Typescript: Component declaration reference is not recognized by parser

Description

Many Typescript libraries publish types in declaration files (.d.ts) alongside their associated .js bundles. In .d.ts files generated through TS compilation, function types are often defined using declaration references, such as:

declare const MyComponent: React.FunctionComponent<ComponentProps>;

Currently declaration references are not recognized by reactDocgen.parse(). When react-docgen parses a .d.ts file with a single declaration reference, it emits an error: Error: No suitable component definition found..

Desired Behavior

The following code:

import * as React from 'react';

interface ComponentProps {
  foo: string;
}

/**
 * My component is so darn cool!
 */
const Component1: React.FunctionComponent<ComponentProps> = () => <div />;

/**
 * Mine too!
 */
declare const Component2: React.FunctionComponent<ComponentProps>;

Results in the following output:

[
  {
    "description": "My component is so darn cool!",
    "displayName": "Component1",
    "methods": [],
    "props": {
      "foo": {
        "required": true,
        "tsType": {
          "name": "string"
        },
        "description": ""
      }
    }
  },
  {
    "description": "Mine too!",
    "displayName": "Component2",
    "methods": [],
    "props": {
      "foo": {
        "required": true,
        "tsType": {
          "name": "string"
        },
        "description": ""
      }
    }
  }
]

Actual Behavior

The same code results in the following output:

[
  {
    "description": "My component is so darn cool!",
    "displayName": "Component1",
    "methods": [],
    "props": {
      "foo": {
        "required": true,
        "tsType": {
          "name": "string"
        },
        "description": ""
      }
    }
  }
]

Steps to Reproduce

Paste the .tsx sample code from the "Expected Behavior" section into the react-docgen playground with Language set to Typescript.

Beginne damit, das Problem im react-docgen-Playground zu reproduzieren, wobei Language auf Typescript gesetzt ist, das .tsx-Beispiel verwendet wird und reactDocgen.parse() für die Deklarationsreferenz aufgerufen wird. Verfolge den Parser-Einstiegspunkt für .d.ts-Deklarationen und vergleiche das Ergebnis mit der erwarteten Ausgabe, in der Component2 mit seiner Beschreibung, displayName, methods und props enthalten ist.