Implement `Display` for macro expansion errors

1 files changed, 11 insertions, 0 deletions

diff --git a/crates/tt/src/lib.rs b/crates/tt/src/lib.rs
index 20c3f5eab..7c796f564 100644
--- a/crates/tt/src/lib.rs
+++ b/crates/tt/src/lib.rs
@@ -240,6 +240,17 @@ pub enum ExpansionError {
     ExpansionError(String),
 }
 
+impl fmt::Display for ExpansionError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            ExpansionError::IOError(e) => write!(f, "I/O error: {}", e),
+            ExpansionError::JsonError(e) => write!(f, "JSON decoding error: {}", e),
+            ExpansionError::Unknown(e) => write!(f, "{}", e),
+            ExpansionError::ExpansionError(e) => write!(f, "proc macro returned error: {}", e),
+        }
+    }
+}
+
 pub trait TokenExpander: Debug + Send + Sync + RefUnwindSafe {
     fn expand(&self, subtree: &Subtree, attrs: Option<&Subtree>)
         -> Result<Subtree, ExpansionError>;