Macro enter_trace_span

macro_rules! enter_trace_span {
    ($name:ident :: $subname:ident $($tt:tt)*) => { ... };
    ($($tt:tt)*) => { ... };
}

Enters a tracing::info_span only if the “tracing” feature is enabled, otherwise does nothing. This is like rustc_const_eval::enter_trace_span except that it does not depend on the Machine trait to check if tracing is enabled, because from the Miri codebase we can directly check whether the “tracing” feature is enabled, unlike from the rustc_const_eval codebase.

In addition to the syntax accepted by tracing::span!, this macro optionally allows passing the span name (i.e. the first macro argument) in the form NAME::SUBNAME (without quotes) to indicate that the span has name “NAME” (usually the name of the component) and has an additional more specific name “SUBNAME” (usually the function name). The latter is passed to the tracing infrastructure as a span field with the name “NAME”. This allows not being distracted by subnames when looking at the trace in https://ui.perfetto.dev, but when deeper introspection is needed within a component, it’s still possible to view the subnames directly in the UI by selecting a span, clicking on the “NAME” argument on the right, and clicking on “Visualize argument values”.

// for example, the first will expand to the second
enter_trace_span!(borrow_tracker::on_stack_pop, /* ... */)
enter_trace_span!("borrow_tracker", borrow_tracker = "on_stack_pop", /* ... */)