That's not how it's supposed to be.

but for example Vec::new() doesn’t highlight anything at all.

If I do Vec::new(foo, bar), I get expected 0 arguments, found 2 (rust-analyzer E0107).

but things like passing too many arguments into the println macro doesn’t throw an error.

I don't get that either, but I'm still running with the Vim configuration I setup on my previous PC from 2011, where I turned off checks that require calling cargo check or cargo clippy in the background. From what I remember, a properly functioning default rust-analyzer config should pick up and display anything cargo check will catch and you can switch it to cargo clippy for even stricter results.

Or how shown in this example, it did not autocomplete the clone method, while also just accepting .clo; at the end of a String (it also didn’t autocomplete “String”).

I get clone(), clone_into(), and clone_from() as proposed completions for .clo on my as-you-type completions for foo where let foo = String::new(); and it proposed a whole bunch of things, with String at the top when I typed Stri. (eg. the stringify! macro, OsString, mixed in with various results from other crates in the project like serde)