Log when buffering a diagnostic.

This is useful in debugging when and where errors are emitted in
logs.

3 files changed, 6 insertions, 0 deletions

diff --git a/src/librustc_errors/Cargo.toml b/src/librustc_errors/Cargo.toml
index 101ca0650c8..b24f8ddf4d9 100644
--- a/src/librustc_errors/Cargo.toml
+++ b/src/librustc_errors/Cargo.toml
@@ -9,6 +9,7 @@ path = "lib.rs"
 crate-type = ["dylib"]
 
 [dependencies]
+log = "0.4"
 serialize = { path = "../libserialize" }
 syntax_pos = { path = "../libsyntax_pos" }
 rustc_data_structures = { path = "../librustc_data_structures" }
diff --git a/src/librustc_errors/diagnostic_builder.rs b/src/librustc_errors/diagnostic_builder.rs
index 5e962a4af32..a4b5b000f87 100644
--- a/src/librustc_errors/diagnostic_builder.rs
+++ b/src/librustc_errors/diagnostic_builder.rs
@@ -108,6 +108,9 @@ impl<'a> DiagnosticBuilder<'a> {
             diagnostic = ::std::ptr::read(&self.diagnostic);
             ::std::mem::forget(self);
         };
+        // Logging here is useful to help track down where in logs an error was
+        // actually emitted.
+        debug!("buffer: diagnostic={:?}", diagnostic);
         buffered_diagnostics.push(diagnostic);
     }
 
diff --git a/src/librustc_errors/lib.rs b/src/librustc_errors/lib.rs
index d0ea6fba5eb..266aa326981 100644
--- a/src/librustc_errors/lib.rs
+++ b/src/librustc_errors/lib.rs
@@ -23,6 +23,8 @@ extern crate atty;
 extern crate termcolor;
 #[cfg(unix)]
 extern crate libc;
+#[macro_use]
+extern crate log;
 extern crate rustc_data_structures;
 extern crate serialize as rustc_serialize;
 extern crate syntax_pos;