Propagate rename_table to inbound ForeignKey references in the schema snapshot

[regiscamimura]

The bug

piccolo migrations new <app> --auto diffs the current tables against a SchemaSnapshot replayed from the migration history. When the history contains a rename_table, the snapshot renames that table — but leaves every ForeignKey on other tables still pointing at the old table class (params["references"]). The live models reference the new class, and SerialisedTableType compares by "{tablename}-{ClassName}", so every subsequent --auto emits an alter_column(references=New, old_params={"references": Old}) for each inbound FK, forever.

Repro from history:

manager_1.add_table("Band", "band")
manager_1.add_table("Concert", "concert")
manager_1.add_column("Concert", "concert", "band", column_class=ForeignKey, params={"references": Band})
manager_2.rename_table("Band", "band", "Performer", "performer")

concert = SchemaSnapshot([manager_1, manager_2]).get_table_from_snapshot("Concert")
concert.columns[0]._meta.params["references"].__name__   # "Band"  — should be "Performer"

In our app, a table rename in August produced the same nine phantom alter_columns in every one of the ten migrations generated since, each stripped by hand. (They execute no SQL — alter_column never acts on references — so committing them once also works around it downstream, which is how we found the cause.)

The fix

In SchemaSnapshot.get_snapshot, after applying a rename_table, walk every table's ForeignKey columns and replace a references that names the old class/tablename with a subclass carrying the new class name and tablename (via create_table_class), updating both _meta.params["references"] and _foreign_key_meta.references.

Test

test_rename_table_updates_foreign_key_references — asserts the snapshot's FK now names the new class and tablename, and that a DiffableTable built from the renamed model diffs to no alter_columns. Fails on master ("Band" != "Performer"), passes with the fix. tests/apps/migrations: 79 passed, 84 skipped (SQLite). black / isort / flake8 / mypy clean on the two files.

🤖 Generated with Claude Code

https://claude.ai/code/session_018o8TvRZFEEBXJWXvR1ikd9