rollup merge of #21457: alexcrichton/issue-21436

Conflicts:
	src/liballoc/boxed.rs
	src/librustc/middle/traits/error_reporting.rs
	src/libstd/sync/mpsc/mod.rs

2 files changed, 4 insertions, 2 deletions

diff --git a/src/libsyntax/ext/deriving/mod.rs b/src/libsyntax/ext/deriving/mod.rs
index 603c4478007..e52a2b513ce 100644
--- a/src/libsyntax/ext/deriving/mod.rs
+++ b/src/libsyntax/ext/deriving/mod.rs
@@ -99,7 +99,9 @@ pub fn expand_meta_derive(cx: &mut ExtCtxt,
 
                             "Rand" => expand!(rand::expand_deriving_rand),
 
+                            // NOTE(stage0): remove "Show"
                             "Show" => expand!(show::expand_deriving_show),
+                            "Debug" => expand!(show::expand_deriving_show),
 
                             "Default" => expand!(default::expand_deriving_default),
 
diff --git a/src/libsyntax/ext/deriving/show.rs b/src/libsyntax/ext/deriving/show.rs
index 48034ce50ab..f5b5d4dda19 100644
--- a/src/libsyntax/ext/deriving/show.rs
+++ b/src/libsyntax/ext/deriving/show.rs
@@ -35,7 +35,7 @@ pub fn expand_deriving_show<F>(cx: &mut ExtCtxt,
     let trait_def = TraitDef {
         span: span,
         attributes: Vec::new(),
-        path: Path::new(vec!("std", "fmt", "Show")),
+        path: Path::new(vec!("std", "fmt", "Debug")),
         additional_bounds: Vec::new(),
         generics: LifetimeBounds::empty(),
         methods: vec!(
@@ -67,7 +67,7 @@ fn show_substructure(cx: &mut ExtCtxt, span: Span,
         Struct(_) => substr.type_ident,
         EnumMatching(_, v, _) => v.node.name,
         EnumNonMatchingCollapsed(..) | StaticStruct(..) | StaticEnum(..) => {
-            cx.span_bug(span, "nonsensical .fields in `#[derive(Show)]`")
+            cx.span_bug(span, "nonsensical .fields in `#[derive(Debug)]`")
         }
     };