Flow's generic types

[GeneZharov]

It seems that import-js does not recognize flow's generic types:

function Fn<T>(x: T): T { return x; }

It cause import-js to insert:

import { T } from "lodash/fp";

Though T is not a function, and it is already defined in this code snippet. Here is the generic's doc: https://flow.org/en/docs/types/generics/

I tried to fix this, but it is a too complex task. I see that "babylon" parses generic type definitions correctly. I think we need to add generic type declarations to the context so that we can filter this names in "lib/findUndefinedIdentifiers.js". But we must treat js names and flow names in the context differently. If T is used as a js name then we need to import it. If T is used as a flow type then it is already defined.

This are the tests I wrote for this task:

describe('should recognize flow\'s generic type', () => {
  test('function statement', () => {
    expect(findUndefinedIdentifiers(parse(`
      function Fn<T>(x: T): T {
        return x;
      }
    `))).toEqual(new Set([]));
  });

  test('function expression', () => {
    expect(findUndefinedIdentifiers(parse(`
      const Fn = function Fn<T>(x: T): T {
        return x;
      };
    `))).toEqual(new Set([]));
  });

  test('arrow function', () => {
    expect(findUndefinedIdentifiers(parse(`
      const Fn = <T>(x: T): T => x;
    `))).toEqual(new Set([]));
  });

  test('type statement', () => {
    expect(findUndefinedIdentifiers(parse(`
      type Some<T> = T[];
    `))).toEqual(new Set([]));
  });

  test('class', () => {
    expect(findUndefinedIdentifiers(parse(`
      class Some<T> {
        prop: T;
        constructor(param: T) {
          this.prop = param;
        }
      }
    `))).toEqual(new Set([]));
  });

  test('interface', () => {
    expect(findUndefinedIdentifiers(parse(`
      interface Some<T> {
        foo: T,
        bar: T
      }
    `))).toEqual(new Set([]));
  });
});

[trotzig]

Thanks for the report and the reproduction steps in the form of unit tests! Let's see if someone else is willing to take this on. I don't have much investment in flowscript unfortunately, the only project using it is (ironically) import-js.