Declare externs on the global this when window is not present.

This fix an issue where externs weren't assumed to be propeties on any object
when `window` is absent from the externs. This could cause the compiler to
improperly rename properties which are actually references to externs.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=195872147

src/com/google/javascript/jscomp/DeclaredGlobalExternsOnWindow.java

@@ -31,6 +31,8 @@
  */
 class DeclaredGlobalExternsOnWindow implements CompilerPass, NodeTraversal.Callback {
 
+  private static final String WINDOW_NAME = "window";
+
   private final AbstractCompiler compiler;
   private final Set<Node> nodes = new LinkedHashSet<>();
 
@@ -48,23 +50,21 @@ public void process(Node externs, Node root) {
   }
 
   private void addWindowProperties() {
-    if (!nodes.isEmpty() && windowInExterns) {
+    if (!nodes.isEmpty()) {
       for (Node node : nodes) {
-        addExtern(node);
+        addExtern(node, windowInExterns);
         compiler.reportChangeToEnclosingScope(node);
       }
     }
   }
 
-  private static void addExtern(Node node) {
+  private static void addExtern(Node node, boolean defineOnWindow) {
     String name = node.getString();
     JSDocInfo oldJSDocInfo = NodeUtil.getBestJSDocInfo(node);
 
-    // TODO(tbreisacher): Consider adding externs to 'this' instead of 'window',
-    // for environments where the global object is not called 'window.'
-    Node window = IR.name("window");
+    Node globalRef = defineOnWindow ? IR.name(WINDOW_NAME) : IR.thisNode();
     Node string = IR.string(name);
-    Node getprop = IR.getprop(window, string);
+    Node getprop = IR.getprop(globalRef, string);
     Node newNode = getprop;
 
     if (oldJSDocInfo != null) {
@@ -131,7 +131,7 @@ public void visit(NodeTraversal t, Node n, Node parent) {
       nodes.add(n.getFirstChild());
     } else if (n.isVar()) {
       for (Node c : n.children()) {
-        if (c.getString().equals("window")) {
+        if (c.getString().equals(WINDOW_NAME)) {
           windowInExterns = true;
           continue;
         }

test/com/google/javascript/jscomp/DeclaredGlobalExternsOnWindowTest.java

@@ -43,9 +43,9 @@ public void testWindowProperty1a() {
     testExternChanges("var window; var a;", "", "var window;var a;window.a");
   }
 
-  // No "var window;" so this is a no-op.
+  // No "var window;" so use "this" instead.
   public void testWindowProperty1b() {
-    testExternChanges("var a", "", "var a");
+    testExternChanges("var a;", "", "var a;this.a");
   }
 
   public void testWindowProperty2() {
@@ -57,9 +57,9 @@ public void testWindowProperty3a() {
         "var window;function f(){}window.f;");
   }
 
-  // No "var window;" so this is a no-op.
+  // No "var window;" so use "this" instead.
   public void testWindowProperty3b() {
-    testExternChanges("function f() {}", "var b", "function f(){}");
+    testExternChanges("function f() {}", "var b", "function f(){}this.f");
   }
 
   public void testWindowProperty4() {
@@ -73,9 +73,9 @@ public void testWindowProperty5a() {
         "var window;var x=function(){};window.x;");
   }
 
-  // No "var window;" so this is a no-op.
+  // No "var window;" so use "this" instead.
   public void testWindowProperty5b() {
-    testExternChanges("var x = function f() {}", "var b", "var x=function f(){}");
+    testExternChanges("var x = function f() {};", "var b", "var x=function f(){};this.x");
   }
 
   public void testWindowProperty5c() {

test/com/google/javascript/jscomp/IntegrationTest.java

@@ -2013,11 +2013,11 @@ public void testClassWithGettersIsRemoved() {
     // Investigate why are they kept when ran together with other passes.
     String expected =
         LINE_JOINER.join(
-        "('undefined'!=typeof window&&window===this?this:'undefined'!=typeof ",
-        "global&&null!=global?global:this).",
-        "c.defineProperties(function() {},",
-        "{e:{a:!0,b:!0,d:function(){}},",  // renamed from init
-        "f:{a:!0,b:!0,g:function(){}}})");  // renamed from prop
+            "('undefined'!=typeof window&&window===this?this:'undefined'!=typeof ",
+            "global&&null!=global?global:this).",
+            "Object.defineProperties(function() {},",
+            "{d:{a:!0,b:!0,c:function(){}},", // renamed from init
+            "e:{a:!0,b:!0,f:function(){}}})"); // renamed from prop
 
     options.setLanguageIn(LanguageMode.ECMASCRIPT_2015);
     options.setLanguageOut(LanguageMode.ECMASCRIPT5);
@@ -5141,7 +5141,6 @@ protected CompilerOptions createCompilerOptions() {
     options.setDevMode(DevMode.EVERY_PASS);
     options.setCodingConvention(new GoogleCodingConvention());
     options.setRenamePrefixNamespaceAssumeCrossModuleNames(true);
-    options.declaredGlobalExternsOnWindow = false;
     return options;
   }
 }

test/com/google/javascript/jscomp/SymbolTableTest.java

@@ -89,8 +89,9 @@ public void testGlobalVar() throws Exception {
   }
 
   public void testGlobalThisReferences() throws Exception {
-    SymbolTable table =
-        createSymbolTable("var x = this; function f() { return this + this + this; }");
+    SymbolTable table = createSymbolTable(
+        "var x = this; function f() { return this + this + this; }",
+        /* externsCode= */ "");
 
     Symbol global = getGlobalVar(table, "*global*");
     assertNotNull(global);
@@ -101,7 +102,7 @@ public void testGlobalThisReferences() throws Exception {
 
   public void testGlobalThisReferences2() throws Exception {
     // Make sure the global this is declared, even if it isn't referenced.
-    SymbolTable table = createSymbolTable("");
+    SymbolTable table = createSymbolTable("", /* externsCode= */ "");
 
     Symbol global = getGlobalVar(table, "*global*");
     assertNotNull(global);
@@ -111,7 +112,8 @@ public void testGlobalThisReferences2() throws Exception {
   }
 
   public void testGlobalThisReferences3() throws Exception {
-    SymbolTable table = createSymbolTable("this.foo = {}; this.foo.bar = {};");
+    SymbolTable table =
+        createSymbolTable("this.foo = {}; this.foo.bar = {};", /* externsCode= */ "");
 
     Symbol global = getGlobalVar(table, "*global*");
     assertNotNull(global);
@@ -343,7 +345,7 @@ public void testGlobalVarInExterns() throws Exception {
     SymbolTable table = createSymbolTable("customExternFn(1);");
     Symbol fn = getGlobalVar(table, "customExternFn");
     List<Reference> refs = table.getReferenceList(fn);
-    assertThat(refs).hasSize(2);
+    assertThat(refs).hasSize(3);
 
     SymbolScope scope = table.getEnclosingScope(refs.get(0).getNode());
     assertTrue(scope.isGlobalScope());
@@ -1184,6 +1186,15 @@ private SymbolTable createSymbolTable(String input) {
     return assertSymbolTableValid(compiler.buildKnownSymbolTable());
   }
 
+  private SymbolTable createSymbolTable(String input, String externsCode) {
+    List<SourceFile> inputs = ImmutableList.of(SourceFile.fromCode("in1", input));
+    List<SourceFile> externs = ImmutableList.of(SourceFile.fromCode("externs1", externsCode));
+
+    Compiler compiler = new Compiler(new BlackHoleErrorManager());
+    compiler.compile(externs, inputs, options);
+    return assertSymbolTableValid(compiler.buildKnownSymbolTable());
+  }
+
   /**
    * Asserts that the symbol table meets some invariants. Returns the same table for easy chaining.
    */