TypeScript interface augmentation for `SymbolConstructor` conflicts with `symbol-observable`

[aikoven]

RxJS version:

6.1.0

Code to reproduce:

Include rxjs@6.1.0 and symbol-observable@1.2.0 into compilation

Expected behavior:

No TypeScript errors

Actual behavior:

TypeScript error

node_modules/rxjs/internal/symbol/observable.d.ts(4,9): error TS2687: 
    All declarations of 'observable' must have identical modifiers.

Additional information:

Type definition from symbol-observable:

declare global {
  export interface SymbolConstructor {
    readonly observable: symbol;
  }
}

Type definition from rxjs:

declare global {
  interface SymbolConstructor {
    observable: symbol;
  }
}

Note the difference in readonly.

[jichang]

I don't know whether this will help. But this error happens when compiling code below

import { ajax } from "rxjs/ajax";

export function get() {
  return ajax("/api/v1/books");
}

get().subscribe(() => console.log('done'))

but when adding import "rxjs"; It works

import "rxjs"
import { ajax } from "rxjs/ajax";

export function get() {
  return ajax("/api/v1/books");
}

get().subscribe(() => console.log('done'))

I guess this happens when you don't import corresponding type definitions

[benlesh]

We should be defining it as readonly as well.