python: allow it as a build-tool again (#49201)

Python was removed from being a build tool in #46980, due to issues
when reusing specs. This PR adds a new rule to match the interpreter
among different Python packages, in clingo.

It also adds a bunch of new "build-tools", so that specs like:
```
py-matplotlib backend=tkagg
```
can be concretized in one go.

Modifications:
- [x] Make `py-matplotlib backend=tkagg` concretizable
- [x] Add unit-tests to ensure situations like in #46980 do not happen

---------

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

lib/spack/spack/solver/asp.py

@@ -1658,13 +1658,16 @@ def track_dependencies(input_spec, requirements):
                     return requirements + [fn.attr("track_dependencies", input_spec.name)]
 
                 def dependency_holds(input_spec, requirements):
-                    return remove_node(input_spec, requirements) + [
+                    result = remove_node(input_spec, requirements) + [
                         fn.attr(
                             "dependency_holds", pkg.name, input_spec.name, dt.flag_to_string(t)
                         )
                         for t in dt.ALL_FLAGS
                         if t & depflag
                     ]
+                    if input_spec.name not in pkg.extendees:
+                        return result
+                    return result + [fn.attr("extends", pkg.name, input_spec.name)]
 
                 context = ConditionContext()
                 context.source = ConstraintOrigin.append_type_suffix(

lib/spack/spack/solver/concretize.lp

@@ -524,6 +524,16 @@ error(10, "'{0}' is not a valid dependency for any package in the DAG", Package)
   :- attr("node", node(ID, Package)),
      not needed(node(ID, Package)).
 
+
+% Extensions depending on each other must all extend the same node (e.g. all Python packages
+% depending on each other must depend on the same Python interpreter)
+error(100, "{0} and {1} must depend on the same {2}", ExtensionParent, ExtensionChild, ExtendeePackage)
+  :- depends_on(ExtensionParent, ExtensionChild),
+     attr("extends", ExtensionParent, ExtendeePackage),
+     depends_on(ExtensionParent, node(X, ExtendeePackage)),
+     depends_on(ExtensionChild,  node(Y, ExtendeePackage)),
+     X != Y.
+
 #defined dependency_type/2.
 
 %-----------------------------------------------------------------------------

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

@@ -2888,6 +2888,23 @@ def test_specifying_different_versions_build_deps(self):
         assert any(x.satisfies(hdf5_str) for x in result.specs)
         assert any(x.satisfies(pinned_str) for x in result.specs)
 
+    @pytest.mark.regression("44289")
+    def test_all_extensions_depend_on_same_extendee(self):
+        """Tests that we don't reuse dependencies that bring in a different extendee"""
+        setuptools = spack.concretize.concretize_one("py-setuptools ^python@3.10")
+
+        solver = spack.solver.asp.Solver()
+        setup = spack.solver.asp.SpackSolverSetup()
+        result, _, _ = solver.driver.solve(
+            setup, [Spec("py-floating ^python@3.11")], reuse=list(setuptools.traverse())
+        )
+        assert len(result.specs) == 1
+
+        floating = result.specs[0]
+        assert all(setuptools.dag_hash() != x.dag_hash() for x in floating.traverse())
+        pythons = [x for x in floating.traverse() if x.name == "python"]
+        assert len(pythons) == 1 and pythons[0].satisfies("@3.11")
+
 
 @pytest.mark.parametrize(
     "v_str,v_opts,checksummed",