Implement behavior for public fields with the @nocollapse JsDoc.

CheckJsDoc will now throw `JSC_MISPLACED_ANNOTATION` on fields with a `@nocollapse` that are not static. Field assignments inside constructors with the `@nocollpase` JsDoc present will also throw `JSC_MISPLACED_ANNOTATION`. Unit tests have been added for these additions. This pass puts the team closer to enabling public fields for the compiler.

PiperOrigin-RevId: 554887149

Author: Closure Team

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

@@ -420,14 +420,23 @@ private void validateNoCollapse(Node n, JSDocInfo info) {
     }
     if (NodeUtil.isPrototypePropertyDeclaration(n.getParent())
         || (n.getParent().isClassMembers() && !n.isStaticMember())) {
-      reportMisplaced(n, "nocollapse", "This JSDoc has no effect on prototype properties.");
+      reportMisplaced(
+          n,
+          "nocollapse",
+          "This JSDoc has no effect on prototype properties and non-static fields.");
+    }
+    if (n.isAssign()) {
+      final Node assignee = n.getFirstChild();
+      if (assignee.isQualifiedName()) {
+        final Node rootOfQname = NodeUtil.getRootOfQualifiedName(assignee);
+        if (!rootOfQname.isName()) {
+          reportMisplaced(n, "nocollapse", "This JSDoc has no effect.");
+        }
+      }
     }
   }
 
-  /**
-   * Checks that JSDoc intended for a function is actually attached to a
-   * function.
-   */
+  /** Checks that JSDoc intended for a function is actually attached to a function. */
   private void validateFunctionJsDoc(Node n, JSDocInfo info) {
     if (info == null) {
       return;

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

@@ -122,6 +122,52 @@ public void testInlineJsDocOnDeclaration() {
     testWarning("var /** {x: number} */ {x} = someObj;", CheckJSDoc.MISPLACED_ANNOTATION);
   }
 
+  @Test
+  public void testFieldMisplacedAnnotation() {
+    testWarning(
+        lines(
+            "class Foo {", //
+            "  /** @nocollapse */",
+            "  x = 5;",
+            "}"),
+        CheckJSDoc.MISPLACED_ANNOTATION);
+  }
+
+  @Test
+  public void testStaticFieldNoCollapse() {
+    testSame(
+        lines(
+            "class Bar {", //
+            "  /** @nocollapse */",
+            "  static y = 1",
+            "}"));
+  }
+
+  @Test
+  public void testThisPropertyMisplacedAnnotation() {
+    testWarning(
+        lines(
+            "class Foo {", //
+            "  constructor() {",
+            "    /** @nocollapse */",
+            "    this.x = 4;",
+            "  }",
+            "}"),
+        CheckJSDoc.MISPLACED_ANNOTATION);
+  }
+
+  @Test
+  public void testThisInFunctionMisplacedAnnotation() {
+    testWarning(
+        lines(
+            "/** @constructor */", //
+            "function Bar() {",
+            " /** @nocollapse */",
+            " this.x = 4;",
+            "}"),
+        CheckJSDoc.MISPLACED_ANNOTATION);
+  }
+
   @Test
   public void testInvalidJsDocOnDestructuringDeclaration() {
     // Type annotations are not allowed on any declaration containing >=1 destructuring pattern.