Clarify the reason why there is the restriction on changing the set o…

…f stores (#760)

* Clarify the reason why there is the restriction on changing the set of stores

Fixes #745

* Update README.md

Co-Authored-By: Daniel K. <FredyC@users.noreply.github.com>

README.md

@@ -308,10 +308,13 @@ Notes:
 
 - It is possible to read the stores provided by `Provider` using `React.useContext`, by using the `MobXProviderContext` context that can be imported from `mobx-react`.
 - If a component asks for a store and receives a store via a property with the same name, the property takes precedence. Use this to your advantage when testing!
-- Values provided through `Provider` should be final. Make sure that if you put things in `context` that might change over time, that they are `@observable` or provide some other means to listen to changes, like callbacks. However, if your stores will change over time, like an observable value of another store, MobX will throw an error.
 - When using both `@inject` and `@observer`, make sure to apply them in the correct order: `observer` should be the inner decorator, `inject` the outer. There might be additional decorators in between.
 - The original component wrapped by `inject` is available as the `wrappedComponent` property of the created higher order component.
 
+#### "The set of provided stores has changed" error
+Values provided through `Provider` should be final. Make sure that if you put things in `context` that might change over time, that they are `@observable` or provide some other means to listen to changes, like callbacks. However, if your stores will change over time, like an observable value of another store, MobX will throw an error.
+This restriction exists mainly for legacy reasons. If you have a scenario where you need to modify the set of stores, please leave a comment about it in this issue https://github.com/mobxjs/mobx-react/issues/745. Or a preferred way is to [use React Context](https://mobx-react.js.org/recipes-context) directly which does not have this restriction.
+
 #### Inject as function
 
 The above example in ES5 would start like:

src/Provider.js

@@ -15,7 +15,7 @@ export function Provider({ children, ...stores }) {
  const newValue = { ...value, ...stores } // spread in previous state for the context based stores
  if (!shallowEqual(value, newValue)) {
  throw new Error(
- "MobX Provider: The set of provided stores has changed. Please avoid changing stores as the change might not propagate to all children"
+ "MobX Provider: The set of provided stores has changed. See: https://github.com/mobxjs/mobx-react#the-set-of-provided-stores-has-changed-error."
  )
  }
  }

test/Provider.test.js

@@ -79,9 +79,7 @@ describe("Provider", () => {
  withConsole(() => {
  expect(() => {
  rerender(<A foo={2} />)
- }).toThrow(
- "The set of provided stores has changed. Please avoid changing stores as the change might not propagate to all children"
- )
+ }).toThrow("The set of provided stores has changed.")
  })
  })
 })