From 6ee3f0269b2fe2120d396a4a19e4f31978ddc93a Mon Sep 17 00:00:00 2001
From: Ondrej Lhotak <olhotak@uwaterloo.ca>
Date: Mon, 7 Mar 2022 15:50:04 +0100
Subject: [PATCH 01/12] add eq/ne extension for AnyRef|Null to Scala3RunTime

---
 library/src/scala/runtime/Scala3RunTime.scala | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/library/src/scala/runtime/Scala3RunTime.scala b/library/src/scala/runtime/Scala3RunTime.scala
index b1645f5242aa..32f3687e88c6 100644
--- a/library/src/scala/runtime/Scala3RunTime.scala
+++ b/library/src/scala/runtime/Scala3RunTime.scala
@@ -19,4 +19,10 @@ object Scala3RunTime:
     if (isNull) throw new NullPointerException("tried to cast away nullability, but value is null")
     else x.asInstanceOf[x.type & T]
 
+  extension (inline x: AnyRef | Null)
+    inline def eq(inline y: AnyRef | Null): Boolean =
+      x.asInstanceOf[AnyRef] eq y.asInstanceOf[AnyRef]
+    inline def ne(inline y: AnyRef | Null): Boolean =
+      !(x eq y)
+
 end Scala3RunTime

From 33a4c8aef1e5959b9e9bc5859f31a6c17c6dbaa4 Mon Sep 17 00:00:00 2001
From: Ondrej Lhotak <olhotak@uwaterloo.ca>
Date: Mon, 7 Mar 2022 16:45:53 +0100
Subject: [PATCH 02/12] add @since("3.2")

---
 library/src/scala/runtime/Scala3RunTime.scala | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/library/src/scala/runtime/Scala3RunTime.scala b/library/src/scala/runtime/Scala3RunTime.scala
index 32f3687e88c6..2eed853114cc 100644
--- a/library/src/scala/runtime/Scala3RunTime.scala
+++ b/library/src/scala/runtime/Scala3RunTime.scala
@@ -1,5 +1,7 @@
 package scala.runtime
 
+import scala.annotation.since
+
 object Scala3RunTime:
 
   // Called by inline def assert's. Extracted to minimize the bytecode size at call site.
@@ -20,8 +22,10 @@ object Scala3RunTime:
     else x.asInstanceOf[x.type & T]
 
   extension (inline x: AnyRef | Null)
+    @since("3.2")
     inline def eq(inline y: AnyRef | Null): Boolean =
       x.asInstanceOf[AnyRef] eq y.asInstanceOf[AnyRef]
+    @since("3.2")
     inline def ne(inline y: AnyRef | Null): Boolean =
       !(x eq y)
 

From 4acac5276b6374afdfe4fbdcbbb2da7d990688b9 Mon Sep 17 00:00:00 2001
From: Ondrej Lhotak <olhotak@uwaterloo.ca>
Date: Mon, 14 Mar 2022 11:52:28 +0100
Subject: [PATCH 03/12] move extension methods to Predef instead of
 Scala3RunTime

---
 library/src/scala/runtime/Scala3RunTime.scala        | 10 ----------
 library/src/scala/runtime/stdLibPatches/Predef.scala | 11 +++++++++++
 2 files changed, 11 insertions(+), 10 deletions(-)

diff --git a/library/src/scala/runtime/Scala3RunTime.scala b/library/src/scala/runtime/Scala3RunTime.scala
index 2eed853114cc..b1645f5242aa 100644
--- a/library/src/scala/runtime/Scala3RunTime.scala
+++ b/library/src/scala/runtime/Scala3RunTime.scala
@@ -1,7 +1,5 @@
 package scala.runtime
 
-import scala.annotation.since
-
 object Scala3RunTime:
 
   // Called by inline def assert's. Extracted to minimize the bytecode size at call site.
@@ -21,12 +19,4 @@ object Scala3RunTime:
     if (isNull) throw new NullPointerException("tried to cast away nullability, but value is null")
     else x.asInstanceOf[x.type & T]
 
-  extension (inline x: AnyRef | Null)
-    @since("3.2")
-    inline def eq(inline y: AnyRef | Null): Boolean =
-      x.asInstanceOf[AnyRef] eq y.asInstanceOf[AnyRef]
-    @since("3.2")
-    inline def ne(inline y: AnyRef | Null): Boolean =
-      !(x eq y)
-
 end Scala3RunTime
diff --git a/library/src/scala/runtime/stdLibPatches/Predef.scala b/library/src/scala/runtime/stdLibPatches/Predef.scala
index 13dfc77ac60b..f26544dfea50 100644
--- a/library/src/scala/runtime/stdLibPatches/Predef.scala
+++ b/library/src/scala/runtime/stdLibPatches/Predef.scala
@@ -1,5 +1,7 @@
 package scala.runtime.stdLibPatches
 
+import scala.annotation.since
+
 object Predef:
   import compiletime.summonFrom
 
@@ -47,4 +49,13 @@ object Predef:
    */
   extension [T](x: T | Null) inline def nn: x.type & T =
     scala.runtime.Scala3RunTime.nn(x)
+
+  extension (inline x: AnyRef | Null)
+    @since("3.2")
+    inline def eq(inline y: AnyRef | Null): Boolean =
+      x.asInstanceOf[AnyRef] eq y.asInstanceOf[AnyRef]
+    @since("3.2")
+    inline def ne(inline y: AnyRef | Null): Boolean =
+      !(x eq y)
+
 end Predef

From adf8b779af392e683ef6bc835635385d38924793 Mon Sep 17 00:00:00 2001
From: Ondrej Lhotak <olhotak@uwaterloo.ca>
Date: Mon, 14 Mar 2022 11:57:45 +0100
Subject: [PATCH 04/12] reclassify unsafe-eq test as pos/eq-ne

---
 tests/explicit-nulls/pos/eq-ne.scala             | 16 ++++++++++++++++
 .../explicit-nulls/unsafe-common/unsafe-eq.scala | 16 ----------------
 2 files changed, 16 insertions(+), 16 deletions(-)
 create mode 100644 tests/explicit-nulls/pos/eq-ne.scala
 delete mode 100644 tests/explicit-nulls/unsafe-common/unsafe-eq.scala

diff --git a/tests/explicit-nulls/pos/eq-ne.scala b/tests/explicit-nulls/pos/eq-ne.scala
new file mode 100644
index 000000000000..ac2c9742ea64
--- /dev/null
+++ b/tests/explicit-nulls/pos/eq-ne.scala
@@ -0,0 +1,16 @@
+val s1: String = ???
+val s2: String | Null = ???
+
+def f = {
+  s1 eq s2
+  s2 eq s1
+
+  s1 ne s2
+  s2 ne s1
+
+  s1 eq null
+  s2 eq null
+
+  null eq s1
+  null eq s2
+}
diff --git a/tests/explicit-nulls/unsafe-common/unsafe-eq.scala b/tests/explicit-nulls/unsafe-common/unsafe-eq.scala
deleted file mode 100644
index 48fcd07bef80..000000000000
--- a/tests/explicit-nulls/unsafe-common/unsafe-eq.scala
+++ /dev/null
@@ -1,16 +0,0 @@
-val s1: String = ???
-val s2: String | Null = ???
-
-def f = {
-  s1 eq s2 // error
-  s2 eq s1 // error
-
-  s1 ne s2 // error
-  s2 ne s1 // error
-
-  s1 eq null // error
-  s2 eq null // error
-
-  null eq s1 // error
-  null eq s2 // error
-}
\ No newline at end of file

From bb3696b4dc678086e6e93efe0b0b8f03e1eec062 Mon Sep 17 00:00:00 2001
From: Ondrej Lhotak <olhotak@uwaterloo.ca>
Date: Mon, 7 Mar 2022 15:50:04 +0100
Subject: [PATCH 05/12] add eq/ne extension for AnyRef|Null to Scala3RunTime

---
 library/src/scala/runtime/Scala3RunTime.scala | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/library/src/scala/runtime/Scala3RunTime.scala b/library/src/scala/runtime/Scala3RunTime.scala
index b1645f5242aa..32f3687e88c6 100644
--- a/library/src/scala/runtime/Scala3RunTime.scala
+++ b/library/src/scala/runtime/Scala3RunTime.scala
@@ -19,4 +19,10 @@ object Scala3RunTime:
     if (isNull) throw new NullPointerException("tried to cast away nullability, but value is null")
     else x.asInstanceOf[x.type & T]
 
+  extension (inline x: AnyRef | Null)
+    inline def eq(inline y: AnyRef | Null): Boolean =
+      x.asInstanceOf[AnyRef] eq y.asInstanceOf[AnyRef]
+    inline def ne(inline y: AnyRef | Null): Boolean =
+      !(x eq y)
+
 end Scala3RunTime

From e279a7b3509242805af04a08a5de9d7801eb6fab Mon Sep 17 00:00:00 2001
From: Ondrej Lhotak <olhotak@uwaterloo.ca>
Date: Mon, 7 Mar 2022 16:45:53 +0100
Subject: [PATCH 06/12] add @since("3.2")

---
 library/src/scala/runtime/Scala3RunTime.scala | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/library/src/scala/runtime/Scala3RunTime.scala b/library/src/scala/runtime/Scala3RunTime.scala
index 32f3687e88c6..2eed853114cc 100644
--- a/library/src/scala/runtime/Scala3RunTime.scala
+++ b/library/src/scala/runtime/Scala3RunTime.scala
@@ -1,5 +1,7 @@
 package scala.runtime
 
+import scala.annotation.since
+
 object Scala3RunTime:
 
   // Called by inline def assert's. Extracted to minimize the bytecode size at call site.
@@ -20,8 +22,10 @@ object Scala3RunTime:
     else x.asInstanceOf[x.type & T]
 
   extension (inline x: AnyRef | Null)
+    @since("3.2")
     inline def eq(inline y: AnyRef | Null): Boolean =
       x.asInstanceOf[AnyRef] eq y.asInstanceOf[AnyRef]
+    @since("3.2")
     inline def ne(inline y: AnyRef | Null): Boolean =
       !(x eq y)
 

From 755c6755009bdc9e98547a8bf73bd419ee3c3cab Mon Sep 17 00:00:00 2001
From: Ondrej Lhotak <olhotak@uwaterloo.ca>
Date: Mon, 14 Mar 2022 11:52:28 +0100
Subject: [PATCH 07/12] move extension methods to Predef instead of
 Scala3RunTime

---
 library/src/scala/runtime/Scala3RunTime.scala | 10 ----------
 1 file changed, 10 deletions(-)

diff --git a/library/src/scala/runtime/Scala3RunTime.scala b/library/src/scala/runtime/Scala3RunTime.scala
index 2eed853114cc..b1645f5242aa 100644
--- a/library/src/scala/runtime/Scala3RunTime.scala
+++ b/library/src/scala/runtime/Scala3RunTime.scala
@@ -1,7 +1,5 @@
 package scala.runtime
 
-import scala.annotation.since
-
 object Scala3RunTime:
 
   // Called by inline def assert's. Extracted to minimize the bytecode size at call site.
@@ -21,12 +19,4 @@ object Scala3RunTime:
     if (isNull) throw new NullPointerException("tried to cast away nullability, but value is null")
     else x.asInstanceOf[x.type & T]
 
-  extension (inline x: AnyRef | Null)
-    @since("3.2")
-    inline def eq(inline y: AnyRef | Null): Boolean =
-      x.asInstanceOf[AnyRef] eq y.asInstanceOf[AnyRef]
-    @since("3.2")
-    inline def ne(inline y: AnyRef | Null): Boolean =
-      !(x eq y)
-
 end Scala3RunTime

From cc87f351765d3805427ac1ad5b8869c3bceb4232 Mon Sep 17 00:00:00 2001
From: Ondrej Lhotak <olhotak@uwaterloo.ca>
Date: Thu, 5 May 2022 19:07:46 +0200
Subject: [PATCH 08/12] use @experimental instead of @since("3.2")

(as suggested in today's LAMP meeting)
---
 library/src/scala/runtime/stdLibPatches/Predef.scala | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/library/src/scala/runtime/stdLibPatches/Predef.scala b/library/src/scala/runtime/stdLibPatches/Predef.scala
index f26544dfea50..64e76d3b8fd9 100644
--- a/library/src/scala/runtime/stdLibPatches/Predef.scala
+++ b/library/src/scala/runtime/stdLibPatches/Predef.scala
@@ -1,6 +1,6 @@
 package scala.runtime.stdLibPatches
 
-import scala.annotation.since
+import scala.annotation.experimental
 
 object Predef:
   import compiletime.summonFrom
@@ -51,10 +51,10 @@ object Predef:
     scala.runtime.Scala3RunTime.nn(x)
 
   extension (inline x: AnyRef | Null)
-    @since("3.2")
+    @experimental
     inline def eq(inline y: AnyRef | Null): Boolean =
       x.asInstanceOf[AnyRef] eq y.asInstanceOf[AnyRef]
-    @since("3.2")
+    @experimental
     inline def ne(inline y: AnyRef | Null): Boolean =
       !(x eq y)
 

From 5aef5a2990b1155628461e722fb02340b76d379c Mon Sep 17 00:00:00 2001
From: Ondrej Lhotak <olhotak@uwaterloo.ca>
Date: Mon, 9 May 2022 11:20:24 +0200
Subject: [PATCH 09/12] add eq and ne extension methods to
 stdlibExperimentalDefinitions.scala

---
 .../tasty-inspector/stdlibExperimentalDefinitions.scala      | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/tests/run-custom-args/tasty-inspector/stdlibExperimentalDefinitions.scala b/tests/run-custom-args/tasty-inspector/stdlibExperimentalDefinitions.scala
index 63b95c280b61..0d86b5c05caa 100644
--- a/tests/run-custom-args/tasty-inspector/stdlibExperimentalDefinitions.scala
+++ b/tests/run-custom-args/tasty-inspector/stdlibExperimentalDefinitions.scala
@@ -76,6 +76,11 @@ val experimentalDefinitionInLibrary = Set(
   // Need experimental annotation macros to check that design works.
   "scala.quoted.Quotes.reflectModule.ClassDefModule.apply",
   "scala.quoted.Quotes.reflectModule.SymbolModule.newClass",
+
+  //// New extension methods: Explicit Nulls
+  // Should be stabilized in 3.2.0.
+  "scala.Predef$.eq",
+  "scala.Predef$.ne",
 )
 
 

From bb3dbf7564e917b0e19e09028aab405e1ee151b3 Mon Sep 17 00:00:00 2001
From: Ondrej Lhotak <olhotak@uwaterloo.ca>
Date: Mon, 9 May 2022 14:36:00 +0200
Subject: [PATCH 10/12] update coverage test checkfile

---
 tests/coverage/pos/Inlined.scoverage.check | 54 +++++++++++-----------
 1 file changed, 27 insertions(+), 27 deletions(-)

diff --git a/tests/coverage/pos/Inlined.scoverage.check b/tests/coverage/pos/Inlined.scoverage.check
index f3cb3b5d9026..7d0e717a7aac 100644
--- a/tests/coverage/pos/Inlined.scoverage.check
+++ b/tests/coverage/pos/Inlined.scoverage.check
@@ -42,9 +42,9 @@ Inlined$package$
 Object
 covtest.Inlined$package$
 testInlined
-340
-367
-9
+378
+405
+11
 Scala3RunTime
 Select
 false
@@ -59,9 +59,9 @@ Inlined$package$
 Object
 covtest.Inlined$package$
 testInlined
-340
-382
-9
+378
+420
+11
 assertFailed
 Apply
 false
@@ -76,9 +76,9 @@ Inlined$package$
 Object
 covtest.Inlined$package$
 testInlined
-340
-382
-9
+378
+420
+11
 <none>
 Block
 true
@@ -127,9 +127,9 @@ Inlined$package$
 Object
 covtest.Inlined$package$
 testInlined
-340
-367
-9
+378
+405
+11
 Scala3RunTime
 Select
 false
@@ -144,9 +144,9 @@ Inlined$package$
 Object
 covtest.Inlined$package$
 testInlined
-340
-382
-9
+378
+420
+11
 assertFailed
 Apply
 false
@@ -161,9 +161,9 @@ Inlined$package$
 Object
 covtest.Inlined$package$
 testInlined
-340
-382
-9
+378
+420
+11
 <none>
 Block
 true
@@ -212,9 +212,9 @@ Inlined$package$
 Object
 covtest.Inlined$package$
 testInlined
-340
-367
-9
+378
+405
+11
 Scala3RunTime
 Select
 false
@@ -229,9 +229,9 @@ Inlined$package$
 Object
 covtest.Inlined$package$
 testInlined
-340
-382
-9
+378
+420
+11
 assertFailed
 Apply
 false
@@ -246,9 +246,9 @@ Inlined$package$
 Object
 covtest.Inlined$package$
 testInlined
-340
-382
-9
+378
+420
+11
 <none>
 Block
 true

From 03b391cedc6370ec4f08fd40a100e0271393ebb5 Mon Sep 17 00:00:00 2001
From: Ondrej Lhotak <olhotak@uwaterloo.ca>
Date: Mon, 9 May 2022 22:31:08 +0200
Subject: [PATCH 11/12] add comment

---
 library/src/scala/runtime/stdLibPatches/Predef.scala | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/library/src/scala/runtime/stdLibPatches/Predef.scala b/library/src/scala/runtime/stdLibPatches/Predef.scala
index 64e76d3b8fd9..8c9d6fae392d 100644
--- a/library/src/scala/runtime/stdLibPatches/Predef.scala
+++ b/library/src/scala/runtime/stdLibPatches/Predef.scala
@@ -50,6 +50,9 @@ object Predef:
   extension [T](x: T | Null) inline def nn: x.type & T =
     scala.runtime.Scala3RunTime.nn(x)
 
+  /** Enables an expression of type `T|Null`, where `T` is a subtype of `AnyRef`, to be checked for `null`
+   *  using `eq` and `ne`, rather than only `==` and `!=`. This is needed because `Null` no longer has
+   *  `eq` or `ne` methods, only `==` and `!=` inherited from `Any`. */
   extension (inline x: AnyRef | Null)
     @experimental
     inline def eq(inline y: AnyRef | Null): Boolean =

From 7c6b5596ab74aa0071fddde7906824cb26182db6 Mon Sep 17 00:00:00 2001
From: Ondrej Lhotak <olhotak@uwaterloo.ca>
Date: Mon, 9 May 2022 23:00:22 +0200
Subject: [PATCH 12/12] split comment for each method, not whole extension
 block

---
 library/src/scala/runtime/stdLibPatches/Predef.scala | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/library/src/scala/runtime/stdLibPatches/Predef.scala b/library/src/scala/runtime/stdLibPatches/Predef.scala
index 8c9d6fae392d..080a3957f79f 100644
--- a/library/src/scala/runtime/stdLibPatches/Predef.scala
+++ b/library/src/scala/runtime/stdLibPatches/Predef.scala
@@ -50,13 +50,16 @@ object Predef:
   extension [T](x: T | Null) inline def nn: x.type & T =
     scala.runtime.Scala3RunTime.nn(x)
 
-  /** Enables an expression of type `T|Null`, where `T` is a subtype of `AnyRef`, to be checked for `null`
-   *  using `eq` and `ne`, rather than only `==` and `!=`. This is needed because `Null` no longer has
-   *  `eq` or `ne` methods, only `==` and `!=` inherited from `Any`. */
   extension (inline x: AnyRef | Null)
+    /** Enables an expression of type `T|Null`, where `T` is a subtype of `AnyRef`, to be checked for `null`
+     *  using `eq` rather than only `==`. This is needed because `Null` no longer has
+     *  `eq` or `ne` methods, only `==` and `!=` inherited from `Any`. */
     @experimental
     inline def eq(inline y: AnyRef | Null): Boolean =
       x.asInstanceOf[AnyRef] eq y.asInstanceOf[AnyRef]
+    /** Enables an expression of type `T|Null`, where `T` is a subtype of `AnyRef`, to be checked for `null`
+     *  using `ne` rather than only `!=`. This is needed because `Null` no longer has
+     *  `eq` or `ne` methods, only `==` and `!=` inherited from `Any`. */
     @experimental
     inline def ne(inline y: AnyRef | Null): Boolean =
       !(x eq y)