Function rustc_ap_rustc_span::with_source_map

pub fn with_source_map<T, F: FnOnce() -> T>(
    source_map: Lrc<SourceMap>, 
    f: F
) -> T

Calls the provided closure, using the provided SourceMap to format any spans that are debug-printed during the closure's execution.

Normally, the global TyCtxt is used to retrieve the SourceMap (see rustc_interface::callbacks::span_debug1). However, some parts of the compiler (e.g. rustc_parse) may debug-print Spans before a TyCtxt is available. In this case, we fall back to the SourceMap provided to this function. If that is not available, we fall back to printing the raw Span field values.