From 05aea7e8b73859fde8e50302f5d9e4b44044eb22 Mon Sep 17 00:00:00 2001
From: roboomp <omp@can.ac>
Date: Mon, 10 Aug 2026 08:20:23 +0000
Subject: [PATCH] fix(omptype): rejected output-changing schema overrides

- Made type.withJsonSchema reject defaults, structural morphs, and pipe steps instead of returning a Type whose runtime output silently remained the original input.
- Kept validation-only narrow/filter schemas composable, preserving the legacy Type.Unsafe use case and nested JSON Schema emission.
- Added regressions for defaulted and parsed schemas and documented the validation-only contract.

Fixes #8143
---
 packages/omptype/CHANGELOG.md      |  2 +-
 packages/omptype/src/type.ts       | 19 ++++++++++++++-----
 packages/omptype/test/type.test.ts | 12 ++++++++++++
 3 files changed, 27 insertions(+), 6 deletions(-)

diff --git a/packages/omptype/CHANGELOG.md b/packages/omptype/CHANGELOG.md
index e2e3c51cc..542ae301a 100644
--- a/packages/omptype/CHANGELOG.md
+++ b/packages/omptype/CHANGELOG.md
@@ -4,7 +4,7 @@
 
 ### Added
 
-- Added `type.withJsonSchema(schema, json)`, wrapping a schema so JSON Schema emission yields `json` verbatim even when embedded in objects, arrays, or unions — a `.toJsonSchema()` method override is dropped at nested positions because parents emit a child's IR directly.
+- Added `type.withJsonSchema(schema, json)`, wrapping a validation-only schema so JSON Schema emission yields `json` verbatim even when embedded in objects, arrays, or unions — a `.toJsonSchema()` method override is dropped at nested positions because parents emit a child's IR directly. Schemas with defaults or output-changing morphs are rejected to prevent their transformed outputs from being discarded.
 
 ## [17.2.10] - 2026-08-06
 
diff --git a/packages/omptype/src/type.ts b/packages/omptype/src/type.ts
index 43780f6c2..eff13bcc2 100644
--- a/packages/omptype/src/type.ts
+++ b/packages/omptype/src/type.ts
@@ -3677,16 +3677,25 @@ export namespace type {
 	}
 
 	/**
-	 * Return a schema that validates exactly like `schema` but emits `json`
-	 * verbatim as its JSON Schema — even when embedded in an object, array, or
-	 * union.
+	 * Return a validation-only schema that emits `json` verbatim — even when
+	 * embedded in an object, array, or union.
 	 *
 	 * A `.toJsonSchema()` method override cannot survive nesting: a parent schema
 	 * emits each child's IR directly and never calls the child's method, so the
 	 * override silently disappears from the wire schema. This stores the override
-	 * on the IR instead, so structural composition keeps it.
+	 * on the IR instead.
+	 *
+	 * # Errors
+	 *
+	 * Throws when `schema` has a default or output-changing morph/pipe. A refine
+	 * can preserve validation and the input value, but silently discarding a
+	 * transformed output would violate the returned {@link Type}.
 	 */
 	export function withJsonSchema<t, i = t>(schema: Type<t, i>, json: Record<string, unknown>): Type<t, i> {
+		const internal = schema as unknown as InternalType;
+		if (internal.hasDefault || hasMorph(internal.ir) || internal[kSteps].some(step => step.kind === "pipe")) {
+			throw new OmpTypeError("type.withJsonSchema cannot wrap schemas with defaults or output-changing morphs");
+		}
 		return makeType<t, i>(
 			{
 				k: "refine",
@@ -3700,7 +3709,7 @@ export namespace type {
 			},
 			[],
 			{},
-		) as unknown as Type<t, i>;
+		);
 	}
 }
 
diff --git a/packages/omptype/test/type.test.ts b/packages/omptype/test/type.test.ts
index a2050cb5b..a079a66c8 100644
--- a/packages/omptype/test/type.test.ts
+++ b/packages/omptype/test/type.test.ts
@@ -513,4 +513,16 @@ describe("type.withJsonSchema", () => {
 		expect(object({ mode: "b" })).toEqual({ mode: "b" });
 		expect(object({ mode: "c" })).toBeInstanceOf(OmpErrors);
 	});
+
+	it("rejects defaults and output-changing morphs", () => {
+		expect(() => type.withJsonSchema(type.string.default("fallback"), { type: "string" })).toThrow(
+			"cannot wrap schemas with defaults or output-changing morphs",
+		);
+		expect(() =>
+			type.withJsonSchema(type("string.integer.parse"), {
+				type: "string",
+				pattern: "^[0-9]+$",
+			}),
+		).toThrow("cannot wrap schemas with defaults or output-changing morphs");
+	});
 });