concretizer: update reuse: default to True (#41302)

etc/spack/defaults/concretizer.yaml

@@ -15,7 +15,7 @@ concretizer:
   # as possible, rather than building. If `false`, we'll always give you a fresh
   # concretization. If `dependencies`, we'll only reuse dependencies but
   # give you a fresh concretization for your root specs.
-  reuse: dependencies
+  reuse: true
   # Options that tune which targets are considered for concretization. The
   # concretization process is very sensitive to the number targets, and the time
   # needed to reach a solution increases noticeably with the number of targets

lib/spack/spack/solver/asp.py

@@ -3566,7 +3566,7 @@ def __init__(self):
 
         # These properties are settable via spack configuration, and overridable
         # by setting them directly as properties.
-        self.reuse = spack.config.get("concretizer:reuse", False)
+        self.reuse = spack.config.get("concretizer:reuse", True)
 
     @staticmethod
     def _check_input_and_extract_concrete_specs(specs):

lib/spack/spack/test/cmd/common/arguments.py

@@ -123,17 +123,18 @@ def test_root_and_dep_match_returns_root(mock_packages, mutable_mock_env_path):
 
 
 @pytest.mark.parametrize(
-    "arg,config", [("--reuse", True), ("--fresh", False), ("--reuse-deps", "dependencies")]
+    "arg,conf", [("--reuse", True), ("--fresh", False), ("--reuse-deps", "dependencies")]
 )
-def test_concretizer_arguments(mutable_config, mock_packages, arg, config):
+def test_concretizer_arguments(mutable_config, mock_packages, arg, conf):
     """Ensure that ConfigSetAction is doing the right thing."""
     spec = spack.main.SpackCommand("spec")
 
-    assert spack.config.get("concretizer:reuse", None) is None
+    assert spack.config.get("concretizer:reuse", None, scope="command_line") is None
 
     spec(arg, "zlib")
 
-    assert spack.config.get("concretizer:reuse", None) == config
+    assert spack.config.get("concretizer:reuse", None) == conf
+    assert spack.config.get("concretizer:reuse", None, scope="command_line") == conf
 
 
 def test_use_buildcache_type():

lib/spack/spack/test/concretize.py

@@ -1346,6 +1346,9 @@ def mock_fn(*args, **kwargs):
     def test_reuse_installed_packages_when_package_def_changes(
         self, context, mutable_database, repo_with_changing_recipe
     ):
+        # test applies only with reuse turned off in concretizer
+        spack.config.set("concretizer:reuse", False)
+
         # Install a spec
         root = Spec("root").concretized()
         dependency = root["changing"].copy()
@@ -2120,7 +2123,11 @@ def test_external_python_extension_find_dependency_from_installed(self, monkeypa
 
         # install python external
         python = Spec("python").concretized()
-        monkeypatch.setattr(spack.store.STORE.db, "query", lambda x: [python])
+
+        def query(*args, **kwargs):
+            return [python]
+
+        monkeypatch.setattr(spack.store.STORE.db, "query", query)
 
         # ensure that we can't be faking this by getting it from config
         external_conf.pop("python")

lib/spack/spack/test/data/config/concretizer.yaml

@@ -1,5 +1,5 @@
 concretizer:
-  # reuse is missing on purpose, see "test_concretizer_arguments"
+  reuse: True
   targets:
     granularity: microarchitectures
     host_compatible: false