Merge pull request #265 from dtolnay/lexerror

Implement Display and Error for LexError

Author: dtolnay

build.rs

@@ -69,6 +69,10 @@ fn main() {
         println!("cargo:rustc-cfg=no_bind_by_move_pattern_guard");
     }
 
+    if version.minor >= 44 {
+        println!("cargo:rustc-cfg=lexerror_display");
+    }
+
     if version.minor >= 45 {
         println!("cargo:rustc-cfg=hygiene");
     }

src/fallback.rs

@@ -148,6 +148,12 @@ impl FromStr for TokenStream {
     }
 }
 
+impl Display for LexError {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.write_str("cannot parse string into token stream")
+    }
+}
+
 impl Display for TokenStream {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         let mut joint = false;

src/lib.rs

@@ -105,6 +105,7 @@ mod imp;
 
 use crate::marker::Marker;
 use std::cmp::Ordering;
+use std::error::Error;
 use std::fmt::{self, Debug, Display};
 use std::hash::{Hash, Hasher};
 use std::iter::FromIterator;
@@ -254,6 +255,14 @@ impl Debug for LexError {
     }
 }
 
+impl Display for LexError {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        Display::fmt(&self.inner, f)
+    }
+}
+
+impl Error for LexError {}
+
 /// The source file of a given `Span`.
 ///
 /// This type is semver exempt and not exposed by default.

src/wrapper.rs

@@ -264,6 +264,18 @@ impl Debug for LexError {
     }
 }
 
+impl Display for LexError {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match self {
+            #[cfg(lexerror_display)]
+            LexError::Compiler(e) => Display::fmt(e, f),
+            #[cfg(not(lexerror_display))]
+            LexError::Compiler(_e) => Display::fmt(&fallback::LexError, f),
+            LexError::Fallback(e) => Display::fmt(e, f),
+        }
+    }
+}
+
 #[derive(Clone)]
 pub(crate) enum TokenTreeIter {
     Compiler(proc_macro::token_stream::IntoIter),