Rust doesn't want to have exceptions; it prefers return value based error handling ("monadic error handling", specifically). A lot of people seem to be under the impression that Rust's error handling model is a way of emulating exceptions -- it's not; it's a different model, and we don't want to emulate exceptions. The fact that error propagation is a common task doesn't mean that Rust's way of providing it is done to emulate exceptions.
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In a sense, every part of Rust's error handling model is "necessary because Rust doesn't have exceptions". Similarly, every part of Java's error handling model is "necessary because Java makes it hard to do monadic error handling". Saying "X is only necessary because you don't have Y" when X is an alternative to Y isn't a very useful statement.
> something an exception system does for you for free.
That's the point, it doesn't, you pay for the exception system and the implicitness that comes with it. Your comment portrays exceptions as the default that monadic errors are playing catch-up with. I could easily do the reverse.
> is a workaround to make it less of a pain.
You say workaround, I say feature.
Ultimately, monadic errors and exceptions have tradeoffs.
Like I said, given any tradeoff between feature A and feature B, you can always say "subfeature X of A exists because we don't have B". It's not a meaningful thing to say.
I didn't avoid an answer, I genuinely think that your comment has no substance to it because it pretends that exceptions are a "default" system.
Rust doesn't want to have exceptions; it prefers return value based error handling ("monadic error handling", specifically). A lot of people seem to be under the impression that Rust's error handling model is a way of emulating exceptions -- it's not; it's a different model, and we don't want to emulate exceptions. The fact that error propagation is a common task doesn't mean that Rust's way of providing it is done to emulate exceptions.
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In a sense, every part of Rust's error handling model is "necessary because Rust doesn't have exceptions". Similarly, every part of Java's error handling model is "necessary because Java makes it hard to do monadic error handling". Saying "X is only necessary because you don't have Y" when X is an alternative to Y isn't a very useful statement.