[api-extractor] dts rollup cannot handle "import Foo = Bar.Baz" syntax as external import correctly

[adventure-yunfei]

Please prefix the issue title with the project name i.e. [rush], [api-extractor] etc.

Is this a feature or a bug?

• Feature
• Bug

Please describe the actual behavior.

If we use "import Foo = Bar.Baz" syntax for external package, dts rollup will treat those symbols as local symbols, and produce incorrect dts result.

If the issue is a bug, how can we reproduce it? Please provide detailed steps and include a GitHub branch if applicable. Your issue will get resolved faster if you can make it easy to investigate.

With following "foo" package definition:

// node_modules/foo/index.d.ts
export declare class Class_inside_foo {
	mem: number;
}

And following dts file:

// src/index.d.ts
import * as foo from 'foo';
import Class_inside_foo = foo.Class_inside_foo;
export declare class NormalClass {
    mem: Class_inside_foo;
}

Dts rollup by api-extractor will generator following dts result:

// dts.rollup.d.ts
declare class Class_inside_foo {
	mem: number;
}

export declare class NormalClass {
    mem: Class_inside_foo;
}

export { }

The "Class_inside_foo " declaration should be an external import, but instead it's treated as local declaration here.

What is the expected behavior?

May produce something like:

// dts.rollup.d.ts
import * as foo from 'foo';

export declare class NormalClass {
    mem: foo.Class_inside_foo;
}

export {}

If this is a bug, please provide the tool version, Node.js version, and OS.

• Tool: api-extractor
• Tool Version: 7.9.1
• Node Version: v10.21.0
  • Is this a LTS version? yes
  • Have you tested on a LTS version?
• OS: window 10

[adventure-yunfei]

This syntax may be weird, but it's very useful if an external package has exports with multiple hierarchies.

BTW I've been little confused recently about different import/export syntax.
There're some discussions like microsoft/TypeScript#7185 (comment), and official Modules document. But I didn't find the description for import Foo = Bar.Baz; syntax. The most similar case is import Foo = require('bar'), and they both have the same syntax kind "ImportEqualsDeclaration".

[adventure-yunfei]

A working prototype: adventure-yunfei#4