From 0219dbb359df6933062e24c2698bb3f37be3da9b Mon Sep 17 00:00:00 2001
From: Martin von Zweigbergk <martinvonz@google.com>
Date: Wed, 23 Dec 2020 01:06:05 -0800
Subject: [PATCH] transaction: make evolution_mut() return a mutable reference

This includes fixing a lifetime bound on `MutableEvolution` that was
reversed.
---
 lib/src/evolution.rs   | 2 +-
 lib/src/transaction.rs | 8 +++++---
 2 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/lib/src/evolution.rs b/lib/src/evolution.rs
index 4a4b78826..c899cf683 100644
--- a/lib/src/evolution.rs
+++ b/lib/src/evolution.rs
@@ -309,7 +309,7 @@ impl<'r> ReadonlyEvolution<'r> {
     }
 }
 
-pub struct MutableEvolution<'r, 'm: 'r> {
+pub struct MutableEvolution<'r: 'm, 'm> {
     repo: &'m MutableRepo<'r>,
     state: State,
 }
diff --git a/lib/src/transaction.rs b/lib/src/transaction.rs
index 3de8c6686..1e8fd6f5d 100644
--- a/lib/src/transaction.rs
+++ b/lib/src/transaction.rs
@@ -219,8 +219,10 @@ impl<'r> Repo for MutableRepo<'r> {
     }
 }
 
-impl MutableRepo<'_> {
-    pub fn evolution_mut(&mut self) -> &MutableEvolution {
-        self.evolution.as_mut().unwrap()
+impl<'r> MutableRepo<'r> {
+    pub fn evolution_mut<'m>(&'m mut self) -> &'m mut MutableEvolution<'r, 'm> {
+        let evolution: &mut MutableEvolution<'static, 'static> = self.evolution.as_mut().unwrap();
+        let evolution: &mut MutableEvolution<'r, 'm> = unsafe { std::mem::transmute(evolution) };
+        evolution
     }
 }