Fix #16173: SJS: Fix the detection of inferred types of = js.native. (#16184)

Author: sjrd

compiler/src/dotty/tools/dotc/transform/sjs/PrepJSInterop.scala

@@ -979,9 +979,9 @@ class PrepJSInterop extends MacroTransform with IdentityDenotTransformer { thisP
           report.error(s"$longKindStr may only call js.native.", pos)
       }
 
-      // Check that the resul type was explicitly specified
+      // Check that the result type was explicitly specified
       // (This is stronger than Scala 2, which only warns, and only if it was inferred as Nothing.)
-      if (tree.tpt.span.isSynthetic)
+      if (tree.tpt.isInstanceOf[InferredTypeTree])
         report.error(i"The type of ${tree.name} must be explicitly specified because it is JS native.", tree)
     }
 

tests/sjs-junit/test/org/scalajs/testsuite/compiler/RegressionTestScala3.scala

@@ -78,6 +78,18 @@ class RegressionTestScala3 {
     val f3 = { () => i += 1 }
     assertSame(f3, Thunk.asFunction0(f3()))
   }
+
+  @Test def literalTypeJSNativeIssue16173(): Unit = {
+    js.eval("""
+      var RegressionTestScala3_Issue16173_foo = "constant";
+      var RegressionTestScala3_Issue16173_bar = function() { return 5; };
+    """)
+
+    assertEquals("constant", Issue16173.foo1)
+    assertEquals("constant", Issue16173.foo2)
+
+    assertEquals(5, Issue16173.bar1())
+  }
 }
 
 object RegressionTestScala3 {
@@ -148,6 +160,20 @@ object RegressionTestScala3 {
     val entries = js.Object.entries(obj)
     val js.Tuple2(k, v) = entries(0): @unchecked
   }
+
+  object Issue16173 {
+    @js.native
+    @JSGlobal("RegressionTestScala3_Issue16173_foo")
+    val foo1: "constant" = js.native
+
+    @js.native
+    @JSGlobal("RegressionTestScala3_Issue16173_foo")
+    def foo2: "constant" = js.native
+
+    @js.native
+    @JSGlobal("RegressionTestScala3_Issue16173_bar")
+    def bar1(): 5 = js.native
+  }
 }
 
 // This class needs to be at the top-level, not in an object, to reproduce the issue