Type comments bugs

Already known issue
Type comments are not used, with union types
https://github.com/YousefED/typescript-json-schema/pull/64#issuecomment-255235376

Type comments are not used, when type is imported from another file

String type, null type and pattern are applied.

/**
 * @pattern \d{4}-\d{2}-\d{2}T\d{2}\:\d{2}\:\d{2}\.\d{3}[+-]\d{4}
 */
export type StringDateNullable = string | null; // "1992-04-10T20:00:00.000+0000"


export interface Person {
    birthDate: StringDateNullable;
}

Only string and null types are applyed, not pattern.

import {
    StringDateNullable
} from './common.types';


export interface Person {
    birthDate: StringDateNullable;
}

Full property info

"birthDate": {
    "pattern": "\\d{4}-\\d{2}-\\d{2}T\\d{2}\\:\\d{2}\\:\\d{2}\\.\\d{3}[+-]\\d{4}",
    "type": [
        "null",
        "string"
    ]
},

Full case

// common.types.ts
/**
 * @pattern \d{4}-\d{2}-\d{2}T\d{2}\:\d{2}\:\d{2}\.\d{3}[+-]\d{4}
 */
export type StringDate = string; // "1992-04-10T20:00:00.000+0000"

// person.types.ts
import {
    StringDate
} from './common.types';


export interface Person {
    birthDate: StringDate | null;
}

Expected result

{
    "$schema": "http://json-schema.org/draft-04/schema#",
    "properties": {
        "birthDate": {
            "anyOf": [
                {
                    "pattern": "\\d{4}-\\d{2}-\\d{2}T\\d{2}\\:\\d{2}\\:\\d{2}\\.\\d{3}[+-]\\d{4}",
                    "type": "string"
                },
                {
                    "type": "null"
                }
            ]
        }
    },
    "type": "object"
}

Current result

{
    "$schema": "http://json-schema.org/draft-04/schema#",
    "properties": {
        "birthDate": {
            "type": [
                "null",
                "string"
            ]
        }
    },
    "type": "object"
}

Start with the TypeScript reproductions in the issue, including the union type and imported type-comment cases, and compare their expected and current JSON schemas. Trace how type comments are handled for unions and imported types, then add regression coverage showing that the pattern is preserved while the union becomes separate string and null schemas.