Label shadowing causes a warning that cannot be allowed

[KamilaBorowska]

macro_rules! m {
    ($a:expr) => {
        'label: for _ in 0..1 {
            $a;
        }
    }
}

fn main() {
    m!(m!(1));
}

causes the following warning:

warning: label name `'label` shadows a label name that is already in scope
  --> src/main.rs:3:9
   |
3  |         'label: for _ in 0..1 {
   |         ^^^^^^
   |         |
   |         first declared here
   |         lifetime 'label already in scope
...
10 |     m!(m!(1));
   |        ----- in this macro invocation

There is no way to allow the warning.

[Mark-Simulacrum]

This

rust/src/librustc/middle/resolve_lifetime.rs

Lines 1147 to 1158 in 152527f

	// shadowing involving a label is only a warning, due to issues with
	// labels and lifetimes not being macro-hygienic.
	tcx.sess.struct_span_warn(
	shadower.span,
	&format!(
	"{} name `{}` shadows a \
	{} name that is already in scope",
	shadower.kind.desc(),
	name,
	orig.kind.desc()
	),
	)

piece of code should be converted to emitting a lint versus a warning, I think

[KamilaBorowska]

Duplicate of #31745, closing.