input_analysis.py: fix conditional requirements (#50194)

Fixes a logic bug where a -> b was assumed to imply not a -> not b
in conditional requirements.

Signed-off-by: Massimiliano Culpo <massimiliano.culpo@gmail.com>

lib/spack/spack/solver/input_analysis.py

@@ -85,8 +85,10 @@ def is_virtual(self, name: str) -> bool:
     def is_allowed_on_this_platform(self, *, pkg_name: str) -> bool:
         """Returns true if a package is allowed on the current host"""
         pkg_cls = self.repo.get_pkg_class(pkg_name)
+        no_condition = spack.spec.Spec()
         for when_spec, conditions in pkg_cls.requirements.items():
-            if not when_spec.intersects(self._platform_condition):
+            # Restrict analysis to unconditional requirements
+            if when_spec != no_condition:
                 continue
             for requirements, _, _ in conditions:
                 if not any(x.intersects(self._platform_condition) for x in requirements):

lib/spack/spack/test/concretization/core.py

@@ -3366,3 +3366,17 @@ def test_reuse_when_requiring_build_dep(
     with spack.config.override("concretizer:reuse", True):
         result = spack.concretize.concretize_one("pkg-b")
         assert pkgb_old.dag_hash() == result.dag_hash(), result.tree()
+
+
+@pytest.mark.regression("50167")
+def test_input_analysis_and_conditional_requirements(default_mock_concretization):
+    """Tests that input analysis doesn't account for conditional requirement
+    to discard possible dependencies.
+
+    If the requirement is conditional, and impossible to achieve on the current
+    platform, the valid search space is still the complement of the condition that
+    activates the requirement.
+    """
+    libceed = default_mock_concretization("libceed")
+    assert libceed["libxsmm"].satisfies("@main")
+    assert libceed["libxsmm"].satisfies("platform=test")