Show macro name in 'this error originates in macro' message

When there are multiple macros in use, it can be difficult to tell
which one was responsible for producing an error.

compiler/rustc_errors/src/emitter.rs

@@ -309,8 +309,8 @@ pub trait Emitter {
                     // are some which do actually involve macros.
                     ExpnKind::Inlined | ExpnKind::Desugaring(..) | ExpnKind::AstPass(..) => None,
 
-                    ExpnKind::Macro { kind: macro_kind, name: _, proc_macro: _ } => {
-                        Some(macro_kind)
+                    ExpnKind::Macro { kind: macro_kind, name, proc_macro: _ } => {
+                        Some((macro_kind, name))
                     }
                 }
             });
@@ -322,13 +322,12 @@ pub trait Emitter {
         self.render_multispans_macro_backtrace(span, children, backtrace);
 
         if !backtrace {
-            if let Some(macro_kind) = has_macro_spans {
+            if let Some((macro_kind, name)) = has_macro_spans {
+                let descr = macro_kind.descr();
+
                 let msg = format!(
-                    "this {} originates in {} {} \
+                    "this {level} originates in the {descr} `{name}` \
                     (in Nightly builds, run with -Z macro-backtrace for more info)",
-                    level,
-                    macro_kind.article(),
-                    macro_kind.descr(),
                 );
 
                 children.push(SubDiagnostic {

compiler/rustc_errors/src/lib.rs

@@ -6,6 +6,7 @@
 #![feature(crate_visibility_modifier)]
 #![feature(backtrace)]
 #![feature(extended_key_value_attributes)]
+#![feature(format_args_capture)]
 #![feature(iter_zip)]
 #![feature(nll)]