**Feature summary** (what you would like to be able to do and where):
`mw.Api()` should show warnings returned by the Action API, e.g. by logging them via `console.warn()`.
**Use case(s)** (list the steps that you performed to discover that problem, and describe the actual underlying problem which you want to solve. Do not describe only a solution):
As a gadget or user script developer, I want to know when I use deprecated API usage patterns. When the API returns warnings, I expect `mw.Api()` to show them.
**Benefits** (why should this be implemented?):
Helps to discover user scripts and gadgets that need to be fixed.
**Example**:
```lang=js
await new mw.Api().get( { action: 'query', prop: 'revisions', rvprop: 'content', pageids: 1 } )
```
The API returns a warning (about the usage of `rvprop=content` without `rvslots=`, but it’s only visible if you look at the response yourself.
By contrast:
```lang=js
await new mw.Api().get( { action: 'edit' } )
```
The API returns an error, which `mw.Api` reports as a promise rejection. Users don’t have to check `response.errors ?? [ response.error ]` themselves.