format_push_string doesn't trigger "indirectly"

[Rudxain]

Summary

My xorsum crate has a fn to convert a byte-vector to its hex-encoded form, it repeatedly calls format! appending its result to a String, but Clippy didn't show a warning

Lint Name

format_push_string

Reproducer

I tried this code:

#![warn(clippy::format_push_string)]

pub fn u8vec_to_hex(vector: &Vec<u8>, upper: bool) -> String {
	let mut hex = String::with_capacity(vector.len() * 2);
	for byte in vector {
		hex += &(if upper {
			format!("{byte:02X}")
		} else {
			format!("{byte:02x}")
		});
	}
	hex
}

I expected to see this happen: Warning

Instead, this happened: Nothing

Version

rustc 1.63.0 (4b91a6ea7 2022-08-08)
binary: rustc
commit-hash: 4b91a6ea7258a947e59c6522cd5898e7c0a6a88f
commit-date: 2022-08-08
host: x86_64-unknown-linux-gnu
release: 1.63.0
LLVM version: 14.0.5