rollup merge of #20481: seanmonstar/fmt-show-string

Conflicts:
	src/compiletest/runtest.rs
	src/libcore/fmt/mod.rs
	src/libfmt_macros/lib.rs
	src/libregex/parse.rs
	src/librustc/middle/cfg/construct.rs
	src/librustc/middle/dataflow.rs
	src/librustc/middle/infer/higher_ranked/mod.rs
	src/librustc/middle/ty.rs
	src/librustc_back/archive.rs
	src/librustc_borrowck/borrowck/fragments.rs
	src/librustc_borrowck/borrowck/gather_loans/mod.rs
	src/librustc_resolve/lib.rs
	src/librustc_trans/back/link.rs
	src/librustc_trans/save/mod.rs
	src/librustc_trans/trans/base.rs
	src/librustc_trans/trans/callee.rs
	src/librustc_trans/trans/common.rs
	src/librustc_trans/trans/consts.rs
	src/librustc_trans/trans/controlflow.rs
	src/librustc_trans/trans/debuginfo.rs
	src/librustc_trans/trans/expr.rs
	src/librustc_trans/trans/monomorphize.rs
	src/librustc_typeck/astconv.rs
	src/librustc_typeck/check/method/mod.rs
	src/librustc_typeck/check/mod.rs
	src/librustc_typeck/check/regionck.rs
	src/librustc_typeck/collect.rs
	src/libsyntax/ext/format.rs
	src/libsyntax/ext/source_util.rs
	src/libsyntax/ext/tt/transcribe.rs
	src/libsyntax/parse/mod.rs
	src/libsyntax/parse/token.rs
	src/test/run-pass/issue-8898.rs

src/libsyntax/attr.rs

@@ -28,6 +28,7 @@ use ptr::P;
 use std::cell::{RefCell, Cell};
 use std::collections::BitvSet;
 use std::collections::HashSet;
+use std::fmt;
 
 thread_local! { static USED_ATTRS: RefCell<BitvSet> = RefCell::new(BitvSet::new()) }
 
@@ -357,6 +358,12 @@ pub enum StabilityLevel {
     Locked
 }
 
+impl fmt::String for StabilityLevel {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        fmt::Show::fmt(self, f)
+    }
+}
+
 pub fn find_stability_generic<'a,
                               AM: AttrMetaMethods,
                               I: Iterator<Item=&'a AM>>