From 7b20806417a713caef6a2c36af3b3a92eb6c5768 Mon Sep 17 00:00:00 2001
From: Kevin Leimkuhler <kevin@kleimkuhler.com>
Date: Thu, 18 Oct 2018 15:05:28 -0700
Subject: [PATCH] Initial removal of Eq bound on `Q::Val`

---
 examples/compiler/class_table.rs |  3 ++-
 examples/hello_world/README.md   |  2 +-
 src/derived.rs                   | 33 +++++++++++++++++++++-----------
 src/input.rs                     |  3 +++
 src/lib.rs                       |  2 +-
 5 files changed, 29 insertions(+), 14 deletions(-)

diff --git a/examples/compiler/class_table.rs b/examples/compiler/class_table.rs
index db21980a..b8c14d49 100644
--- a/examples/compiler/class_table.rs
+++ b/examples/compiler/class_table.rs
@@ -39,6 +39,7 @@ fn all_fields(db: &impl ClassTableDatabase, (): ()) -> Arc<Vec<DefId>> {
             .flat_map(|def_id| {
                 let fields = db.fields(def_id);
                 (0..fields.len()).map(move |i| fields[i])
-            }).collect(),
+            })
+            .collect(),
     )
 }
diff --git a/examples/hello_world/README.md b/examples/hello_world/README.md
index d84b4165..369cc030 100644
--- a/examples/hello_world/README.md
+++ b/examples/hello_world/README.md
@@ -44,7 +44,7 @@ need.
 The `HelloWorldDatabase` trait has one supertrait:
 `salsa::Database`. If we were defining more query groups in our
 application, and we wanted to invoke some of those queries from within
-this query group, we might list those query groupes here. You can also
+this query group, we might list those query groups here. You can also
 list any other traits you want, so long as your final database type
 implements them (this lets you add custom state and so forth to your
 database).
diff --git a/src/derived.rs b/src/derived.rs
index 5cca054b..95ff907d 100644
--- a/src/derived.rs
+++ b/src/derived.rs
@@ -53,6 +53,8 @@ where
 {
     fn should_memoize_value(key: &Q::Key) -> bool;
 
+    fn memoized_value_eq(old_value: &Q::Value, new_value: &Q::Value) -> bool;
+
     fn should_track_inputs(key: &Q::Key) -> bool;
 }
 
@@ -60,12 +62,17 @@ pub enum AlwaysMemoizeValue {}
 impl<DB, Q> MemoizationPolicy<DB, Q> for AlwaysMemoizeValue
 where
     Q: QueryFunction<DB>,
+    Q::Value: Eq,
     DB: Database,
 {
     fn should_memoize_value(_key: &Q::Key) -> bool {
         true
     }
 
+    fn memoized_value_eq(old_value: &Q::Value, new_value: &Q::Value) -> bool {
+        old_value == new_value
+    }
+
     fn should_track_inputs(_key: &Q::Key) -> bool {
         true
     }
@@ -81,6 +88,10 @@ where
         false
     }
 
+    fn memoized_value_eq(_old_value: &Q::Value, _new_value: &Q::Value) -> bool {
+        panic!("cannot reach since we never memoize")
+    }
+
     fn should_track_inputs(_key: &Q::Key) -> bool {
         true
     }
@@ -101,6 +112,10 @@ where
         true
     }
 
+    fn memoized_value_eq(_old_value: &Q::Value, _new_value: &Q::Value) -> bool {
+        false
+    }
+
     fn should_track_inputs(_key: &Q::Key) -> bool {
         false
     }
@@ -243,7 +258,7 @@ where
                 match map.insert(key.clone(), QueryState::in_progress(runtime.id())) {
                     Some(QueryState::Memoized(old_memo)) => Some(old_memo),
                     Some(QueryState::InProgress { .. }) => unreachable!(),
-                    None => None
+                    None => None,
                 }
             }
         };
@@ -262,13 +277,7 @@ where
                 let changed_at = memo.changed_at;
 
                 let new_value = StampedValue { value, changed_at };
-                self.overwrite_placeholder(
-                    runtime,
-                    descriptor,
-                    key,
-                    old_memo.unwrap(),
-                    &new_value,
-                );
+                self.overwrite_placeholder(runtime, descriptor, key, old_memo.unwrap(), &new_value);
                 return Ok(new_value);
             }
         }
@@ -299,9 +308,11 @@ where
         // "backdate" its `changed_at` revision to be the same as the
         // old value.
         if let Some(old_memo) = &old_memo {
-            if old_memo.value.as_ref() == Some(&stamped_value.value) {
-                assert!(old_memo.changed_at <= stamped_value.changed_at);
-                stamped_value.changed_at = old_memo.changed_at;
+            if let Some(old_value) = &old_memo.value {
+                if MP::memoized_value_eq(&old_value, &stamped_value.value) {
+                    assert!(old_memo.changed_at <= stamped_value.changed_at);
+                    stamped_value.changed_at = old_memo.changed_at;
+                }
             }
         }
 
diff --git a/src/input.rs b/src/input.rs
index 81fff76e..437eca25 100644
--- a/src/input.rs
+++ b/src/input.rs
@@ -42,6 +42,7 @@ struct IsConstant(bool);
 impl<DB, Q> InputStorage<DB, Q>
 where
     Q: Query<DB>,
+    Q::Value: Eq,
     DB: Database,
     Q::Value: Default,
 {
@@ -137,6 +138,7 @@ where
 impl<DB, Q> QueryStorageOps<DB, Q> for InputStorage<DB, Q>
 where
     Q: Query<DB>,
+    Q::Value: Eq,
     DB: Database,
     Q::Value: Default,
 {
@@ -197,6 +199,7 @@ where
 impl<DB, Q> InputQueryStorageOps<DB, Q> for InputStorage<DB, Q>
 where
     Q: Query<DB>,
+    Q::Value: Eq,
     DB: Database,
     Q::Value: Default,
 {
diff --git a/src/lib.rs b/src/lib.rs
index 682bda79..24696816 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -56,7 +56,7 @@ pub trait ParallelDatabase: Database + Send {
 
 pub trait Query<DB: Database>: Debug + Default + Sized + 'static {
     type Key: Clone + Debug + Hash + Eq;
-    type Value: Clone + Debug + Hash + Eq;
+    type Value: Clone + Debug;
     type Storage: plumbing::QueryStorageOps<DB, Self> + Send + Sync;
 }