Basic `typePolicies` plugin for Graphql Codegen. Will generate a typePolicies object with relay-style query fields configured for pagination.

replay-type-policies.js

const graphql = require('graphql');

function isRelayConnection(typeField, type) {
	if (!typeField.type) {
		return false;
	}

	if (!typeField.type.toString().includes('Connection')) { // This might be too opiniated
		return false;
	}

	const fieldsNames = Object.keys(type.getFields()).filter(
		(f) => !f.startsWith('__'),
	);

	if (!fieldsNames.includes('edges') || !fieldsNames.includes('pageInfo')) {
		return false;
	}

	return true;
}

module.exports = {
	/**
	 * Generates typePolicies argument for Apollo's InMemoryCache
	 * for the schema's relay connection
	 * @param {graphql.GraphQLSchema} schema
	 */
	plugin: (schema) => {
		const typeMap = schema.getTypeMap();

		const typePolicies = [];

		Object.keys(typeMap).forEach((typeName) => {
			const type = typeMap[typeName];

			if (
				typeName.startsWith('__') ||
				(!graphql.isObjectType(type) && !graphql.isInterfaceType(type))
			) {
				return;
			}

			const fields = type.getFields();
			let connectionFieldChilds = [];

			for (const fieldIndex in fields) {
				const field = fields[fieldIndex];

				const fieldType = field.type.toString();
				const fieldTypeName = fieldType.endsWith('!')
					? fieldType.substring(0, fieldType.length - 1)
					: fieldType;

				if (
					!graphql.isObjectType(typeMap[fieldTypeName]) &&
					!graphql.isInterfaceType(typeMap[fieldTypeName])
				) {
					continue;
				}

				if (isRelayConnection(fields[fieldIndex], typeMap[fieldTypeName])) {
					connectionFieldChilds.push(`${field.name}: relayStylePagination(),`);
				}
			}

			if (connectionFieldChilds.length) {
				typePolicies.push(
					`${typeName}: {
		fields: {
			${connectionFieldChilds.join('\n			')}
		},
	},`,
				);
			}
		});

		if (!typePolicies.length) {
			return;
		}

		return `import { relayStylePagination } from "@apollo/client/utilities";
export default {
	${typePolicies.join('\n')}
};`;
	},
};