Module darling::util::parse_expr

Functions to use with #[darling(with = "...")] that control how quoted values in Meta instances are parsed into Expr fields.

Version 1 of syn did not permit expressions on the right-hand side of the = in a MetaNameValue, so darling accepted string literals and then parsed their contents as expressions. Passing a string literal in this version would have required the use of a raw string to add quotation marks inside the literal.

Version 2 of syn removes the requirement that the right-hand side be a literal. For most types, such as Path, the FromMeta impl can accept the version without quotation marks without causing ambiguity; a path cannot start and end with quotation marks, so removal is automatic.

Expr is the one type where this ambiguity is new and unavoidable. To address this, this module provides different functions for different expected behaviors.

Functions

• parse_str_literal
  Parse a Meta to an Expr; if the value is a string literal, the string’s contents will be parsed as an expression and emitted.
• preserve_str_literal
  Parse a Meta to an Expr; if the value is a string literal, the emitted expression will be a string literal.