preProcessFile does not detect "import type" statements

[kitsonk]

TypeScript Version: 3.8.3

Search Terms:

preProcessFile, type only import, ambientExternalModules

Code

import ts from "typescript";

const text = `import type { Func } from "./subdir/types.ts";

const func: Func = t => t;
`;

console.log(ts.preProcessFile(text, true));

Expected behavior:

That the type only import would be referenced somehow. As of TypeScript 3.8, ambientExternalModules was introduced, so I can only assume that is where it should go, but it isn't populated. In addition, ambientExternalModules is of type string[] unlike the other properties which are FileReference[].

Actual behavior:

{
  referencedFiles: [],
  typeReferenceDirectives: [],
  libReferenceDirectives: [],
  importedFiles: [],
  isLibFile: false,
  ambientExternalModules: undefined
}

[RyanCavanaugh]

Also pinging @andrewbranch for opinions on what the best behavior here is

[sheetalkamat]

Its definitely bug and it should return importedFiles to contain the actual file form import type