Update with comments

A bunch of nits fixed, and a new test for pretty printing the AST.

src/test/ui/const-generics/defaults/default-annotation.rs

@@ -0,0 +1,20 @@
+// run-pass
+#![feature(staged_api)]
+
+#![feature(const_generics)]
+#![feature(const_generics_defaults)]
+#![allow(incomplete_features)]
+
+#![stable(feature = "const_default_test", since="none")]
+
+
+#[unstable(feature = "const_default_stable", issue="none")]
+pub struct ConstDefaultUnstable<const N: usize = 3>;
+
+#[stable(feature = "const_default_unstable", since="none")]
+pub struct ConstDefaultStable<const N: usize = {
+  #[stable(feature = "const_default_unstable_val", since="none")]
+  3
+}>;
+
+fn main() {}

src/test/ui/const-generics/defaults/pretty-printing-ast.rs

@@ -0,0 +1,13 @@
+// Test the AST pretty printer correctly handles default values for const generics
+// check-pass
+// compile-flags: -Z unpretty=expanded
+
+#![crate_type = "lib"]
+#![feature(const_generics_defaults)]
+#![allow(incomplete_features)]
+
+trait Foo<const KIND: bool = true> {}
+
+fn foo<const SIZE: usize = 5>() {}
+
+struct Range<const FROM: usize = 0, const LEN: usize = 0, const TO: usize = {FROM + LEN}>;

src/test/ui/const-generics/defaults/pretty-printing-ast.stdout

@@ -0,0 +1,20 @@
+#![feature(prelude_import)]
+#![no_std]
+// Test the AST pretty printer correctly handles default values for const generics
+// check-pass
+// compile-flags: -Z unpretty=expanded
+
+#![crate_type = "lib"]
+#![feature(const_generics_defaults)]
+#![allow(incomplete_features)]
+#[prelude_import]
+use ::std::prelude::rust_2015::*;
+#[macro_use]
+extern crate std;
+
+trait Foo<const KIND : bool = true> { }
+
+fn foo<const SIZE : usize = 5>() { }
+
+struct Range<const FROM : usize = 0, const LEN : usize = 0, const TO : usize =
+             { FROM + LEN }>;