pub(crate) fn validate_postfix(val: &str, span: &dyn ToTokens) -> Result<()>Expand description
Parse the value of a name = "..." meta item as a string literal.
Returns a compile error spanning the offending token when the RHS is not a
&str literal. field is used in the diagnostic (e.g. "c_symbol").
postfix = "..." must be a non-empty R identifier fragment: it is appended
verbatim to the Rust name, so anything outside letters, digits, _ and .
would produce an R name that needs backticks.