Function walk_span_to_context

pub fn walk_span_to_context(span: Span, outer: SyntaxContext) -> Option<Span>

Walks the span up to the target context, thereby returning the macro call site if the span is 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

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:

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).