Update with comments

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

compiler/rustc_ast_pretty/src/pprust/state.rs

@@ -2660,11 +2660,10 @@ impl<'a> State<'a> {
                     s.print_type(ty);
                     s.print_type_bounds(":", &param.bounds);
                     // FIXME(const_generic_defaults)
-                    if let Some(ref _default) = default {
+                    if let Some(ref default) = default {
-                        // FIXME(const_generics_defaults): print the `default` value here
                         s.s.space();
                         s.word_space("=");
-                        // s.print_anon_const(&default);
+                        s.print_expr(&default.value);
                     }
                 }
             }

compiler/rustc_infer/src/infer/error_reporting/mod.rs

@@ -963,10 +963,11 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
             .rev()
             .filter_map(|param| match param.kind {
                 ty::GenericParamDefKind::Lifetime => None,
-                ty::GenericParamDefKind::Const { has_default }
+                ty::GenericParamDefKind::Type { has_default, .. } => {
-                | ty::GenericParamDefKind::Type { has_default, .. } => {
                     Some((param.def_id, has_default))
                 }
+                // FIXME(const_generics:defaults)
+                ty::GenericParamDefKind::Const { has_default: _has_default } => None,
             })
             .peekable();
         let has_default = {

compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs

@@ -122,7 +122,7 @@ provide! { <'tcx> tcx, def_id, other, cdata,
     promoted_mir => { tcx.arena.alloc(cdata.get_promoted_mir(tcx, def_id.index)) }
     mir_abstract_const => { cdata.get_mir_abstract_const(tcx, def_id.index) }
     unused_generic_params => { cdata.get_unused_generic_params(def_id.index) }
-    const_param_default => { tcx.arena.alloc(cdata.get_const_param_default(tcx, def_id.index)) }
+    const_param_default => { tcx.mk_const(cdata.get_const_param_default(tcx, def_id.index)) }
     mir_const_qualif => { cdata.mir_const_qualif(def_id.index) }
     fn_sig => { cdata.fn_sig(def_id.index, tcx) }
     inherent_impls => { cdata.get_inherent_implementations_for_type(tcx, def_id.index) }

compiler/rustc_metadata/src/rmeta/mod.rs

@@ -307,6 +307,7 @@ define_tables! {
     mir_for_ctfe: Table<DefIndex, Lazy!(mir::Body<'tcx>)>,
     promoted_mir: Table<DefIndex, Lazy!(IndexVec<mir::Promoted, mir::Body<'tcx>>)>,
     mir_abstract_consts: Table<DefIndex, Lazy!(&'tcx [mir::abstract_const::Node<'tcx>])>,
+    const_defaults: Table<DefIndex, Lazy<rustc_middle::ty::Const<'tcx>>>,
     unused_generic_params: Table<DefIndex, Lazy<FiniteBitSet<u32>>>,
     // `def_keys` and `def_path_hashes` represent a lazy version of a
     // `DefPathTable`. This allows us to avoid deserializing an entire
@@ -314,7 +315,6 @@ define_tables! {
     // definitions from any given crate.
     def_keys: Table<DefIndex, Lazy<DefKey>>,
     def_path_hashes: Table<DefIndex, Lazy<DefPathHash>>,
-    const_defaults: Table<DefIndex, Lazy<rustc_middle::ty::Const<'tcx>>>,
 }
 
 #[derive(Copy, Clone, MetadataEncodable, MetadataDecodable)]

compiler/rustc_middle/src/ty/consts.rs

@@ -206,8 +206,7 @@ impl<'tcx> Const<'tcx> {
 pub fn const_param_default<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId) -> &'tcx Const<'tcx> {
     let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
     let default_def_id = match tcx.hir().get(hir_id) {
-        hir::Node::AnonConst(ac)
+        hir::Node::GenericParam(hir::GenericParam {
-        | hir::Node::GenericParam(hir::GenericParam {
             kind: hir::GenericParamKind::Const { ty: _, default: Some(ac) },
             ..
         }) => tcx.hir().local_def_id(ac.hir_id),

compiler/rustc_middle/src/ty/generics.rs

@@ -120,10 +120,12 @@ impl<'tcx> Generics {
         for param in &self.params {
             match param.kind {
                 GenericParamDefKind::Lifetime => (),
-                GenericParamDefKind::Type { has_default, .. }
+                GenericParamDefKind::Type { has_default, .. } => {
-                | GenericParamDefKind::Const { has_default } => {
                     own_defaults.types += has_default as usize;
                 }
+                GenericParamDefKind::Const { has_default } => {
+                    own_defaults.consts += has_default as usize;
+                }
             }
         }
 

compiler/rustc_privacy/src/lib.rs

@@ -931,10 +931,7 @@ impl ReachEverythingInTheInterfaceVisitor<'_, 'tcx> {
                 GenericParamDefKind::Const { has_default, .. } => {
                     self.visit(self.ev.tcx.type_of(param.def_id));
                     if has_default {
-                        // FIXME(const_generic_defaults)
+                        self.visit(self.ev.tcx.const_param_default(param.def_id));
-                        // how should the error case be handled here?
-                        // let default_const = self.ev.tcx.const_eval_poly(param.def_id).unwrap();
-                        // self.visit(default_const);
                     }
                 }
             }
@@ -1747,6 +1744,7 @@ impl SearchInterfaceForPrivateItemsVisitor<'tcx> {
                         self.visit(self.tcx.type_of(param.def_id));
                     }
                 }
+                // FIXME(const_evaluatable_checked): May want to look inside const here
                 GenericParamDefKind::Const { .. } => {
                     self.visit(self.tcx.type_of(param.def_id));
                 }

compiler/rustc_typeck/src/collect.rs

@@ -258,9 +258,9 @@ impl Visitor<'tcx> for CollectItemTypesVisitor<'tcx> {
                     let def_id = self.tcx.hir().local_def_id(param.hir_id);
                     self.tcx.ensure().type_of(def_id);
                     if let Some(default) = default {
-                        let def_id = self.tcx.hir().local_def_id(default.hir_id);
+                        let default_def_id = self.tcx.hir().local_def_id(default.hir_id);
                         // need to store default and type of default
-                        self.tcx.ensure().type_of(def_id);
+                        self.tcx.ensure().type_of(default_def_id);
                         self.tcx.ensure().const_param_default(def_id);
                     }
                 }

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 }>;