feat: Address Bar Query String Friendly (AQF) syntax

This is the initial AQF implementation. The vast majority of
JsonUrlGrammar has been pulled out into AbstractGrammar.java so it can
be shared by two implementations -- the base syntax and the AQF syntax.

Author: dmaccormack

config/checkstyle.xml

@@ -216,6 +216,7 @@ Checkstyle configuration that checks the Google coding conventions from Google J
       <property name="tokens" value="SINGLE_LINE_COMMENT, BLOCK_COMMENT_BEGIN"/>
     </module>
     <module name="SuppressionCommentFilter"/>
+    <module name="SuppressWarningsHolder" />
   </module>
   <module name="BeforeExecutionExclusionFileFilter">
     <property name="fileNamePattern" value="module\-info\.java$"/>
@@ -228,4 +229,5 @@ Checkstyle configuration that checks the Google coding conventions from Google J
     <property name="ignorePattern" value="^package.*|^import.*|a href|href|http://|https://|ftp://"/>
     <property name="max" value="100"/>
   </module>
+  <module name="SuppressWarningsFilter" />
 </module>

module/jsonurl-core/src/main/java/org/jsonurl/JsonUrlOption.java

@@ -43,6 +43,7 @@ public enum JsonUrlOption {
     /**
      * The implied-string-literals option.
      * If this option is enabled then all literals are assumed to be strings.
+     * @see #enableImpliedStringLiterals(Set)
      * @see <a href="https://github.com/jsonurl/specification/#292-implied-objects"
      * >JSON&#x2192;URL specification, section 2.9.2</a>
      */
@@ -76,7 +77,12 @@ public enum JsonUrlOption {
      * If this option is enabled then {@code null} values in the
      * input or output will be replaced with an empty string.
      */
-    COERCE_NULL_TO_EMPTY_STRING;
+    COERCE_NULL_TO_EMPTY_STRING,
+
+    /**
+     * Address bar query string friendly.
+     */
+    AQF;
 
     /**
      * Create an empty set of options. This is just a convenience wrapper
@@ -93,7 +99,7 @@ public static final Set<JsonUrlOption> newSet() {
     public static final Set<JsonUrlOption> newSet(
             JsonUrlOption first,
             JsonUrlOption...rest) {
-        return EnumSet.of(first, rest);
+        return first == null ? null : EnumSet.of(first, rest);
     }
 
     /**
@@ -218,4 +224,16 @@ public static final boolean optionCoerceNullToEmptyString(
         return options != null
                 && options.contains(COERCE_NULL_TO_EMPTY_STRING);
     }
+
+    /**
+     * Test if the {@link #AQF} option is enabled,
+     * supplying the default value if necessary.
+     * @param options a valid Set or {@code null}.
+     */
+    @SuppressWarnings("checkstyle:AbbreviationAsWordInName")
+    public static final boolean optionAQF(
+            Set<JsonUrlOption> options) {
+        return options != null && options.contains(AQF);
+    }
+
 }

module/jsonurl-core/src/main/java/org/jsonurl/SyntaxException.java

@@ -39,6 +39,8 @@ public enum Message {
         MSG_BAD_PCT_ENC("invalid percent-encoded sequence"),
         /** Invalid encoded UTF-8 sequence. */
         MSG_BAD_UTF8("invalid encoded UTF-8 sequence"),
+        /** Invalid escape sequence. */
+        MSG_BAD_ESCAPE("invalid escape sequence"),
         /** Text missing. */
         MSG_NO_TEXT("text missing"),
         /** Expected literal value. */

module/jsonurl-core/src/main/java/org/jsonurl/ValueType.java

@@ -30,43 +30,27 @@ public enum ValueType {
     /**
      * A {@code null} literal.
      */
-    NULL(null),
+    NULL,
     /**
      * A {@code true} or {@code false} literal.
      */
-    BOOLEAN(null),
+    BOOLEAN,
     /**
      * A number literal (e.g. 1, 1.2, 1e3, etc).
      */
-    NUMBER(null),
+    NUMBER,
     /**
      * A string literal.
      */
-    STRING(null),
+    STRING,
     /**
      * An array.
      */
-    ARRAY(CompositeType.ARRAY),
+    ARRAY,
     /**
      * An object.
      */
-    OBJECT(CompositeType.OBJECT);
-
-    /**
-     * see {@link #isPrimitive()}.
-     */
-    private final CompositeType ctype;
-
-    ValueType(CompositeType ctype) {
-        this.ctype = ctype;
-    }
-
-    /**
-     * Get the {@link CompositeType} for this ValueType.
-     */
-    public CompositeType getCompositeType() {
-        return ctype;
-    }
+    OBJECT;
 
     /**
      * Test if the given EnumSet contains a composite value.