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I think sometimes the error message is appropriate (it is about assignment) and sometimes it is not (for closures? Not sure about other cases). So you'll have to do more that just change the error message, you must detect which case you're in and give the right error message.

You might need to change some tests to match the error message too.

You're right this isn't enough. I'll keep looking. In the last test case of borrowck-closures-unique.rs, the error thrown is "closure cannot assign to immutable argument x". The 'assign to' is right, but the description 'immutable argument x' isn't. It does make sense for the other case where this error message is thrown, though.

What's the status of this PR?