From faad07130cc7a0d51777e8869bd33f3d47a905a9 Mon Sep 17 00:00:00 2001
From: Pete Bacon Darwin <pbacondarwin@cloudflare.com>
Date: Wed, 4 Nov 2026 22:11:37 +0000
Subject: [PATCH] fix: resolve allOf field types in OpenAPI compatibility guard

---
 .../cli/generator/flag-names-cli-compat.ts    | 24 +++++++++-
 .../generator/flag-names-cli-compat.test.ts   | 45 +++++++++++++++++++
 2 files changed, 67 insertions(+), 2 deletions(-)

diff --git a/packages/cli/generator/flag-names-cli-compat.ts b/packages/cli/generator/flag-names-cli-compat.ts
index ed2384e1cf..2f3c192913 100644
--- a/packages/cli/generator/flag-names-cli-compat.ts
+++ b/packages/cli/generator/flag-names-cli-compat.ts
@@ -79,8 +79,9 @@ function staleness(
 	if (field === undefined) {
 		return "field missing";
 	}
-	if (field["type"] !== entry.type) {
-		return `field type is now ${JSON.stringify(field["type"])}`;
+	const type = fieldType(openapi, field);
+	if (type !== entry.type) {
+		return `field type is now ${JSON.stringify(type)}`;
 	}
 	const overrides = operation["x-forge-params"] as Overrides | undefined;
 	if (overrides?.[entry.wire]?.["flagName"] !== undefined) {
@@ -103,6 +104,25 @@ function bodyField(
 	return deref(openapi, record(schema?.["properties"])?.[wire]);
 }
 
+function fieldType(
+	openapi: ForgeOpenApiDocument,
+	field: Record<string, unknown>
+): unknown {
+	let schema: Record<string, unknown> | undefined = field;
+	for (let depth = 0; depth < 10 && schema !== undefined; depth++) {
+		if (schema["type"] !== undefined) {
+			return schema["type"];
+		}
+		// Forge can wrap a reference in allOf to attach property annotations.
+		const allOf = schema["allOf"];
+		if (!Array.isArray(allOf) || allOf.length !== 1) {
+			return undefined;
+		}
+		schema = deref(openapi, allOf[0]);
+	}
+	return undefined;
+}
+
 function deref(
 	openapi: ForgeOpenApiDocument,
 	value: unknown
diff --git a/packages/cli/src/__tests__/generator/flag-names-cli-compat.test.ts b/packages/cli/src/__tests__/generator/flag-names-cli-compat.test.ts
index 6b485f8a4b..aa8624b299 100644
--- a/packages/cli/src/__tests__/generator/flag-names-cli-compat.test.ts
+++ b/packages/cli/src/__tests__/generator/flag-names-cli-compat.test.ts
@@ -68,6 +68,33 @@ describe("applyTemporaryFlagNames", () => {
 		});
 	});
 
+	it.each([
+		{ type: "string" },
+		{ $ref: "#/components/schemas/precursor_mode" },
+		{ allOf: [{ $ref: "#/components/schemas/precursor_mode" }] },
+	])("names a field wrapped in a single allOf: %j", (schema) => {
+		const doc = document();
+		const schemas = doc.components?.["schemas"] as Record<string, object>;
+		const mode = {
+			allOf: [schema],
+			"x-fern-property-name": "precursor-mode",
+		};
+		schemas["precursor_config"] = {
+			type: "object",
+			properties: { mode },
+		};
+
+		applyTemporaryFlagNames(doc);
+
+		expect(overrides(doc, PRECURSOR, "put")).toEqual({
+			mode: { flagName: "detection-mode" },
+		});
+		expect(mode).toEqual({
+			allOf: [schema],
+			"x-fern-property-name": "precursor-mode",
+		});
+	});
+
 	it.each<[string, (doc: ForgeOpenApiDocument) => void, string]>([
 		[
 			"a missing operation",
@@ -106,6 +133,24 @@ describe("applyTemporaryFlagNames", () => {
 			},
 			'field type is now "integer"',
 		],
+		[
+			"a retyped field wrapped in allOf",
+			(doc) => {
+				const schemas = doc.components?.["schemas"] as Record<string, object>;
+				schemas["precursor_mode"] = { allOf: [{ type: "integer" }] };
+			},
+			'field type is now "integer"',
+		],
+		[
+			"a field with conflicting allOf types",
+			(doc) => {
+				const schemas = doc.components?.["schemas"] as Record<string, object>;
+				schemas["precursor_mode"] = {
+					allOf: [{ type: "string" }, { type: "integer" }],
+				};
+			},
+			"field type is now undefined",
+		],
 		[
 			"an upstream flagName",
 			(doc) => {