A bit messy around here. I feel like if any better way.

Could you replace this branch by changing the if nonelided_generic_args to if nonelided_generic_args || !elide_lifetimes below the loop?

Yeah, that would work fine. But I have a concern that it would make nonelided_generic_args differ from what is inferred from its name.
Because in that case, nonelided_generic_args can be false, even when we have lifetime generic_args that are not elided.

Isn't it a concern that much? (or do I understand wrong?)

nonelided_generic_args is only used in one place, just below, so I'm not really concerned. If you want to fix that, you can change the name.
Another possibility: make lt.is_elided() into an arm guard, and let the non-elided case fall through the _ => case.
I'll let this to your judgement.

nonelided_generic_args is only used in one place, just below, so I'm not really concerned.

Ah, indeed.

Another possibility: make lt.is_elided() into an arm guard, and let the non-elided case fall through the _ => case.

Thanks for the suggestion! I prefer this one a bit. But looks like non-elided case cannot fall to the _ => case, so may be like this:

                GenericArg::Lifetime(lt) if lt.is_elided() => true,
                GenericArg::Lifetime(_) => {
                    nonelided_generic_args = true;
                    false
                }
                _ => {
                    nonelided_generic_args = true;
                    true
                }

done.