decoder return type should forbid excess properties

[jasonkuhrt]

Screenshot

Description

size2 should not be allowed because it is not a known property. (Notice size is not required because it has a default).

[jasonkuhrt]

Oh darn, right, this is not possible currently:

• Don't widen return types of function expressions microsoft/TypeScript#241
• https://stackoverflow.com/questions/63258306/how-to-force-typescript-excess-property-check-on-function-return-value
• Don't widen inferred return types when a contextual signature is available microsoft/TypeScript#40311