Ensure diagnostics are printed in the correct order

Even when buffered. Ideally we would flush only when the emitter is
done, but that requires larger changes. This gives most of the benefit
of buffering in any case.

1 files changed, 4 insertions, 2 deletions

diff --git a/src/librustc_errors/json.rs b/src/librustc_errors/json.rs
index f0cfd815a2c..97b9ca924bb 100644
--- a/src/librustc_errors/json.rs
+++ b/src/librustc_errors/json.rs
@@ -104,7 +104,8 @@ impl Emitter for JsonEmitter {
             writeln!(&mut self.dst, "{}", as_pretty_json(&data))
         } else {
             writeln!(&mut self.dst, "{}", as_json(&data))
-        };
+        }
+        .and_then(|_| self.dst.flush());
         if let Err(e) = result {
             panic!("failed to print diagnostics: {:?}", e);
         }
@@ -116,7 +117,8 @@ impl Emitter for JsonEmitter {
             writeln!(&mut self.dst, "{}", as_pretty_json(&data))
         } else {
             writeln!(&mut self.dst, "{}", as_json(&data))
-        };
+        }
+        .and_then(|_| self.dst.flush());
         if let Err(e) = result {
             panic!("failed to print notification: {:?}", e);
         }