true }.
+opt_criterion(20, "default values of variants not being used (non-roots)").
+#minimize{ 0@220: #true }.
+#minimize{ 0@20: #true }.
 #minimize{
-    1@4+Priority,Package,Variant,Value
+    1@20+Priority,Package,Variant,Value
     : variant_default_not_used(Package, Variant, Value),
       not root(Package),
       build_priority(Package, Priority)
 }.
 
 % Try to use preferred compilers
-opt_criterion(3, "non-preferred compilers").
-#minimize{ 0@203: #true }.
-#minimize{ 0@3: #true }.
+opt_criterion(15, "non-preferred compilers").
+#minimize{ 0@215: #true }.
+#minimize{ 0@15: #true }.
 #minimize{
-    Weight@3+Priority,Package
+    Weight@15+Priority,Package
     : compiler_weight(Package, Weight),
       build_priority(Package, Priority)
 }.
 
 % Minimize the number of mismatches for targets in the DAG, try
 % to select the preferred target.
-opt_criterion(2, "target mismatches").
-#minimize{ 0@202: #true }.
-#minimize{ 0@2: #true }.
+opt_criterion(10, "target mismatches").
+#minimize{ 0@210: #true }.
+#minimize{ 0@10: #true }.
 #minimize{
-    1@2+Priority,Package,Dependency
+    1@10+Priority,Package,Dependency
     : node_target_mismatch(Package, Dependency),
       build_priority(Package, Priority)
 }.
 
-opt_criterion(1, "non-preferred targets").
-#minimize{ 0@201: #true }.
-#minimize{ 0@1: #true }.
+opt_criterion(5, "non-preferred targets").
+#minimize{ 0@205: #true }.
+#minimize{ 0@5: #true }.
 #minimize{
-    Weight@1+Priority,Package
+    Weight@5+Priority,Package
     : node_target_weight(Package, Weight),
       build_priority(Package, Priority)
 }.
diff --git a/lib/spack/spack/test/concretize_preferences.py b/lib/spack/spack/test/concretize_preferences.py
index 379e5447d0..9ad5a498ee 100644
--- a/lib/spack/spack/test/concretize_preferences.py
+++ b/lib/spack/spack/test/concretize_preferences.py
@@ -12,24 +12,12 @@ import spack.config
 import spack.package_prefs
 import spack.repo
 import spack.util.spack_yaml as syaml
-from spack.config import ConfigError, ConfigScope
+from spack.config import ConfigError
 from spack.spec import Spec
 from spack.version import Version
 
 
 @pytest.fixture()
-def concretize_scope(mutable_config, tmpdir):
-    """Adds a scope for concretization preferences"""
-    tmpdir.ensure_dir("concretize")
-    mutable_config.push_scope(ConfigScope("concretize", str(tmpdir.join("concretize"))))
-
-    yield
-
-    mutable_config.pop_scope()
-    spack.repo.path._provider_index = None
-
-
-@pytest.fixture()
 def configure_permissions():
     conf = syaml.load_config(
         """\
diff --git a/lib/spack/spack/test/concretize_requirements.py b/lib/spack/spack/test/concretize_requirements.py
new file mode 100644
index 0000000000..42d680dd72
--- /dev/null
+++ b/lib/spack/spack/test/concretize_requirements.py
@@ -0,0 +1,299 @@
+# Copyright 2013-2022 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)
+
+import sys
+
+import pytest
+
+import spack.config
+import spack.repo
+import spack.util.spack_yaml as syaml
+from spack.solver.asp import UnsatisfiableSpecError
+from spack.spec import Spec
+
+pytestmark = pytest.mark.skipif(sys.platform == "win32", reason="Windows uses old concretizer")
+
+
+def update_packages_config(conf_str):
+    conf = syaml.load_config(conf_str)
+    spack.config.set("packages", conf["packages"], scope="concretize")
+
+
+_pkgx = (
+    "x",
+    """\
+class X(Package):
+    version('1.1')
+    version('1.0')
+    version('0.9')
+
+    variant('shared', default=True,
+            description='Build shared libraries')
+
+    depends_on('y')
+""",
+)
+
+
+_pkgy = (
+    "y",
+    """\
+class Y(Package):
+    version('2.5')
+    version('2.4')
+    version('2.3', deprecated=True)
+
+    variant('shared', default=True,
+            description='Build shared libraries')
+""",
+)
+
+
+_pkgv = (
+    "v",
+    """\
+class V(Package):
+    version('2.1')
+    version('2.0')
+""",
+)
+
+
+@pytest.fixture
+def create_test_repo(tmpdir, mutable_config):
+    repo_path = str(tmpdir)
+    repo_yaml = tmpdir.join("repo.yaml")
+    with open(str(repo_yaml), "w") as f:
+        f.write(
+            """\
+repo:
+  namespace: testcfgrequirements
+"""
+        )
+
+    packages_dir = tmpdir.join("packages")
+    for (pkg_name, pkg_str) in [_pkgx, _pkgy, _pkgv]:
+        pkg_dir = packages_dir.ensure(pkg_name, dir=True)
+        pkg_file = pkg_dir.join("package.py")
+        with open(str(pkg_file), "w") as f:
+            f.write(pkg_str)
+
+    yield spack.repo.Repo(repo_path)
+
+
+@pytest.fixture
+def test_repo(create_test_repo, monkeypatch, mock_stage):
+    with spack.repo.use_repositories(create_test_repo) as mock_repo_path:
+        yield mock_repo_path
+
+
+class MakeStage(object):
+    def __init__(self, stage):
+        self.stage = stage
+
+    def __call__(self, *args, **kwargs):
+        return self.stage
+
+
+@pytest.fixture
+def fake_installs(monkeypatch, tmpdir):
+    stage_path = str(tmpdir.ensure("fake-stage", dir=True))
+    universal_unused_stage = spack.stage.DIYStage(stage_path)
+    monkeypatch.setattr(
+        spack.package_base.Package, "_make_stage", MakeStage(universal_unused_stage)
+    )
+
+
+def test_requirement_isnt_optional(concretize_scope, test_repo):
+    """If a user spec requests something that directly conflicts
+    with a requirement, make sure we get an error.
+    """
+    if spack.config.get("config:concretizer") == "original":
+        pytest.skip("Original concretizer does not support configuration" " requirements")
+
+    conf_str = """\
+packages:
+  x:
+    require: "@1.0"
+"""
+    update_packages_config(conf_str)
+    with pytest.raises(UnsatisfiableSpecError):
+        Spec("x@1.1").concretize()
+
+
+def test_requirement_is_successfully_applied(concretize_scope, test_repo):
+    """If a simple requirement can be satisfied, make sure the
+    concretization succeeds and the requirement spec is applied.
+    """
+    if spack.config.get("config:concretizer") == "original":
+        pytest.skip("Original concretizer does not support configuration" " requirements")
+
+    s1 = Spec("x").concretized()
+    # Without any requirements/preferences, the later version is preferred
+    assert s1.satisfies("@1.1")
+
+    conf_str = """\
+packages:
+  x:
+    require: "@1.0"
+"""
+    update_packages_config(conf_str)
+    s2 = Spec("x").concretized()
+    # The requirement forces choosing the eariler version
+    assert s2.satisfies("@1.0")
+
+
+def test_multiple_packages_requirements_are_respected(concretize_scope, test_repo):
+    """Apply requirements to two packages; make sure the concretization
+    succeeds and both requirements are respected.
+    """
+    if spack.config.get("config:concretizer") == "original":
+        pytest.skip("Original concretizer does not support configuration" " requirements")
+
+    conf_str = """\
+packages:
+  x:
+    require: "@1.0"
+  y:
+    require: "@2.4"
+"""
+    update_packages_config(conf_str)
+    spec = Spec("x").concretized()
+    assert spec["x"].satisfies("@1.0")
+    assert spec["y"].satisfies("@2.4")
+
+
+def test_oneof(concretize_scope, test_repo):
+    """'one_of' allows forcing the concretizer to satisfy one of
+    the specs in the group (but not all have to be satisfied).
+    """
+    if spack.config.get("config:concretizer") == "original":
+        pytest.skip("Original concretizer does not support configuration" " requirements")
+
+    conf_str = """\
+packages:
+  y:
+    require:
+    - one_of: ["@2.4", "~shared"]
+"""
+    update_packages_config(conf_str)
+    spec = Spec("x").concretized()
+    # The concretizer only has to satisfy one of @2.4/~shared, and @2.4
+    # comes first so it is prioritized
+    assert spec["y"].satisfies("@2.4+shared")
+
+
+def test_one_package_multiple_oneof_groups(concretize_scope, test_repo):
+    """One package has two 'one_of' groups; check that both are
+    applied.
+    """
+    if spack.config.get("config:concretizer") == "original":
+        pytest.skip("Original concretizer does not support configuration" " requirements")
+
+    conf_str = """\
+packages:
+  y:
+    require:
+    - one_of: ["@2.4%gcc", "@2.5%clang"]
+    - one_of: ["@2.5~shared", "@2.4+shared"]
+"""
+    update_packages_config(conf_str)
+
+    s1 = Spec("y@2.5").concretized()
+    assert s1.satisfies("%clang~shared")
+
+    s2 = Spec("y@2.4").concretized()
+    assert s2.satisfies("%gcc+shared")
+
+
+def test_requirements_for_package_that_is_not_needed(concretize_scope, test_repo):
+    """Specify requirements for specs that are not concretized or
+    a dependency of a concretized spec (in other words, none of
+    the requirements are used for the requested spec).
+    """
+    if spack.config.get("config:concretizer") == "original":
+        pytest.skip("Original concretizer does not support configuration" " requirements")
+
+    # Note that the exact contents aren't important since this isn't
+    # intended to be used, but the important thing is that a number of
+    # packages have requirements applied
+    conf_str = """\
+packages:
+  x:
+    require: "@1.0"
+  y:
+    require:
+    - one_of: ["@2.4%gcc", "@2.5%clang"]
+    - one_of: ["@2.5~shared", "@2.4+shared"]
+"""
+    update_packages_config(conf_str)
+
+    s1 = Spec("v").concretized()
+    assert s1.satisfies("@2.1")
+
+
+def test_oneof_ordering(concretize_scope, test_repo):
+    """Ensure that earlier elements of 'one_of' have higher priority.
+    This priority should override default priority (e.g. choosing
+    later versions).
+    """
+    if spack.config.get("config:concretizer") == "original":
+        pytest.skip("Original concretizer does not support configuration" " requirements")
+
+    conf_str = """\
+packages:
+  y:
+    require:
+    - one_of: ["@2.4", "@2.5"]
+"""
+    update_packages_config(conf_str)
+
+    s1 = Spec("y").concretized()
+    assert s1.satisfies("@2.4")
+
+    s2 = Spec("y@2.5").concretized()
+    assert s2.satisfies("@2.5")
+
+
+def test_reuse_oneof(concretize_scope, create_test_repo, mutable_database, fake_installs):
+    if spack.config.get("config:concretizer") == "original":
+        pytest.skip("Original concretizer does not support configuration" " requirements")
+
+    conf_str = """\
+packages:
+  y:
+    require:
+    - one_of: ["@2.5", "%gcc"]
+"""
+
+    with spack.repo.use_repositories(create_test_repo):
+        s1 = Spec("y@2.5%gcc").concretized()
+        s1.package.do_install(fake=True, explicit=True)
+
+        update_packages_config(conf_str)
+
+        with spack.config.override("concretizer:reuse", True):
+            s2 = Spec("y").concretized()
+            assert not s2.satisfies("@2.5 %gcc")
+
+
+def test_requirements_are_higher_priority_than_deprecation(concretize_scope, test_repo):
+    """Test that users can override a deprecated version with a requirement."""
+    if spack.config.get("config:concretizer") == "original":
+        pytest.skip("Original concretizer does not support configuration" " requirements")
+
+    # @2.3 is a deprecated versions. Ensure that any_of picks both constraints,
+    # since they are possible
+    conf_str = """\
+packages:
+  y:
+    require:
+    - any_of: ["@2.3", "%gcc"]
+"""
+    update_packages_config(conf_str)
+
+    s1 = Spec("y").concretized()
+    assert s1.satisfies("@2.3")
+    assert s1.satisfies("%gcc")
diff --git a/lib/spack/spack/test/conftest.py b/lib/spack/spack/test/conftest.py
index 3440351e93..1bf7af5f3b 100644
--- a/lib/spack/spack/test/conftest.py
+++ b/lib/spack/spack/test/conftest.py
@@ -706,6 +706,20 @@ def mutable_empty_config(tmpdir_factory, configuration_dir):
         yield cfg
 
 
+@pytest.fixture(scope="function")
+def concretize_scope(mutable_config, tmpdir):
+    """Adds a scope for concretization preferences"""
+    tmpdir.ensure_dir("concretize")
+    mutable_config.push_scope(
+        spack.config.ConfigScope("concretize", str(tmpdir.join("concretize")))
+    )
+
+    yield
+
+    mutable_config.pop_scope()
+    spack.repo.path._provider_index = None
+
+
 @pytest.fixture
 def no_compilers_yaml(mutable_config):
     """Creates a temporary configuration without compilers.yaml"""