pub fn setting(
name: &str,
lookup: impl Fn(&str) -> Option<String>,
) -> Option<String>Expand description
The value of setting name, preferring the current spelling over the legacy one.
First one set wins and the rest are not looked at, which is what makes the old name an
alias rather than a second setting — the same order usage-config gives deprecated_envs.
Nothing is warned about: one name set is the ordinary case, and the settings read here are
read before there is a logger to warn with.
An empty or blank value reads as unset at each name, matching the FOO= cmd convention for
switching something off, so blanking the current name falls through to the legacy one
rather than to nothing.