> Make a function async and your entire call graph has to be made async, unless they handle the future manually without await.
You can "handle the future manually without await" very easily, it's just one function call. The same sort of thing is available in most other languages with async/await- you can prevent async from going up the call stack by synchronously blocking on a future instead of awaiting it.
The caller is absolutely in charge of whether something runs asynchronously. The only difference is a syntactic default- and in fact some languages even make async functions calls default to synchronous execution. For example take a look at Kotlin's `suspend fun`s.
You can "handle the future manually without await" very easily, it's just one function call. The same sort of thing is available in most other languages with async/await- you can prevent async from going up the call stack by synchronously blocking on a future instead of awaiting it.
The caller is absolutely in charge of whether something runs asynchronously. The only difference is a syntactic default- and in fact some languages even make async functions calls default to synchronous execution. For example take a look at Kotlin's `suspend fun`s.