impl FromStr for proc_macro::Literal

library/proc_macro/src/lib.rs

@@ -91,6 +91,12 @@ pub struct LexError {
     _inner: (),
 }
 
+impl LexError {
+    fn new() -> Self {
+        LexError { _inner: () }
+    }
+}
+
 #[stable(feature = "proc_macro_lexerror_impls", since = "1.44.0")]
 impl fmt::Display for LexError {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
@@ -1171,6 +1177,28 @@ impl Literal {
     }
 }
 
+/// Parse a single literal from its stringified representation.
+///
+/// In order to parse successfully, the input string must not contain anything
+/// but the literal token. Specifically, it must not contain whitespace or
+/// comments in addition to the literal.
+///
+/// The resulting literal token will have a `Span::call_site()` span.
+///
+/// NOTE: some errors may cause panics instead of returning `LexError`. We
+/// reserve the right to change these errors into `LexError`s later.
+#[stable(feature = "proc_macro_literal_parse", since = "1.54.0")]
+impl FromStr for Literal {
+    type Err = LexError;
+
+    fn from_str(src: &str) -> Result<Self, LexError> {
+        match bridge::client::Literal::from_str(src) {
+            Ok(literal) => Ok(Literal(literal)),
+            Err(()) => Err(LexError::new()),
+        }
+    }
+}
+
 // N.B., the bridge only provides `to_string`, implement `fmt::Display`
 // based on it (the reverse of the usual relationship between the two).
 #[stable(feature = "proc_macro_lib", since = "1.15.0")]