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Parser: Propose new hand-coded PHP parser
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For some time we've needed a more performant PHP parser for the first
stage of parsing the `post_content` document.

See #1681 (early exploration)
See #8044 (parser performance issue)
See #1775 (parser performance, fixed in php-pegjs)

I'm proposing this implementation of the spec parser as an alternative
to the auto-generated parser from the PEG definition.

This is not yet ready to go but I wanted to get the code in a branch
so I can iterate on it and garner early feedback.

This should eventually provide a setup fixture for #6831 wherein we
are testing alternate parser implementations.

 - designed as a basic recursive-descent
 - but doesn't recurse on the call-stack, recurses via trampoline
 - moves linearly through document in one pass
 - relies on RegExp for tokenization

 - nested blocks include the nested content in their `innerHTML`
   this needs to go away
 - create test fixutre
 - figure out where to save this file
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@dmsnell
dmsnell committed Aug 30, 2018
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221 changes: 221 additions & 0 deletions lib/paresr-rd-trampoline.php
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<?php

class MyParser {
public $document;
public $offset;
public $output;
public $stack;

function __construct( $document ) {
$this->document = $document;
$this->offset = 0;
$this->output = array();
$this->stack = array();
}

function parse() {
do {
# twiddle our thumbs
} while ( $this->proceed() );

return $this->output;
}

function proceed() {
list( $token_type, $block_name, $attrs, $start_offset, $token_length ) = $this->next_token();

switch ( $token_type ) {
case 'no-more-tokens':
# if not in a block then flush output
if ( 0 === count( $this->stack ) ) {
$this->add_freeform();
$this->offset = strlen( $this->document );
return false;
}

# Otherwise we have a problem
# This is an error
$this->error( 'in a block but found no closer' );
$this->error( 'failed at ' . $this->offset );

# we have options
# - treat it all as freeform text
# - assume an implicit closer (easiest when not nesting)

# for the easy case we'll assume and implicit closer
if ( 1 === count( $this->stack ) ) {
$this->error( ' - treating as implicit closer' );
$this->pop_stack();
$this->offset = strlen( $this->document );
return false;
}

# for the nested case where it's more difficult we'll
# have to assume that multiple closers are missing
# and so we'll collapse the whole stack piecewise
$this->error( ' - multiple closers are missing' );
$this->error( ' - recursively collapsing stack of blocks' );
while ( 0 < count( $this->stack ) ) {
$this->pop_stack();
}
$this->offset = strlen( $this->document );
return false;

case 'void-block':
# easy case is if we stumbled upon a void block
# in the top-level of the document
if ( 0 === count( $this->stack ) ) {
$this->add_block( $block_name, $attrs, array(), '' );
$this->offset = $start_offset + $token_length;
return true;
}

# otherwise we found an inner block
$this->add_inner_block( $block_name, $attrs, array(), '' );
$this->offset = $start_offset + $token_length;
return true;

case 'block-opener':
$this->push_stack( $block_name, $attrs, $start_offset, $token_length );
$this->offset = $start_offset + $token_length;
return true;

case 'block-closer':
# if we're missing an opener we're in trouble
# This is an error
if ( 0 === count( $this->stack ) ) {
$this->error( 'found a closer with no opening block' );
$this->error( 'failed at offset ' . $start_offset );

# we have options
# - assume an implicit opener
# - assume _this_ is the opener
# - give up and close out the document
$this->add_freeform();
$this->offset = strlen( $this->document );
return false;
}

# if we're not nesting then this is easy - close the block
if ( 1 === count( $this->stack ) ) {
$this->pop_stack( $start_offset );
$this->offset = $start_offset + $token_length;
return true;
}

# otherwise we're nested and we have to close out the current
# block and add it as a new innerBlock to the parent
$block = array_pop( $this->stack );
$this->add_inner_block( array(
'blockName' => $block[ 0 ],
'attrs' => $block[ 1 ],
'innerBlocks' => $block[ 2 ],
'innerHTML' => substr( $this->document, $block[ 3 ] + $block[ 4 ], $start_offset - $block[ 3 ] - $block[ 4 ] ),
) );
$this->offset = $start_offset + $token_length;
return true;

default:
# This is an error
$this->error( 'found unexpected token at offset ' . $this->offset );
$this->add_freeform();
$this->offset = strlen( $this->document );
return false;
}
}

function next_token() {
$matches = null;

$has_match = preg_match(
'/<!--\s+(?<closer>\/)?wp:(?<name>[a-z][a-z0-9_-]*)\s+(?<attrs>{(?:(?!}\s+-->).)+}\s+)?(?<void>\/)?-->/',
$this->document,
$matches,
PREG_OFFSET_CAPTURE,
$this->offset
);

# we have no more tokens
if ( 0 === $has_match ) {
return array( 'no-more-tokens' );
}

list( $match, $started_at ) = $matches[ 0 ];

$length = strlen( $match );
$is_closer = isset( $matches[ 'closer' ] ) && -1 !== $matches[ 'closer' ][ 1 ];
$is_void = isset( $matches[ 'void' ] ) && -1 !== $matches[ 'void' ][ 1 ];
$name = $matches[ 'name' ][ 0 ];
$has_attrs = isset( $matches[ 'attrs' ] ) && -1 !== $matches[ 'attrs' ][ 1 ];
$attrs = $has_attrs ? json_decode( $matches[ 'attrs' ][ 0 ] ) : new stdClass();

# This state isn't allowed
# This is an error
if ( $is_closer && ( $is_void || $has_attrs ) ) {
$this->error( 'closing comment delimiters must not have attributes or void closers' );
$this->error( 'failed at offset ' . $started_at . ': ' . $match );

# we can ignore them since they don't hurt anything
}

if ( $is_void ) {
return array( 'void-block', $name, $attrs, $started_at, $length );
}

if ( $is_closer ) {
return array( 'block-closer', $name, null, $started_at, $length );
}

return array( 'block-opener', $name, $attrs, $started_at, $length );
}

function add_block( $block_name, $attrs, $inner_blocks, $inner_html ) {
$this->output[] = array(
'blockName' => $block_name,
'attrs' => $attrs,
'innerBlocks' => $inner_blocks,
'innerHTML' => $inner_html,
);
}

function add_freeform( $length = null ) {
$this->output[] = isset( $length )
? self::freeform( substr( $this->document, $this->offset, $length ) )
: self::freeform( substr( $this->document, $this->offset ) );
}

function add_inner_block( $block ) {
# optimized way of pushing new block onto $inner_blocks of parent stack block
$this->stack[ count( $this->stack ) - 1 ][ 2 ][] = $block;
}

function push_stack( $block_name, $attrs, $start_offset, $length ) {
array_push( $this->stack, array( $block_name, $attrs, array(), $start_offset, $length ) );
}

function pop_stack( $end_offset = null ) {
list( $block_name, $attrs, $inner_blocks, $start_offset, $length ) = array_pop( $this->stack );

$inner_html = isset( $end_offset )
? substr( $this->document, $start_offset + $length, $end_offset - $start_offset - $length )
: substr( $this->document, $start_offset + $length );

$this->output[] = array(
'blockName' => $block_name,
'attrs' => $attrs,
'innerBlocks' => $inner_blocks,
'innerHTML' => $inner_html,
);
}

function error( $message ) {
error_log( $message );
}

static function freeform( $s ) {
return array(
'attrs' => new stdClass(),
'innerHTML' => $s,
);
}
}

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