Remove duplicate error about raw underscore lifetime

[xizheyin]

Fixes #143152

r? @fee1-dead

[compiler-errors]

Can you instead use tcx.sess.psess.raw_identifier_spans to look for the raw lifetime span? I think we populate raw_identifier_spans with raw lifetimes too.

If not, then I don't think this hack should land. Using span_to_snippet here seems fragile.

[compiler-errors]

r? compiler-errors

[xizheyin]

Can you instead use tcx.sess.psess.raw_identifier_spans to look for the raw lifetime span? I think we populate raw_identifier_spans with raw lifetimes too.

I have a try on it, and it works.

[xizheyin]

I'm wondering if I should split it into 2 parts, as this doesn't seem very aesthetically pleasing taking up so many lines. However it seems to give the wrong impression that the variable in the middle will be used multiple times.

[compiler-errors]

Use emit_unless, and also we don't need to factor this into a variable.

Suggested change

	// To avoid emitting two duplicate errors, we need to check if the span is a raw underscore lifetime, see issue #143152
	let is_raw_underscore = self
	.r
	.tcx
	.sess
	.psess
	.raw_identifier_spans
	.iter()
	.any(|span| span == param.span());
	if param.ident.name == kw::UnderscoreLifetime && !is_raw_underscore {
	self.r
	.dcx()
	.emit_err(errors::UnderscoreLifetimeIsReserved { span: param.ident.span });
	self.r
	.dcx()
	.create_err(errors::UnderscoreLifetimeIsReserved {
	span: param.ident.span,
	})
	// To avoid emitting two duplicate errors, we need to check if the span is a raw underscore lifetime, see issue #143152
	.emit_unless(
	kw::UnderscoreLifetime
	&& self
	.r
	.tcx
	.sess
	.psess
	.raw_identifier_spans
	.iter()
	.any(|span| span == param.span()),
	);

[compiler-errors]

Also I think the comment could be tweaked; instead of "two duplicate errors", b/c the error is not duplicate, we should say something different.