Return original snippet when macro contains invalid syntax

src/macros.rs

@@ -113,14 +113,14 @@ pub fn rewrite_macro(mac: &ast::Mac,
                 Ok(expr) => {
                     // Recovered errors.
                     if context.parse_session.span_diagnostic.has_errors() {
-                        return None;
+                        return Some(context.snippet(mac.span));
                     }
 
                     expr
                 }
                 Err(mut e) => {
                     e.cancel();
-                    return None;
+                    return Some(context.snippet(mac.span));
                 }
             };
 

tests/source/macros.rs

@@ -78,6 +78,11 @@ fn main() {
         // comment
         not function like
     );
+
+    // #1577
+    let json = json!({
+        "foo": "bar",
+    });
 }
 
 impl X {

tests/target/macros.rs

@@ -83,6 +83,11 @@ fn main() {
         // comment
         not function like
     );
+
+    // #1577
+    let json = json!({
+        "foo": "bar",
+    });
 }
 
 impl X {