The new Abstract Syntax Tree (AST) in PHP 7 means the way our PHP code is being executed has changed. Understanding this new fundamental compilation step is key to understanding how our code is being run.
To demonstrate, James will show how a basic compiler works and how introducing an AST simplifies this process. We’ll look into how these magical time-warp techniques* can also be used in your code to introspect, analyse and modify code in a way that was never possible before.
After seeing this talk, you’ll have a great insight as to the wonders of an AST, and how it can be applied to both compilers and userland code.
(*actual magic or time-warp not guaranteed)
80. @asgrim
Order tokens by operator precedence
if ($token->isOperator()) {
$tokenPrecedence = self::$operatorPrecedence[$token->getToken()];
while (
count($operators)
&& self::$operatorPrecedence[$operators[count($operators) - 1]->getToken()]
> $tokenPrecedence
) {
$higherOp = array_pop($operators);
$stack[] = $higherOp;
}
$operators[] = $token;
next($tokens);
continue;
}
81. @asgrim
Order tokens by operator precedence
if ($token->isOperator()) {
$tokenPrecedence = self::$operatorPrecedence[$token->getToken()];
while (
count($operators)
&& self::$operatorPrecedence[$operators[count($operators) - 1]->getToken()]
> $tokenPrecedence
) {
$higherOp = array_pop($operators);
$stack[] = $higherOp;
}
$operators[] = $token;
next($tokens);
continue;
}
82. @asgrim
Order tokens by operator precedence
if ($token->isOperator()) {
$tokenPrecedence = self::$operatorPrecedence[$token->getToken()];
while (
count($operators)
&& self::$operatorPrecedence[$operators[count($operators) - 1]->getToken()]
> $tokenPrecedence
) {
$higherOp = array_pop($operators);
$stack[] = $higherOp;
}
$operators[] = $token;
next($tokens);
continue;
}
83. @asgrim
Order tokens by operator precedence
if ($token->isOperator()) {
$tokenPrecedence = self::$operatorPrecedence[$token->getToken()];
while (
count($operators)
&& self::$operatorPrecedence[$operators[count($operators) - 1]->getToken()]
> $tokenPrecedence
) {
$higherOp = array_pop($operators);
$stack[] = $higherOp;
}
$operators[] = $token;
next($tokens);
continue;
}
84. @asgrim
Order tokens by operator precedence
// Clean up by moving any remaining operators onto the token stack
while (count($operators)) {
$stack[] = array_pop($operators);
}
return $stack;
107. @asgrim
astkit example usage
$if = AstKit::parseString(<<<EOD
if (true) {
echo "This is a triumph.n";
} else {
echo "The cake is a lie.n";
}
EOD
);
$if->execute(); // First run, program is as-seen above
$const = $if->getChild(0)->getChild(0);
// Replace the "true" constant in the condition with false
$const->graft(0, false);
// Can also graft other AstKit nodes, instead of constants
$if->execute(); // Second run now takes the else path
114. @asgrim
Class BetterReflection
public function sourceLocator() : SourceLocator
{
$astLocator = $this->astLocator();
return $this->sourceLocator
?? $this->sourceLocator = new MemoizingSourceLocator(new AggregateSourceLocator([
new PhpInternalSourceLocator($astLocator),
new EvaledCodeSourceLocator($astLocator),
new AutoloadSourceLocator($astLocator),
]));
}
public function classReflector() : ClassReflector
{
return $this->classReflector
?? $this->classReflector = new ClassReflector($this->sourceLocator());
}
115. @asgrim
Given a class structure...
<?php
class Foo
{
private $bar;
public function thing()
{
}
}
116. @asgrim
… we get the AST!
Class, name Foo
|-- Statements
| |-- Property, name bar
| | |-- Type [private]
| | `-- Attributes [start line: 7, end line: 9]
| `-- Method, name thing
| |-- Type [public]
| |-- Parameters [...]
| |-- Statements [...]
| `-- Attributes [start line: 7, end line: 9]
`-- Attributes [start line: 3, end line: 10]
119. @asgrim
Monkey patching example
use RoaveBetterReflectionReflectorClassReflector;
use RoaveBetterReflectionSourceLocatorTypeSingleFileSourceLocator;
use RoaveBetterReflectionUtilAutoloadClassLoader;
use RoaveBetterReflectionUtilAutoloadClassLoaderMethodFileCacheLoader;
$loader = new ClassLoader(FileCacheLoader::defaultFileCacheLoader(__DIR__));
// Create the reflection first (without loading)
$classInfo = (new ClassReflector(
new SingleFileSourceLocator(
__DIR__ . '/MyClass.php',
(new BetterReflection())->astLocator()
)
))->reflect('MyClass');
$loader->addClass($classInfo);
120. @asgrim
Monkey patching example
use RoaveBetterReflectionReflectorClassReflector;
use RoaveBetterReflectionSourceLocatorTypeSingleFileSourceLocator;
use RoaveBetterReflectionUtilAutoloadClassLoader;
use RoaveBetterReflectionUtilAutoloadClassLoaderMethodFileCacheLoader;
$loader = new ClassLoader(FileCacheLoader::defaultFileCacheLoader(__DIR__));
// Create the reflection first (without loading)
$classInfo = (new ClassReflector(
new SingleFileSourceLocator(
__DIR__ . '/MyClass.php',
(new BetterReflection())->astLocator()
)
))->reflect('MyClass');
$loader->addClass($classInfo);
121. @asgrim
Monkey patching example
// Override the body...!
$classInfo->getMethod('foo')->setBodyFromClosure(
function () {
return 4;
}
);
$c = new MyClass();
echo $c->foo() . "n";
122. @asgrim
Monkey patching example
// Override the body...!
$classInfo->getMethod('foo')->setBodyFromClosure(
function () {
return 4;
}
);
$c = new MyClass();
echo $c->foo() . "n"; // returns 4, not 5
123. @asgrim
To summarise
● For PHP engine:
○ AST is an efficient data structure to represent code
○ AST means faster compilation (ignoring opcache)
○ Separation in PHP engine for parser and compiler
○ https://wiki.php.net/rfc/abstract_syntax_tree
● Concepts can be used in userland
○ PHP Parser library - https://github.com/nikic/php-parser
○ Better Reflection - https://github.com/Roave/BetterReflection
■ Reflect on not-yet-loaded files
■ Monkey patching in userland code (!)
○ Static analysis opportunities
■ Better Reflection
■ Exakat static analysis (uses own AST)
■ Phan (uses php-ast extension)