From 0a1f6dd8a8c27caf913a16eb0a1afeaa8183b983 Mon Sep 17 00:00:00 2001
From: Michael Woerister <michaelwoerister@posteo>
Date: Thu, 16 Nov 2017 18:07:49 +0100
Subject: [PATCH] Add doc comment for LocalDefId.

---
 src/librustc/hir/def_id.rs | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/src/librustc/hir/def_id.rs b/src/librustc/hir/def_id.rs
index 05d021ac6d2..f6fcff37ca5 100644
--- a/src/librustc/hir/def_id.rs
+++ b/src/librustc/hir/def_id.rs
@@ -198,7 +198,7 @@ impl DefId {
         self.krate == LOCAL_CRATE
     }
 
-     #[inline]
+    #[inline]
     pub fn to_local(self) -> LocalDefId {
         LocalDefId::from_def_id(self)
     }
@@ -207,7 +207,12 @@ impl DefId {
 impl serialize::UseSpecializedEncodable for DefId {}
 impl serialize::UseSpecializedDecodable for DefId {}
 
-
+/// A LocalDefId is equivalent to a DefId with `krate == LOCAL_CRATE`. Since
+/// we encode this information in the type, we can ensure at compile time that
+/// no DefIds from upstream crates get thrown into the mix. There are quite a
+/// few cases where we know that only DefIds from the local crate are expected
+/// and a DefId from a different crate would signify a bug somewhere. This
+/// is when LocalDefId comes in handy.
 #[derive(Clone, Copy, Eq, PartialEq, Ord, PartialOrd, Hash)]
 pub struct LocalDefId(DefIndex);