Fix scala-js#1983: Warn if @ScalaJSDefined overrides js names differ.

Author: nicolasstucki

compiler/src/main/scala/org/scalajs/core/compiler/PrepJSInterop.scala

@@ -724,6 +724,18 @@ abstract class PrepJSInterop extends plugins.PluginComponent
                 "A Scala.js-defined JS trait cannot contain private members")
           }
         }
+
+        // @ScalaJSDefined overrides with different js names - issue #1983
+        sym.allOverriddenSymbols.headOption match {
+          case Some(overridedSym) =>
+            if (jsInterop.jsNameOf(sym) != jsInterop.jsNameOf(overridedSym)) {
+              reporter.warning(tree.pos,
+                  "A Scala.js-defined JS class member is overriding another " +
+                  "with a different exported name.")
+            }
+
+          case None => // Do nothing
+        }
       }
 
       if (sym.isPrimaryConstructor || sym.isValueParameter ||

compiler/src/test/scala/org/scalajs/core/compiler/test/JSInteropTest.scala

@@ -764,4 +764,111 @@ class JSInteropTest extends DirectTest with TestHelpers {
 
   }
 
+  @Test
+  def scalaJSDefinedJSNameOverrideWarnings: Unit = {
+    """
+    @ScalaJSDefined
+    abstract class A extends js.Object {
+      def bar(): Int
+    }
+    @ScalaJSDefined
+    class B extends A {
+      override def bar() = 1
+    }
+    """.hasNoWarns
+
+    """
+    @ScalaJSDefined
+    abstract class A extends js.Object {
+      @JSName("foo")
+      def bar(): Int
+    }
+    @ScalaJSDefined
+    class B extends A {
+      @JSName("foo")
+      override def bar() = 1
+    }
+    """.hasNoWarns
+
+    """
+    @ScalaJSDefined
+    abstract class A extends js.Object {
+      @JSName("foo")
+      def bar(): Int
+    }
+    @ScalaJSDefined
+    class B extends A {
+      @JSName("baz")
+      override def bar() = 1
+    }
+    """ hasWarns
+      """
+        |newSource1.scala:13: warning: A Scala.js-defined JS class member is overriding another with a different exported name.
+        |      override def bar() = 1
+        |                   ^
+      """
+
+    """
+    @ScalaJSDefined
+    abstract class A extends js.Object {
+      @JSName("foo")
+      def bar(): Int
+    }
+    @ScalaJSDefined
+    class B extends A {
+      override def bar() = 1
+    }
+    """ hasWarns
+    """
+      |newSource1.scala:12: warning: A Scala.js-defined JS class member is overriding another with a different exported name.
+      |      override def bar() = 1
+      |                   ^
+    """
+
+    """
+    @ScalaJSDefined
+    abstract class A extends js.Object {
+      @JSName("foo")
+      def bar(): Object
+    }
+    @ScalaJSDefined
+    abstract class B extends A {
+      override def bar(): String
+    }
+    @ScalaJSDefined
+    class C extends B {
+      override def bar() = "1"
+    }
+    """ hasWarns
+    """
+      |newSource1.scala:12: warning: A Scala.js-defined JS class member is overriding another with a different exported name.
+      |      override def bar(): String
+      |                   ^
+    """
+
+    """
+    @ScalaJSDefined
+    abstract class A extends js.Object {
+      def bar(): Object
+    }
+    @ScalaJSDefined
+    abstract class B extends A {
+    @JSName("foo")
+      override def bar(): String
+    }
+    @ScalaJSDefined
+    class C extends B {
+      override def bar() = "1"
+    }
+    """ hasWarns
+    """
+      |newSource1.scala:12: warning: A Scala.js-defined JS class member is overriding another with a different exported name.
+      |      override def bar(): String
+      |                   ^
+      |newSource1.scala:16: warning: A Scala.js-defined JS class member is overriding another with a different exported name.
+      |      override def bar() = "1"
+      |                   ^
+    """
+  }
+
 }