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False positive error report for interface type missing index signature, thus not assignable to object type with `unknown` values.

See original GitHub issue

TypeScript Version: 3.6.0-dev.20190704 (3.4.3 doesn’t have this bug)

Search Terms: index signature, unknown, assignable, interface

Code

interface A {
  properties?: { [Key: string]: unknown };
}

type Bar = {
  key?: "value";
};

interface Baz {
  key?: "value";
}

interface B extends A { // ok
  properties?: Bar;
}

interface C extends A { // error: Baz is not assignable to { [Key: string]: unknown } -> Index signature is missing
  properties?: Baz;
}

Expected behavior: No error expected, interface C extends A correctly.

Actual behavior: Error because interface C does not extend interface A

Playground Link: http://www.typescriptlang.org/play/#code/JYOwLgpgTgZghgYwgAgILIN4ChnIA5QD2e0YwEAzgPwBcmyA2gNIQCedFYUoA5gLp0AriADWIQgHcQyAL4BuLDKxYwrEsgBCcKMgC8mHMhFtayAEQA3OABtBEMwvnLQkWIhRaAXgdzHWpyxs7B0VncGh4JE1kCAAPSBAAEwo0egB6NORCEUMCYlJyajotKEcw10iUAGEY+IgklPQMZAyYqCIoYrhvYBTxMGQ4CgpgHhA4ACNrFDBCemY2Di5eAWRhMUlpGWQAWgA+ZABJJLjkEbG4MEEoFF7kAFtekZAeXKISKDJKUy8yoA

Related Issues: #30977 (this one is specifically for enums)

Issue Analytics

State:
Created 4 years ago
Comments:6 (1 by maintainers)

Top GitHub Comments

9reactions

jack-williamscommented, Jul 5, 2019

The reason intellisense for TypeScript is so performant is because the TypeScript team want to have auto-completion while editing checker.ts[1] - so if anything, we should be encouraging them to make it larger.

_{[1] I made that up}

3reactions

woutervh-commented, Jul 5, 2019

Thanks @jack-williams , I didn’t know about this specific assignability rule. Do you know if there is a comprehensive list of type assignability rules out there? I tried to search for one but couldn’t find.