diff --git a/src/cargo/cargo.rs b/src/cargo/cargo.rs
index aac5339a540..eeab4a85c82 100644
--- a/src/cargo/cargo.rs
+++ b/src/cargo/cargo.rs
@@ -104,7 +104,7 @@ fn load_pkg(filename: str) -> option::t<pkg> {
     let sess = @{
         cm: cm,
         mutable next_id: 0,
-        diagnostic: diagnostic::mk_codemap_handler(cm)
+        diagnostic: diagnostic::mk_codemap_handler(cm, none)
     };
     let c = parser::parse_crate_from_crate_file(filename, [], sess);
 
diff --git a/src/comp/driver/diagnostic.rs b/src/comp/driver/diagnostic.rs
index e1c360daf12..58c357d724d 100644
--- a/src/comp/driver/diagnostic.rs
+++ b/src/comp/driver/diagnostic.rs
@@ -3,10 +3,14 @@
 import syntax::codemap;
 import codemap::span;
 
-export emit_diagnostic;
+export emitter, emit_diagnostic;
 export diagnostictype, fatal, error, warning, note;
 export handler, mk_codemap_handler;
 
+type emitter = fn@(cmsp: option<(codemap::codemap, span)>,
+                   msg: str, t: diagnostictype);
+
+
 iface handler {
     fn span_fatal(sp: span, msg: str) -> !;
     fn fatal(msg: str) -> !;
@@ -26,24 +30,25 @@
 
 type codemap_t = @{
     cm: codemap::codemap,
-    mutable err_count: uint
+    mutable err_count: uint,
+    emit: emitter
 };
 
 impl codemap_handler of handler for codemap_t {
     fn span_fatal(sp: span, msg: str) -> ! {
-        emit_diagnostic(some((self.cm, sp)), msg, fatal);
+        self.emit(some((self.cm, sp)), msg, fatal);
         fail;
     }
     fn fatal(msg: str) -> ! {
-        emit_diagnostic(none, msg, fatal);
+        self.emit(none, msg, fatal);
         fail;
     }
     fn span_err(sp: span, msg: str) {
-        emit_diagnostic(some((self.cm, sp)), msg, error);
+        self.emit(some((self.cm, sp)), msg, error);
         self.err_count += 1u;
     }
     fn err(msg: str) {
-        emit_diagnostic(none, msg, error);
+        self.emit(none, msg, error);
         self.err_count += 1u;
     }
     fn has_errors() -> bool { self.err_count > 0u }
@@ -53,16 +58,16 @@ fn abort_if_errors() {
         }
     }
     fn span_warn(sp: span, msg: str) {
-        emit_diagnostic(some((self.cm, sp)), msg, warning);
+        self.emit(some((self.cm, sp)), msg, warning);
     }
     fn warn(msg: str) {
-        emit_diagnostic(none, msg, warning);
+        self.emit(none, msg, warning);
     }
     fn span_note(sp: span, msg: str) {
-        emit_diagnostic(some((self.cm, sp)), msg, note);
+        self.emit(some((self.cm, sp)), msg, note);
     }
     fn note(msg: str) {
-        emit_diagnostic(none, msg, note);
+        self.emit(none, msg, note);
     }
     fn span_bug(sp: span, msg: str) -> ! {
         self.span_fatal(sp, #fmt["internal compiler error %s", msg]);
@@ -76,10 +81,24 @@ fn span_unimpl(sp: span, msg: str) -> ! {
     fn unimpl(msg: str) -> ! { self.bug("unimplemented " + msg); }
 }
 
-fn mk_codemap_handler(cm: codemap::codemap) -> handler {
+fn mk_codemap_handler(cm: codemap::codemap,
+                      emitter: option<emitter>) -> handler {
+
+    let emit = alt emitter {
+      some(e) { e }
+      none. {
+        let f = fn@(cmsp: option<(codemap::codemap, span)>,
+            msg: str, t: diagnostictype) {
+            emit_diagnostic(cmsp, msg, t);
+        };
+        f
+      }
+    };
+
     @{
         cm: cm,
         mutable err_count: 0u,
+        emit: emit
     } as handler
 }
 
diff --git a/src/comp/driver/driver.rs b/src/comp/driver/driver.rs
index 278ffb9b605..6a578a3f0cf 100644
--- a/src/comp/driver/driver.rs
+++ b/src/comp/driver/driver.rs
@@ -452,7 +452,7 @@ fn build_session(sopts: @session::options, input: str) -> session::session {
         sopts.target_triple,
         sopts.addl_lib_search_paths);
     let codemap = codemap::new_codemap();
-    let diagnostic_handler = diagnostic::mk_codemap_handler(codemap);
+    let diagnostic_handler = diagnostic::mk_codemap_handler(codemap, none);
     @{targ_cfg: target_cfg,
       opts: sopts,
       cstore: cstore,
diff --git a/src/fuzzer/fuzzer.rs b/src/fuzzer/fuzzer.rs
index 9800032ed98..343035fe681 100644
--- a/src/fuzzer/fuzzer.rs
+++ b/src/fuzzer/fuzzer.rs
@@ -262,7 +262,7 @@ fn check_variants_T<T: copy>(
                 let str3 =
                     as_str(bind pprust::print_crate(
                         codemap,
-                        diagnostic::mk_codemap_handler(codemap),
+                        diagnostic::mk_codemap_handler(codemap, none),
                         crate2,
                         filename,
                         io::string_reader(""), _,
@@ -419,7 +419,7 @@ fn parse_and_print(code: str) -> str {
     let sess = @{
         cm: cm,
         mutable next_id: 0,
-        diagnostic: diagnostic::mk_codemap_handler(cm)
+        diagnostic: diagnostic::mk_codemap_handler(cm, none)
     };
     write_file(filename, code);
     let crate = parser::parse_crate_from_source_str(
@@ -566,7 +566,7 @@ fn check_variants(files: [str], cx: context) {
         let sess = @{
             cm: cm,
             mutable next_id: 0,
-            diagnostic: diagnostic::mk_codemap_handler(cm)
+            diagnostic: diagnostic::mk_codemap_handler(cm, none)
         };
         let crate =
             parser::parse_crate_from_source_str(
diff --git a/src/rustdoc/rustdoc.rs b/src/rustdoc/rustdoc.rs
index d743eafcbca..733b1fecc0e 100755
--- a/src/rustdoc/rustdoc.rs
+++ b/src/rustdoc/rustdoc.rs
@@ -194,7 +194,7 @@ fn main(argv: [str]) {
     let sess = @{
         cm: cm,
         mutable next_id: 0,
-        diagnostic: diagnostic::mk_codemap_handler(cm)
+        diagnostic: diagnostic::mk_codemap_handler(cm, none)
     };
     let rd = { ps: pprust::rust_printer(w), w: w };
     doc_header(rd, argv[1]);