`format_args!` does not respect integer literals' type

[endorpersand]

When using the 1234i8 syntax in the Display format in formatting macros, the i8 is ignored and treated as a u128.

I tried this code:

fn main() {
    println!("{}", 0x8Fi8);
}

I expected to see this happen: Getting an error that 0x8F is out of the bounds for type i8.

Instead, this happened: This function compiles and prints 143.

Meta

rustc --version --verbose:

rustc 1.71.1 (eb26296b5 2023-08-03)
binary: rustc
commit-hash: eb26296b556cef10fb713a38f3d16b9886080f26
commit-date: 2023-08-03
host: x86_64-apple-darwin
release: 1.71.1
LLVM version: 16.0.5

[konnorandrews]

I went and looked through the format_args!() implementation and found where the issue comes from. The check at https://github.com/rust-lang/rust/blob/master/compiler/rustc_ast_lowering/src/format.rs#L131 ignores the integer type, and it blindly calls n.string() on the u128 value of the literal.

[gurry]

@rustbot claim

[apiraino]

WG-prioritization assigning priority (Zulip discussion).

@rustbot label -I-prioritize +P-medium