[thin_dump] Keep the error context for debugging

src/thin/dump.rs

@@ -198,9 +198,7 @@ fn emit_leaf(v: &mut MappingVisitor, b: &Block) -> Result<()> {
             keys,
             values,
         } => {
-            if let Err(_e) = v.visit(&path, &kr, &header, &keys, &values) {
-                return Err(anyhow!("couldn't emit leaf node"));
-            }
+            v.visit(&path, &kr, &header, &keys, &values)?;
         }
     }
 
@@ -223,15 +221,20 @@ where
     Ok(())
 }
 
-fn emit_leaves(engine: Arc<dyn IoEngine>, out: &mut dyn MetadataVisitor, ls: &[u64]) -> Result<()> {
+fn emit_leaves(
+    engine: Arc<dyn IoEngine>,
+    out: &mut dyn MetadataVisitor,
+    leaves: &[u64],
+) -> Result<()> {
     let mut v = MappingVisitor::new(out);
     let proc = |b| {
         emit_leaf(&mut v, &b)?;
         Ok(())
     };
 
-    read_for(engine, ls, proc)?;
-    v.end_walk().map_err(|_| anyhow!("failed to emit leaves"))
+    read_for(engine, leaves, proc)?;
+    v.end_walk()
+        .map_err(|e| anyhow!("failed to emit leaves: {}", e))
 }
 
 fn emit_entries(