Summary

Update several methods of the utility interface javax/lang/model/util/Elements to be default methods and clarify handling of modules in other existing methods.

Problem

Further examination of the javax.lang.model support for modules revealed a small number of oversights and areas for improvement. These should be fixed.

Solution

Add default methods where appropriate, correct/refine enclosing element of a package when running in a non-module environment.

Specification

--- old/src/java.compiler/share/classes/javax/lang/model/element/Element.java   2017-02-01 12:13:24.828591070 -0800
+++ new/src/java.compiler/share/classes/javax/lang/model/element/Element.java   2017-02-01 12:13:24.728591066 -0800
@@ -139,7 +139,7 @@
      *
      * <li> If this is a {@linkplain
      * PackageElement#getEnclosingElement package}, its module is
-     * returned.
+     * returned if such a module exists. Otherwise, {@code null} is returned.
      *
      * <li> If this is a {@linkplain
      * TypeParameterElement#getEnclosingElement type parameter},
--- old/src/java.compiler/share/classes/javax/lang/model/element/PackageElement.java    2017-02-01 12:13:25.148591081 -0800
+++ new/src/java.compiler/share/classes/javax/lang/model/element/PackageElement.java    2017-02-01 12:13:25.044591078 -0800
@@ -83,9 +83,16 @@
     boolean isUnnamed();
 
     /**
-     * Returns the enclosing module.
+     * Returns the enclosing module if such a module exists; otherwise
+     * returns {@code null}.
      *
-     * @return the enclosing module
+     * One situation where a module does not exist for a package is if
+     * the environment does not include modules, such as an annotation
+     * processing environment configured for a {@linkplain
+     * javax.annotation.processing.ProcessingEnvironment#getSourceVersion
+     * source version} without modules.
+     *
+     * @return the enclosing module or {@code null} if no such module exists
      */
     @Override
     Element getEnclosingElement();
--- old/src/java.compiler/share/classes/javax/lang/model/type/NoType.java       2017-02-01 12:13:25.480591093 -0800
+++ new/src/java.compiler/share/classes/javax/lang/model/type/NoType.java       2017-02-01 12:13:25.380591090 -0800
@@ -34,6 +34,7 @@
  * <ul>
  * <li>{@link TypeKind#VOID VOID} - corresponds to the keyword {@code void}.
  * <li>{@link TypeKind#PACKAGE PACKAGE} - the pseudo-type of a package element.
+ * <li>{@link TypeKind#MODULE MODULE} - the pseudo-type of a module element.
  * <li>{@link TypeKind#NONE NONE} - used in other cases
  *   where no actual type is appropriate; for example, the superclass
  *   of {@code java.lang.Object}.
--- old/src/java.compiler/share/classes/javax/lang/model/util/Elements.java     2017-02-01 12:13:25.784591104 -0800
+++ new/src/java.compiler/share/classes/javax/lang/model/util/Elements.java     2017-02-01 12:13:25.680591100 -0800
@@ -59,12 +59,17 @@
     /**
      * Returns a package given its fully qualified name, as seen from the given module.
      *
+     * @implSpec The default implementation of this method returns
+     * {@code null}.
+     *
      * @param name  fully qualified package name, or an empty string for an unnamed package
      * @param module module relative to which the lookup should happen
      * @return the specified package, or {@code null} if it cannot be found
      * @since 9
      */
-    PackageElement getPackageElement(ModuleElement module, CharSequence name);
+    default PackageElement getPackageElement(ModuleElement module, CharSequence name) {
+        return null;
+    }
 
     /**
      * Returns a type element given its canonical name if the type element is unique in the environment.
@@ -79,12 +84,17 @@
     /**
      * Returns a type element given its canonical name, as seen from the given module.
      *
+     * @implSpec The default implementation of this method returns
+     * {@code null}.
+     *
      * @param name  the canonical name
      * @param module module relative to which the lookup should happen
      * @return the named type element, or {@code null} if it cannot be found
      * @since 9
      */
-    TypeElement getTypeElement(ModuleElement module, CharSequence name);
+    default TypeElement getTypeElement(ModuleElement module, CharSequence name) {
+        return null;
+    }
 
     /**
      * Returns a module element given its fully qualified name.
@@ -95,11 +105,16 @@
      * javax.annotation.processing.ProcessingEnvironment#getSourceVersion
      * source version} without modules.
      *
+     * @implSpec The default implementation of this method returns
+     * {@code null}.
+     *
      * @param name  the name
      * @return the named module element, or {@code null} if it cannot be found
      * @since 9
      */
-    ModuleElement getModuleElement(CharSequence name);
+    default ModuleElement getModuleElement(CharSequence name) {
+        return null;
+    }
 
     /**
      * Returns the values of an annotation's elements, including defaults.
@@ -337,11 +352,16 @@
      * javax.annotation.processing.ProcessingEnvironment#getSourceVersion
      * source version} without modules.
      *
+     * @implSpec The default implementation of this method returns
+     * {@code null}.
+     *
      * @param type the element being examined
      * @return the module of an element
      * @since 9
      */
-    ModuleElement getModuleOf(Element type);
+    default ModuleElement getModuleOf(Element type) {
+        return null;
+    }
 
     /**
      * Returns all members of a type element, whether inherited or