fix(bb-distributed-data): reject ALTER TABLE DROP [COLUMN] for DSQL

.changeset/dsql-alter-table-drop.md

@@ -0,0 +1,8 @@
+---
+"@aws-blocks/bb-distributed-data": patch
+"@aws-blocks/blocks": patch
+---
+
+Reject `ALTER TABLE DROP COLUMN` at dev time, including the keyword-less Postgres shorthand (`ALTER TABLE t DROP col` / `DROP IF EXISTS col`). It is not in DSQL's supported `ALTER TABLE` subset ("unsupported ALTER TABLE DROP COLUMN statement", 0A000), but the PGlite-based local mock previously accepted it, so the error only surfaced on deploy. Migration and mock validation now fail locally instead. The supported forms — `ALTER COLUMN ... DROP DEFAULT` / `DROP NOT NULL` / `DROP EXPRESSION` / `DROP IDENTITY` and `DROP CONSTRAINT` — are not affected.
+
+The `@aws-blocks/blocks` umbrella package receives a `patch` because its published `docs/` folder is assembled from sibling block READMEs at build time (`scripts/sync-block-docs.mjs`), so this `bb-distributed-data` README update changes `@aws-blocks/blocks` packaged content.

packages/bb-distributed-data/DESIGN.md

@@ -75,6 +75,7 @@ The core insight: PGlite supports everything DSQL doesn't. Without validation, c
 | `SET TRANSACTION ISOLATION LEVEL` | Fixed Repeatable Read |
 | `COLLATE` | C collation only |
 | `CREATE INDEX ... ASC/DESC` | Sort direction on index keys (NULLS FIRST/LAST is allowed) |
+| `ALTER TABLE ... DROP [COLUMN]` | Not in DSQL's supported ALTER TABLE subset (`DROP CONSTRAINT` and `ALTER COLUMN ... DROP DEFAULT/NOT NULL/EXPRESSION/IDENTITY` are supported) |
 
 ### Transaction Tracking
 

packages/bb-distributed-data/README.md

@@ -109,6 +109,7 @@ DSQL is a subset of PostgreSQL. The local mock enforces these restrictions so co
 | Extensions | Not available |
 | ADD COLUMN with DEFAULT | Add column without default, handle nulls in app |
 | Index key sort direction (`ASC`/`DESC`) | Omit it; enforce ordering with `ORDER BY` in queries (`NULLS FIRST/LAST` is supported) |
+| `ALTER TABLE DROP [COLUMN]` | Leave the column in place and stop referencing it; or rebuild the table (create new → `INSERT INTO ... SELECT` → `DROP` → `RENAME TO`, one migration file per step) |
 
 ### Transaction Constraints
 

packages/bb-distributed-data/src/e2e-mock.test.ts

@@ -8,12 +8,12 @@
 import { describe, it, before, after } from 'node:test';
 import assert from 'node:assert/strict';
 import { rmSync } from 'node:fs';
 import { DatabaseBase, sql, type Transaction } from '@aws-blocks/data-common';
 import { DsqlMockEngine } from './engines/dsql-mock-engine.js';
 import { DistributedDatabaseErrors } from './errors.js';
 import { runMigrations } from './migrations.js';
 import { transactionWithRetry } from './transaction.js';
 import type { TransactionOptions } from './types.js';
 
 const DIR = '.bb-data/__test_dsql_e2e__';
 
@@ -214,6 +214,14 @@
     );
   });
 
+  it('rejects ALTER TABLE DROP COLUMN', async () => {
+    await engine.withDdl(() => db.execute(sql`CREATE TABLE legacy (id TEXT PRIMARY KEY, obsolete TEXT)`));
+    await assert.rejects(
+      () => engine.withDdl(() => db.execute(sql`ALTER TABLE legacy DROP COLUMN obsolete`)),
+      /DROP COLUMN/i,
+    );
+  });
+
   it('does not strip ASYNC outside of CREATE INDEX (column named "async")', async () => {
     await engine.withDdl(() => db.execute(sql`CREATE TABLE jobs (id TEXT PRIMARY KEY, async BOOLEAN)`));
     await db.execute(sql`INSERT INTO jobs (id, async) VALUES (${'j1'}, ${true})`);

packages/bb-distributed-data/src/validation.test.ts

@@ -50,13 +50,43 @@ describe('validateStatement', () => {
     ['ISOLATION LEVEL', 'SET TRANSACTION ISOLATION LEVEL SERIALIZABLE'],
     // DSQL only supports C collation — locale-aware sorting is not available
     ['COLLATE', 'SELECT * FROM t ORDER BY name COLLATE "en_US"'],
+    // DROP COLUMN is not in DSQL's supported ALTER TABLE subset — rebuild the table instead
+    ['DROP COLUMN', 'ALTER TABLE t DROP COLUMN x'],
+    // Postgres allows omitting the COLUMN keyword — same DROP COLUMN action, same rejection
+    ['DROP COLUMN shorthand', 'ALTER TABLE t DROP x'],
+    ['DROP COLUMN IF EXISTS shorthand', 'ALTER TABLE t DROP IF EXISTS x'],
+    ['DROP COLUMN quoted shorthand', 'ALTER TABLE t DROP "identity"'],
   ] as const;
 
   for (const [label, sql] of rejects) {
     it(`rejects ${label}`, () => {
       assert.throws(() => validateStatement(sql), { name: 'DsqlValidationError' });
     });
   }
+
+  it('allows supported ALTER TABLE forms that contain DROP', () => {
+    // Per the DSQL ALTER TABLE grammar, the ALTER COLUMN ... DROP actions and
+    // DROP CONSTRAINT are supported — must not be confused with the
+    // unsupported DROP [COLUMN].
+    // https://docs.aws.amazon.com/aurora-dsql/latest/userguide/alter-table-syntax-support.html
+    assert.doesNotThrow(() => validateStatement('ALTER TABLE t ALTER COLUMN c DROP IDENTITY'));
+    assert.doesNotThrow(() => validateStatement('ALTER TABLE t ALTER COLUMN c DROP DEFAULT'));
+    assert.doesNotThrow(() => validateStatement('ALTER TABLE t ALTER COLUMN c DROP NOT NULL'));
+    assert.doesNotThrow(() => validateStatement('ALTER TABLE t ALTER COLUMN c DROP EXPRESSION'));
+    assert.doesNotThrow(() => validateStatement('ALTER TABLE t DROP CONSTRAINT c'));
+    assert.doesNotThrow(() => validateStatement('ALTER TABLE t DROP CONSTRAINT IF EXISTS c CASCADE'));
+    assert.doesNotThrow(() => validateStatement('ALTER TABLE t RENAME TO t2'));
+    assert.doesNotThrow(() => validateStatement('DROP TABLE t'));
+  });
+
+  it('allows a supported ALTER TABLE followed by an unrelated statement in one batch', () => {
+    // The DROP COLUMN rule must not match across a statement boundary: the
+    // ALTER TABLE here is a supported DROP DEFAULT, and the DROP TABLE that
+    // follows the semicolon belongs to a different statement.
+    assert.doesNotThrow(() =>
+      validateStatement('ALTER TABLE t ALTER COLUMN c DROP DEFAULT; DROP TABLE archived'),
+    );
+  });
 });
 
 describe('classifyStatement', () => {

packages/bb-distributed-data/src/validation.ts

@@ -78,6 +78,7 @@ const RULES: ValidationRule[] = [
   { pattern: /\b(LISTEN|NOTIFY)\b/i, message: 'DSQL does not support LISTEN/NOTIFY.', severity: 'error' },
   { pattern: /\bCREATE\s+EXTENSION\b/i, message: 'DSQL does not support extensions.', severity: 'error' },
   { pattern: /\bALTER\s+TABLE\b[\s\S]*\bADD\s+COLUMN\b[\s\S]*\bDEFAULT\b/i, message: 'DSQL does not support ADD COLUMN with DEFAULT.', severity: 'error' },
+  { pattern: /\bALTER\s+TABLE\b[^;]*\bDROP\s+(?:COLUMN\b|IF\s+EXISTS\b|(?!(?:DEFAULT|NOT|EXPRESSION|IDENTITY|CONSTRAINT)\b)[\w"])/i, message: 'DSQL does not support ALTER TABLE DROP COLUMN. Leave the column in place and stop referencing it, or rebuild the table (create a new table → INSERT INTO ... SELECT → DROP → RENAME TO). (DSQL: "unsupported ALTER TABLE DROP COLUMN statement")', severity: 'error' },
   { pattern: /\bALTER\s+DEFAULT\s+PRIVILEGES\b/i, message: 'DSQL does not support ALTER DEFAULT PRIVILEGES.', severity: 'error' },
   { pattern: /\b(CREATE\s+POLICY|ENABLE\s+ROW\s+LEVEL\s+SECURITY)\b/i, message: 'DSQL does not support Row Level Security.', severity: 'error' },
   { pattern: /\bCREATE\s+(TEMP|TEMPORARY)\s+TABLE\b/i, message: 'DSQL does not support temporary tables.', severity: 'error' },