Module columns 

Column-level diffing inside an AlterTable.

Pairs columns by name. Logical column order is intentionally not enforced in v0.1 — the IR records it, but reordering would require a table rewrite. If the user wants a specific physical order, they must drop and recreate the table.

Widening whitelist

is_widening returns true only for type changes Postgres can perform without rewriting data: int2 → int4 → int8, varchar(N) → varchar(M>N), varchar(*) → text. Everything else is conservative and tagged Destructiveness::RequiresApprovalAndDataLossWarning.

Functions

diff_columns

Diff columns in target against source, appending entries to out.