From b6462388fbdbc03bb659cb697b76b9b6bef4f030 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?S=C3=A9bastien=20Doeraene?= <sjrdoeraene@gmail.com>
Date: Thu, 13 Mar 2025 17:05:16 +0100
Subject: [PATCH] Fix #22794: Emit the definition of `Arrays.newArray` even
 though it's a primitive.

Until 3.6.x, we used the user-space definition of `Arrays.newArray`
in Scala.js. We changed it to a primitve in
2852168e8ddac8aa318635a73c79f64282aa39d1, to match the behavior of
the JVM backend.

However, that had the side effect of not emitting its definition
at all, like other primitives. For backward binary compat reasons,
we do need that definition.

We specifically make an exception for that method, which is now
emitted, even though it is otherwise treated as a primitive.

[Cherry-picked 9c7193a2889b139e2cdbee2e4ea06cf82428e404]
---
 compiler/src/dotty/tools/backend/sjs/JSCodeGen.scala         | 2 +-
 sbt-test/scalajs/backward-compat/build.sbt                   | 5 +++++
 sbt-test/scalajs/backward-compat/project/plugins.sbt         | 2 ++
 .../src/test/scala/NewArrayIssue22794Test.scala              | 5 +++++
 sbt-test/scalajs/backward-compat/test                        | 1 +
 5 files changed, 14 insertions(+), 1 deletion(-)
 create mode 100644 sbt-test/scalajs/backward-compat/build.sbt
 create mode 100644 sbt-test/scalajs/backward-compat/project/plugins.sbt
 create mode 100644 sbt-test/scalajs/backward-compat/src/test/scala/NewArrayIssue22794Test.scala
 create mode 100644 sbt-test/scalajs/backward-compat/test

diff --git a/compiler/src/dotty/tools/backend/sjs/JSCodeGen.scala b/compiler/src/dotty/tools/backend/sjs/JSCodeGen.scala
index 9e5743147122..4e63d31b6842 100644
--- a/compiler/src/dotty/tools/backend/sjs/JSCodeGen.scala
+++ b/compiler/src/dotty/tools/backend/sjs/JSCodeGen.scala
@@ -1496,7 +1496,7 @@ class JSCodeGen()(using genCtx: Context) {
 
       def jsParams = params.map(genParamDef(_))
 
-      if (primitives.isPrimitive(sym)) {
+      if (primitives.isPrimitive(sym) && sym != defn.newArrayMethod) {
         None
       } else if (sym.is(Deferred) && currentClassSym.isNonNativeJSClass) {
         // scala-js/#4409: Do not emit abstract methods in non-native JS classes
diff --git a/sbt-test/scalajs/backward-compat/build.sbt b/sbt-test/scalajs/backward-compat/build.sbt
new file mode 100644
index 000000000000..552452b72f6f
--- /dev/null
+++ b/sbt-test/scalajs/backward-compat/build.sbt
@@ -0,0 +1,5 @@
+enablePlugins(ScalaJSPlugin)
+
+scalaVersion := sys.props("plugin.scalaVersion")
+
+libraryDependencies += "org.scalameta" %%% "munit" % "1.0.0-M10"
diff --git a/sbt-test/scalajs/backward-compat/project/plugins.sbt b/sbt-test/scalajs/backward-compat/project/plugins.sbt
new file mode 100644
index 000000000000..b30c6e8c5ec8
--- /dev/null
+++ b/sbt-test/scalajs/backward-compat/project/plugins.sbt
@@ -0,0 +1,2 @@
+
+addSbtPlugin("org.scala-js" % "sbt-scalajs" % sys.props("plugin.scalaJSVersion"))
diff --git a/sbt-test/scalajs/backward-compat/src/test/scala/NewArrayIssue22794Test.scala b/sbt-test/scalajs/backward-compat/src/test/scala/NewArrayIssue22794Test.scala
new file mode 100644
index 000000000000..0385b537bfe4
--- /dev/null
+++ b/sbt-test/scalajs/backward-compat/src/test/scala/NewArrayIssue22794Test.scala
@@ -0,0 +1,5 @@
+class NewArrayIssue22794Test extends munit.FunSuite {
+  test("foo") {
+    assert(2 + 2 == 4)
+  }
+}
diff --git a/sbt-test/scalajs/backward-compat/test b/sbt-test/scalajs/backward-compat/test
new file mode 100644
index 000000000000..dfffb838b4b3
--- /dev/null
+++ b/sbt-test/scalajs/backward-compat/test
@@ -0,0 +1 @@
+> test