[SQLite-kit] Keep column UNIQUE when the same column also has a plain index

[soya-miyoshi]

Fixes #6060

Problem

In the SQLite schema serializer, a column declared with .unique() silently loses its UNIQUE constraint when the same column also has a plain, non-unique index() declared on it. Nothing is emitted in its place — no inline UNIQUE, no CREATE UNIQUE INDEX — so uniqueness disappears from the generated DDL and duplicate rows become insertable.

This is most visible on the push table-recreate path (__new_<table> + INSERT ... SELECT + DROP + RENAME), where an existing UNIQUE guarantee is dropped without any prompt or warning. It affects generate too, since both share the serializer.

A sibling .unique() column without a plain index keeps its constraint, which isolates the trigger to the .unique() + index() combination on the same column — a very common pattern (unique business key + a covering query index).

Root cause

fromDrizzleSchema in drizzle-kit/src/dialects/sqlite/drizzle.ts computes a hasUniqueIndex flag whose purpose is to avoid emitting an inline UNIQUE on top of a column that is already covered by a uniqueIndex() (which would duplicate the constraint). The predicate, however, never checks whether the matched index is actually unique — it matches any single-column index on that column. So a plain index() suppresses the inline UNIQUE just as a uniqueIndex() would, but without providing any replacement enforcement.

Fix

Ignore non-unique indexes in that lookup:

const hasUniqueIndex = Boolean(it.config.indexes.find((item) => {
  const i = item.config;
  if (!i.unique) return false; // a plain index enforces nothing — must not suppress UNIQUE
  const column = i.columns.length === 1 ? i.columns[0] : null;
  return column && !is(column, SQL) && column.name === name;
}));

Deduplication against a real uniqueIndex() is unchanged; only plain indexes stop suppressing the constraint.

Tests

Added coverage in drizzle-kit/tests/sqlite/sqlite-constraints.test.ts for the bug and its neighbors:

• .unique() + plain index() on the same column → keeps UNIQUE
• .unique() + real uniqueIndex() on the same column → still deduplicated (no double constraint)
• sibling .unique() column without an index → unaffected

Full file passes:

✓ tests/sqlite/sqlite-constraints.test.ts (59 tests)
Test Files  1 passed (1)
     Tests  59 passed (59)

Notes

• Targeted at beta (1.0.0-rc.4), which is where the reported code path (src/dialects/sqlite/drizzle.ts) lives.