Type intersection on type with nested type breaks extra properties error

[Emily]

TypeScript Version: 3.4.0-dev.20190131 (I spot checked versions since 3.0.1, all had this issue

Search Terms: intersection extra properties

Code

type Problematic = { one?: string } & { nested?: { two?: string } }
function problem(input: Problematic) {}

// nested containing bad property unexpectedly doesn't cause error
problem({
  nested: {
    two: 'hello',
    bad: 123
  }
})

Expected behavior:
bad: 123 should cause an extra properties error.

Actual behavior:
bad: 123 does not cause the extra properties error.

Playground Link: expanded examples

Related Issues: #28642

For anyone tripped up by this, there's a convenient work-around:

type Merge<T extends object> = { [K in keyof T]: T[K] };
type Problematic = { one?: string } & { nested?: { two?: string } }
function problemGone(input: Merge<Problematic>) {}

// works as expected
problemGone({
  nested: {
    two: 'hello',
    bad: 123
  }
})

[jack-williams]

Duplicate of #13813

[typescript-bot]

This issue has been marked as a 'Duplicate' and has seen no recent activity. It has been automatically closed for house-keeping purposes.