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.

Comienza reproduciendo el problema en el playground de react-docgen con Language establecido en Typescript, utilizando el ejemplo .tsx y llamando a reactDocgen.parse() sobre la referencia a la declaración. Sigue el punto de entrada del parser para las declaraciones .d.ts y compara el resultado con la salida esperada, en la que Component2 aparece con su descripción, displayName, methods y props.