diagnostic regression - unused variables from destructuring with rename  #24142

TypeScript Version: 2.9.0-dev.20180509 and up

Code

export function testRenamingDestructure() {
  let {a: b} = {a: 4};
}

Expected behavior:

Error produced in 2.9.0-dev.20180506 and before:

test.ts:2:8 - error TS6133: 'b' is declared but its value is never read.

2   let {a: b} = {a: 4};
         ~~~~

Actual behavior:

Error produced in 2.9.0-dev.20180509 and after:

test.ts:2:7 - error TS6133: 'a' is declared but its value is never read.

2   let {a: b} = {a: 4};
        ~~~~~~

Description:

Our TSLint tests based off of TypeScript@next started breaking a few days ago. I tracked one of the breaks down to the change in error messages noted above. The older error message seems more correct here - in the example above, a cannot actually be accessed.

Related Issues: Possibly related to #23805?