feat(migrate-ts): drop-check restore down + allow.dropCheck gating

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: dmealing

server/typescript/packages/migrate-ts/src/diff/status.ts

@@ -27,6 +27,8 @@ function blockedReasonFor(c: Change, allow: AllowOptions): string | null {
       return allow.dropIndex ? null : "destructive: drop-index not allowed (pass allow.dropIndex)";
     case "drop-fk":
       return allow.dropFk ? null : "destructive: drop-fk not allowed (pass allow.dropFk)";
+    case "drop-check":
+      return allow.dropCheck ? null : "destructive: drop-check not allowed (pass allow.dropCheck)";
 
     case "change-column-type":
       if (isWidening(c.from, c.to)) return null;     // widening always allowed
@@ -48,7 +50,6 @@ function blockedReasonFor(c: Change, allow: AllowOptions): string | null {
     case "add-index":
     case "add-fk":
     case "add-check":
-    case "drop-check":
     case "create-view":
     case "drop-view":
     case "replace-view":

server/typescript/packages/migrate-ts/src/emit/postgres.ts

@@ -123,7 +123,10 @@ function renderDown(c: Change): string {
     // add-check / drop-check down arms: declared but not yet produced by the diff
     // (checks are create-time-only; see renderUp note).
     case "add-check":              return `ALTER TABLE ${quoteQualified(c.table, c.schema)} DROP CONSTRAINT ${quote(c.check.name)};`;
-    case "drop-check":             return `-- WARNING: down migration cannot restore the original CHECK definition`;
+    case "drop-check":
+      return c.restore
+        ? `ALTER TABLE ${quoteQualified(c.table, c.schema)} ADD CONSTRAINT ${quote(c.restore.name)} CHECK (${c.restore.expression});`
+        : `-- WARNING: down migration cannot restore the original CHECK definition`;
     case "create-view":            return `DROP VIEW ${quoteQualifiedView(c.view.name, c.schema)};`;
     case "drop-view":              return `-- WARNING: down migration cannot restore the original view definition`;
     case "replace-view":           return `-- WARNING: down migration cannot restore the original view definition`;

server/typescript/packages/migrate-ts/src/types.ts

@@ -139,7 +139,7 @@ export type Change =
   | { kind: "add-fk"; table: string; schema?: string; fk: FkDescriptor; status: ChangeStatus }
   | { kind: "drop-fk"; table: string; schema?: string; fk: string; restore?: FkDescriptor; status: ChangeStatus }
   | { kind: "add-check"; table: string; schema?: string; check: CheckDescriptor; status: ChangeStatus }
-  | { kind: "drop-check"; table: string; schema?: string; check: string; status: ChangeStatus }
+  | { kind: "drop-check"; table: string; schema?: string; check: string; restore?: CheckDescriptor; status: ChangeStatus }
   // Declared for v0.3, never produced in v0.1:
   | { kind: "create-view"; view: ViewDescriptor; schema?: string; status: ChangeStatus }
   | { kind: "drop-view"; view: string; schema?: string; status: ChangeStatus }
@@ -163,6 +163,7 @@ export interface AllowOptions {
   typeChange?: boolean;
   dropIndex?: boolean;
   dropFk?: boolean;
+  dropCheck?: boolean;
   /** Existing data must satisfy NOT NULL; diff cannot verify this. */
   nullableToNotNull?: boolean;
 }

server/typescript/packages/migrate-ts/test/check-evolution/drop-check-down.test.ts

@@ -0,0 +1,28 @@
+import { describe, test, expect } from "bun:test";
+import type { Change } from "../../src/types.js";
+import { emit } from "../../src/emit/index.js";
+import { applyStatus } from "../../src/diff/status.js";
+
+const CHK = { name: "orders_qty_numeric_chk", expression: "qty >= 1" };
+
+describe("drop-check: restore down + allow gating", () => {
+  test("drop-check with restore → down re-adds the constraint", () => {
+    const c = { kind: "drop-check", table: "orders", check: CHK.name, restore: CHK, status: { state: "allowed" } } as unknown as Change;
+    const r = emit([c], { dialect: "postgres" });
+    expect(r.up).toContain(`ALTER TABLE "orders" DROP CONSTRAINT "orders_qty_numeric_chk";`);
+    expect(r.down).toContain(`ALTER TABLE "orders" ADD CONSTRAINT "orders_qty_numeric_chk" CHECK (qty >= 1);`);
+  });
+  test("drop-check is blocked unless allow.dropCheck", () => {
+    const blocked = [{ kind: "drop-check", table: "orders", check: CHK.name, status: { state: "allowed" } } as unknown as Change];
+    applyStatus(blocked, {});
+    expect(blocked[0]!.status.state).toBe("blocked");
+    const allowed = [{ kind: "drop-check", table: "orders", check: CHK.name, status: { state: "allowed" } } as unknown as Change];
+    applyStatus(allowed, { dropCheck: true });
+    expect(allowed[0]!.status.state).toBe("allowed");
+  });
+  test("add-check stays always-allowed", () => {
+    const c = [{ kind: "add-check", table: "orders", check: CHK, status: { state: "allowed" } } as unknown as Change];
+    applyStatus(c, {});
+    expect(c[0]!.status.state).toBe("allowed");
+  });
+});