Bootstrapping: swap store before configuration (#22631)

fixes #22294

A combination of the swapping order for global variables and
the fact that most of them are lazily evaluated resulted in
custom install tree not being taken into account if clingo
had to be bootstrapped.

This commit fixes that particular issue, but a broader refactor
may be needed to ensure that similar situations won't affect us
in the future.

lib/spack/spack/bootstrap.py

@@ -216,12 +216,12 @@ def _bootstrap_config_scopes():
 @contextlib.contextmanager
 def ensure_bootstrap_configuration():
     with spack.architecture.use_platform(spack.architecture.real_platform()):
-        # Default configuration scopes excluding command line and builtin
-        # but accounting for platform specific scopes
-        config_scopes = _bootstrap_config_scopes()
-        with spack.config.use_configuration(*config_scopes):
-            with spack.repo.use_repositories(spack.paths.packages_path):
-                with spack.store.use_store(spack.paths.user_bootstrap_store):
+        with spack.repo.use_repositories(spack.paths.packages_path):
+            with spack.store.use_store(spack.paths.user_bootstrap_store):
+                # Default configuration scopes excluding command line
+                # and builtin but accounting for platform specific scopes
+                config_scopes = _bootstrap_config_scopes()
+                with spack.config.use_configuration(*config_scopes):
                     with spack_python_interpreter():
                         yield
 

lib/spack/spack/store.py

@@ -216,6 +216,19 @@ def _store_layout():
 layout = llnl.util.lang.LazyReference(_store_layout)
 
 
+def reinitialize():
+    """Restore globals to the same state they would have at start-up"""
+    global store
+    global root, unpadded_root, db, layout
+
+    store = llnl.util.lang.Singleton(_store)
+
+    root = llnl.util.lang.LazyReference(_store_root)
+    unpadded_root = llnl.util.lang.LazyReference(_store_unpadded_root)
+    db = llnl.util.lang.LazyReference(_store_db)
+    layout = llnl.util.lang.LazyReference(_store_layout)
+
+
 def retrieve_upstream_dbs():
     other_spack_instances = spack.config.get('upstreams', {})
 

lib/spack/spack/test/bootstrap.py

@@ -0,0 +1,26 @@
+# Copyright 2013-2021 Lawrence Livermore National Security, LLC and other
+# Spack Project Developers. See the top-level COPYRIGHT file for details.
+#
+# SPDX-License-Identifier: (Apache-2.0 OR MIT)
+import pytest
+
+import spack.bootstrap
+import spack.store
+
+
+@pytest.mark.regression('22294')
+def test_store_is_restored_correctly_after_bootstrap(mutable_config, tmpdir):
+    # Prepare a custom store path. This should be in a writeable location
+    # since Spack needs to initialize the DB.
+    user_path = str(tmpdir.join('store'))
+    # Reassign global variables in spack.store to the value
+    # they would have at Spack startup.
+    spack.store.reinitialize()
+    # Set the custom user path
+    spack.config.set('config:install_tree:root', user_path)
+
+    # Test that within the context manager we use the bootstrap store
+    # and that outside we restore the correct location
+    with spack.bootstrap.ensure_bootstrap_configuration():
+        assert str(spack.store.root) == spack.paths.user_bootstrap_store
+    assert str(spack.store.root) == user_path