libproc_macro: Implement Display for LexError

Implement the Display trait for LexError by writing an error string to
the the output formatter.

ChangeLog:

	* librust/proc_macro/rust/lib.rs: Implement Display for
	LexError.

Signed-off-by: Pierre-Emmanuel Patry <pierre-emmanuel.patry@embecosm.com>

1 files changed, 2 insertions, 2 deletions

diff --git a/librust/proc_macro/rust/lib.rs b/librust/proc_macro/rust/lib.rs
index 31676f1..13f66f0 100644
--- a/librust/proc_macro/rust/lib.rs
+++ b/librust/proc_macro/rust/lib.rs
@@ -124,8 +124,8 @@ impl From<Literal> for TokenTree {
 pub struct LexError;
 
 impl fmt::Display for LexError {
-    fn fmt(&self, _f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        todo!("Implement this function")
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.write_str("cannot parse string into token stream")
     }
 }