mxschmitt / playwright-go / 31999264115

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fix: reject unusable event predicates instead of panicking in the dispatch goroutine (#635)

The generic ExpectEvent/WaitForEvent APIs on Page, BrowserContext and WebSocket
take `Predicate any` — necessarily untyped, since the event argument type
differs per event — and invoked it through reflection with no validation:

    if predicate == nil || reflect.ValueOf(predicate).IsNil() {
    ...
    result := reflect.ValueOf(predicate).Call([]reflect.Value{reflect.ValueOf(ev[0])})

Both lines panic on a predicate the caller got wrong:

    Predicate: "not-a-function"
    panic: reflect: call of reflect.Value.IsNil on string Value

    Predicate: func(playwright.Request) bool   // on a "console" event
    panic: reflect: Call using *playwright.consoleMessageImpl as type playwright.Request

These fire inside eventEmitter.Emit → callHandlers, i.e. the library's own
dispatch goroutine, so they take down the process and the caller cannot recover
them.

Upstream wraps the predicate call in try/catch and rejects the wait
(client/waiter.ts), so a bad predicate surfaces as an error on the awaited
promise. Do the same: validate the predicate's kind and signature, check the
event argument is assignable, and recover a panic raised by the predicate body,
reporting each as an error through the existing reject path.

Also guards the same unchecked reflect.Call in RejectOnEvent. Its predicates are
supplied internally today, so this is consistency rather than a live bug.

Typed nil predicates (e.g. a nil `func(any) bool` variable) now mean "no
predicate", matching an untyped nil, instead of panicking in IsNil.


Claude-Session: https://claude.ai/code/session_01Hr35MBUfsUG9DnxhBgBcZW

Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>

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