feat(migrate-ts): normalizeCheckExpr — compare CHECK exprs across PG rewrite

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

Author: dmealing

server/typescript/packages/migrate-ts/src/check-expr-compare.ts

@@ -0,0 +1,24 @@
+// src/check-expr-compare.ts
+//
+// CHECK-expression comparison. Postgres rewrites a stored CHECK body — adding
+// parens around terms, normalizing whitespace/case — so the raw text we generate
+// (`col >= 0 AND col <= 100`) and the introspected text (`(col >= 0) AND (col <= 100)`)
+// differ textually but mean the same thing. This reduces both to ONE canonical
+// form for comparison. Reliable here because every check expression we emit is
+// machine-derived with a simple, known shape (comparison / IN / length / regex) —
+// there is no arbitrary author SQL to mis-normalize.
+
+/** Canonical form: drop all parens, collapse whitespace, trim, lower-case. */
+export function normalizeCheckExpr(expr: string): string {
+  return expr
+    .replace(/[()]/g, " ")
+    .replace(/\s+/g, " ")
+    .trim()
+    .toLowerCase();
+}
+
+/** True when two CHECK expressions are equivalent after normalization. */
+export function checkExprEquals(a: string | undefined, b: string | undefined): boolean {
+  if (a === undefined || b === undefined) return false;
+  return normalizeCheckExpr(a) === normalizeCheckExpr(b);
+}

server/typescript/packages/migrate-ts/test/check-evolution/normalize.test.ts

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+import { describe, test, expect } from "bun:test";
+import { normalizeCheckExpr, checkExprEquals } from "../../src/check-expr-compare.js";
+
+describe("normalizeCheckExpr", () => {
+  test("strips parens, collapses whitespace, lowercases", () => {
+    expect(normalizeCheckExpr("(price >= 0) AND (price <= 100)")).toBe("price >= 0 and price <= 100");
+    expect(normalizeCheckExpr("price >= 0 AND price <= 100")).toBe("price >= 0 and price <= 100");
+  });
+  test("PG-rewritten form equals the generated form", () => {
+    expect(checkExprEquals("(col >= 0) AND (col <= 100)", "col >= 0 AND col <= 100")).toBe(true);
+    expect(checkExprEquals("length(code) >= 3", "(length(code) >= 3)")).toBe(true);
+    expect(checkExprEquals("status IN ('A', 'B')", "status in ('A', 'B')")).toBe(true);
+  });
+  test("genuinely different expressions are not equal", () => {
+    expect(checkExprEquals("col >= 0", "col >= 5")).toBe(false);
+  });
+  test("undefined is never equal", () => {
+    expect(checkExprEquals(undefined, "x")).toBe(false);
+  });
+});