Allow for empty JS namespaces to represent top-level symbols

We currently don't have a way to overlay a native type that has form:

``` js
goog.module('TopLevelClass');

exports = class {};
```

With this change you'd now represent this as:

``` java
@jstype(isNative = true, namespace = "", name = "TopLevelClass")
class TopLevelClass {}
```

This all works since we currently treat the first component of the `name`
attribute as the last component of the `goog.require` statement for `@JsType`.

PiperOrigin-RevId: 599223849

transpiler/java/com/google/j2cl/transpiler/passes/JsInteropRestrictionsChecker.java

@@ -1102,7 +1102,16 @@ private void checkQualifiedJsName(Type type) {
     }
 
     checkJsName(type);
-    checkJsNamespace(type);
+
+    String namespace = type.getJsNamespace();
+    // Permit empty namespaces on native JsTypes to represent a top-level non-extern type. This
+    // works since the first component of the name is always used as the last component of the
+    // import statement.
+    boolean isValidEmptyNamespace = namespace.isEmpty() && type.getDeclaration().isNative();
+
+    if (!isValidEmptyNamespace) {
+      checkJsNamespace(type);
+    }
   }
 
   private boolean checkQualifiedJsName(Member member) {

transpiler/javatests/com/google/j2cl/readable/java/nativejstypes/Main.java

@@ -69,4 +69,14 @@ public static void testNativeTypeObjectMethods() {
     int unusedHash = bar.hashCode();
     boolean unusedEq = bar.equals(new Object());
   }
+
+  public static void testTopLevel() {
+    TopLevel.x = 2;
+
+    TopLevel.Nested nested = new TopLevel.Nested();
+    nested.x = 3;
+
+    TopLevelNestedReference topLevelNestedReference = new TopLevelNestedReference();
+    topLevelNestedReference.x = 4;
+  }
 }

transpiler/javatests/com/google/j2cl/readable/java/nativejstypes/TopLevel.java

@@ -0,0 +1,35 @@
+/*
+ * Copyright 2024 Google Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not
+ * use this file except in compliance with the License. You may obtain a copy of
+ * the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+ * License for the specific language governing permissions and limitations under
+ * the License.
+ */
+package nativejstypes;
+
+import jsinterop.annotations.JsType;
+
+@JsType(isNative = true, namespace = "", name = "toplevel")
+class TopLevel {
+  private TopLevel() {}
+
+  public static int x;
+
+  @JsType(isNative = true)
+  static class Nested {
+    public int x;
+  }
+}
+
+@JsType(isNative = true, namespace = "", name = "toplevel.Nested")
+class TopLevelNestedReference {
+  public int x;
+}

transpiler/javatests/com/google/j2cl/readable/java/nativejstypes/native_sources/toplevel.js

@@ -0,0 +1,24 @@
+// Copyright 2024 Google Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+goog.module('toplevel');
+
+exports.Nested = class Nested {
+  constructor() {
+    /** @type {number} */
+    this.x = 1;
+  }
+};
+
+/** @type {number} */
+exports.x = 1;

transpiler/javatests/com/google/j2cl/readable/java/nativejstypes/output_closure/Main.impl.java.js.txt

@@ -7,6 +7,8 @@ let Foo = goog.forwardDeclare('com.acme.MyFoo');
 let Class = goog.forwardDeclare('java.lang.Class$impl');
 let Bar = goog.forwardDeclare('nativejstypes.Bar');
 let $synthetic_nativejstypes_Bar = goog.forwardDeclare('nativejstypes.Bar');
+let TopLevel = goog.forwardDeclare('toplevel');
+let toplevel = goog.forwardDeclare('toplevel');
 let $JavaScriptObject = goog.forwardDeclare('vmbootstrap.JavaScriptObject$impl');
 let $Objects = goog.forwardDeclare('vmbootstrap.Objects$impl');
 
@@ -85,6 +87,15 @@ class Main extends j_l_Object {
   let unusedEq = $Objects.m_equals__java_lang_Object__java_lang_Object__boolean(bar, j_l_Object.$create__());
  }
  /** @nodts */
+ static m_testTopLevel__void() {
+  Main.$clinit();
+  TopLevel.x = 2;
+  let nested = new TopLevel.Nested();
+  nested.x = 3;
+  let topLevelNestedReference = new toplevel.Nested();
+  topLevelNestedReference.x = 4;
+ }
+ /** @nodts */
  static $clinit() {
   Main.$clinit = () =>{};
   Main.$loadModules();
@@ -101,6 +112,8 @@ class Main extends j_l_Object {
   Class = goog.module.get('java.lang.Class$impl');
   Bar = goog.module.get('nativejstypes.Bar');
   $synthetic_nativejstypes_Bar = goog.module.get('nativejstypes.Bar');
+  TopLevel = goog.module.get('toplevel');
+  toplevel = goog.module.get('toplevel');
   $JavaScriptObject = goog.module.get('vmbootstrap.JavaScriptObject$impl');
   $Objects = goog.module.get('vmbootstrap.Objects$impl');
  }

transpiler/javatests/com/google/j2cl/readable/java/nativejstypes/output_closure/Main.java.js.txt

@@ -5,6 +5,7 @@ goog.require('java.lang.Class');
 goog.require('java.lang.Object');
 goog.require('nativebootstrap.Util');
 goog.require('nativejstypes.Bar');
+goog.require('toplevel');
 goog.require('vmbootstrap.JavaScriptObject');
 goog.require('vmbootstrap.Objects');
 

transpiler/javatests/com/google/j2cl/readable/java/nativejstypes/output_closure/Main.js.mappings.txt

@@ -87,6 +87,18 @@
 [unusedHash] => [unusedHash] "unusedHash"
 [boolean unusedEq = bar.equals(new Object());] => [let unusedEq = $Objects.m_equals__java_lang_Object__java_lang_Object__boolean(bar, j_l_Object.$create__());] "nativejstypes.Main.testNativeTypeObjectMethods"
 [unusedEq] => [unusedEq] "unusedEq"
+[testTopLevel] => [m_testTopLevel__void]
+[{
+    TopLevel.x = 2;
+...    topLevelNestedReference.x = 4;
+  }] => [Main.$clinit();] "nativejstypes.Main.testTopLevel"
+[TopLevel.x = 2;] => [TopLevel.x = 2;] "nativejstypes.Main.testTopLevel"
+[TopLevel.Nested nested = new TopLevel.Nested();] => [let nested = new TopLevel.Nested();] "nativejstypes.Main.testTopLevel"
+[nested] => [nested] "nested"
+[nested.x = 3;] => [nested.x = 3;] "nativejstypes.Main.testTopLevel"
+[TopLevelNestedReference topLevelNestedReference = new TopLevelNestedReference();] => [let topLevelNestedReference = new toplevel.Nested();] "nativejstypes.Main.testTopLevel"
+[topLevelNestedReference] => [topLevelNestedReference] "topLevelNestedReference"
+[topLevelNestedReference.x = 4;] => [topLevelNestedReference.x = 4;] "nativejstypes.Main.testTopLevel"
 [Main] => [$clinit]
 [Main] => [Main.$clinit = () =>{};] "nativejstypes.Main.<clinit>"
 [Main] => [Main.$loadModules();] "nativejstypes.Main.<clinit>"

transpiler/javatests/com/google/j2cl/readable/java/nativejstypes/output_closure/TopLevel$$Overlay.impl.java.js.txt

@@ -0,0 +1,25 @@
+goog.module('nativejstypes.TopLevel.$Overlay$impl');
+
+const $Util = goog.require('nativebootstrap.Util$impl');
+const TopLevel = goog.require('toplevel');
+
+/** @nodts */
+class $Overlay {
+ /** @nodts */
+ static $clinit() {
+  $Overlay.$clinit = () =>{};
+  $Overlay.$loadModules();
+ }
+ /** @nodts @return {boolean} */
+ static $isInstance(/** ? */ instance) {
+  return instance instanceof TopLevel;
+ }
+
+ /** @nodts */
+ static $loadModules() {}
+}
+$Util.$setClassMetadata($Overlay, 'toplevel');
+
+exports = $Overlay;
+
+//# sourceMappingURL=TopLevel$$Overlay.js.map

transpiler/javatests/com/google/j2cl/readable/java/nativejstypes/output_closure/TopLevel$$Overlay.java.js.txt

@@ -0,0 +1,8 @@
+goog.module('nativejstypes.TopLevel.$Overlay');
+
+goog.require('nativebootstrap.Util');
+goog.require('toplevel');
+
+const $Overlay = goog.require('nativejstypes.TopLevel.$Overlay$impl');
+/** @nodts */
+exports = $Overlay;

transpiler/javatests/com/google/j2cl/readable/java/nativejstypes/output_closure/TopLevel$$Overlay.js.mappings.txt

@@ -0,0 +1,4 @@
+[TopLevel] => [$Overlay]
+[TopLevel] => [$clinit]
+[TopLevel] => [$Overlay.$clinit = () =>{};] "nativejstypes.TopLevel$$Overlay.<clinit>"
+[TopLevel] => [$Overlay.$loadModules();] "nativejstypes.TopLevel$$Overlay.<clinit>"

transpiler/javatests/com/google/j2cl/readable/java/nativejstypes/output_closure/TopLevel$Nested$$Overlay.impl.java.js.txt

@@ -0,0 +1,25 @@
+goog.module('nativejstypes.TopLevel.Nested.$Overlay$impl');
+
+const $Util = goog.require('nativebootstrap.Util$impl');
+const TopLevel = goog.require('toplevel');
+
+/** @nodts */
+class $Overlay {
+ /** @nodts */
+ static $clinit() {
+  $Overlay.$clinit = () =>{};
+  $Overlay.$loadModules();
+ }
+ /** @nodts @return {boolean} */
+ static $isInstance(/** ? */ instance) {
+  return instance instanceof TopLevel.Nested;
+ }
+
+ /** @nodts */
+ static $loadModules() {}
+}
+$Util.$setClassMetadata($Overlay, 'toplevel.Nested');
+
+exports = $Overlay;
+
+//# sourceMappingURL=TopLevel$Nested$$Overlay.js.map

transpiler/javatests/com/google/j2cl/readable/java/nativejstypes/output_closure/TopLevel$Nested$$Overlay.java.js.txt

@@ -0,0 +1,8 @@
+goog.module('nativejstypes.TopLevel.Nested.$Overlay');
+
+goog.require('nativebootstrap.Util');
+goog.require('toplevel');
+
+const $Overlay = goog.require('nativejstypes.TopLevel.Nested.$Overlay$impl');
+/** @nodts */
+exports = $Overlay;

transpiler/javatests/com/google/j2cl/readable/java/nativejstypes/output_closure/TopLevel$Nested$$Overlay.js.mappings.txt

@@ -0,0 +1,4 @@
+[Nested] => [$Overlay]
+[Nested] => [$clinit]
+[Nested] => [$Overlay.$clinit = () =>{};] "nativejstypes.TopLevel$Nested$$Overlay.<clinit>"
+[Nested] => [$Overlay.$loadModules();] "nativejstypes.TopLevel$Nested$$Overlay.<clinit>"

transpiler/javatests/com/google/j2cl/readable/java/nativejstypes/output_closure/TopLevelNestedReference$$Overlay.impl.java.js.txt

@@ -0,0 +1,25 @@
+goog.module('nativejstypes.TopLevelNestedReference.$Overlay$impl');
+
+const $Util = goog.require('nativebootstrap.Util$impl');
+const toplevel = goog.require('toplevel');
+
+/** @nodts */
+class $Overlay {
+ /** @nodts */
+ static $clinit() {
+  $Overlay.$clinit = () =>{};
+  $Overlay.$loadModules();
+ }
+ /** @nodts @return {boolean} */
+ static $isInstance(/** ? */ instance) {
+  return instance instanceof toplevel.Nested;
+ }
+
+ /** @nodts */
+ static $loadModules() {}
+}
+$Util.$setClassMetadata($Overlay, 'toplevel.Nested');
+
+exports = $Overlay;
+
+//# sourceMappingURL=TopLevelNestedReference$$Overlay.js.map

transpiler/javatests/com/google/j2cl/readable/java/nativejstypes/output_closure/TopLevelNestedReference$$Overlay.java.js.txt

@@ -0,0 +1,8 @@
+goog.module('nativejstypes.TopLevelNestedReference.$Overlay');
+
+goog.require('nativebootstrap.Util');
+goog.require('toplevel');
+
+const $Overlay = goog.require('nativejstypes.TopLevelNestedReference.$Overlay$impl');
+/** @nodts */
+exports = $Overlay;

transpiler/javatests/com/google/j2cl/readable/java/nativejstypes/output_closure/TopLevelNestedReference$$Overlay.js.mappings.txt

@@ -0,0 +1,4 @@
+[TopLevelNestedReference] => [$Overlay]
+[TopLevelNestedReference] => [$clinit]
+[TopLevelNestedReference] => [$Overlay.$clinit = () =>{};] "nativejstypes.TopLevelNestedReference$$Overlay.<clinit>"
+[TopLevelNestedReference] => [$Overlay.$loadModules();] "nativejstypes.TopLevelNestedReference$$Overlay.<clinit>"

transpiler/javatests/com/google/j2cl/readable/java/nativejstypes/output_closure/com/google/j2cl/readable/java/nativejstypes/native_sources/toplevel.js.txt

@@ -0,0 +1,24 @@
+// Copyright 2024 Google Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+goog.module('toplevel');
+
+exports.Nested = class Nested {
+  constructor() {
+    /** @type {number} */
+    this.x = 1;
+  }
+}
+
+/** @type {number} */
+exports.x = 1;

transpiler/javatests/com/google/j2cl/readable/java/nativejstypes/output_kt/Main+J2ObjCCompat.h.txt

@@ -45,4 +45,8 @@ NS_INLINE void NativejstypesMain_testNativeTypeObjectMethods(void) {
  [J2ktNativejstypesMainCompanion.shared testNativeTypeObjectMethods];
 }
 
+NS_INLINE void NativejstypesMain_testTopLevel(void) {
+ [J2ktNativejstypesMainCompanion.shared testTopLevel];
+}
+
 NS_ASSUME_NONNULL_END

transpiler/javatests/com/google/j2cl/readable/java/nativejstypes/output_kt/Main.kt.txt

@@ -34,6 +34,8 @@ import nativejstypes.Bar
 import nativejstypes.BarInnerWithDotInName
 import nativejstypes.Foo
 import nativejstypes.Headers
+import nativejstypes.TopLevel
+import nativejstypes.TopLevelNestedReference
 
 @ObjCName("J2ktNativejstypesMain", exact = true)
 open class Main {
@@ -104,5 +106,15 @@ open class Main {
    val unusedHash: Int = bar!!.hashCode()
    val unusedEq: Boolean = bar!!.equals(Any())
   }
+
+  @JvmStatic
+  @ObjCName("testTopLevel")
+  fun testTopLevel() {
+   TopLevel.x = 2
+   val nested: TopLevel.Nested? = TopLevel.Nested()
+   nested!!.x = 3
+   val topLevelNestedReference: TopLevelNestedReference? = TopLevelNestedReference()
+   topLevelNestedReference!!.x = 4
+  }
  }
 }

transpiler/javatests/com/google/j2cl/readable/java/nativejstypes/output_kt/TopLevel.kt.txt

@@ -0,0 +1,46 @@
+// Generated from "nativejstypes/TopLevel.java"
+@file:Suppress(
+ "ALWAYS_NULL",
+ "PARAMETER_NAME_CHANGED_ON_OVERRIDE",
+ "REPEATED_BOUND",
+ "SENSELESS_COMPARISON",
+ "UNCHECKED_CAST",
+ "UNNECESSARY_LATEINIT",
+ "UNNECESSARY_NOT_NULL_ASSERTION",
+ "UNREACHABLE_CODE",
+ "UNUSED_ANONYMOUS_PARAMETER",
+ "UNUSED_PARAMETER",
+ "UNUSED_VARIABLE",
+ "USELESS_CAST",
+ "VARIABLE_IN_SINGLETON_WITHOUT_THREAD_LOCAL",
+ "VARIABLE_WITH_REDUNDANT_INITIALIZER")
+
+package nativejstypes
+
+import javaemul.lang.*
+import jsinterop.annotations.JsType
+import kotlin.Int
+import kotlin.Suppress
+import kotlin.jvm.JvmField
+
+@JsType(name = "toplevel", namespace = "", isNative = true)
+open class TopLevel {
+ internal constructor()
+
+ companion object {
+  @JvmField
+  var x: Int = 0
+ }
+
+ @JsType(isNative = true)
+ open class Nested internal constructor() {
+  @JvmField
+  var x: Int = 0
+ }
+}
+
+@JsType(name = "toplevel.Nested", namespace = "", isNative = true)
+open class TopLevelNestedReference internal constructor() {
+ @JvmField
+ var x: Int = 0
+}