snippet_opt(cx, span).map_or_else(|| Cow::Borrowed(default), From::from)
}
-/// Same as `snippet`, but it adapts the applicability level by following rules:
+/// Same as [`snippet`], but it adapts the applicability level by following rules:
///
/// - Applicability level `Unspecified` will never be changed.
/// - If the span is inside a macro, change the applicability level to `MaybeIncorrect`.
/// inside a macro expansion, or the original span if it is not. Note this will return `None` in the
/// case of the span being in a macro expansion, but the target context is from expanding a macro
/// argument.
+///
+/// Given the following
+///
+/// ```rust,ignore
+/// macro_rules! m { ($e:expr) => { f($e) }; }
+/// g(m!(0))
+/// ```
+///
+/// If called with a span of the call to `f` and a context of the call to `g` this will return a
+/// span containing `m!(0)`. However, if called with a span of the literal `0` this will give a span
+/// containing `0` as the context is the same as the outer context.
+///
+/// This will traverse through multiple macro calls. Given the following:
+///
+/// ```rust,ignore
+/// macro_rules! m { ($e:expr) => { n!($e, 0) }; }
+/// macro_rules! n { ($e:expr, $f:expr) => { f($e, $f) }; }
+/// g(m!(0))
+/// ```
+///
+/// If called with a span of the call to `f` and a context of the call to `g` this will return a
+/// span containing `m!(0)`.
pub fn walk_span_to_context(span: Span, outer: SyntaxContext) -> Option<Span> {
let outer_span = hygiene::walk_chain(span, outer);
(outer_span.ctxt() == outer).then(|| outer_span)