fix Debug impls

src/librustc/middle/region.rs

@@ -18,6 +18,7 @@ use ich::{StableHashingContext, NodeIdHashingMode};
 use util::nodemap::{FxHashMap, FxHashSet};
 use ty;
 
+use std::fmt;
 use std::mem;
 use std::rc::Rc;
 use syntax::codemap;
@@ -96,7 +97,11 @@ use rustc_data_structures::stable_hasher::{HashStable, StableHasher,
 /// placate the same deriving in `ty::FreeRegion`, but we may want to
 /// actually attach a more meaningful ordering to scopes than the one
 /// generated via deriving here.
-#[derive(Clone, PartialEq, PartialOrd, Eq, Ord, Hash, Debug, Copy, RustcEncodable, RustcDecodable)]
+///
+/// Scope is a bit-packed to save space - if `code` is SCOPE_DATA_REMAINDER_MAX
+/// or less, it is a `ScopeData::Remainder`, otherwise it is a type specified
+/// by the bitpacking.
+#[derive(Clone, PartialEq, PartialOrd, Eq, Ord, Hash, Copy, RustcEncodable, RustcDecodable)]
 pub struct Scope {
     pub(crate) id: hir::ItemLocalId,
     pub(crate) code: u32
@@ -152,7 +157,7 @@ pub struct BlockRemainder {
 }
 
 #[derive(Clone, PartialEq, PartialOrd, Eq, Ord, Hash, RustcEncodable,
-         RustcDecodable, Debug, Copy)]
+         RustcDecodable, Copy)]
 pub struct FirstStatementIndex { pub idx: u32 }
 
 impl Idx for FirstStatementIndex {
@@ -166,6 +171,12 @@ impl Idx for FirstStatementIndex {
     }
 }
 
+impl fmt::Debug for FirstStatementIndex {
+    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        fmt::Debug::fmt(&self.index(), formatter)
+    }
+}
+
 impl From<ScopeData> for Scope {
     #[inline]
     fn from(scope_data: ScopeData) -> Self {
@@ -180,6 +191,12 @@ impl From<ScopeData> for Scope {
     }
 }
 
+impl fmt::Debug for Scope {
+    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        fmt::Debug::fmt(&self.data(), formatter)
+    }
+}
+
 #[allow(non_snake_case)]
 impl Scope {
     #[inline]