What is the expected behavior?

Can pass an object containing a readonly array as a request matching object.

What is the actual behavior?

TSC compares against each type in the union DataMatcher, fails to match on the type DataMatcherArray, reaches the last type in the union - DataMatcherMap - and raises a confusing error message, masking the root cause.

error TS2345: Argument of type 'Foo' is not assignable to parameter of type 'string | RegExp | Buffer | DataMatcherArray | DataMatcherMap | ((body: any) => boolean) | undefined'.
  Type 'Foo' is not assignable to type 'DataMatcherMap'.
    Index signature is missing in type 'Foo'.

Possible solution

Change the definition of DataMatcherArray, from this:

interface DataMatcherArray extends Array<DataMatcher> {}

To this:

interface DataMatcherArray extends ReadonlyArray<DataMatcher> {}

How to reproduce the issue

interface Foo {
  bar: readonly string[];
}

const requestToMatch: Foo = {
  bar: ['baz']
};

nock(someHost)
  .post(someUrl, requestToMatch) // <-- TSC error occurs here
  .reply(201);

Does the bug have a test case?

No, it affects the type definitions.

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