Package requirements: allow single specs in requirement lists (#36258)

If you have a "require:" section in your packages config, and you
use it to specify a list of requirements, the list elements can
now include strings (before this, each element in the list had to
be a `one_of` or `any_of` specification, which is awkward if you
wanted to apply just one spec with no alternatives).

lib/spack/spack/schema/packages.py

@@ -32,11 +32,16 @@
                             {
                                 "type": "array",
                                 "items": {
-                                    "type": "object",
-                                    "properties": {
-                                        "one_of": {"type": "array"},
-                                        "any_of": {"type": "array"},
-                                    },
+                                    "oneOf": [
+                                        {
+                                            "type": "object",
+                                            "properties": {
+                                                "one_of": {"type": "array"},
+                                                "any_of": {"type": "array"},
+                                            },
+                                        },
+                                        {"type": "string"},
+                                    ]
                                 },
                             },
                             # Shorthand for a single requirement group with

lib/spack/spack/solver/asp.py

@@ -1017,9 +1017,14 @@ def _rules_from_requirements(self, pkg_name, 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]))
+                if isinstance(requirement, str):
+                    # A string represents a spec that must be satisfied. It is
+                    # equivalent to a one_of group with a single element
+                    rules.append((pkg_name, "one_of", [requirement]))
+                else:
+                    for policy in ("one_of", "any_of"):
+                        if policy in requirement:
+                            rules.append((pkg_name, policy, requirement[policy]))
         return rules
 
     def pkg_rules(self, pkg, tests):

lib/spack/spack/test/concretize_requirements.py

@@ -107,12 +107,28 @@ def fake_installs(monkeypatch, tmpdir):
     )
 
 
+def test_one_package_multiple_reqs(concretize_scope, test_repo):
+    if spack.config.get("config:concretizer") == "original":
+        pytest.skip("Original concretizer does not support configuration requirements")
+
+    conf_str = """\
+packages:
+  y:
+    require:
+    - "@2.4"
+    - "~shared"
+"""
+    update_packages_config(conf_str)
+    y_spec = Spec("y").concretized()
+    assert y_spec.satisfies("@2.4~shared")
+
+
 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")
+        pytest.skip("Original concretizer does not support configuration requirements")
 
     conf_str = """\
 packages: