From 4174c20d7c583c3109475710e5f583e3682159a3 Mon Sep 17 00:00:00 2001
From: Tshepang Lekhonkhobe <tshepang@gmail.com>
Date: Tue, 24 Sep 2019 13:15:46 +0200
Subject: [PATCH] derive(Default) is too aggressive

I don't really understand the details, so will just list sources:

- https://github.com/rust-lang/polonius/pull/122#discussion_r324344120
- https://rust-lang.zulipchat.com/#narrow/stream/122657-t-compiler.2Fwg-nll/topic/rustc-and-polonius.20integration/near/127049249
---
 polonius-engine/src/facts.rs | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/polonius-engine/src/facts.rs b/polonius-engine/src/facts.rs
index eb90b3f2846..edd23b25f5d 100644
--- a/polonius-engine/src/facts.rs
+++ b/polonius-engine/src/facts.rs
@@ -64,6 +64,10 @@ pub struct AllFacts<Origin: Atom, Loan: Atom, Point: Atom, Variable: Atom, MoveP
     pub path_accessed_at: Vec<(MovePath, Point)>,
 }
 
+// We impl Default manually because the more convenient
+// `#[derive(Default)]` syntax would result in, for example,
+// `rustc::ty::RegionVid`, an `Atom`, also having to impl `Default`,
+// something that does not make sense for that type.
 impl<Origin: Atom, Loan: Atom, Point: Atom, Variable: Atom, MovePath: Atom> Default
     for AllFacts<Origin, Loan, Point, Variable, MovePath>
 {