Diag
This will allow us to eagerly translate messages on a top-level diagnostic, such as a `LintDiagnostic`. As a bonus, we can remove the awkward closure passed into Subdiagnostic and make better use of `Into`.
markdown::parse::Context
String
-Zmacro-backtrace
use
abs_diff
cfg(not(parallel))
Option<&Lrc<T>>
Option<&T>