Fix outdated comment

[ldm0]

Logics in libsyntax/ext/expand.rs:MacroExpander::expand() have been moved to libsyntax_expand/expand.rs:MacroExpander::fully_expand_fragment()
This pull request fixs the dangling file path.

Old

rust/src/libsyntax/ext/expand.rs

Lines 285 to 301 in 3517686

	let derive_allowed = match item {
	Annotatable::Item(ref item) => match item.node {
	ast::ItemKind::Struct(..) |
	ast::ItemKind::Enum(..) |
	ast::ItemKind::Union(..) => true,
	_ => false,
	},
	_ => false,
	};
	if !derive_allowed {
	let span = item.attrs().iter()
	.find(|attr| attr.check_name("derive"))
	.expect("`derive` attribute should exist").span;
	self.cx.span_err(span,
	"`derive` may only be applied to structs, enums \
	and unions");
	}

New

rust/src/libsyntax_expand/expand.rs

Lines 421 to 439 in 9ff30a7

	if !item.derive_allowed() {
	let attr = attr::find_by_name(item.attrs(), sym::derive)
	.expect("`derive` attribute should exist");
	let span = attr.span;
	let mut err = self.cx.struct_span_err(span,
	"`derive` may only be applied to structs, enums and unions");
	if let ast::AttrStyle::Inner = attr.style {
	let trait_list = derives.iter()
	.map(|t| pprust::path_to_string(t))
	.collect::<Vec<_>>();
	let suggestion = format!("#[derive({})]", trait_list.join(", "));
	err.span_suggestion(
	span, "try an outer attribute", suggestion,
	// We don't 𝑘𝑛𝑜𝑤 that the following item is an ADT
	Applicability::MaybeIncorrect
	);
	}
	err.emit();
	}

rust/src/libsyntax_expand/base.rs

Lines 224 to 234 in 9ff30a7

	pub fn derive_allowed(&self) -> bool {
	match *self {
	Annotatable::Item(ref item) => match item.kind {
	ast::ItemKind::Struct(..) |
	ast::ItemKind::Enum(..) |
	ast::ItemKind::Union(..) => true,
	_ => false,
	},
	_ => false,
	}
	}

[rust-highfive]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @nikomatsakis (or someone else) soon.

If any changes to this PR are deemed necessary, please add them as extra commits. This ensures that the reviewer can see what has changed since they last reviewed the code. Due to the way GitHub handles out-of-date commits, this should also make it reasonably obvious what issues have or haven't been addressed. Large or tricky changes may require several passes of review and changes.

Please see the contribution instructions for more information.

[Centril]

r? @petrochenkov

[Dylan-DPC-zz]

@ldm0 please do not merge changes, rather rebase over master. Thanks

[ldm0]

@Dylan-DPC Sorry, fixed

[petrochenkov]

@bors r+ rollup

[bors]

📌 Commit decb959 has been approved by petrochenkov