allow typescript compiler to call setState on only one react state property

Solution 1:

Edit

The definitions for react were updated and the signature for setState are now:

setState<K extends keyof S>(state: Pick<S, K>, callback?: () => any): void;

Where Pick<S, K> is a built-in type which was added in Typescript 2.1:

type Pick<T, K extends keyof T> = {
    [P in K]: T[P];
}

See Mapped Types for more info.
If you still have this error then you might want to consider updating your react definitions.

Original answer:

I'm facing the same thing.

The two ways I manage to get around this annoying issue are:

(1) casting/assertion:

this.setState({
    editorState: editorState
} as MainState);

(2) declaring the interface fields as optional:

interface MainState {
    todos?: Todo[];
    hungry?: Boolean;
    editorState?: EditorState;
}

If anyone has a better solution I'd be happy to know!

Edit

While this is still an issue, there are two discussions on new features that will solve this problem:
Partial Types (Optionalized Properties for Existing Types)
and
More accurate typing of Object.assign and React component setState()

Solution 2:

Update state explicitly, example with the counter

this.setState((current) => ({ ...current, counter: current.counter + 1 }))

Solution 3:

I think that the best way to do it is to use Partial

Declare your component in the following way

class Main extends React.Component<MainProps, Partial<MainState>> {
}

Partial automatically changes all of the keys to optional.