[RFC ] Errors handling

packages/core/rfcs/errors-habdling-in-composables.md

@@ -0,0 +1,63 @@
+# Errors handling in composables
+
+## Motivation
+
+We need to handle errors, that are caused by external api calls provided by factory params.
+Furthermore, it must be something to recognize where that error comes from (which call).
+
+We can solve it by introducing fields inside the errors object and the `AgnosticError`:
+
+Factory
+```js
+const useProductFactory = (factoryParams) => {
+  const useProduct = () => {
+    const products = ref([]);
+    const errors = ref({};)
+
+
+    const search = async (params) => {
+      try {
+        products.value = factoryParams.searchProducts(params);
+      } catch (err) {
+        errors.searchProducts = factoryParams.convertError(err);
+      }
+    }
+
+
+    return { products, search }
+  }
+}
+
+export default useProductFactory
+```
+
+Usage:
+
+```js
+import { useProductFactory } from '@vue-storefront/factories';
+
+
+const factoryParams = {
+  searchProducts: async (params) => {
+    return await getProductsFromApi(params);
+  },
+  convertError: (error) => {
+    if ('this is search product error ?') {
+      return 'this is error message for searching products';
+    }
+
+    return error;
+  }
+};
+
+export default useProductFactory()
+
+```
+
+Summary:
+- factory catches errors, and convert them to the readable message using `convertError`
+- `convertError` is a new factory param, you have to provide it in order to handle and react on errors
+
+
+## Migration process
+Transparent, `convertError` is optional, also you don't have to implement errors if you don't need now