impl FromStr for proc_macro::Literal

compiler/rustc_expand/src/proc_macro_server.rs

@@ -1,9 +1,7 @@
 use crate::base::{ExtCtxt, ResolverExpand};
 
 use rustc_ast as ast;
-use rustc_ast::token;
-use rustc_ast::token::Nonterminal;
-use rustc_ast::token::NtIdent;
+use rustc_ast::token::{self, Nonterminal, NtIdent, TokenKind};
 use rustc_ast::tokenstream::{self, CanSynthesizeMissingTokens};
 use rustc_ast::tokenstream::{DelimSpan, Spacing::*, TokenStream, TreeAndSpacing};
 use rustc_ast_pretty::pprust;
@@ -541,6 +539,33 @@ impl server::Ident for Rustc<'_> {
 }
 
 impl server::Literal for Rustc<'_> {
+    fn from_str(&mut self, s: &str) -> Result<Self::Literal, ()> {
+        let override_span = None;
+        let stream = parse_stream_from_source_str(
+            FileName::proc_macro_source_code(s),
+            s.to_owned(),
+            self.sess,
+            override_span,
+        );
+        if stream.len() != 1 {
+            return Err(());
+        }
+        let tree = stream.into_trees().next().unwrap();
+        let token = match tree {
+            tokenstream::TokenTree::Token(token) => token,
+            tokenstream::TokenTree::Delimited { .. } => return Err(()),
+        };
+        let span_data = token.span.data();
+        if (span_data.hi.0 - span_data.lo.0) as usize != s.len() {
+            // There is a comment or whitespace adjacent to the literal.
+            return Err(());
+        }
+        let lit = match token.kind {
+            TokenKind::Literal(lit) => lit,
+            _ => return Err(()),
+        };
+        Ok(Literal { lit, span: self.call_site })
+    }
     fn debug_kind(&mut self, literal: &Self::Literal) -> String {
         format!("{:?}", literal.lit.kind)
     }

library/proc_macro/src/bridge/mod.rs

@@ -107,6 +107,7 @@ macro_rules! with_api {
             Literal {
                 fn drop($self: $S::Literal);
                 fn clone($self: &$S::Literal) -> $S::Literal;
+                fn from_str(s: &str) -> Result<$S::Literal, ()>;
                 fn debug_kind($self: &$S::Literal) -> String;
                 fn symbol($self: &$S::Literal) -> String;
                 fn suffix($self: &$S::Literal) -> Option<String>;
@@ -315,6 +316,19 @@ impl<T: Unmark> Unmark for Option<T> {
     }
 }
 
+impl<T: Mark, E: Mark> Mark for Result<T, E> {
+    type Unmarked = Result<T::Unmarked, E::Unmarked>;
+    fn mark(unmarked: Self::Unmarked) -> Self {
+        unmarked.map(T::mark).map_err(E::mark)
+    }
+}
+impl<T: Unmark, E: Unmark> Unmark for Result<T, E> {
+    type Unmarked = Result<T::Unmarked, E::Unmarked>;
+    fn unmark(self) -> Self::Unmarked {
+        self.map(T::unmark).map_err(E::unmark)
+    }
+}
+
 macro_rules! mark_noop {
     ($($ty:ty),* $(,)?) => {
         $(

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")]