ASP-based solve: minimize compiler mismatches (#23016)

fixes #22718

Instead of trying to maximize the number of
matches (preferred behavior), try to minimize
the number of mismatches (unwanted behavior).

lib/spack/spack/solver/concretize.lp

@@ -603,32 +603,19 @@ node_compiler_version(Package, Compiler, Version) :- node_compiler_version_set(P
    not compiler_supports_os(Compiler, Version, OS),
    not allow_compiler(Compiler, Version).
 
-% If the compiler is what was prescribed from command line etc.
+% If a package and one of its dependencies don't have the
-% or is the same as a root node, there is a version match
+% same compiler there's a mismatch.
-
+compiler_mismatch(Package, Dependency)
-% Compiler prescribed in the root spec
-node_compiler_version_match_pref(Package, Compiler, V)
- :- node_compiler_set(Package, Compiler),
-    node_compiler_version(Package, Compiler, V),
-    not external(Package).
-
-% Compiler inherited from a parent node
-node_compiler_version_match_pref(Dependency, Compiler, V)
   :- depends_on(Package, Dependency),
-    node_compiler_version_match_pref(Package, Compiler, V),
+     node_compiler_version(Package, Compiler1, _),
-    node_compiler_version(Dependency, Compiler, V),
+     node_compiler_version(Dependency, Compiler2, _),
-    not node_compiler_set(Dependency, Compiler).
+     Compiler1 != Compiler2.
 
-% Compiler inherited from the root package
+compiler_mismatch(Package, Dependency)
-node_compiler_version_match_pref(Dependency, Compiler, V)
   :- depends_on(Package, Dependency),
-    node_compiler_version(Package, Compiler, V), root(Package),
+     node_compiler_version(Package, Compiler, Version1),
-    node_compiler_version(Dependency, Compiler, V),
+     node_compiler_version(Dependency, Compiler, Version2),
-    not node_compiler_set(Dependency, Compiler).
+     Version1 != Version2.
-
-compiler_version_match(Package, 1)
- :- node_compiler_version(Package, Compiler, V),
-    node_compiler_version_match_pref(Package, Compiler, V).
 
 #defined node_compiler_set/2.
 #defined node_compiler_version_set/3.
@@ -772,14 +759,10 @@ opt_criterion(8, "count of non-root multi-valued variants").
     not root(Package)
 }.
 
-% Try to maximize the number of compiler matches in the DAG,
+% Try to minimize the number of compiler mismatches in the DAG.
-% while minimizing the number of nodes. This is done because
+opt_criterion(7, "compiler mismatches").
-% a maximization on the number of matches for compilers is highly
-% correlated to a preference to have as many nodes as possible
-opt_criterion(7, "compiler matches + number of nodes").
 #minimize{ 0@7 : #true }.
-#minimize{ 1@7,Package : node(Package) }.
+#minimize{ 1@7,Package,Dependency : compiler_mismatch(Package, Dependency) }.
-#maximize{ Weight@7,Package : compiler_version_match(Package, Weight) }.
 
 % Choose more recent versions for nodes
 opt_criterion(6, "version badness").

lib/spack/spack/test/concretize.py

@@ -1199,3 +1199,14 @@ def test_os_selection_when_multiple_choices_are_possible(
 
         for node in s.traverse():
             assert node.satisfies(expected_os)
+
+    @pytest.mark.regression('22718')
+    @pytest.mark.parametrize('spec_str,expected_compiler', [
+        ('mpileaks', '%gcc@4.5.0'),
+        ('mpileaks ^mpich%clang@3.3', '%clang@3.3')
+    ])
+    def test_compiler_is_unique(self, spec_str, expected_compiler):
+        s = Spec(spec_str).concretized()
+
+        for node in s.traverse():
+            assert node.satisfies(expected_compiler)