Macro error

macro_rules! error {
    ($fmt:literal $(, $arg:expr)* $(,)?) => { ... };
    (
        $fmt:literal $(, $arg:expr)*
        $(; hint: $hint:literal $(, $hint_arg:expr)*)*
        $(,)?
    ) => { ... };
    (
        $span:expr, $fmt:literal $(, $arg:expr)*
        $(; hint: $hint:literal $(, $hint_arg:expr)*)*
        $(,)?
    ) => { ... };
}

Construct an EcoString, HintedString or SourceDiagnostic with severity Error.