InlineAndCollapseProperties fix for new TS 5.2 emit shape

TS 5.2. emits code like this:

```
// Alias variable created without being initialized.
var alias;
var C = class {
  // references to alias in here, because TS doesn't like using
  // the class name.
};
alias = C;
C.staticProperty = someValue;
```

This code shape confused `InlineAndCollapseProperties`
causing it both to back off from some inlining (bigger output code)
and fail to back off similarly for collapsing (broken output code).

PiperOrigin-RevId: 564552797

Author: brad4d

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

@@ -410,6 +410,7 @@ private boolean declarationHasFollowingObjectSpreadSibling(Node declaration) {
   private class BuildGlobalNamespace extends NodeTraversal.AbstractPreOrderCallback {
     private @Nullable Node curModuleRoot = null;
     private @Nullable ModuleMetadata curMetadata = null;
+
     /** Collect the references in pre-order. */
     @Override
     public boolean shouldTraverse(NodeTraversal t, Node n, Node parent) {
@@ -1216,9 +1217,13 @@ final class Name implements StaticSlot {
 
     // The children of this name. Must be null if there are no children.
     @Nullable List<Name> props;
-    /** The first global assignment to a name. */
+
+    /** The declaration of a name. */
     private @Nullable Ref declaration;
 
+    /** The first global assignment to a name. */
+    private @Nullable Ref initialization;
+
     /**
      * Keep track of which Nodes are Refs for this Name.
      *
@@ -1311,6 +1316,10 @@ boolean usesHasOwnProperty() {
       return declaration;
     }
 
+    public @Nullable Ref getInitialization() {
+      return initialization;
+    }
+
     boolean isFunction() {
       return getBooleanProperty(NameProp.FUNCTION);
     }
@@ -1455,6 +1464,12 @@ private void updateStateForAddedRef(Ref ref) {
           if (declaration == null) {
             declaration = ref;
           }
+          if (initialization == null && !ref.isUninitializedDeclaration()) {
+            // Record the reference where the first value is actually assigned.
+            // Do not include the automatically-assigned `undefined` value case.
+            // e.g. `var name;`
+            initialization = ref;
+          }
           if (firstDeclarationJSDocInfo == null) {
             // JSDocInfo from the first SET_FROM_GLOBAL will be assumed to be canonical
             // Note that this will not change if the first declaration is later removed
@@ -1725,7 +1740,8 @@ boolean isCollapsingExplicitlyDenied() {
      */
     Inlinability calculateInlinability() {
       // Only simple aliases with direct usage are inlineable.
-      if (inExterns() || globalSets != 1 || localSets != 0) {
+      // Exactly 2 global sets could be OK, if the first is the declaration with no initializer.
+      if (inExterns() || !hasOneRealGlobalSet() || localSets != 0) {
         return Inlinability.DO_NOT_INLINE;
       }
 
@@ -1761,6 +1777,10 @@ Inlinability calculateInlinability() {
       return collapsibility;
     }
 
+    private boolean hasOneRealGlobalSet() {
+      return globalSets == 1 || (globalSets == 2 && declaration.isUninitializedDeclaration());
+    }
+
     boolean canCollapse() {
       return canCollapseOrInline().canCollapse();
     }
@@ -1914,13 +1934,13 @@ private void logDecision(Inlinability inlinability, String reason) {
 
     private Inlinability getUnsafeInlinabilityBasedOnDeclaredType() {
       if (this.getBooleanProperty(NameProp.CONSTRUCTOR_TYPE)) {
-          return Inlinability.INLINE_BUT_KEEP_DECLARATION_CLASS;
+        return Inlinability.INLINE_BUT_KEEP_DECLARATION_CLASS;
       } else if (this.getBooleanProperty(NameProp.INTERFACE_TYPE)) {
-          return Inlinability.INLINE_BUT_KEEP_DECLARATION_INTERFACE;
+        return Inlinability.INLINE_BUT_KEEP_DECLARATION_INTERFACE;
       } else if (this.getBooleanProperty(NameProp.ENUM_TYPE)) {
-          return Inlinability.INLINE_BUT_KEEP_DECLARATION_ENUM;
+        return Inlinability.INLINE_BUT_KEEP_DECLARATION_ENUM;
       } else if (this.getBooleanProperty(NameProp.NOT_A_TYPE)) {
-          return Inlinability.DO_NOT_INLINE;
+        return Inlinability.DO_NOT_INLINE;
       }
       throw new IllegalStateException(
           SimpleFormat.format("name missing declaredType value: %s", this));
@@ -2133,11 +2153,11 @@ private boolean valueImplicitlySupportsAliasing() {
         return true;
       }
       if (getBooleanProperty(NameProp.FUNCTION)) {
-          // We want ES5 ctors/interfaces to behave consistently with ES6 because:
-          // - transpilation should not change behaviour
-          // - updating code shouldn't be hindered by behaviour changes
-          @Nullable JSDocInfo jsdoc = getJSDocInfo();
-          return jsdoc != null && jsdoc.isConstructorOrInterface();
+        // We want ES5 ctors/interfaces to behave consistently with ES6 because:
+        // - transpilation should not change behaviour
+        // - updating code shouldn't be hindered by behaviour changes
+        @Nullable JSDocInfo jsdoc = getJSDocInfo();
+        return jsdoc != null && jsdoc.isConstructorOrInterface();
       }
       return false;
     }
@@ -2472,6 +2492,11 @@ boolean isSetFromGlobal() {
       return this.type == Type.SET_FROM_GLOBAL || this.type == Type.GET_AND_SET_FROM_GLOBAL;
     }
 
+    /** True for `var name;` and similar cases. */
+    boolean isUninitializedDeclaration() {
+      return node.isName() && NodeUtil.isNameDeclaration(node.getParent()) && !node.hasChildren();
+    }
+
     @Override
     public String toString() {
       return MoreObjects.toStringHelper(this)

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

@@ -835,8 +835,8 @@ private void inlineGlobalAliasIfPossible(Name name, Ref alias, GlobalNamespace n
 
         if (aliasInlinability.shouldRemoveDeclaration()) {
           // Rewrite the initialization of the alias.
-          Ref aliasDeclaration = aliasingName.getDeclaration();
-          if (aliasDeclaration.isTwin()) {
+          Ref aliasInitialization = aliasingName.getInitialization();
+          if (aliasInitialization.isTwin()) {
             // This is in a nested assign.
             // Replace
             //   a.b = aliasing.name = aliased.name
@@ -846,7 +846,7 @@ private void inlineGlobalAliasIfPossible(Name name, Ref alias, GlobalNamespace n
             Node aliasGrandparent = aliasParent.getParent();
             aliasParent.replaceWith(alias.getNode().detach());
             // Remove the ref to 'aliasing.name' entirely
-            aliasingName.removeRef(aliasDeclaration);
+            aliasingName.removeRef(aliasInitialization);
             // Force GlobalNamespace to revisit the new reference to 'aliased.name' and update its
             // internal state.
             newNodes.add(new AstChange(alias.scope, alias.getNode()));

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

@@ -83,10 +83,10 @@ public void testTs52OutputChange() {
                 "  method2() {",
                 "    return alias.staticPropOnAlias;",
                 "  }",
-                "}",
+                "};",
                 "alias = module$exports$C;",
                 "(() => {",
-                "  alias.staticPropOnAlias = 1",
+                "  alias.staticPropOnAlias = 1;",
                 "})();",
                 "module$exports$C.staticPropOnC = 2;",
                 "")),
@@ -96,19 +96,18 @@ public void testTs52OutputChange() {
                 "var alias;",
                 "var module$exports$C = class {",
                 "  method1() {",
-                "    return alias.staticPropOnC;",
+                "    return module$exports$C$staticPropOnC;",
                 "  }",
                 "  method2() {",
-                "    return alias.staticPropOnAlias;",
+                "    return module$exports$C$staticPropOnAlias;",
                 "  }",
-                "}",
-                "alias = module$exports$C;",
+                "};",
+                "var module$exports$C$staticPropOnAlias;",
+                "alias = null;",
                 "(() => {",
-                "  alias.staticPropOnAlias = 1",
+                "  module$exports$C$staticPropOnAlias = 1;",
                 "})();",
-                // TODO : b/299055739 - bad collapse
                 "var module$exports$C$staticPropOnC = 2;",
-                "",
                 "")));
   }
 

test/com/google/javascript/jscomp/integration/ES2021IntegrationTest.java

@@ -133,8 +133,12 @@ public void logicalAssignmentPropertyReferenceNotTranspiledOutput1() {
         options,
         lines(
             "const foo = {}", //
-            "foo.x &&= 'something';"),
-        lines("let a; (a = {}).a && (a.a = 'something')"));
+            "foo.x &&= 'something';",
+            "alert(foo.x);"),
+        lines(
+            "var a;", //
+            "a &&= 'something';",
+            "alert(a);"));
   }
 
   @Test
@@ -281,10 +285,12 @@ public void logicalAsssignmentsPropertyReferenceCastType_supportedOnlyWithoutTra
         lines(
             "const obj = {};", //
             "obj.baa = true;",
-            "/** @type {?} */ (obj.baa) &&= 5"),
+            "/** @type {?} */ (obj.baa) &&= 5;",
+            "alert(obj.baa);"),
         lines(
-            "const a = {a:!0}", //
-            "a.a && (a.a = 5)"));
+            "var a = !0;", //
+            "a = 5;",
+            "alert(a);"));
   }
 
   @Test
@@ -322,10 +328,12 @@ public void logicalAsssignmentsPropertyReferenceCastType_supportedWithTranspilat
         lines(
             "const obj = {};", //
             "obj.baa = true;",
-            "/** @type {?} */ (obj.baa) &&= 5"),
+            "/** @type {?} */ (obj.baa) &&= 5",
+            "alert(obj.baa);"),
         lines(
-            "const a = {a:!0}", //
-            "a.a && (a.a = 5)"));
+            "var a = !0;", //
+            "a = 5;",
+            "alert(a);"));
   }
 
   @Test