Preprocessor_Hash.php

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<?php
// phpcs:ignore Squiz.Classes.ValidClassName.NotCamelCaps
class Preprocessor_Hash extends Preprocessor {
    protected const CACHE_VERSION = 4;
 
    protected $cacheThreshold;
 
    public function __construct(
        Parser $parser,
        WANObjectCache $wanCache = null,
        array $options = []
    ) {
        parent::__construct( $parser, $wanCache, $options );
 
        $this->cacheThreshold = $options['cacheThreshold'] ?? false;
    }
 
    public function newFrame() {
        return new PPFrame_Hash( $this );
    }
 
    public function newCustomFrame( $args ) {
        return new PPCustomFrame_Hash( $this, $args );
    }
 
    public function newPartNodeArray( $values ) {
        $list = [];
 
        foreach ( $values as $k => $val ) {
            if ( is_int( $k ) ) {
                $store = [ [ 'part', [
                    [ 'name', [ [ '@index', [ $k ] ] ] ],
                    [ 'value', [ strval( $val ) ] ],
                ] ] ];
            } else {
                $store = [ [ 'part', [
                    [ 'name', [ strval( $k ) ] ],
                    '=',
                    [ 'value', [ strval( $val ) ] ],
                ] ] ];
            }
 
            $list[] = new PPNode_Hash_Tree( $store, 0 );
        }
 
        return new PPNode_Hash_Array( $list );
    }
 
    public function preprocessToObj( $text, $flags = 0 ) {
        if ( $this->disableLangConversion ) {
            // Language conversions are globally disabled; implicitly set flag
            $flags |= self::DOM_LANG_CONVERSION_DISABLED;
        }
 
        $domTreeArray = null;
        if (
            $this->cacheThreshold !== false &&
            strlen( $text ) >= $this->cacheThreshold &&
            ( $flags & self::DOM_UNCACHED ) != self::DOM_UNCACHED
        ) {
            $domTreeJson = $this->wanCache->getWithSetCallback(
                $this->wanCache->makeKey( 'preprocess-hash', sha1( $text ), $flags ),
                $this->wanCache::TTL_DAY,
                function () use ( $text, $flags, &$domTreeArray ) {
                    $domTreeArray = $this->buildDomTreeArrayFromText( $text, $flags );
 
                    return json_encode(
                        $domTreeArray,
                        JSON_UNESCAPED_SLASHES | JSON_UNESCAPED_UNICODE
                    );
                },
                [ 'version' => self::CACHE_VERSION, 'segmentable' => true ]
            );
            $domTreeArray ??= json_decode( $domTreeJson );
        }
 
        $domTreeArray ??= $this->buildDomTreeArrayFromText( $text, $flags );
 
        return new PPNode_Hash_Tree( $domTreeArray, 0 );
    }
 
    private function buildDomTreeArrayFromText( $text, $flags ) {
        $forInclusion = ( $flags & self::DOM_FOR_INCLUSION );
        $langConversionDisabled = ( $flags & self::DOM_LANG_CONVERSION_DISABLED );
 
        $xmlishElements = $this->parser->getStripList();
        $xmlishAllowMissingEndTag = [ 'includeonly', 'noinclude', 'onlyinclude' ];
        $enableOnlyinclude = false;
        if ( $forInclusion ) {
            $ignoredTags = [ 'includeonly', '/includeonly' ];
            $ignoredElements = [ 'noinclude' ];
            $xmlishElements[] = 'noinclude';
            if ( str_contains( $text, '<onlyinclude>' )
                && str_contains( $text, '</onlyinclude>' )
            ) {
                $enableOnlyinclude = true;
            }
        } else {
            $ignoredTags = [ 'noinclude', '/noinclude', 'onlyinclude', '/onlyinclude' ];
            $ignoredElements = [ 'includeonly' ];
            $xmlishElements[] = 'includeonly';
        }
        $xmlishRegex = implode( '|', array_merge( $xmlishElements, $ignoredTags ) );
 
        // Use "A" modifier (anchored) instead of "^", because ^ doesn't work with an offset
        $elementsRegex = "~(?:$xmlishRegex)(?=\s|\/>|>)|!--~iA";
 
        $stack = new PPDStack_Hash;
 
        $searchBase = "[{<\n";
        if ( !$langConversionDisabled ) {
            $searchBase .= '-';
        }
 
        // For fast reverse searches
        $revText = strrev( $text );
        $lengthText = strlen( $text );
 
        // Input pointer, starts out pointing to a pseudo-newline before the start
        $i = 0;
        // Current accumulator. See the doc comment for Preprocessor_Hash for the format.
        $accum =& $stack->getAccum();
        // True to find equals signs in arguments
        $findEquals = false;
        // True to take notice of pipe characters
        $findPipe = false;
        $headingIndex = 1;
        // True if $i is inside a possible heading
        $inHeading = false;
        // True if there are no more greater-than (>) signs right of $i
        $noMoreGT = false;
        // Map of tag name => true if there are no more closing tags of given type right of $i
        $noMoreClosingTag = [];
        // True to ignore all input up to the next <onlyinclude>
        $findOnlyinclude = $enableOnlyinclude;
        // Do a line-start run without outputting an LF character
        $fakeLineStart = true;
 
        while ( true ) {
            if ( $findOnlyinclude ) {
                // Ignore all input up to the next <onlyinclude>
                $startPos = strpos( $text, '<onlyinclude>', $i );
                if ( $startPos === false ) {
                    // Ignored section runs to the end
                    $accum[] = [ 'ignore', [ substr( $text, $i ) ] ];
                    break;
                }
                $tagEndPos = $startPos + 13; // past-the-end of <onlyinclude>
                $accum[] = [ 'ignore', [ substr( $text, $i, $tagEndPos - $i ) ] ];
                $i = $tagEndPos;
                $findOnlyinclude = false;
            }
 
            if ( $fakeLineStart ) {
                $found = 'line-start';
                $curChar = '';
            } else {
                # Find next opening brace, closing brace or pipe
                $search = $searchBase;
                if ( $stack->top === false ) {
                    $currentClosing = '';
                } else {
                    $currentClosing = $stack->top->close;
                    $search .= $currentClosing;
                }
                if ( $findPipe ) {
                    $search .= '|';
                }
                if ( $findEquals ) {
                    // First equals will be for the template
                    $search .= '=';
                }
                $rule = null;
                # Output literal section, advance input counter
                $literalLength = strcspn( $text, $search, $i );
                if ( $literalLength > 0 ) {
                    self::addLiteral( $accum, substr( $text, $i, $literalLength ) );
                    $i += $literalLength;
                }
                if ( $i >= $lengthText ) {
                    if ( $currentClosing === "\n" ) {
                        // Do a past-the-end run to finish off the heading
                        $curChar = '';
                        $found = 'line-end';
                    } else {
                        # All done
                        break;
                    }
                } else {
                    $curChar = $curTwoChar = $text[$i];
                    if ( $i + 1 < $lengthText ) {
                        $curTwoChar .= $text[$i + 1];
                    }
                    if ( $curChar === '|' ) {
                        $found = 'pipe';
                    } elseif ( $curChar === '=' ) {
                        $found = 'equals';
                    } elseif ( $curChar === '<' ) {
                        $found = 'angle';
                    } elseif ( $curChar === "\n" ) {
                        if ( $inHeading ) {
                            $found = 'line-end';
                        } else {
                            $found = 'line-start';
                        }
                    } elseif ( $curTwoChar === $currentClosing ) {
                        $found = 'close';
                        $curChar = $curTwoChar;
                    } elseif ( $curChar === $currentClosing ) {
                        $found = 'close';
                    } elseif ( isset( $this->rules[$curTwoChar] ) ) {
                        $curChar = $curTwoChar;
                        $found = 'open';
                        $rule = $this->rules[$curChar];
                    } elseif ( isset( $this->rules[$curChar] ) ) {
                        $found = 'open';
                        $rule = $this->rules[$curChar];
                    } else {
                        # Some versions of PHP have a strcspn which stops on
                        # null characters; ignore these and continue.
                        # We also may get '-' and '}' characters here which
                        # don't match -{ or $currentClosing.  Add these to
                        # output and continue.
                        if ( $curChar === '-' || $curChar === '}' ) {
                            self::addLiteral( $accum, $curChar );
                        }
                        ++$i;
                        continue;
                    }
                }
            }
 
            if ( $found === 'angle' ) {
                // Handle </onlyinclude>
                if ( $enableOnlyinclude
                    && substr_compare( $text, '</onlyinclude>', $i, 14 ) === 0
                ) {
                    $findOnlyinclude = true;
                    continue;
                }
 
                // Determine element name
                if ( !preg_match( $elementsRegex, $text, $matches, 0, $i + 1 ) ) {
                    // Element name missing or not listed
                    self::addLiteral( $accum, '<' );
                    ++$i;
                    continue;
                }
                $name = $matches[0];
                // Handle comments
                if ( $name === '!--' ) {
                    // To avoid leaving blank lines, when a sequence of
                    // space-separated comments is both preceded and followed by
                    // a newline (ignoring spaces), then
                    // trim leading and trailing spaces and the trailing newline.
 
                    // Find the end
                    $endPos = strpos( $text, '-->', $i + 4 );
                    if ( $endPos === false ) {
                        // Unclosed comment in input, runs to end
                        $inner = substr( $text, $i );
                        $accum[] = [ 'comment', [ $inner ] ];
                        $i = $lengthText;
                    } else {
                        // Search backwards for leading whitespace
                        // $wsStart is the first char of the comment (first of the leading space or '<')
                        $wsStart = $i ? ( $i - strspn( $revText, " \t", $lengthText - $i ) ) : 0;
 
                        // $wsEnd will be the char *after* the comment (after last space or the '>' if there's no space)
                        $wsEnd = $endPos + 3; // add length of -->
                        // Search forwards for trailing whitespace
                        $wsEnd += strspn( $text, " \t", $wsEnd );
 
                        // Keep looking forward as long as we're finding more comments on the line
                        $comments = [ [ $wsStart, $wsEnd ] ];
                        while ( substr_compare( $text, '<!--', $wsEnd, 4 ) === 0 ) {
                            $c = strpos( $text, '-->', $wsEnd + 4 );
                            if ( $c === false ) {
                                break;
                            }
                            $c += 3; // add length of -->
                            // Search forwards for trailing whitespace
                            $c += strspn( $text, " \t", $c );
                            $comments[] = [ $wsEnd, $c ];
                            $wsEnd = $c;
                        }
 
                        // Eat the line if possible
                        // TODO: This could theoretically be done if $wsStart === 0, i.e. for comments at
                        // the overall start. That's not how Sanitizer::removeHTMLcomments() did it, but
                        // it's a possible beneficial b/c break.
                        if ( $wsStart > 0 && substr_compare( $text, "\n", $wsStart - 1, 1 ) === 0
                            && substr_compare( $text, "\n", $wsEnd, 1 ) === 0
                        ) {
                            // Remove leading whitespace from the end of the accumulator
                            $wsLength = $i - $wsStart;
                            $endIndex = count( $accum ) - 1;
 
                            if ( $wsLength > 0
                                && $endIndex >= 0
                                && is_string( $accum[$endIndex] )
                                && strspn( $accum[$endIndex], " \t", -$wsLength ) === $wsLength
                            ) {
                                $accum[$endIndex] = substr( $accum[$endIndex], 0, -$wsLength );
                            }
 
                            // Dump all but the last comment to the accumulator
                            // $endPos includes the newline from the if above, want also eat that
                            [ $startPos, $endPos ] = array_pop( $comments );
                            foreach ( $comments as $com ) {
                                [ $cStartPos, $cEndPos ] = $com;
                                // $cEndPos is the next char, no +1 needed to get correct length between start/end
                                $inner = substr( $text, $cStartPos, $cEndPos - $cStartPos );
                                $accum[] = [ 'comment', [ $inner ] ];
                            }
 
                            // Do a line-start run next time to look for headings after the comment
                            $fakeLineStart = true;
                        } else {
                            // No line to eat, just take the comment itself
                            $startPos = $i;
                            $endPos += 2;
                        }
 
                        if ( $stack->top ) {
                            $part = $stack->top->getCurrentPart();
                            if ( $part->commentEnd !== $wsStart - 1 ) {
                                $part->visualEnd = $wsStart;
                            }
                            // Else comments abutting, no change in visual end
                            $part->commentEnd = $endPos;
                        }
                        $i = $endPos + 1;
                        $inner = substr( $text, $startPos, $endPos - $startPos + 1 );
                        $accum[] = [ 'comment', [ $inner ] ];
                    }
                    continue;
                }
                $attrStart = $i + strlen( $name ) + 1;
 
                // Find end of tag
                $tagEndPos = $noMoreGT ? false : strpos( $text, '>', $attrStart );
                if ( $tagEndPos === false ) {
                    // Infinite backtrack
                    // Disable tag search to prevent worst-case O(N^2) performance
                    $noMoreGT = true;
                    self::addLiteral( $accum, '<' );
                    ++$i;
                    continue;
                }
 
                $lowerName = strtolower( $name );
                // Handle ignored tags
                if ( in_array( $lowerName, $ignoredTags ) ) {
                    $accum[] = [ 'ignore', [ substr( $text, $i, $tagEndPos - $i + 1 ) ] ];
                    $i = $tagEndPos + 1;
                    continue;
                }
 
                $tagStartPos = $i;
                if ( $text[$tagEndPos - 1] === '/' ) {
                    // Short end tag
                    $attrEnd = $tagEndPos - 1;
                    $inner = null;
                    $i = $tagEndPos + 1;
                    $close = null;
                } else {
                    $attrEnd = $tagEndPos;
                    // Find closing tag
                    if (
                        !isset( $noMoreClosingTag[$lowerName] ) &&
                        preg_match( "/<\/" . preg_quote( $name, '/' ) . "\s*>/i",
                            $text, $matches, PREG_OFFSET_CAPTURE, $tagEndPos + 1 )
                    ) {
                        [ $close, $closeTagStartPos ] = $matches[0];
                        $inner = substr( $text, $tagEndPos + 1, $closeTagStartPos - $tagEndPos - 1 );
                        $i = $closeTagStartPos + strlen( $close );
                    } else {
                        // No end tag
                        if ( in_array( $name, $xmlishAllowMissingEndTag ) ) {
                            // Let it run out to the end of the text.
                            $inner = substr( $text, $tagEndPos + 1 );
                            $i = $lengthText;
                            $close = null;
                        } else {
                            // Don't match the tag, treat opening tag as literal and resume parsing.
                            $i = $tagEndPos + 1;
                            self::addLiteral( $accum, substr( $text, $tagStartPos, $tagEndPos + 1 - $tagStartPos ) );
                            // Cache results, otherwise we have O(N^2) performance for input like <foo><foo><foo>...
                            $noMoreClosingTag[$lowerName] = true;
                            continue;
                        }
                    }
                }
                // <includeonly> and <noinclude> just become <ignore> tags
                if ( in_array( $lowerName, $ignoredElements ) ) {
                    $accum[] = [ 'ignore', [ substr( $text, $tagStartPos, $i - $tagStartPos ) ] ];
                    continue;
                }
 
                if ( $attrEnd <= $attrStart ) {
                    $attr = '';
                } else {
                    // Note that the attr element contains the whitespace between name and attribute,
                    // this is necessary for precise reconstruction during pre-save transform.
                    $attr = substr( $text, $attrStart, $attrEnd - $attrStart );
                }
 
                $children = [
                    [ 'name', [ $name ] ],
                    [ 'attr', [ $attr ] ],
                ];
                if ( $inner !== null ) {
                    $children[] = [ 'inner', [ $inner ] ];
                }
                if ( $close !== null ) {
                    $children[] = [ 'close', [ $close ] ];
                }
                $accum[] = [ 'ext', $children ];
            } elseif ( $found === 'line-start' ) {
                // Is this the start of a heading?
                // Line break belongs before the heading element in any case
                if ( $fakeLineStart ) {
                    $fakeLineStart = false;
                } else {
                    self::addLiteral( $accum, $curChar );
                    $i++;
                }
 
                // Examine upto 6 characters
                $count = strspn( $text, '=', $i, min( $lengthText, 6 ) );
                if ( $count === 1 && $findEquals ) {
                    // DWIM: This looks kind of like a name/value separator.
                    // Let's let the equals handler have it and break the potential
                    // heading. This is heuristic, but AFAICT the methods for
                    // completely correct disambiguation are very complex.
                } elseif ( $count > 0 ) {
                    $piece = [
                        'open' => "\n",
                        'close' => "\n",
                        'parts' => [ new PPDPart_Hash( str_repeat( '=', $count ) ) ],
                        'startPos' => $i,
                        'count' => $count,
                    ];
                    $stack->push( $piece );
                    $accum =& $stack->getAccum();
                    $stackFlags = $stack->getFlags();
                    if ( isset( $stackFlags['findEquals'] ) ) {
                        $findEquals = $stackFlags['findEquals'];
                    }
                    if ( isset( $stackFlags['findPipe'] ) ) {
                        $findPipe = $stackFlags['findPipe'];
                    }
                    if ( isset( $stackFlags['inHeading'] ) ) {
                        $inHeading = $stackFlags['inHeading'];
                    }
                    $i += $count;
                }
            } elseif ( $found === 'line-end' ) {
                $piece = $stack->top;
                // A heading must be open, otherwise \n wouldn't have been in the search list
                // FIXME: Don't use assert()
                // phpcs:ignore MediaWiki.Usage.ForbiddenFunctions.assert
                assert( $piece->open === "\n" );
                $part = $piece->getCurrentPart();
                // Search back through the input to see if it has a proper close.
                // Do this using the reversed string since the other solutions
                // (end anchor, etc.) are inefficient.
                $wsLength = strspn( $revText, " \t", $lengthText - $i );
                $searchStart = $i - $wsLength;
                if ( $part->commentEnd === $searchStart - 1 ) {
                    // Comment found at line end
                    // Search for equals signs before the comment
                    $searchStart = $part->visualEnd;
                    $searchStart -= strspn( $revText, " \t", $lengthText - $searchStart );
                }
                $equalsLength = strspn( $revText, '=', $lengthText - $searchStart );
                if ( $equalsLength > 0 ) {
                    if ( $searchStart - $equalsLength === $piece->startPos ) {
                        // This is just a single string of equals signs on its own line
                        // Replicate the doHeadings behavior /={count}(.+)={count}/
                        // First find out how many equals signs there really are (don't stop at 6)
                        if ( $equalsLength < 3 ) {
                            $count = 0;
                        } else {
                            $count = min( 6, intval( ( $equalsLength - 1 ) / 2 ) );
                        }
                    } else {
                        $count = min( $equalsLength, $piece->count );
                    }
                    if ( $count > 0 ) {
                        // Normal match, output <h>
                        $element = [ [ 'possible-h',
                            array_merge(
                                [
                                    [ '@level', [ $count ] ],
                                    [ '@i', [ $headingIndex++ ] ]
                                ],
                                $accum
                            )
                        ] ];
                    } else {
                        // Single equals sign on its own line, count=0
                        $element = $accum;
                    }
                } else {
                    // No match, no <h>, just pass down the inner text
                    $element = $accum;
                }
                // Unwind the stack
                $stack->pop();
                $accum =& $stack->getAccum();
                $stackFlags = $stack->getFlags();
                if ( isset( $stackFlags['findEquals'] ) ) {
                    $findEquals = $stackFlags['findEquals'];
                }
                if ( isset( $stackFlags['findPipe'] ) ) {
                    $findPipe = $stackFlags['findPipe'];
                }
                if ( isset( $stackFlags['inHeading'] ) ) {
                    $inHeading = $stackFlags['inHeading'];
                }
 
                // Append the result to the enclosing accumulator
                array_splice( $accum, count( $accum ), 0, $element );
 
                // Note that we do NOT increment the input pointer.
                // This is because the closing linebreak could be the opening linebreak of
                // another heading. Infinite loops are avoided because the next iteration MUST
                // hit the heading open case above, which unconditionally increments the
                // input pointer.
            } elseif ( $found === 'open' ) {
                # count opening brace characters
                $curLen = strlen( $curChar );
                $count = $curLen > 1
                    # allow the final character to repeat
                    ? strspn( $text, $curChar[$curLen - 1], $i + 1 ) + 1
                    : strspn( $text, $curChar, $i );
 
                $savedPrefix = '';
                $lineStart = $i > 0 && $text[$i - 1] === "\n";
 
                if ( $curChar === "-{" && $count > $curLen ) {
                    // -{ => {{ transition because rightmost wins
                    $savedPrefix = '-';
                    $i++;
                    $curChar = '{';
                    $count--;
                    $rule = $this->rules[$curChar];
                }
 
                # we need to add to stack only if opening brace count is enough for one of the rules
                if ( $count >= $rule['min'] ) {
                    # Add it to the stack
                    $piece = [
                        'open' => $curChar,
                        'close' => $rule['end'],
                        'savedPrefix' => $savedPrefix,
                        'count' => $count,
                        'lineStart' => $lineStart,
                    ];
 
                    $stack->push( $piece );
                    $accum =& $stack->getAccum();
                    $stackFlags = $stack->getFlags();
                    if ( isset( $stackFlags['findEquals'] ) ) {
                        $findEquals = $stackFlags['findEquals'];
                    }
                    if ( isset( $stackFlags['findPipe'] ) ) {
                        $findPipe = $stackFlags['findPipe'];
                    }
                    if ( isset( $stackFlags['inHeading'] ) ) {
                        $inHeading = $stackFlags['inHeading'];
                    }
                } else {
                    # Add literal brace(s)
                    self::addLiteral( $accum, $savedPrefix . str_repeat( $curChar, $count ) );
                }
                $i += $count;
            } elseif ( $found === 'close' ) {
                $piece = $stack->top;
                '@phan-var PPDStackElement_Hash $piece';
                # lets check if there are enough characters for closing brace
                $maxCount = $piece->count;
                if ( $piece->close === '}-' && $curChar === '}' ) {
                    $maxCount--; # don't try to match closing '-' as a '}'
                }
                $curLen = strlen( $curChar );
                $count = $curLen > 1
                    ? $curLen
                    : strspn( $text, $curChar, $i, $maxCount );
 
                # check for maximum matching characters (if there are 5 closing
                # characters, we will probably need only 3 - depending on the rules)
                $rule = $this->rules[$piece->open];
                if ( $count > $rule['max'] ) {
                    # The specified maximum exists in the callback array, unless the caller
                    # has made an error
                    $matchingCount = $rule['max'];
                } else {
                    # Count is less than the maximum
                    # Skip any gaps in the callback array to find the true largest match
                    # Need to use array_key_exists not isset because the callback can be null
                    $matchingCount = $count;
                    while ( $matchingCount > 0 && !array_key_exists( $matchingCount, $rule['names'] ) ) {
                        --$matchingCount;
                    }
                }
 
                if ( $matchingCount <= 0 ) {
                    # No matching element found in callback array
                    # Output a literal closing brace and continue
                    $endText = substr( $text, $i, $count );
                    self::addLiteral( $accum, $endText );
                    $i += $count;
                    continue;
                }
                // @phan-suppress-next-line PhanTypeArraySuspiciousNullable
                $name = $rule['names'][$matchingCount];
                if ( $name === null ) {
                    // No element, just literal text
                    $endText = substr( $text, $i, $matchingCount );
                    $element = $piece->breakSyntax( $matchingCount );
                    self::addLiteral( $element, $endText );
                } else {
                    # Create XML element
                    $parts = $piece->parts;
                    $titleAccum = $parts[0]->out;
                    unset( $parts[0] );
 
                    $children = [];
 
                    # The invocation is at the start of the line if lineStart is set in
                    # the stack, and all opening brackets are used up.
                    if ( $maxCount === $matchingCount &&
                        $piece->lineStart &&
                        $piece->savedPrefix === ''
                    ) {
                        $children[] = [ '@lineStart', [ 1 ] ];
                    }
                    $titleNode = [ 'title', $titleAccum ];
                    $children[] = $titleNode;
                    $argIndex = 1;
                    foreach ( $parts as $part ) {
                        if ( isset( $part->eqpos ) ) {
                            $equalsNode = $part->out[$part->eqpos];
                            $nameNode = [ 'name', array_slice( $part->out, 0, $part->eqpos ) ];
                            $valueNode = [ 'value', array_slice( $part->out, $part->eqpos + 1 ) ];
                            $partNode = [ 'part', [ $nameNode, $equalsNode, $valueNode ] ];
                            $children[] = $partNode;
                        } else {
                            $nameNode = [ 'name', [ [ '@index', [ $argIndex++ ] ] ] ];
                            $valueNode = [ 'value', $part->out ];
                            $partNode = [ 'part', [ $nameNode, $valueNode ] ];
                            $children[] = $partNode;
                        }
                    }
                    $element = [ [ $name, $children ] ];
                }
 
                # Advance input pointer
                $i += $matchingCount;
 
                # Unwind the stack
                $stack->pop();
                $accum =& $stack->getAccum();
 
                # Re-add the old stack element if it still has unmatched opening characters remaining
                if ( $matchingCount < $piece->count ) {
                    $piece->parts = [ new PPDPart_Hash ];
                    $piece->count -= $matchingCount;
                    # do we still qualify for any callback with remaining count?
                    $min = $this->rules[$piece->open]['min'];
                    if ( $piece->count >= $min ) {
                        $stack->push( $piece );
                        $accum =& $stack->getAccum();
                    } elseif ( $piece->count === 1 && $piece->open === '{' && $piece->savedPrefix === '-' ) {
                        $piece->savedPrefix = '';
                        $piece->open = '-{';
                        $piece->count = 2;
                        $piece->close = $this->rules[$piece->open]['end'];
                        $stack->push( $piece );
                        $accum =& $stack->getAccum();
                    } else {
                        $s = substr( $piece->open, 0, -1 );
                        $s .= str_repeat(
                            substr( $piece->open, -1 ),
                            $piece->count - strlen( $s )
                        );
                        self::addLiteral( $accum, $piece->savedPrefix . $s );
                    }
                } elseif ( $piece->savedPrefix !== '' ) {
                    self::addLiteral( $accum, $piece->savedPrefix );
                }
 
                $stackFlags = $stack->getFlags();
                if ( isset( $stackFlags['findEquals'] ) ) {
                    $findEquals = $stackFlags['findEquals'];
                }
                if ( isset( $stackFlags['findPipe'] ) ) {
                    $findPipe = $stackFlags['findPipe'];
                }
                if ( isset( $stackFlags['inHeading'] ) ) {
                    $inHeading = $stackFlags['inHeading'];
                }
 
                # Add XML element to the enclosing accumulator
                array_splice( $accum, count( $accum ), 0, $element );
            } elseif ( $found === 'pipe' ) {
                $findEquals = true; // shortcut for getFlags()
                $stack->addPart();
                $accum =& $stack->getAccum();
                ++$i;
            } elseif ( $found === 'equals' ) {
                $findEquals = false; // shortcut for getFlags()
                $accum[] = [ 'equals', [ '=' ] ];
                $stack->getCurrentPart()->eqpos = count( $accum ) - 1;
                ++$i;
            }
        }
 
        # Output any remaining unclosed brackets
        foreach ( $stack->stack as $piece ) {
            array_splice( $stack->rootAccum, count( $stack->rootAccum ), 0, $piece->breakSyntax() );
        }
 
        # Enable top-level headings
        foreach ( $stack->rootAccum as &$node ) {
            if ( is_array( $node ) && $node[PPNode_Hash_Tree::NAME] === 'possible-h' ) {
                $node[PPNode_Hash_Tree::NAME] = 'h';
            }
        }
 
        return [ [ 'root', $stack->rootAccum ] ];
    }
 
    private static function addLiteral( array &$accum, $text ) {
        $n = count( $accum );
        if ( $n && is_string( $accum[$n - 1] ) ) {
            $accum[$n - 1] .= $text;
        } else {
            $accum[] = $text;
        }
    }
}