typechecking of return types broken with `try/catch` when `strictNullChecks` and `noImplicitAny` are enabled

Bug Report

🔎 Search Terms

try/catch, exception handling, strict mode

🕗 Version & Regression Information

Broken in 4.3.5, still broken in nightly

⏯ Playground Link

Playground link with strict mode

Disable --noImplicitAny and --strict (but leave --strictNullChecks) and typechecker will correctly note that val may have type null

💻 Code

declare function bar(): any;

async function foo(): Promise<string> {
    let val = null;
    try {
        val = bar();
    } catch (e) {}
    return val;
}

🙁 Actual behavior

Compile with --strict and observe no errors
Compile simply with --strictNullChecks and typechecker will correctly note that val may have type null and does not conform to the return type

🙂 Expected behavior

typechecker should correctly determine that val can have type null and does not conform to the return type

Commencez par la reproduction liée dans TypeScript Playground, en utilisant la async function montrée et en comparant --strict avec --strictNullChecks. Suivez le traitement par le typechecker de l’affectation du try/catch et du type de retour ; c’est terminé lorsque la configuration stricte signale que val peut être null et ne peut pas satisfaire Promise.