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Generic parameters not fully type-checked (e.g., Promise) #14770
Description
TypeScript Version: 2.2.1
Code
const a: Promise<{ foo: 'bar' }> = Promise.resolve({ foo: 'typo' });
const b: Promise<{ foo: 'bar' }> = Promise.resolve({});Expected behavior:
ashould type-check: it constrainsfooto'bar'but is given'typo'.bshould type-check: it requiresfoobut is given an object withoutfoo.
Actual behavior:
Neither type-check.
The same types check fine when resolved directly:
// Type '{ foo: "typo"; }' is not assignable to type '{ foo: "bar"; }'.
// Types of property 'foo' are incompatible.
// Type '"typo"' is not assignable to type '"bar"'.
const a: { foo: 'bar' } = { foo: 'typo' });
// Type '{}' is not assignable to type '{ foo: "bar"; }'.
// Property 'foo' is missing in type '{}'.
const b: { foo: 'bar' } = {};Generic parameter type checks fail for objects/types of different shapes:
// Type 'Promise<{ foo: string; bar: string; }>' is not assignable to type 'Promise<{ foo: "bar"; }>'.
// Type '{ foo: string; bar: string; }' is not assignable to type '{ foo: "bar"; }'.
// Types of property 'foo' are incompatible.
// Type 'string' is not assignable to type '"bar"'.
const a: Promise<{ foo: 'bar' }> = Promise.resolve({ foo: 'bar', bar: 'baz' });
// Type 'Promise<number>' is not assignable to type 'Promise<{ foo: "bar"; }>'.
// Type 'number' is not assignable to type '{ foo: "bar"; }'.
const b: Promise<{ foo: 'bar' }> = Promise.resolve(1);
Activity
[-]Promise.resolve doesn't fully type-check generic parameters[/-][+]Generic parameters not fully type-checked (e.g., Promise)[/+]ikokostya commentedon Mar 23, 2017
Related to #10717. See comment #10717 (comment)
ikokostya commentedon Mar 23, 2017
JFI it works in
flow, because type parameter in promise is declared as covariant.