Make a partly-undone import retryable, and refuse a plan it cannot deliver

migrations/versions/7d38_widen_importbatch_status.py

@@ -0,0 +1,51 @@
+"""Give importbatches.status room for a value longer than 'undone'.
+
+7d37 sized the column String(16), which fitted the two statuses it shipped with.
+'partially-undone' - the status an undo writes when some entries reverted and
+others hit conflicts - is exactly 16 characters. It fits, with nothing to spare:
+the next status anyone adds, or a rename of this one, silently truncates on
+MySQL in non-strict mode and errors in strict.
+
+Widened to 32 rather than left at the exact fit, because a column that happens
+to be wide enough is not the same as a column that is wide enough.
+
+Revision ID: 7d38_widen_importbatch_status
+Revises: 7d37_import_batches_and_journal
+"""
+from alembic import op
+
+import sqlalchemy as sa
+
+
+revision = '7d38_widen_importbatch_status'
+down_revision = '7d37_import_batches_and_journal'
+branch_labels = None
+depends_on = None
+
+
+def _has_table(bind, name):
+    return sa.inspect(bind).has_table(name)
+
+
+def upgrade():
+    bind = op.get_bind()
+    if not _has_table(bind, 'importbatches'):
+        return
+    # SQLite cannot ALTER a column type; it also does not enforce VARCHAR
+    # length, so there is nothing to widen there.
+    if bind.dialect.name == 'sqlite':
+        return
+    op.alter_column('importbatches', 'status',
+                    existing_type=sa.String(length=16),
+                    type_=sa.String(length=32),
+                    existing_nullable=False)
+
+
+def downgrade():
+    bind = op.get_bind()
+    if not _has_table(bind, 'importbatches') or bind.dialect.name == 'sqlite':
+        return
+    op.alter_column('importbatches', 'status',
+                    existing_type=sa.String(length=32),
+                    type_=sa.String(length=16),
+                    existing_nullable=False)