From fb3504cfdfbfb0ecd5f08607afbb1372a354f275 Mon Sep 17 00:00:00 2001
From: David Tolnay <dtolnay@gmail.com>
Date: Mon, 30 Aug 2021 12:14:54 -0700
Subject: [PATCH] Use real Literal::from_str from libproc_macro

---
 build.rs       |  4 ++++
 src/wrapper.rs | 25 ++++++++++++++++---------
 2 files changed, 20 insertions(+), 9 deletions(-)

diff --git a/build.rs b/build.rs
index 815292ec..f32d5c8f 100644
--- a/build.rs
+++ b/build.rs
@@ -78,6 +78,10 @@ fn main() {
         println!("cargo:rustc-cfg=hygiene");
     }
 
+    if version.minor >= 54 {
+        println!("cargo:rustc-cfg=literal_from_str");
+    }
+
     let target = env::var("TARGET").unwrap();
     if !enable_use_proc_macro(&target) {
         return;
diff --git a/src/wrapper.rs b/src/wrapper.rs
index 2829dd79..dc938736 100644
--- a/src/wrapper.rs
+++ b/src/wrapper.rs
@@ -921,18 +921,25 @@ impl FromStr for Literal {
 
     fn from_str(repr: &str) -> Result<Self, Self::Err> {
         if inside_proc_macro() {
-            // TODO: use libproc_macro's FromStr impl once it is available in
-            // rustc. https://github.com/rust-lang/rust/pull/84717
-            let tokens = proc_macro_parse(repr)?;
-            let mut iter = tokens.into_iter();
-            if let (Some(proc_macro::TokenTree::Literal(literal)), None) =
-                (iter.next(), iter.next())
+            #[cfg(literal_from_str)]
             {
-                if literal.to_string().len() == repr.len() {
-                    return Ok(Literal::Compiler(literal));
+                proc_macro::Literal::from_str(repr)
+                    .map(Literal::Compiler)
+                    .map_err(LexError::Compiler)
+            }
+            #[cfg(not(literal_from_str))]
+            {
+                let tokens = proc_macro_parse(repr)?;
+                let mut iter = tokens.into_iter();
+                if let (Some(proc_macro::TokenTree::Literal(literal)), None) =
+                    (iter.next(), iter.next())
+                {
+                    if literal.to_string().len() == repr.len() {
+                        return Ok(Literal::Compiler(literal));
+                    }
                 }
+                Err(LexError::call_site())
             }
-            Err(LexError::call_site())
         } else {
             let literal = fallback::Literal::from_str(repr)?;
             Ok(Literal::Fallback(literal))