Refactor SymbolTable.

* Remove reference to non-existing "UnderflowException" class.
* Introduce "NoActiveScopeException" class.
* Add phpunit tests for SymbolTable.

src/main/php/PDepend/Source/Language/PHP/AbstractPHPParser.php

@@ -61,6 +61,7 @@
 use PDepend\Source\Builder\Builder;
 use PDepend\Source\Parser\InvalidStateException;
 use PDepend\Source\Parser\MissingValueException;
+use PDepend\Source\Parser\NoActiveScopeException;
 use PDepend\Source\Parser\TokenStreamEndException;
 use PDepend\Source\Parser\UnexpectedTokenException;
 use PDepend\Source\Tokenizer\Token;
@@ -420,6 +421,8 @@ protected function setUpEnvironment()
     /**
      * Restores the parser environment back.
      *
+     * @throws NoActiveScopeException
+     *
      * @return void
      * @since 0.9.12
      */
@@ -5808,6 +5811,8 @@ private function parseBoundVariables(\PDepend\Source\AST\ASTClosure $closure)
      * PDepend\Source\Parser::parse();
      * </code>
      *
+     * @throws NoActiveScopeException
+     *
      * @return string
      * @link   http://php.net/manual/en/language.namespaces.importing.php
      */
@@ -5905,6 +5910,8 @@ private function parseQualifiedNameRaw()
     /**
      * This method parses a PHP 5.3 namespace declaration.
      *
+     * @throws NoActiveScopeException
+     *
      * @return void
      * @since 0.9.5
      */
@@ -5989,6 +5996,8 @@ protected function parseUseDeclarations()
      * This method parses a single use declaration and adds a mapping between
      * short name and full qualified name to the use symbol table.
      *
+     * @throws NoActiveScopeException
+     *
      * @return void
      * @since 0.9.5
      */

src/main/php/PDepend/Source/Parser/NoActiveScopeException.php

@@ -0,0 +1,58 @@
+<?php
+/**
+ * This file is part of PDepend.
+ *
+ * PHP Version 5
+ *
+ * Copyright (c) 2008-2015, Manuel Pichler <mapi@pdepend.org>.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ *   * Redistributions of source code must retain the above copyright
+ *     notice, this list of conditions and the following disclaimer.
+ *
+ *   * Redistributions in binary form must reproduce the above copyright
+ *     notice, this list of conditions and the following disclaimer in
+ *     the documentation and/or other materials provided with the
+ *     distribution.
+ *
+ *   * Neither the name of Manuel Pichler nor the names of his
+ *     contributors may be used to endorse or promote products derived
+ *     from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
+ * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ *
+ * @copyright 2008-2015 Manuel Pichler. All rights reserved.
+ * @license http://www.opensource.org/licenses/bsd-license.php BSD License
+ */
+
+namespace PDepend\Source\Parser;
+
+/**
+ * This type of exception is thrown when an operation is performed
+ * on a symbol table and there is no active scope.
+ */
+class NoActiveScopeException extends ParserException
+{
+    /**
+     * Constructs a new no active scope exception.
+     */
+    public function __construct()
+    {
+        parent::__construct('No active scope in symbol table.');
+    }
+}

src/main/php/PDepend/Source/Parser/SymbolTable.php

@@ -76,44 +76,51 @@ public function createScope()
     }
 
     /**
-     * This method destorys the top most scope.
+     * This method destroys the top most scope.
+     *
+     * @throws NoActiveScopeException
      *
      * @return void
      */
     public function destroyScope()
     {
-        // Remove scope from stack
-        array_pop($this->scopeStack);
+        $this->ensureActiveScopeExists();
+
+        // Destroy current active scope
+        $this->scope = null;
 
-        // Update current scope to latest in stack
-        $this->scope = end($this->scopeStack);
+        // Try to restore previously active scope
+        if (count($this->scopeStack) > 0) {
+            $this->scope = array_pop($this->scopeStack);
+        }
     }
 
     /**
      * Adds a new value to the top most scope.
      *
      * @param  string $key   The key of this scope value.
      * @param  mixed  $value A new scope value.
+     *
+     * @throws NoActiveScopeException
+     *
      * @return void
      */
     public function add($key, $value)
     {
-        if (is_array($this->scope) === false) {
-            throw new UnderflowException('No active scope.');
-        }
-        $this->scope[strtolower($key)] = $value;
+        $this->ensureActiveScopeExists();
+        $this->scope[$this->normalizeKey($key)] = $value;
     }
 
     /**
      * Resets the current scope
      *
+     * @throws NoActiveScopeException
+     *
      * @return void
      */
     public function resetScope()
     {
-        if (is_array($this->scope) === false) {
-            throw new UnderflowException('No active scope.');
-        }
+        $this->ensureActiveScopeExists();
         $this->scope = array();
     }
 
@@ -122,19 +129,47 @@ public function resetScope()
      * exists in the current scope. The returned value will <b>null</b> if no
      * value exists for the given key.
      *
-     * @param  string $key The key for a searched scope value.
+     * @param string $key The key for a searched scope value.
+     *
+     * @throws NoActiveScopeException
+     *
      * @return mixed
      */
     public function lookup($key)
     {
-        if (is_array($this->scope) === false) {
-            throw new UnderflowException('No active scope.');
-        }
+        $this->ensureActiveScopeExists();
+
+        $normalizedKey = $this->normalizeKey($key);
+
+        return isset($this->scope[$normalizedKey])
+            ? $this->scope[$normalizedKey]
+            : null;
+    }
 
-        $key = strtolower($key);
-        if (isset($this->scope[$key])) {
-            return $this->scope[$key];
+    /**
+     * Checks if there is an active scope.
+     *
+     * @throws NoActiveScopeException if no active scope exists.
+     *
+     * @return void
+     */
+    private function ensureActiveScopeExists()
+    {
+        if (null === $this->scope) {
+            throw new NoActiveScopeException();
         }
-        return null;
+    }
+
+    /**
+     * Normalizes the <code>$key</code>, so it's the same for
+     * <code>add()</code> and <code>lookup()</code> operations.
+     *
+     * @param string $key
+     *
+     * @return string normalized key
+     */
+    private function normalizeKey($key)
+    {
+        return strtolower($key);
     }
 }