Auto merge of #33002 - mitaa:rdoc-cross-impls, r=alexcrichton

rustdoc: refine cross-crate impl inlining

This changes the current rule that impls within `doc(hidden)` modules aren't inlined, to only inlining impls where the implemented trait and type are reachable in documentation.

fixes #14586
fixes #31948

.. and also applies the reachability checking to cross-crate links.

fixes #28480

r? @alexcrichton

src/librustc/middle/cstore.rs

@@ -113,6 +113,7 @@ pub enum InlinedItemRef<'a> {
 /// LOCAL_CRATE in their DefId.
 pub const LOCAL_CRATE: ast::CrateNum = 0;
 
+#[derive(Copy, Clone)]
 pub struct ChildItem {
     pub def: DefLike,
     pub name: ast::Name,

src/librustc/middle/privacy.rs

@@ -15,10 +15,11 @@
 use util::nodemap::{DefIdSet, FnvHashMap};
 
 use std::hash::Hash;
+use std::fmt;
 use syntax::ast::NodeId;
 
 // Accessibility levels, sorted in ascending order
-#[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord)]
+#[derive(Clone, Copy, Debug, PartialEq, Eq, PartialOrd, Ord)]
 pub enum AccessLevel {
     // Exported items + items participating in various kinds of public interfaces,
     // but not directly nameable. For example, if function `fn f() -> T {...}` is
@@ -56,6 +57,12 @@ impl<Id: Hash + Eq> Default for AccessLevels<Id> {
     }
 }
 
+impl<Id: Hash + Eq + fmt::Debug> fmt::Debug for AccessLevels<Id> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        fmt::Debug::fmt(&self.map, f)
+    }
+}
+
 /// A set containing all exported definitions from external crates.
 /// The set does not contain any entries from local crates.
 pub type ExternalExports = DefIdSet;