comparison vendor/symfony/yaml/Parser.php @ 0:c75dbcec494b

Initial commit from drush-created site

+<?php
+
+/*
+ * This file is part of the Symfony package.
+ *
+ * (c) Fabien Potencier <[e-mail]>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Symfony\Component\Yaml;
+
+use Symfony\Component\Yaml\Exception\ParseException;
+use Symfony\Component\Yaml\Tag\TaggedValue;
+
+/**
+ * Parser parses YAML strings to convert them to PHP arrays.
+ *
+ * @author Fabien Potencier <[e-mail]>
+ *
+ * @final since version 3.4
+ */
+class Parser
+{
+    const TAG_PATTERN = '(?P<tag>![\w!.\/:-]+)';
+    const BLOCK_SCALAR_HEADER_PATTERN = '(?P<separator>\||>)(?P<modifiers>\+|\-|\d+|\+\d+|\-\d+|\d+\+|\d+\-)?(?P<comments> +#.*)?';
+
+    private $filename;
+    private $offset = 0;
+    private $totalNumberOfLines;
+    private $lines = array();
+    private $currentLineNb = -1;
+    private $currentLine = '';
+    private $refs = array();
+    private $skippedLineNumbers = array();
+    private $locallySkippedLineNumbers = array();
+
+    public function __construct()
+    {
+        if (func_num_args() > 0) {
+            @trigger_error(sprintf('The constructor arguments $offset, $totalNumberOfLines, $skippedLineNumbers of %s are deprecated and will be removed in 4.0', self::class), E_USER_DEPRECATED);
+
+            $this->offset = func_get_arg(0);
+            if (func_num_args() > 1) {
+                $this->totalNumberOfLines = func_get_arg(1);
+            }
+            if (func_num_args() > 2) {
+                $this->skippedLineNumbers = func_get_arg(2);
+            }
+        }
+    }
+
+    /**
+     * Parses a YAML file into a PHP value.
+     *
+     * @param string $filename The path to the YAML file to be parsed
+     * @param int    $flags    A bit field of PARSE_* constants to customize the YAML parser behavior
+     *
+     * @return mixed The YAML converted to a PHP value
+     *
+     * @throws ParseException If the file could not be read or the YAML is not valid
+     */
+    public function parseFile($filename, $flags = 0)
+    {
+        if (!is_file($filename)) {
+            throw new ParseException(sprintf('File "%s" does not exist.', $filename));
+        }
+
+        if (!is_readable($filename)) {
+            throw new ParseException(sprintf('File "%s" cannot be read.', $filename));
+        }
+
+        $this->filename = $filename;
+
+        try {
+            return $this->parse(file_get_contents($filename), $flags);
+        } finally {
+            $this->filename = null;
+        }
+    }
+
+    /**
+     * Parses a YAML string to a PHP value.
+     *
+     * @param string $value A YAML string
+     * @param int    $flags A bit field of PARSE_* constants to customize the YAML parser behavior
+     *
+     * @return mixed A PHP value
+     *
+     * @throws ParseException If the YAML is not valid
+     */
+    public function parse($value, $flags = 0)
+    {
+        if (is_bool($flags)) {
+            @trigger_error('Passing a boolean flag to toggle exception handling is deprecated since Symfony 3.1 and will be removed in 4.0. Use the Yaml::PARSE_EXCEPTION_ON_INVALID_TYPE flag instead.', E_USER_DEPRECATED);
+
+            if ($flags) {
+                $flags = Yaml::PARSE_EXCEPTION_ON_INVALID_TYPE;
+            } else {
+                $flags = 0;
+            }
+        }
+
+        if (func_num_args() >= 3) {
+            @trigger_error('Passing a boolean flag to toggle object support is deprecated since Symfony 3.1 and will be removed in 4.0. Use the Yaml::PARSE_OBJECT flag instead.', E_USER_DEPRECATED);
+
+            if (func_get_arg(2)) {
+                $flags |= Yaml::PARSE_OBJECT;
+            }
+        }
+
+        if (func_num_args() >= 4) {
+            @trigger_error('Passing a boolean flag to toggle object for map support is deprecated since Symfony 3.1 and will be removed in 4.0. Use the Yaml::PARSE_OBJECT_FOR_MAP flag instead.', E_USER_DEPRECATED);
+
+            if (func_get_arg(3)) {
+                $flags |= Yaml::PARSE_OBJECT_FOR_MAP;
+            }
+        }
+
+        if (Yaml::PARSE_KEYS_AS_STRINGS & $flags) {
+            @trigger_error('Using the Yaml::PARSE_KEYS_AS_STRINGS flag is deprecated since Symfony 3.4 as it will be removed in 4.0. Quote your keys when they are evaluable instead.', E_USER_DEPRECATED);
+        }
+
+        if (false === preg_match('//u', $value)) {
+            throw new ParseException('The YAML value does not appear to be valid UTF-8.', -1, null, $this->filename);
+        }
+
+        $this->refs = array();
+
+        $mbEncoding = null;
+        $e = null;
+        $data = null;
+
+        if (2 /* MB_OVERLOAD_STRING */ & (int) ini_get('mbstring.func_overload')) {
+            $mbEncoding = mb_internal_encoding();
+            mb_internal_encoding('UTF-8');
+        }
+
+        try {
+            $data = $this->doParse($value, $flags);
+        } catch (\Exception $e) {
+        } catch (\Throwable $e) {
+        }
+
+        if (null !== $mbEncoding) {
+            mb_internal_encoding($mbEncoding);
+        }
+
+        $this->lines = array();
+        $this->currentLine = '';
+        $this->refs = array();
+        $this->skippedLineNumbers = array();
+        $this->locallySkippedLineNumbers = array();
+
+        if (null !== $e) {
+            throw $e;
+        }
+
+        return $data;
+    }
+
+    private function doParse($value, $flags)
+    {
+        $this->currentLineNb = -1;
+        $this->currentLine = '';
+        $value = $this->cleanup($value);
+        $this->lines = explode("\n", $value);
+        $this->locallySkippedLineNumbers = array();
+
+        if (null === $this->totalNumberOfLines) {
+            $this->totalNumberOfLines = count($this->lines);
+        }
+
+        if (!$this->moveToNextLine()) {
+            return null;
+        }
+
+        $data = array();
+        $context = null;
+        $allowOverwrite = false;
+
+        while ($this->isCurrentLineEmpty()) {
+            if (!$this->moveToNextLine()) {
+                return null;
+            }
+        }
+
+        // Resolves the tag and returns if end of the document
+        if (null !== ($tag = $this->getLineTag($this->currentLine, $flags, false)) && !$this->moveToNextLine()) {
+            return new TaggedValue($tag, '');
+        }
+
+        do {
+            if ($this->isCurrentLineEmpty()) {
+                continue;
+            }
+
+            // tab?
+            if ("\t" === $this->currentLine[0]) {
+                throw new ParseException('A YAML file cannot contain tabs as indentation.', $this->getRealCurrentLineNb() + 1, $this->currentLine, $this->filename);
+            }
+
+            Inline::initialize($flags, $this->getRealCurrentLineNb(), $this->filename);
+
+            $isRef = $mergeNode = false;
+            if (self::preg_match('#^\-((?P<leadspaces>\s+)(?P<value>.+))?$#u', rtrim($this->currentLine), $values)) {
+                if ($context && 'mapping' == $context) {
+                    throw new ParseException('You cannot define a sequence item when in a mapping', $this->getRealCurrentLineNb() + 1, $this->currentLine, $this->filename);
+                }
+                $context = 'sequence';
+
+                if (isset($values['value']) && self::preg_match('#^&(?P<ref>[^ ]+) *(?P<value>.*)#u', $values['value'], $matches)) {
+                    $isRef = $matches['ref'];
+                    $values['value'] = $matches['value'];
+                }
+
+                if (isset($values['value'][1]) && '?' === $values['value'][0] && ' ' === $values['value'][1]) {
+                    @trigger_error($this->getDeprecationMessage('Starting an unquoted string with a question mark followed by a space is deprecated since Symfony 3.3 and will throw \Symfony\Component\Yaml\Exception\ParseException in 4.0.'), E_USER_DEPRECATED);
+                }
+
+                // array
+                if (!isset($values['value']) || '' == trim($values['value'], ' ') || 0 === strpos(ltrim($values['value'], ' '), '#')) {
+                    $data[] = $this->parseBlock($this->getRealCurrentLineNb() + 1, $this->getNextEmbedBlock(null, true), $flags);
+                } elseif (null !== $subTag = $this->getLineTag(ltrim($values['value'], ' '), $flags)) {
+                    $data[] = new TaggedValue(
+                        $subTag,
+                        $this->parseBlock($this->getRealCurrentLineNb() + 1, $this->getNextEmbedBlock(null, true), $flags)
+                    );
+                } else {
+                    if (isset($values['leadspaces'])
+                        && self::preg_match('#^(?P<key>'.Inline::REGEX_QUOTED_STRING.'|[^ \'"\{\[].*?) *\:(\s+(?P<value>.+?))?\s*$#u', $this->trimTag($values['value']), $matches)
+                    ) {
+                        // this is a compact notation element, add to next block and parse
+                        $block = $values['value'];
+                        if ($this->isNextLineIndented()) {
+                            $block .= "\n".$this->getNextEmbedBlock($this->getCurrentLineIndentation() + strlen($values['leadspaces']) + 1);
+                        }
+
+                        $data[] = $this->parseBlock($this->getRealCurrentLineNb(), $block, $flags);
+                    } else {
+                        $data[] = $this->parseValue($values['value'], $flags, $context);
+                    }
+                }
+                if ($isRef) {
+                    $this->refs[$isRef] = end($data);
+                }
+            } elseif (
+                self::preg_match('#^(?P<key>(?:![^\s]++\s++)?(?:'.Inline::REGEX_QUOTED_STRING.'|(?:!?!php/const:)?[^ \'"\[\{!].*?)) *\:(\s++(?P<value>.+))?$#u', rtrim($this->currentLine), $values)
+                && (false === strpos($values['key'], ' #') || in_array($values['key'][0], array('"', "'")))
+            ) {
+                if ($context && 'sequence' == $context) {
+                    throw new ParseException('You cannot define a mapping item when in a sequence', $this->currentLineNb + 1, $this->currentLine, $this->filename);
+                }
+                $context = 'mapping';
+
+                try {
+                    $i = 0;
+                    $evaluateKey = !(Yaml::PARSE_KEYS_AS_STRINGS & $flags);
+
+                    // constants in key will be evaluated anyway
+                    if (isset($values['key'][0]) && '!' === $values['key'][0] && Yaml::PARSE_CONSTANT & $flags) {
+                        $evaluateKey = true;
+                    }
+
+                    $key = Inline::parseScalar($values['key'], 0, null, $i, $evaluateKey);
+                } catch (ParseException $e) {
+                    $e->setParsedLine($this->getRealCurrentLineNb() + 1);
+                    $e->setSnippet($this->currentLine);
+
+                    throw $e;
+                }
+
+                if (!is_string($key) && !is_int($key)) {
+                    $keyType = is_numeric($key) ? 'numeric key' : 'non-string key';
+                    @trigger_error($this->getDeprecationMessage(sprintf('Implicit casting of %s to string is deprecated since Symfony 3.3 and will throw \Symfony\Component\Yaml\Exception\ParseException in 4.0. Quote your evaluable mapping keys instead.', $keyType)), E_USER_DEPRECATED);
+                }
+
+                // Convert float keys to strings, to avoid being converted to integers by PHP
+                if (is_float($key)) {
+                    $key = (string) $key;
+                }
+
+                if ('<<' === $key && (!isset($values['value']) || !self::preg_match('#^&(?P<ref>[^ ]+)#u', $values['value'], $refMatches))) {
+                    $mergeNode = true;
+                    $allowOverwrite = true;
+                    if (isset($values['value'][0]) && '*' === $values['value'][0]) {
+                        $refName = substr(rtrim($values['value']), 1);
+                        if (!array_key_exists($refName, $this->refs)) {
+                            throw new ParseException(sprintf('Reference "%s" does not exist.', $refName), $this->getRealCurrentLineNb() + 1, $this->currentLine, $this->filename);
+                        }
+
+                        $refValue = $this->refs[$refName];
+
+                        if (Yaml::PARSE_OBJECT_FOR_MAP & $flags && $refValue instanceof \stdClass) {
+                            $refValue = (array) $refValue;
+                        }
+
+                        if (!is_array($refValue)) {
+                            throw new ParseException('YAML merge keys used with a scalar value instead of an array.', $this->getRealCurrentLineNb() + 1, $this->currentLine, $this->filename);
+                        }
+
+                        $data += $refValue; // array union
+                    } else {
+                        if (isset($values['value']) && '' !== $values['value']) {
+                            $value = $values['value'];
+                        } else {
+                            $value = $this->getNextEmbedBlock();
+                        }
+                        $parsed = $this->parseBlock($this->getRealCurrentLineNb() + 1, $value, $flags);
+
+                        if (Yaml::PARSE_OBJECT_FOR_MAP & $flags && $parsed instanceof \stdClass) {
+                            $parsed = (array) $parsed;
+                        }
+
+                        if (!is_array($parsed)) {
+                            throw new ParseException('YAML merge keys used with a scalar value instead of an array.', $this->getRealCurrentLineNb() + 1, $this->currentLine, $this->filename);
+                        }
+
+                        if (isset($parsed[0])) {
+                            // If the value associated with the merge key is a sequence, then this sequence is expected to contain mapping nodes
+                            // and each of these nodes is merged in turn according to its order in the sequence. Keys in mapping nodes earlier
+                            // in the sequence override keys specified in later mapping nodes.
+                            foreach ($parsed as $parsedItem) {
+                                if (Yaml::PARSE_OBJECT_FOR_MAP & $flags && $parsedItem instanceof \stdClass) {
+                                    $parsedItem = (array) $parsedItem;
+                                }
+
+                                if (!is_array($parsedItem)) {
+                                    throw new ParseException('Merge items must be arrays.', $this->getRealCurrentLineNb() + 1, $parsedItem, $this->filename);
+                                }
+
+                                $data += $parsedItem; // array union
+                            }
+                        } else {
+                            // If the value associated with the key is a single mapping node, each of its key/value pairs is inserted into the
+                            // current mapping, unless the key already exists in it.
+                            $data += $parsed; // array union
+                        }
+                    }
+                } elseif ('<<' !== $key && isset($values['value']) && self::preg_match('#^&(?P<ref>[^ ]++) *+(?P<value>.*)#u', $values['value'], $matches)) {
+                    $isRef = $matches['ref'];
+                    $values['value'] = $matches['value'];
+                }
+
+                $subTag = null;
+                if ($mergeNode) {
+                    // Merge keys
+                } elseif (!isset($values['value']) || '' === $values['value'] || 0 === strpos($values['value'], '#') || (null !== $subTag = $this->getLineTag($values['value'], $flags)) || '<<' === $key) {
+                    // hash
+                    // if next line is less indented or equal, then it means that the current value is null
+                    if (!$this->isNextLineIndented() && !$this->isNextLineUnIndentedCollection()) {
+                        // Spec: Keys MUST be unique; first one wins.
+                        // But overwriting is allowed when a merge node is used in current block.
+                        if ($allowOverwrite || !isset($data[$key])) {
+                            if (null !== $subTag) {
+                                $data[$key] = new TaggedValue($subTag, '');
+                            } else {
+                                $data[$key] = null;
+                            }
+                        } else {
+                            @trigger_error($this->getDeprecationMessage(sprintf('Duplicate key "%s" detected whilst parsing YAML. Silent handling of duplicate mapping keys in YAML is deprecated since Symfony 3.2 and will throw \Symfony\Component\Yaml\Exception\ParseException in 4.0.', $key)), E_USER_DEPRECATED);
+                        }
+                    } else {
+                        $value = $this->parseBlock($this->getRealCurrentLineNb() + 1, $this->getNextEmbedBlock(), $flags);
+                        if ('<<' === $key) {
+                            $this->refs[$refMatches['ref']] = $value;
+
+                            if (Yaml::PARSE_OBJECT_FOR_MAP & $flags && $value instanceof \stdClass) {
+                                $value = (array) $value;
+                            }
+
+                            $data += $value;
+                        } elseif ($allowOverwrite || !isset($data[$key])) {
+                            // Spec: Keys MUST be unique; first one wins.
+                            // But overwriting is allowed when a merge node is used in current block.
+                            if (null !== $subTag) {
+                                $data[$key] = new TaggedValue($subTag, $value);
+                            } else {
+                                $data[$key] = $value;
+                            }
+                        } else {
+                            @trigger_error($this->getDeprecationMessage(sprintf('Duplicate key "%s" detected whilst parsing YAML. Silent handling of duplicate mapping keys in YAML is deprecated since Symfony 3.2 and will throw \Symfony\Component\Yaml\Exception\ParseException in 4.0.', $key)), E_USER_DEPRECATED);
+                        }
+                    }
+                } else {
+                    $value = $this->parseValue(rtrim($values['value']), $flags, $context);
+                    // Spec: Keys MUST be unique; first one wins.
+                    // But overwriting is allowed when a merge node is used in current block.
+                    if ($allowOverwrite || !isset($data[$key])) {
+                        $data[$key] = $value;
+                    } else {
+                        @trigger_error($this->getDeprecationMessage(sprintf('Duplicate key "%s" detected whilst parsing YAML. Silent handling of duplicate mapping keys in YAML is deprecated since Symfony 3.2 and will throw \Symfony\Component\Yaml\Exception\ParseException in 4.0.', $key)), E_USER_DEPRECATED);
+                    }
+                }
+                if ($isRef) {
+                    $this->refs[$isRef] = $data[$key];
+                }
+            } else {
+                // multiple documents are not supported
+                if ('---' === $this->currentLine) {
+                    throw new ParseException('Multiple documents are not supported.', $this->currentLineNb + 1, $this->currentLine, $this->filename);
+                }
+
+                if ($deprecatedUsage = (isset($this->currentLine[1]) && '?' === $this->currentLine[0] && ' ' === $this->currentLine[1])) {
+                    @trigger_error($this->getDeprecationMessage('Starting an unquoted string with a question mark followed by a space is deprecated since Symfony 3.3 and will throw \Symfony\Component\Yaml\Exception\ParseException in 4.0.'), E_USER_DEPRECATED);
+                }
+
+                // 1-liner optionally followed by newline(s)
+                if (is_string($value) && $this->lines[0] === trim($value)) {
+                    try {
+                        $value = Inline::parse($this->lines[0], $flags, $this->refs);
+                    } catch (ParseException $e) {
+                        $e->setParsedLine($this->getRealCurrentLineNb() + 1);
+                        $e->setSnippet($this->currentLine);
+
+                        throw $e;
+                    }
+
+                    return $value;
+                }
+
+                // try to parse the value as a multi-line string as a last resort
+                if (0 === $this->currentLineNb) {
+                    $previousLineWasNewline = false;
+                    $previousLineWasTerminatedWithBackslash = false;
+                    $value = '';
+
+                    foreach ($this->lines as $line) {
+                        // If the indentation is not consistent at offset 0, it is to be considered as a ParseError
+                        if (0 === $this->offset && !$deprecatedUsage && isset($line[0]) && ' ' === $line[0]) {
+                            throw new ParseException('Unable to parse.', $this->getRealCurrentLineNb() + 1, $this->currentLine, $this->filename);
+                        }
+                        if ('' === trim($line)) {
+                            $value .= "\n";
+                        } elseif (!$previousLineWasNewline && !$previousLineWasTerminatedWithBackslash) {
+                            $value .= ' ';
+                        }
+
+                        if ('' !== trim($line) && '\\' === substr($line, -1)) {
+                            $value .= ltrim(substr($line, 0, -1));
+                        } elseif ('' !== trim($line)) {
+                            $value .= trim($line);
+                        }
+
+                        if ('' === trim($line)) {
+                            $previousLineWasNewline = true;
+                            $previousLineWasTerminatedWithBackslash = false;
+                        } elseif ('\\' === substr($line, -1)) {
+                            $previousLineWasNewline = false;
+                            $previousLineWasTerminatedWithBackslash = true;
+                        } else {
+                            $previousLineWasNewline = false;
+                            $previousLineWasTerminatedWithBackslash = false;
+                        }
+                    }
+
+                    try {
+                        return Inline::parse(trim($value));
+                    } catch (ParseException $e) {
+                        // fall-through to the ParseException thrown below
+                    }
+                }
+
+                throw new ParseException('Unable to parse.', $this->getRealCurrentLineNb() + 1, $this->currentLine, $this->filename);
+            }
+        } while ($this->moveToNextLine());
+
+        if (null !== $tag) {
+            $data = new TaggedValue($tag, $data);
+        }
+
+        if (Yaml::PARSE_OBJECT_FOR_MAP & $flags && !is_object($data) && 'mapping' === $context) {
+            $object = new \stdClass();
+
+            foreach ($data as $key => $value) {
+                $object->$key = $value;
+            }
+
+            $data = $object;
+        }
+
+        return empty($data) ? null : $data;
+    }
+
+    private function parseBlock($offset, $yaml, $flags)
+    {
+        $skippedLineNumbers = $this->skippedLineNumbers;
+
+        foreach ($this->locallySkippedLineNumbers as $lineNumber) {
+            if ($lineNumber < $offset) {
+                continue;
+            }
+
+            $skippedLineNumbers[] = $lineNumber;
+        }
+
+        $parser = new self();
+        $parser->offset = $offset;
+        $parser->totalNumberOfLines = $this->totalNumberOfLines;
+        $parser->skippedLineNumbers = $skippedLineNumbers;
+        $parser->refs = &$this->refs;
+
+        return $parser->doParse($yaml, $flags);
+    }
+
+    /**
+     * Returns the current line number (takes the offset into account).
+     *
+     * @internal
+     *
+     * @return int The current line number
+     */
+    public function getRealCurrentLineNb()
+    {
+        $realCurrentLineNumber = $this->currentLineNb + $this->offset;
+
+        foreach ($this->skippedLineNumbers as $skippedLineNumber) {
+            if ($skippedLineNumber > $realCurrentLineNumber) {
+                break;
+            }
+
+            ++$realCurrentLineNumber;
+        }
+
+        return $realCurrentLineNumber;
+    }
+
+    /**
+     * Returns the current line indentation.
+     *
+     * @return int The current line indentation
+     */
+    private function getCurrentLineIndentation()
+    {
+        return strlen($this->currentLine) - strlen(ltrim($this->currentLine, ' '));
+    }
+
+    /**
+     * Returns the next embed block of YAML.
+     *
+     * @param int  $indentation The indent level at which the block is to be read, or null for default
+     * @param bool $inSequence  True if the enclosing data structure is a sequence
+     *
+     * @return string A YAML string
+     *
+     * @throws ParseException When indentation problem are detected
+     */
+    private function getNextEmbedBlock($indentation = null, $inSequence = false)
+    {
+        $oldLineIndentation = $this->getCurrentLineIndentation();
+        $blockScalarIndentations = array();
+
+        if ($this->isBlockScalarHeader()) {
+            $blockScalarIndentations[] = $oldLineIndentation;
+        }
+
+        if (!$this->moveToNextLine()) {
+            return;
+        }
+
+        if (null === $indentation) {
+            $newIndent = null;
+            $movements = 0;
+
+            do {
+                $EOF = false;
+
+                // empty and comment-like lines do not influence the indentation depth
+                if ($this->isCurrentLineEmpty() || $this->isCurrentLineComment()) {
+                    $EOF = !$this->moveToNextLine();
+
+                    if (!$EOF) {
+                        ++$movements;
+                    }
+                } else {
+                    $newIndent = $this->getCurrentLineIndentation();
+                }
+            } while (!$EOF && null === $newIndent);
+
+            for ($i = 0; $i < $movements; ++$i) {
+                $this->moveToPreviousLine();
+            }
+
+            $unindentedEmbedBlock = $this->isStringUnIndentedCollectionItem();
+
+            if (!$this->isCurrentLineEmpty() && 0 === $newIndent && !$unindentedEmbedBlock) {
+                throw new ParseException('Indentation problem.', $this->getRealCurrentLineNb() + 1, $this->currentLine, $this->filename);
+            }
+        } else {
+            $newIndent = $indentation;
+        }
+
+        $data = array();
+        if ($this->getCurrentLineIndentation() >= $newIndent) {
+            $data[] = substr($this->currentLine, $newIndent);
+        } elseif ($this->isCurrentLineEmpty() || $this->isCurrentLineComment()) {
+            $data[] = $this->currentLine;
+        } else {
+            $this->moveToPreviousLine();
+
+            return;
+        }
+
+        if ($inSequence && $oldLineIndentation === $newIndent && isset($data[0][0]) && '-' === $data[0][0]) {
+            // the previous line contained a dash but no item content, this line is a sequence item with the same indentation
+            // and therefore no nested list or mapping
+            $this->moveToPreviousLine();
+
+            return;
+        }
+
+        $isItUnindentedCollection = $this->isStringUnIndentedCollectionItem();
+
+        if (empty($blockScalarIndentations) && $this->isBlockScalarHeader()) {
+            $blockScalarIndentations[] = $this->getCurrentLineIndentation();
+        }
+
+        $previousLineIndentation = $this->getCurrentLineIndentation();
+
+        while ($this->moveToNextLine()) {
+            $indent = $this->getCurrentLineIndentation();
+
+            // terminate all block scalars that are more indented than the current line
+            if (!empty($blockScalarIndentations) && $indent < $previousLineIndentation && '' !== trim($this->currentLine)) {
+                foreach ($blockScalarIndentations as $key => $blockScalarIndentation) {
+                    if ($blockScalarIndentation >= $indent) {
+                        unset($blockScalarIndentations[$key]);
+                    }
+                }
+            }
+
+            if (empty($blockScalarIndentations) && !$this->isCurrentLineComment() && $this->isBlockScalarHeader()) {
+                $blockScalarIndentations[] = $indent;
+            }
+
+            $previousLineIndentation = $indent;
+
+            if ($isItUnindentedCollection && !$this->isCurrentLineEmpty() && !$this->isStringUnIndentedCollectionItem() && $newIndent === $indent) {
+                $this->moveToPreviousLine();
+                break;
+            }
+
+            if ($this->isCurrentLineBlank()) {
+                $data[] = substr($this->currentLine, $newIndent);
+                continue;
+            }
+
+            if ($indent >= $newIndent) {
+                $data[] = substr($this->currentLine, $newIndent);
+            } elseif ($this->isCurrentLineComment()) {
+                $data[] = $this->currentLine;
+            } elseif (0 == $indent) {
+                $this->moveToPreviousLine();
+
+                break;
+            } else {
+                throw new ParseException('Indentation problem.', $this->getRealCurrentLineNb() + 1, $this->currentLine, $this->filename);
+            }
+        }
+
+        return implode("\n", $data);
+    }
+
+    /**
+     * Moves the parser to the next line.
+     *
+     * @return bool
+     */
+    private function moveToNextLine()
+    {
+        if ($this->currentLineNb >= count($this->lines) - 1) {
+            return false;
+        }
+
+        $this->currentLine = $this->lines[++$this->currentLineNb];
+
+        return true;
+    }
+
+    /**
+     * Moves the parser to the previous line.
+     *
+     * @return bool
+     */
+    private function moveToPreviousLine()
+    {
+        if ($this->currentLineNb < 1) {
+            return false;
+        }
+
+        $this->currentLine = $this->lines[--$this->currentLineNb];
+
+        return true;
+    }
+
+    /**
+     * Parses a YAML value.
+     *
+     * @param string $value   A YAML value
+     * @param int    $flags   A bit field of PARSE_* constants to customize the YAML parser behavior
+     * @param string $context The parser context (either sequence or mapping)
+     *
+     * @return mixed A PHP value
+     *
+     * @throws ParseException When reference does not exist
+     */
+    private function parseValue($value, $flags, $context)
+    {
+        if (0 === strpos($value, '*')) {
+            if (false !== $pos = strpos($value, '#')) {
+                $value = substr($value, 1, $pos - 2);
+            } else {
+                $value = substr($value, 1);
+            }
+
+            if (!array_key_exists($value, $this->refs)) {
+                throw new ParseException(sprintf('Reference "%s" does not exist.', $value), $this->currentLineNb + 1, $this->currentLine, $this->filename);
+            }
+
+            return $this->refs[$value];
+        }
+
+        if (self::preg_match('/^(?:'.self::TAG_PATTERN.' +)?'.self::BLOCK_SCALAR_HEADER_PATTERN.'$/', $value, $matches)) {
+            $modifiers = isset($matches['modifiers']) ? $matches['modifiers'] : '';
+
+            $data = $this->parseBlockScalar($matches['separator'], preg_replace('#\d+#', '', $modifiers), (int) abs($modifiers));
+
+            if ('' !== $matches['tag']) {
+                if ('!!binary' === $matches['tag']) {
+                    return Inline::evaluateBinaryScalar($data);
+                } elseif ('tagged' === $matches['tag']) {
+                    return new TaggedValue(substr($matches['tag'], 1), $data);
+                } elseif ('!' !== $matches['tag']) {
+                    @trigger_error($this->getDeprecationMessage(sprintf('Using the custom tag "%s" for the value "%s" is deprecated since Symfony 3.3. It will be replaced by an instance of %s in 4.0.', $matches['tag'], $data, TaggedValue::class)), E_USER_DEPRECATED);
+                }
+            }
+
+            return $data;
+        }
+
+        try {
+            $quotation = '' !== $value && ('"' === $value[0] || "'" === $value[0]) ? $value[0] : null;
+
+            // do not take following lines into account when the current line is a quoted single line value
+            if (null !== $quotation && self::preg_match('/^'.$quotation.'.*'.$quotation.'(\s*#.*)?$/', $value)) {
+                return Inline::parse($value, $flags, $this->refs);
+            }
+
+            $lines = array();
+
+            while ($this->moveToNextLine()) {
+                // unquoted strings end before the first unindented line
+                if (null === $quotation && 0 === $this->getCurrentLineIndentation()) {
+                    $this->moveToPreviousLine();
+
+                    break;
+                }
+
+                $lines[] = trim($this->currentLine);
+
+                // quoted string values end with a line that is terminated with the quotation character
+                if ('' !== $this->currentLine && substr($this->currentLine, -1) === $quotation) {
+                    break;
+                }
+            }
+
+            for ($i = 0, $linesCount = count($lines), $previousLineBlank = false; $i < $linesCount; ++$i) {
+                if ('' === $lines[$i]) {
+                    $value .= "\n";
+                    $previousLineBlank = true;
+                } elseif ($previousLineBlank) {
+                    $value .= $lines[$i];
+                    $previousLineBlank = false;
+                } else {
+                    $value .= ' '.$lines[$i];
+                    $previousLineBlank = false;
+                }
+            }
+
+            Inline::$parsedLineNumber = $this->getRealCurrentLineNb();
+
+            $parsedValue = Inline::parse($value, $flags, $this->refs);
+
+            if ('mapping' === $context && is_string($parsedValue) && '"' !== $value[0] && "'" !== $value[0] && '[' !== $value[0] && '{' !== $value[0] && '!' !== $value[0] && false !== strpos($parsedValue, ': ')) {
+                throw new ParseException('A colon cannot be used in an unquoted mapping value.', $this->getRealCurrentLineNb() + 1, $value, $this->filename);
+            }
+
+            return $parsedValue;
+        } catch (ParseException $e) {
+            $e->setParsedLine($this->getRealCurrentLineNb() + 1);
+            $e->setSnippet($this->currentLine);
+
+            throw $e;
+        }
+    }
+
+    /**
+     * Parses a block scalar.
+     *
+     * @param string $style       The style indicator that was used to begin this block scalar (| or >)
+     * @param string $chomping    The chomping indicator that was used to begin this block scalar (+ or -)
+     * @param int    $indentation The indentation indicator that was used to begin this block scalar
+     *
+     * @return string The text value
+     */
+    private function parseBlockScalar($style, $chomping = '', $indentation = 0)
+    {
+        $notEOF = $this->moveToNextLine();
+        if (!$notEOF) {
+            return '';
+        }
+
+        $isCurrentLineBlank = $this->isCurrentLineBlank();
+        $blockLines = array();
+
+        // leading blank lines are consumed before determining indentation
+        while ($notEOF && $isCurrentLineBlank) {
+            // newline only if not EOF
+            if ($notEOF = $this->moveToNextLine()) {
+                $blockLines[] = '';
+                $isCurrentLineBlank = $this->isCurrentLineBlank();
+            }
+        }
+
+        // determine indentation if not specified
+        if (0 === $indentation) {
+            if (self::preg_match('/^ +/', $this->currentLine, $matches)) {
+                $indentation = strlen($matches[0]);
+            }
+        }
+
+        if ($indentation > 0) {
+            $pattern = sprintf('/^ {%d}(.*)$/', $indentation);
+
+            while (
+                $notEOF && (
+                    $isCurrentLineBlank ||
+                    self::preg_match($pattern, $this->currentLine, $matches)
+                )
+            ) {
+                if ($isCurrentLineBlank && strlen($this->currentLine) > $indentation) {
+                    $blockLines[] = substr($this->currentLine, $indentation);
+                } elseif ($isCurrentLineBlank) {
+                    $blockLines[] = '';
+                } else {
+                    $blockLines[] = $matches[1];
+                }
+
+                // newline only if not EOF
+                if ($notEOF = $this->moveToNextLine()) {
+                    $isCurrentLineBlank = $this->isCurrentLineBlank();
+                }
+            }
+        } elseif ($notEOF) {
+            $blockLines[] = '';
+        }
+
+        if ($notEOF) {
+            $blockLines[] = '';
+            $this->moveToPreviousLine();
+        } elseif (!$notEOF && !$this->isCurrentLineLastLineInDocument()) {
+            $blockLines[] = '';
+        }
+
+        // folded style
+        if ('>' === $style) {
+            $text = '';
+            $previousLineIndented = false;
+            $previousLineBlank = false;
+
+            for ($i = 0, $blockLinesCount = count($blockLines); $i < $blockLinesCount; ++$i) {
+                if ('' === $blockLines[$i]) {
+                    $text .= "\n";
+                    $previousLineIndented = false;
+                    $previousLineBlank = true;
+                } elseif (' ' === $blockLines[$i][0]) {
+                    $text .= "\n".$blockLines[$i];
+                    $previousLineIndented = true;
+                    $previousLineBlank = false;
+                } elseif ($previousLineIndented) {
+                    $text .= "\n".$blockLines[$i];
+                    $previousLineIndented = false;
+                    $previousLineBlank = false;
+                } elseif ($previousLineBlank || 0 === $i) {
+                    $text .= $blockLines[$i];
+                    $previousLineIndented = false;
+                    $previousLineBlank = false;
+                } else {
+                    $text .= ' '.$blockLines[$i];
+                    $previousLineIndented = false;
+                    $previousLineBlank = false;
+                }
+            }
+        } else {
+            $text = implode("\n", $blockLines);
+        }
+
+        // deal with trailing newlines
+        if ('' === $chomping) {
+            $text = preg_replace('/\n+$/', "\n", $text);
+        } elseif ('-' === $chomping) {
+            $text = preg_replace('/\n+$/', '', $text);
+        }
+
+        return $text;
+    }
+
+    /**
+     * Returns true if the next line is indented.
+     *
+     * @return bool Returns true if the next line is indented, false otherwise
+     */
+    private function isNextLineIndented()
+    {
+        $currentIndentation = $this->getCurrentLineIndentation();
+        $movements = 0;
+
+        do {
+            $EOF = !$this->moveToNextLine();
+
+            if (!$EOF) {
+                ++$movements;
+            }
+        } while (!$EOF && ($this->isCurrentLineEmpty() || $this->isCurrentLineComment()));
+
+        if ($EOF) {
+            return false;
+        }
+
+        $ret = $this->getCurrentLineIndentation() > $currentIndentation;
+
+        for ($i = 0; $i < $movements; ++$i) {
+            $this->moveToPreviousLine();
+        }
+
+        return $ret;
+    }
+
+    /**
+     * Returns true if the current line is blank or if it is a comment line.
+     *
+     * @return bool Returns true if the current line is empty or if it is a comment line, false otherwise
+     */
+    private function isCurrentLineEmpty()
+    {
+        return $this->isCurrentLineBlank() || $this->isCurrentLineComment();
+    }
+
+    /**
+     * Returns true if the current line is blank.
+     *
+     * @return bool Returns true if the current line is blank, false otherwise
+     */
+    private function isCurrentLineBlank()
+    {
+        return '' == trim($this->currentLine, ' ');
+    }
+
+    /**
+     * Returns true if the current line is a comment line.
+     *
+     * @return bool Returns true if the current line is a comment line, false otherwise
+     */
+    private function isCurrentLineComment()
+    {
+        //checking explicitly the first char of the trim is faster than loops or strpos
+        $ltrimmedLine = ltrim($this->currentLine, ' ');
+
+        return '' !== $ltrimmedLine && '#' === $ltrimmedLine[0];
+    }
+
+    private function isCurrentLineLastLineInDocument()
+    {
+        return ($this->offset + $this->currentLineNb) >= ($this->totalNumberOfLines - 1);
+    }
+
+    /**
+     * Cleanups a YAML string to be parsed.
+     *
+     * @param string $value The input YAML string
+     *
+     * @return string A cleaned up YAML string
+     */
+    private function cleanup($value)
+    {
+        $value = str_replace(array("\r\n", "\r"), "\n", $value);
+
+        // strip YAML header
+        $count = 0;
+        $value = preg_replace('#^\%YAML[: ][\d\.]+.*\n#u', '', $value, -1, $count);
+        $this->offset += $count;
+
+        // remove leading comments
+        $trimmedValue = preg_replace('#^(\#.*?\n)+#s', '', $value, -1, $count);
+        if (1 === $count) {
+            // items have been removed, update the offset
+            $this->offset += substr_count($value, "\n") - substr_count($trimmedValue, "\n");
+            $value = $trimmedValue;
+        }
+
+        // remove start of the document marker (---)
+        $trimmedValue = preg_replace('#^\-\-\-.*?\n#s', '', $value, -1, $count);
+        if (1 === $count) {
+            // items have been removed, update the offset
+            $this->offset += substr_count($value, "\n") - substr_count($trimmedValue, "\n");
+            $value = $trimmedValue;
+
+            // remove end of the document marker (...)
+            $value = preg_replace('#\.\.\.\s*$#', '', $value);
+        }
+
+        return $value;
+    }
+
+    /**
+     * Returns true if the next line starts unindented collection.
+     *
+     * @return bool Returns true if the next line starts unindented collection, false otherwise
+     */
+    private function isNextLineUnIndentedCollection()
+    {
+        $currentIndentation = $this->getCurrentLineIndentation();
+        $movements = 0;
+
+        do {
+            $EOF = !$this->moveToNextLine();
+
+            if (!$EOF) {
+                ++$movements;
+            }
+        } while (!$EOF && ($this->isCurrentLineEmpty() || $this->isCurrentLineComment()));
+
+        if ($EOF) {
+            return false;
+        }
+
+        $ret = $this->getCurrentLineIndentation() === $currentIndentation && $this->isStringUnIndentedCollectionItem();
+
+        for ($i = 0; $i < $movements; ++$i) {
+            $this->moveToPreviousLine();
+        }
+
+        return $ret;
+    }
+
+    /**
+     * Returns true if the string is un-indented collection item.
+     *
+     * @return bool Returns true if the string is un-indented collection item, false otherwise
+     */
+    private function isStringUnIndentedCollectionItem()
+    {
+        return '-' === rtrim($this->currentLine) || 0 === strpos($this->currentLine, '- ');
+    }
+
+    /**
+     * Tests whether or not the current line is the header of a block scalar.
+     *
+     * @return bool
+     */
+    private function isBlockScalarHeader()
+    {
+        return (bool) self::preg_match('~'.self::BLOCK_SCALAR_HEADER_PATTERN.'$~', $this->currentLine);
+    }
+
+    /**
+     * A local wrapper for `preg_match` which will throw a ParseException if there
+     * is an internal error in the PCRE engine.
+     *
+     * This avoids us needing to check for "false" every time PCRE is used
+     * in the YAML engine
+     *
+     * @throws ParseException on a PCRE internal error
+     *
+     * @see preg_last_error()
+     *
+     * @internal
+     */
+    public static function preg_match($pattern, $subject, &$matches = null, $flags = 0, $offset = 0)
+    {
+        if (false === $ret = preg_match($pattern, $subject, $matches, $flags, $offset)) {
+            switch (preg_last_error()) {
+                case PREG_INTERNAL_ERROR:
+                    $error = 'Internal PCRE error.';
+                    break;
+                case PREG_BACKTRACK_LIMIT_ERROR:
+                    $error = 'pcre.backtrack_limit reached.';
+                    break;
+                case PREG_RECURSION_LIMIT_ERROR:
+                    $error = 'pcre.recursion_limit reached.';
+                    break;
+                case PREG_BAD_UTF8_ERROR:
+                    $error = 'Malformed UTF-8 data.';
+                    break;
+                case PREG_BAD_UTF8_OFFSET_ERROR:
+                    $error = 'Offset doesn\'t correspond to the begin of a valid UTF-8 code point.';
+                    break;
+                default:
+                    $error = 'Error.';
+            }
+
+            throw new ParseException($error);
+        }
+
+        return $ret;
+    }
+
+    /**
+     * Trim the tag on top of the value.
+     *
+     * Prevent values such as `!foo {quz: bar}` to be considered as
+     * a mapping block.
+     */
+    private function trimTag($value)
+    {
+        if ('!' === $value[0]) {
+            return ltrim(substr($value, 1, strcspn($value, " \r\n", 1)), ' ');
+        }
+
+        return $value;
+    }
+
+    private function getLineTag($value, $flags, $nextLineCheck = true)
+    {
+        if ('' === $value || '!' !== $value[0] || 1 !== self::preg_match('/^'.self::TAG_PATTERN.' *( +#.*)?$/', $value, $matches)) {
+            return;
+        }
+
+        if ($nextLineCheck && !$this->isNextLineIndented()) {
+            return;
+        }
+
+        $tag = substr($matches['tag'], 1);
+
+        // Built-in tags
+        if ($tag && '!' === $tag[0]) {
+            throw new ParseException(sprintf('The built-in tag "!%s" is not implemented.', $tag), $this->getRealCurrentLineNb() + 1, $value, $this->filename);
+        }
+
+        if (Yaml::PARSE_CUSTOM_TAGS & $flags) {
+            return $tag;
+        }
+
+        throw new ParseException(sprintf('Tags support is not enabled. You must use the flag `Yaml::PARSE_CUSTOM_TAGS` to use "%s".', $matches['tag']), $this->getRealCurrentLineNb() + 1, $value, $this->filename);
+    }
+
+    private function getDeprecationMessage($message)
+    {
+        $message = rtrim($message, '.');
+
+        if (null !== $this->filename) {
+            $message .= ' in '.$this->filename;
+        }
+
+        $message .= ' on line '.($this->getRealCurrentLineNb() + 1);
+
+        return $message.'.';
+    }
+}