Add config option and compiler support to reuse across OS's (#42693)

* Allow compilers to function across compatible OS's
* Add documentation in the default yaml

Co-authored-by: Massimiliano Culpo <massimiliano.culpo@gmail.com>
Co-authored-by: Gregory Becker <becker33@llnl.gov>

etc/spack/defaults/concretizer.yaml

@@ -42,3 +42,8 @@ concretizer:
     # "minimal": allows the duplication of 'build-tools' nodes only (e.g. py-setuptools, cmake etc.)
     # "full" (experimental): allows separation of the entire build-tool stack (e.g. the entire "cmake" subDAG)
     strategy: minimal
+  # Option to specify compatiblity between operating systems for reuse of compilers and packages
+  # Specified as a key: [list] where the key is the os that is being targeted, and the list contains the OS's 
+  # it can reuse. Note this is a directional compatibility so mutual compatibility between two OS's 
+  # requires two entries i.e. os_compatible: {sonoma: [monterey], monterey: [sonoma]}
+  os_compatible: {}

lib/spack/spack/schema/concretizer.py

@@ -34,6 +34,7 @@
                     "strategy": {"type": "string", "enum": ["none", "minimal", "full"]}
                 },
             },
+            "os_compatible": {"type": "object", "additionalProperties": {"type": "array"}},
         },
     }
 }

lib/spack/spack/solver/asp.py

@@ -1050,6 +1050,15 @@ def package_languages(self, pkg):
                 self.gen.fact(fn.pkg_fact(pkg.name, fn.language(condition_id, language)))
         self.gen.newline()
 
+    def config_compatible_os(self):
+        """Facts about compatible os's specified in configs"""
+        self.gen.h2("Compatible OS from concretizer config file")
+        os_data = spack.config.get("concretizer:os_compatible", {})
+        for recent, reusable in os_data.items():
+            for old in reusable:
+                self.gen.fact(fn.os_compatible(recent, old))
+                self.gen.newline()
+
     def compiler_facts(self):
         """Facts about available compilers."""
 
@@ -2358,6 +2367,7 @@ def setup(
         self.gen.newline()
 
         self.gen.h1("General Constraints")
+        self.config_compatible_os()
         self.compiler_facts()
 
         # architecture defaults

lib/spack/spack/solver/concretize.lp

@@ -1186,7 +1186,8 @@ error(100, "{0} compiler '%{1}@{2}' incompatible with 'os={3}'", Package, Compil
      node_compiler(node(X, Package), CompilerID),
      compiler_name(CompilerID, Compiler),
      compiler_version(CompilerID, Version),
-     not compiler_os(CompilerID, OS),
+     compiler_os(CompilerID, CompilerOS),
+     not os_compatible(CompilerOS, OS),
      not allow_compiler(Compiler, Version),
      build(node(X, Package)).
 

lib/spack/spack/test/concretize.py

@@ -1876,6 +1876,25 @@ def test_not_reusing_incompatible_os_or_compiler(self):
         assert concrete_spec.satisfies("%{}".format(s.compiler))
         assert concrete_spec.satisfies("os={}".format(s.architecture.os))
 
+    @pytest.mark.only_clingo("Use case not supported by the original concretizer")
+    def test_reuse_succeeds_with_config_compatible_os(self):
+        root_spec = Spec("b")
+        s = root_spec.concretized()
+        other_os = s.copy()
+        mock_os = "ubuntu2204"
+        other_os.architecture = spack.spec.ArchSpec(
+            "test-{os}-{target}".format(os=mock_os, target=str(s.architecture.target))
+        )
+        reusable_specs = [other_os]
+        overrides = {"concretizer": {"reuse": True, "os_compatible": {s.os: [mock_os]}}}
+        custom_scope = spack.config.InternalConfigScope("concretize_override", overrides)
+        with spack.config.override(custom_scope):
+            solver = spack.solver.asp.Solver()
+            setup = spack.solver.asp.SpackSolverSetup()
+            result, _, _ = solver.driver.solve(setup, [root_spec], reuse=reusable_specs)
+        concrete_spec = result.specs[0]
+        assert concrete_spec.satisfies("os={}".format(other_os.architecture.os))
+
     def test_git_hash_assigned_version_is_preferred(self):
         hash = "a" * 40
         s = Spec("develop-branch-version@%s=develop" % hash)