src/jdk.compiler/share/classes/com/sun/tools/javac/comp/Check.java

*** 27,36 ****
--- 27,37 ----
  
  import java.util.*;
  import java.util.function.Supplier;
  
  import javax.lang.model.element.ElementKind;
+ import javax.lang.model.element.NestingKind;
  import javax.tools.JavaFileManager;
  
  import com.sun.tools.javac.code.*;
  import com.sun.tools.javac.code.Attribute.Compound;
  import com.sun.tools.javac.code.Directive.ExportsDirective;
*** 3825,3834 ****
--- 3826,3888 ----
              log.warning(pos,
                          Warnings.AuxiliaryClassAccessedFromOutsideOfItsSourceFile(c, c.sourcefile));
          }
      }
  
+     /**
+      * Check for a default constructor in an exported package.
+      */
+     void checkDefaultConstructor(ClassSymbol c, DiagnosticPosition pos) {
+         if (lint.isEnabled(LintCategory.MISSING_DECLARED_CTOR) &&
+             ((c.flags() & (ENUM | RECORD)) == 0) &&
+             !c.isAnonymous() &&
+             ((c.flags() & PUBLIC) != 0) &&
+             Feature.MODULES.allowedInSource(source)) {
+             NestingKind nestingKind = c.getNestingKind();
+             switch (nestingKind) {
+                 case ANONYMOUS,
+                      LOCAL -> {return;}
+                 case TOP_LEVEL -> {;} // No additional checks needed
+                 case MEMBER -> {
+                     // For nested member classes, all the enclosing
+                     // classes must be public.
+                     Symbol owner = c.owner;
+                     while (owner != null && owner.kind == TYP) {
+                         if ((owner.flags() & PUBLIC) == 0)
+                             return;
+                         owner = owner.owner;
+                     }
+                 }
+             }
+ 
+             // Only check classes in named packages exported by its module
+             PackageSymbol pkg = c.packge();
+             if (!pkg.isUnnamed()) {
+                 ModuleSymbol modle = pkg.modle;
+                 for (ExportsDirective exportDir : modle.exports) {
+                     // Report warning only if the containing
+                     // package is unconditionally exported
+                     if (exportDir.packge.equals(pkg)) {
+                         if (exportDir.modules == null || exportDir.modules.isEmpty()) {
+                             // Warning may be suppressed by
+                             // annotations; check again for being
+                             // enabled in the deferred context.
+                             deferredLintHandler.report(() -> {
+                                 if (lint.isEnabled(LintCategory.MISSING_DECLARED_CTOR))
+                                    log.warning(LintCategory.MISSING_DECLARED_CTOR,
+                                                pos, Warnings.MissingDeclaredCtor(c, pkg, modle));
+                                                        });
+                         } else {
+                             return;
+                         }
+                     }
+                 }
+             }
+         }
+         return;
+     }
+ 
      private class ConversionWarner extends Warner {
          final String uncheckedKey;
          final Type found;
          final Type expected;
          public ConversionWarner(DiagnosticPosition pos, String uncheckedKey, Type found, Type expected) {