[nightly] [regression] Control flow analysis for destructured unions gets invalidated by later assignment #57011
Description
🔎 Search Terms
control flow assignment destructured discriminated union
🕗 Version & Regression Information
- This changed between versions 5.3.3 and 5.4.0 nightly
⏯ Playground Link
💻 Code
function test({ other, success, value, }: {other: unknown} & ( | { success: true; value: number } | { success: false; value?: number } )): number { if (success) { return value; // ^^^^^^^^^^^^^ Type 'number | undefined' is not assignable to type 'number'. } other = 4; // comment me out and the type error goes away return 4; }🙁 Actual behavior
Type error because value is not narrowed by success check.
🙂 Expected behavior
No type error because narrowing is correctly applied
Additional information about the issue
Note that this seems to be an extended version of a bug that I discovered has existed since TS 4.6 when control flow analysis for destructured unions was introduced!
function test({ success, value, }: | { success: true; value: number } | { success: false; value?: number }): number { if (success) { return value; // ^^^^^^^^^^^^^ Type 'number | undefined' is not assignable to type 'number'. } value = 4; // comment me out and the type error goes away return 4; }