Numeric enums are assignment compatible with number

[mprobst]

TypeScript Version: Version 3.1.0-dev.20180813

Search Terms: enum number assignment compatible subtype

Code

enum NumericEnum { A = 0, B, C }
enum OtherNumericEnum { A = 0, B, C }
enum StringEnum { D = 'd', E = 'e', F = 'f' }

// This compiles (but should not)
let f: NumericEnum = 0;
let f2: NumericEnum = 123 /* not even a member */;
let f3: OtherNumericEnum = 0;

function takesNumericEnum(f: NumericEnum) {}
takesNumericEnum(123);

// This fails to compile as expected:
let b: StringEnum = 'g';
let b1: StringEnum = 'd';
f = f3;
takesNumericEnum(f3);

function takesStringEnum(f: StringEnum) {}
takesStringEnum('g');

Expected behavior:

Numeric enums should not be assignable from number.

Actual behavior:

They are.

Playground Link:

http://www.typescriptlang.org/play/#src=enum%20NumericEnum%20%7B%20A%20%3D%200%2C%20B%2C%20C%20%7D%0Aenum%20OtherNumericEnum%20%7B%20A%20%3D%200%2C%20B%2C%20C%20%7D%0Aenum%20StringEnum%20%7B%20D%20%3D%20'd'%2C%20E%20%3D%20'e'%2C%20F%20%3D%20'f'%20%7D%0A%0A%2F%2F%20This%20is%20ok%20(but%20should%20not%20be)%0Alet%20f%3A%20NumericEnum%20%3D%200%3B%0Alet%20f2%3A%20NumericEnum%20%3D%20123%20%2F*%20not%20even%20a%20member%20*%2F%3B%0Alet%20f3%3A%20OtherNumericEnum%20%3D%200%3B%0A%0Afunction%20takesNumericEnum(f%3A%20NumericEnum)%20%7B%7D%0AtakesNumericEnum(123)%3B%0A%0A%2F%2F%20But%20this%20is%20not.%0Alet%20b%3A%20StringEnum%20%3D%20'g'%3B%0Alet%20b1%3A%20StringEnum%20%3D%20'd'%3B%0Af%20%3D%20f3%3B%0AtakesNumericEnum(f3)%3B%0A%0Afunction%20takesStringEnum(f%3A%20StringEnum)%20%7B%7D%0AtakesStringEnum('g')%3B%0A%0A

Related Issues:

[RyanCavanaugh]

Duplicate #26362 and many others

[mprobst]

Sorry for the dupe, I think I only searched open issues.