Type inference behave different with or without destructure

[lihz6]

TypeScript Version: 3.2.0-dev.201xxxxx

Search Terms: type inference behave different

Code

type Shape = {
  kind: 'circle',
  data: {
    radius: number
  }
} | {
  kind: 'square',
  data: {
    size: number
  }
};

function getAreaOkay(shape: Shape) {
  switch (shape.kind) {
    case 'circle':
      // okay
      return shape.data.radius;
  }
}
function getAreaFail({ kind, data }: Shape) {
  switch (kind) {
    case 'circle':
      // fail
      return data.radius;
  }
}

Expected behavior: the above two should be identical.

Actual behavior: they are not.

[AlCalzone]

AFAIK, typescript doesn't narrow the type from one variable (kind) to a seperate one (data).

[ahejlsberg]

This is a duplicate of #23613 and several others like it. The core design limitation is that the control flow analyzer doesn't track mutually dependent variables. We're tracking the issue in #12184.

[typescript-bot]

This issue has been marked as a duplicate and has seen no activity in the last day. It has been closed automatic house-keeping purposes.