3.4.8: TransactionSql lost call signatures due to Omit

[danieltroger]

Description

In v3.4.8, commit 36a53f6 changed TransactionSql from:

interface TransactionSql<TTypes extends Record<string, unknown> = {}> extends Sql<TTypes> {

to:

interface TransactionSql<TTypes extends Record<string, unknown> = {}> extends Omit<Sql<TTypes>,
    'parameters' | 'largeObject' | 'subscribe' | 'CLOSE' | 'END' |
    'PostgresError' | 'options' | 'reserve' | 'listen' | 'begin' | 'close' | 'end'
> {

The intent is correct (preventing use of tx.begin(), tx.listen() etc. which don't work inside transactions), but Omit in TypeScript creates a mapped type that only preserves named properties. It silently drops call signatures, so TransactionSql is no longer callable as a tagged template literal.

Reproduction

import postgres from "postgres";

const sql = postgres("...");

// Works fine
await sql`SELECT 1`;

// TS error: "This expression is not callable. Type 'TransactionSql<{}>' has no call signatures."
await sql.begin(async (tx) => {
  await tx`SELECT 1`;
});

Suggested fix

Replace Omit with a hand-written interface that explicitly re-declares the two call signatures from Sql:

interface TransactionSql<TTypes extends Record<string, unknown> = {}> {
  // Re-declare call signatures (Omit strips these)
  <T, K extends Rest<T>>(first: T & First<T, K, TTypes[keyof TTypes]>, ...rest: K): Return<T, K>;
  <T extends readonly (object | undefined)[] = Row[]>(
    template: TemplateStringsArray,
    ...parameters: readonly (ParameterOrFragment<TTypes[keyof TTypes]>)[]
  ): PendingQuery<T>;

  // Pick only the methods that are valid inside a transaction
  unsafe: Sql<TTypes>['unsafe'];
  typed: Sql<TTypes>['typed'];
  types: Sql<TTypes>['types'];
  notify: Sql<TTypes>['notify'];
  array: Sql<TTypes>['array'];
  file: Sql<TTypes>['file'];
  json: Sql<TTypes>['json'];

  savepoint<T>(cb: (sql: TransactionSql<TTypes>) => T | Promise<T>): Promise<UnwrapPromiseArray<T>>;
  savepoint<T>(name: string, cb: (sql: TransactionSql<TTypes>) => T | Promise<T>): Promise<UnwrapPromiseArray<T>>;
  prepare<T>(name: string): Promise<UnwrapPromiseArray<T>>;
}

This achieves the same goal (no begin, listen, subscribe, etc. on tx) without losing the call signatures.

[danieltroger]

Ah damn just saw #1143, this is a duplicate

[porsager]

Your input on the PR would be appreciated though ;) #1144