🐛 Materialize migration iterables (#7491)

`config_can_be_downgraded`, `upgrade_config` and `downgrade_config` search
the migrations iterable repeatedly, so a one-shot iterator (e.g. a generator)
was consumed after the first step and later lookups wrongly failed. Latent
because the default `MIGRATIONS` is a tuple. Materialize to a tuple in each
helper and add generator-based coverage over a multi-step upgrade/downgrade.

Author: agoscinski

src/aiida/manage/configuration/migrations/migrations.py

@@ -517,6 +517,8 @@ def config_can_be_downgraded(
     """
     target = CURRENT_CONFIG_VERSION if target is None else target
     current = get_current_version(config)
+    # Materialize so the iterable can be searched repeatedly, even if a one-shot iterator was passed.
+    migrations = tuple(migrations)
 
     if current <= target or current > MAXIMUM_DOWNGRADE_CONFIG_VERSION:
         return False
@@ -544,6 +546,8 @@ def upgrade_config(
     :return: the migrated configuration dictionary
     """
     current = get_current_version(config)
+    # Materialize so the iterable can be searched repeatedly, even if a one-shot iterator was passed.
+    migrations = tuple(migrations)
     used = []
     while current < target:
         current = get_current_version(config)
@@ -572,6 +576,8 @@ def downgrade_config(
     :return: the migrated configuration dictionary
     """
     current = get_current_version(config)
+    # Materialize so the iterable can be searched repeatedly, even if a one-shot iterator was passed.
+    migrations = tuple(migrations)
     if current > MAXIMUM_DOWNGRADE_CONFIG_VERSION:
         msg = (
             f'Cannot downgrade configuration version {current}: this AiiDA version can only downgrade configuration '

tests/manage/configuration/migrations/test_migrations.py

@@ -92,13 +92,19 @@ def test_config_needs_migrating_incompatible_version(monkeypatch):
 
 
 def test_config_can_be_downgraded():
-    """Test detecting whether a configuration can be downgraded by this AiiDA version."""
+    """Test detecting whether a configuration can be downgraded by this AiiDA version.
+
+    The migrations are passed as one-shot generators over a multi-step chain to ensure the iterable is materialized
+    before being searched repeatedly (a consumed iterator would make the second lookup wrongly fail).
+    """
     assert config_can_be_downgraded(
         {'CONFIG_VERSION': {'CURRENT': MAXIMUM_DOWNGRADE_CONFIG_VERSION, 'OLDEST_COMPATIBLE': 0}},
-        target=MAXIMUM_DOWNGRADE_CONFIG_VERSION - 1,
+        target=MAXIMUM_DOWNGRADE_CONFIG_VERSION - 2,
+        migrations=(m for m in MIGRATIONS),
     )
     assert not config_can_be_downgraded(
-        {'CONFIG_VERSION': {'CURRENT': MAXIMUM_DOWNGRADE_CONFIG_VERSION + 1, 'OLDEST_COMPATIBLE': 0}}
+        {'CONFIG_VERSION': {'CURRENT': MAXIMUM_DOWNGRADE_CONFIG_VERSION + 1, 'OLDEST_COMPATIBLE': 0}},
+        migrations=(m for m in MIGRATIONS),
     )
 
 
@@ -115,6 +121,24 @@ def test_migrate_full(load_config_sample, monkeypatch):
     assert config_migrated == config_target
 
 
+def test_migrate_full_downgrade(load_config_sample, monkeypatch):
+    """Test the full config downgrade, as a counterpart to :func:`test_migrate_full`.
+
+    The oldest sample is upgraded to the latest version and then downgraded all the way back, exercising the full
+    migration chain in both directions. Downgrades are lossy by design (e.g. a profile UUID added on upgrade is
+    intentionally kept), so this asserts the versions reached rather than round-trip equality. The migrations are
+    passed as one-shot generators, which additionally guards that the iterable is materialized before the repeated
+    per-step lookups (a consumed iterator would stop finding migrations after the first step).
+    """
+    monkeypatch.setattr(uuid, 'uuid4', lambda: uuid.UUID(hex='0' * 32))
+
+    upgraded = upgrade_config(load_config_sample('input/0.json'), 10, migrations=(m for m in MIGRATIONS))
+    assert upgraded['CONFIG_VERSION']['CURRENT'] == 10
+
+    downgraded = downgrade_config(upgraded, 0, migrations=(m for m in MIGRATIONS))
+    assert downgraded['CONFIG_VERSION']['CURRENT'] == 0
+
+
 @pytest.mark.parametrize('initial, target', ((m.down_revision, m.up_revision) for m in MIGRATIONS))
 def test_migrate_individual(load_config_sample, initial, target, monkeypatch):
     """Test the individual config migrations."""