Allow broadening visibility when overriding JS class methods.

PiperOrigin-RevId: 566739971

Author: shicks

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

@@ -869,15 +869,14 @@ private void checkPropertyOverrideVisibility(
 
     // Check that:
     // (a) the property *can* be overridden,
-    // (b) the visibility of the override is the same as the
+    // (b) the visibility of the override is the same as (or broader than) the
     //     visibility of the original property,
     // (c) the visibility is explicitly redeclared if the override is in
     //     a file with default visibility in the @fileoverview block.
     if (visibility == Visibility.PRIVATE && !sameInput) {
       compiler.report(
           JSError.make(propRef.getSourceNode(), PRIVATE_OVERRIDE, objectType.toString()));
-    } else if (overridingVisibility != Visibility.INHERITED
-        && overridingVisibility != visibility
+    } else if (!canOverrideVisibility(visibility, overridingVisibility)
         && fileOverviewVisibility == null) {
       compiler.report(
           JSError.make(
@@ -889,6 +888,14 @@ private void checkPropertyOverrideVisibility(
     }
   }
 
+  private static boolean canOverrideVisibility(
+      Visibility superclassVisibility, Visibility subclassVisibility) {
+    // This allows INHERITED to override anything, PUBLIC to override anything (except INHERITED),
+    // and PROTECTED to override anything (except PUBLIC or INHERITED). PRIVATE was already handled
+    // in a previous check, leaving PACKAGE as the lowest visibility.
+    return superclassVisibility.compareTo(subclassVisibility) <= 0;
+  }
+
   private void checkPropertyAccessVisibility(
       PropertyReference propRef,
       Visibility visibility,

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

@@ -3005,6 +3005,22 @@ public void testGoodOverrideOfProtectedProperty() {
                 "}")));
   }
 
+  @Test
+  public void testPublicOverrideOfProtectedProperty() {
+    test(
+        srcs(
+            lines(
+                "class Foo {", //
+                "  /** @protected */",
+                "  bar() {}",
+                "}"),
+            lines(
+                "class SubFoo extends Foo {", //
+                "  /** @public */",
+                "  bar() {}",
+                "}")));
+  }
+
   @Test
   public void testBadOverrideOfProtectedProperty() {
     test(
@@ -3022,6 +3038,22 @@ public void testBadOverrideOfProtectedProperty() {
         error(VISIBILITY_MISMATCH));
   }
 
+  @Test
+  public void testProtectedOverrideOfPackageProperty() {
+    test(
+        srcs(
+            lines(
+                "class Foo {", //
+                "  /** @package */",
+                "  bar() {}",
+                "}"),
+            lines(
+                "class SubFoo extends Foo {", //
+                "  /** @protected */",
+                "  bar() {}",
+                "}")));
+  }
+
   @Test
   public void testBadOverrideOfPrivateProperty() {
     test(