Compile error if I named last array destructuring element.

[heroboy]

TypeScript Version: v4.0.5

Search Terms: destructuring assignment , Object literal may only specify known properties

Code

declare function foo<T extends { dataType: 'a' | 'b'; }>(template: T): [T, any, any]; //<-- there no error, when it is [any,any,any]
declare function bar<T extends { dataType: 'a' | 'b'; }>(template: T): [T, any];

function test_foo() {

  const [, ,] = foo({ dataType: 'a', day: 0 });
  const [x, y, z] = foo({ dataType: 'a', day: 0 });
  const [, , t] = foo({ dataType: 'a', day: 0 }); //<-- red line under the `day`
  console.log(x, y, z, t);
}

function test_bar() {

  const [,] = bar({ dataType: 'a', day: 0 });
  const [x, y] = bar({ dataType: 'a', day: 0 });
  const [, z] = bar({ dataType: 'a', day: 0 });//<-- red line under the `day`
  console.log(x, y, z);
}

Expected behavior: no compile error Actual behavior:

    Argument of type '{ dataType: "a"; day: number; }' is not assignable to parameter of type '{ dataType: "a" | "b"; }'. Object literal may only specify known properties, and 'day' does not exist in type '{ dataType: "a" | "b"; }'.

**Playground Link: link

Related Issues:

[theGreen233]

Hello, we are a group of researchers developing machine learning techniques to locate issues suitable for newcomers, and our model consider this issue as likely a "good first issue". May we recommend you to label it as "good first issue" so newcomers know where to choose?

Thank you!

[andrewbranch]

This is not a good first issue

[typescript-bot]

:wave: Hi, I'm the Repro bot. I can help narrow down and track compiler bugs across releases! This comment reflects the current state of the repro in the issue body running against the nightly TypeScript.

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Issue body code block by @heroboy

:x: Failed: -

• Object literal may only specify known properties, and 'day' does not exist in type '{ dataType: "a" | "b"; }'.
• Object literal may only specify known properties, and 'day' does not exist in type '{ dataType: "a" | "b"; }'.

Historical Information

Version

Reproduction Outputs

4.2.2, 4.3.2, 4.4.2, 4.5.2, 4.6.2

:x: Failed: - Argument of type '{ dataType: "a"; day: number; }' is not assignable to parameter of type '{ dataType: "a" | "b"; }'. Object literal may only specify known properties, and 'day' does not exist in type '{ dataType: "a" | "b"; }'. Argument of type '{ dataType: "a"; day: number; }' is not assignable to parameter of type '{ dataType: "a" | "b"; }'. Object literal may only specify known properties, and 'day' does not exist in type '{ dataType: "a" | "b"; }'.