Cache the class path Symbol on the class

Additional improvements here:

* rubyName no longer reverses the parents list before iterating.
* Factored out common path string-building logic.
* Smaller initial parents list (more than 5 parents is very rare).

core/src/main/java/org/jruby/RubyModule.java

@@ -654,8 +654,7 @@ public void setBaseName(String name) {
      * @return The generated class name
      */
     public String getName() {
-        if (cachedName != null) return cachedName;
-        return calculateName();
+        return cachedName != null ? cachedName : calculateName();
     }
 
     /**
@@ -670,6 +669,24 @@ public RubyString rubyName() {
         return cachedRubyName != null ? cachedRubyName : calculateRubyName();
     }
 
+    /**
+     * Generate a fully-qualified class name or a #-style name as a Symbol. If any element of the path is anonymous,
+     * returns null.
+     *
+     * @return a properly encoded non-anonymous class path as a Symbol, or null.
+     */
+    public RubySymbol symbolName() {
+        IRubyObject symbolName = cachedSymbolName;
+
+        if (symbolName == null) {
+            cachedSymbolName = symbolName = calculateSymbolName();
+        }
+
+        if (symbolName == UNDEF) return null;
+
+        return (RubySymbol) symbolName;
+    }
+
     public RubyString rubyBaseName() {
         String baseName = getBaseName();
 
@@ -691,16 +708,18 @@ private RubyString calculateRubyName() {
 
         if (getBaseName() == null) return calculateAnonymousRubyName(); // no name...anonymous!
 
+        Ruby runtime = getRuntime();
+
         if (usingTemporaryName()) { // temporary name
-            cachedRubyName = getRuntime().newSymbol(baseName).toRubyString(getRuntime().getCurrentContext());
+            cachedRubyName = runtime.newSymbol(baseName).toRubyString(getRuntime().getCurrentContext());
             return cachedRubyName;
         }
-
-        Ruby runtime = getRuntime();
+
         RubyClass objectClass = runtime.getObject();
-        List<RubyString> parents = new ArrayList<>();
-        for (RubyModule p = getParent(); p != null && p != objectClass; p = p.getParent()) {
-            if (p == this) break;  // Break out of cyclic namespaces like C::A = C2; C2::A = C (jruby/jruby#2314)
+        List<RubyString> parents = new ArrayList<>(5);
+        for (RubyModule p = getParent();
+             p != null && p != objectClass && p != this; // Break out of cyclic namespaces like C::A = C2; C2::A = C (jruby/jruby#2314)
+             p = p.getParent()) {
 
             RubyString name = p.rubyBaseName();
 
@@ -717,21 +736,60 @@ private RubyString calculateRubyName() {
             parents.add(name);
         }
 
-        Collections.reverse(parents);
+        RubyString fullName = buildPathString(runtime, parents);
+
+        if (cache) cachedRubyName = fullName;
 
+        return fullName;
+    }
+
+    /**
+     * Calculate the module's name path as a Symbol. If any element in the path is anonymous, this will return null.
+     *
+     * Used primarily by Marshal.dump for class names.
+     *
+     * @return a non-anonymous class path as a Symbol, or null
+     */
+    private IRubyObject calculateSymbolName() {
+        if (getBaseName() == null) return UNDEF;
+
+        Ruby runtime = getRuntime();
+
+        if (usingTemporaryName()) { // temporary name
+            return runtime.newSymbol(baseName);
+        }
+
+        RubyClass objectClass = runtime.getObject();
+        List<RubyString> parents = new ArrayList<>(5);
+        for (RubyModule p = getParent();
+             p != null && p != objectClass && p != this; // Break out of cyclic namespaces like C::A = C2; C2::A = C (jruby/jruby#2314)
+             p = p.getParent()) {
+
+            RubyString name = p.rubyBaseName();
+
+            if (name == null) {
+                return UNDEF;
+            }
+
+            parents.add(name);
+        }
+
+        RubyString fullName = buildPathString(runtime, parents);
+
+        return fullName.intern();
+    }
+
+    private RubyString buildPathString(Ruby runtime, List<RubyString> parents) {
         RubyString colons = runtime.newString("::");
         RubyString fullName = runtime.newString();       // newString creates empty ByteList which ends up as
         fullName.setEncoding(USASCIIEncoding.INSTANCE);  // ASCII-8BIT.  8BIT is unfriendly to string concats.
-        for (RubyString parent:  parents) {
-            RubyString rubyString = fullName.catWithCodeRange(parent);
+        for (int i = parents.size() - 1; i >= 0; i--) {
+            RubyString rubyString = fullName.catWithCodeRange(parents.get(i));
             rubyString.catWithCodeRange(colons);
         }
         fullName.catWithCodeRange(rubyBaseName());
 
         fullName.setFrozen(true);
-
-        if (cache) cachedRubyName = fullName;
-
         return fullName;
     }
 
@@ -5779,6 +5837,7 @@ public IRubyObject initialize(Block block) {
      */
     private transient String cachedName;
     private transient RubyString cachedRubyName;
+    private transient IRubyObject cachedSymbolName;
 
     @SuppressWarnings("unchecked")
     private volatile Map<String, ConstantEntry> constants = Collections.EMPTY_MAP;

core/src/main/java/org/jruby/runtime/marshal/NewMarshal.java

@@ -278,25 +278,27 @@ private void dumpType(ThreadContext context, RubyOutputStream out, IRubyObject v
         }
     }
 
-    public static String getPathFromClass(ThreadContext context, RubyModule clazz) {
+    public static RubySymbol getPathFromClass(ThreadContext context, RubyModule clazz) {
         Ruby runtime = context.runtime;
-        RubyString path = clazz.rubyName();
+        RubySymbol pathSym = clazz.symbolName();
 
-        if (path.charAt(0) == '#') {
+        if (pathSym == null) {
             String type = clazz.isClass() ? "class" : "module";
             throw typeError(context, str(runtime, "can't dump anonymous " + type + " ", types(runtime, clazz)));
         }
+
+        String path = pathSym.idString();
 
         RubyModule real = clazz.isModule() ? clazz : ((RubyClass)clazz).getRealClass();
 
         // FIXME: This is weird why we do this.  rubyName should produce something which can be referred so what example
         // will this fail on?  If there is a failing case then passing asJavaString may be broken since it will not be
         // a properly encoded string.  If this is an issue we should make a clazz.IdPath where all segments are returned
         // by their id names.
-        if (runtime.getClassFromPath(path.asJavaString()) != real) {
+        if (runtime.getClassFromPath(path) != real) {
             throw typeError(context, str(runtime, types(runtime, clazz), " can't be referred"));
         }
-        return path.asJavaString();
+        return pathSym;
     }
 
     private void writeObjectData(ThreadContext context, RubyOutputStream out, IRubyObject value) {