From 2c85db8eb6bac4a9106e7373840c0b3d209188a6 Mon Sep 17 00:00:00 2001
From: Jonas Schievink <jonasschievink@gmail.com>
Date: Thu, 26 Nov 2020 16:56:22 +0100
Subject: Implement `Display` for macro expansion errors

---
 crates/tt/src/lib.rs | 11 +++++++++++
 1 file changed, 11 insertions(+)

(limited to 'crates/tt/src')

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>;
-- 
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