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[POC] Support calling global functions from constant expressions
- Currently, this treats all functions as global functions. Function resolution is straightforward to implement, I just haven't implemented it for a proof of concept. - Argument unpacking isn't supported, but would be easy to implement. - It turns out parameter defaults evaluate some constants every time, depending on whether the PHP value is immutable. It's likely we want to change this for expressions containing function calls, which can be more expensive than evaluating a regular constant AST. (e.g. reading files) - This handles recursive definitions. - Static calls with known classes (other than static::) may also be easy to implement. - This also constrains function return values to be valid constants, (for what define() would accept) and throws an error otherwise. In the future, `const X = [my_call()->x];` may be possible. - Variables aren't supported, because they depend on the declaration's scope, which may cease to exist. - This throws an Error if a function call in a constant begins when it's still in progress. Aside: https://github.com/TysonAndre/php-src/pull/10/files is an alternative approach to a simple syntax to declaring constants with dynamic values, which instead limits dynamic expressions of any type to `static const`. ------- It turns out that function calls can already be invoked when evaluating a constant, e.g. from php's error handler. So it seems viable for PHP's to support this, which this POC attempts to do. (Imagine an error handler defining SOME_DYNAMIC_CONST123 to be a dynamic value if a notice is emitted) for `const X = [[]['undefined_index'], SOME_DYNAMIC_CONST123][1];`
1 parent 986da2a commit 1197f8f

17 files changed

+420
-3
lines changed

‎Zend/tests/call_in_const/class_const01.phpt

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--TEST--
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Can call internal functions from class constants
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--FILE--
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<?php
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class Example {
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const X = sprintf("Hello, %s\n", "World");
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public static function main() {
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echo "X is " . self::X . "\n";
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}
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}
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Example::main();
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?>
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--EXPECT--
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X is Hello, World

‎Zend/tests/call_in_const/class_const02.phpt

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--TEST--
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Can call internal functions from class constants
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--FILE--
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<?php
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function normalize_keys(array $x) {
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// Should only invoke normalize_keys once
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echo "Normalizing the keys\n";
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$result = [];
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foreach ($x as $k => $value) {
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$result["prefix_$k"] = $value;
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}
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return $result;
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}
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class Example {
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const X = [
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'key1' => 'value1',
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'key2' => 'value2',
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];
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const Y = array_flip(self::X);
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const Z = normalize_keys(self::Y);
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}
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var_export(Example::Z);
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var_export(Example::Z);
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var_export(Example::Y);
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?>
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--EXPECT--
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Normalizing the keys
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array (
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'prefix_value1' => 'key1',
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'prefix_value2' => 'key2',
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)array (
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'prefix_value1' => 'key1',
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'prefix_value2' => 'key2',
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)array (
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'value1' => 'key1',
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'value2' => 'key2',
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)

‎Zend/tests/call_in_const/global_const01.phpt

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--TEST--
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Can call internal functions from global constants
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--FILE--
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<?php
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const NIL = var_export(null, true);
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echo "NIL is " . NIL . "\n";
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?>
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--EXPECT--
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NIL is NULL

‎Zend/tests/call_in_const/global_const02.phpt

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--TEST--
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Cannot declare constants with function calls that contain objects
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--FILE--
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<?php
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function make_object_array() {
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return [new stdClass()];
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}
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const OBJECT_VALUES = make_object_array();
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?>
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--EXPECTF--
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Fatal error: Uncaught Error: Calls in constants may only evaluate to scalar values, arrays or resources in %s:5
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Stack trace:
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#0 {main}
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thrown in %s on line 5

‎Zend/tests/call_in_const/param_defaults.phpt

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--TEST--
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Can call internal functions from parameter default
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--FILE--
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<?php
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function evaluated_user_function() {
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// NOTE: PHP only caches non-refcounted values in the RECV_INIT value,
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// meaning that if the returned value is dynamic, this will get called every time.
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// TODO: Would it be worth it to convert refcounted values to immutable values?
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echo "Evaluating default\n";
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return sprintf("%s default", "Dynamic");
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}
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function test_default($x = evaluated_user_function()) {
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echo "x is $x\n";
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}
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test_default();
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test_default(2);
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test_default();
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?>
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--EXPECT--
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Evaluating default
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x is Dynamic default
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x is 2
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Evaluating default
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x is Dynamic default

‎Zend/tests/call_in_const/property_default01.phpt

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--TEST--
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Can call user-defined functions from defaults of static properties
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--FILE--
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<?php
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namespace NS;
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function log_call($arg) {
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echo "log_call(" . var_export($arg, true) . ")\n";
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return $arg;
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}
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class MyClass {
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public static $DEBUG = log_call(true);
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public static $DEBUG2 = namespace\log_call(range(1,2));
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}
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echo "Start\n";
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var_export(MyClass::$DEBUG); echo "\n";
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var_export(MyClass::$DEBUG2); echo "\n";
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var_export(MyClass::$DEBUG); echo "\n";
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MyClass::$DEBUG = "New value";
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echo MyClass::$DEBUG . "\n";
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?>
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--EXPECT--
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Start
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log_call(true)
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log_call(array (
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0 => 1,
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1 => 2,
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))
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true
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array (
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0 => 1,
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1 => 2,
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)
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true
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New value

‎Zend/tests/call_in_const/recursion.phpt

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--TEST--
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Recursion in calls in class constants causes an error
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--FILE--
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<?php
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function x_plus_1() {
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echo "Computing X + 1\n";
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return Recursion::X + 1;
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}
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class Recursion {
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const X = x_plus_1();
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const MISSING = MISSING_GLOBAL + 1;
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}
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try {
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echo "Recursion::X=" . Recursion::X . "\n";
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} catch (Error $e) {
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printf("Caught %s: %s\n", get_class($e), $e->getMessage());
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}
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try {
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echo "Recursion::X=" . Recursion::X . "\n";
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} catch (Error $e) {
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printf("Second call caught %s: %s\n", get_class($e), $e->getMessage());
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}
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try {
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echo "Recursion::MISSING=" . Recursion::MISSING;
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} catch (Error $e) {
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printf("Caught %s: %s\n", get_class($e), $e->getMessage());
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}
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try {
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echo "Recursion::MISSING=" . Recursion::MISSING;
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} catch (Error $e) {
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printf("Second call caught %s: %s\n", get_class($e), $e->getMessage());
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}
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?>
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--EXPECT--
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Computing X + 1
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Caught Error: Unrecoverable error calling x_plus_1() in recursive constant definition
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Computing X + 1
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Second call caught Error: Unrecoverable error calling x_plus_1() in recursive constant definition
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Caught Error: Undefined constant 'MISSING_GLOBAL'
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Second call caught Error: Undefined constant 'MISSING_GLOBAL'

‎Zend/tests/call_in_const/static_default01.phpt

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--TEST--
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Can call internal functions from defaults of static variables
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--FILE--
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<?php
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function main() {
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static $call = SPRINTF("%s!", sprintf("Hello, %s", "World"));
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echo "$call\n";
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}
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main();
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main();
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?>
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--EXPECT--
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Hello, World!
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Hello, World!

‎Zend/tests/call_in_const/static_default02.phpt

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--TEST--
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Can call user-defined functions from defaults of static variables
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--FILE--
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<?php
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function log_call(string $arg) {
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echo "log_call('$arg')\n";
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return $arg;
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}
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$f = function () {
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static $call = log_call(sprintf("Hello, %s", "World"));
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echo "$call\n";
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};
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$f();
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$f();
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?>
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--EXPECT--
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log_call('Hello, World')
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Hello, World
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Hello, World

‎Zend/tests/call_in_const/static_default03.phpt

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--TEST--
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Can call internal functions from defaults of static variables
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--FILE--
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<?php
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function main() {
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static $call = missing_sprintf("%s!", sprintf("Hello, %s", "World"));
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echo "$call\n";
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}
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for ($i = 0; $i < 2; $i++) {
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try {
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main();
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} catch (Error $e) {
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printf("Caught %s: %s at line %d\n", get_class($e), $e->getMessage(), $e->getLine());
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}
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}
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?>
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--EXPECT--
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Caught Error: Call to undefined function missing_sprintf() at line 3
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Caught Error: Call to undefined function missing_sprintf() at line 3

‎Zend/zend.c

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@@ -927,6 +927,9 @@ int zend_startup(zend_utility_functions *utility_functions) /* {{{ */
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#endif
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EG(error_reporting) = E_ALL & ~E_NOTICE;
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930+
CG(active_calls_in_constants) = (HashTable *)malloc(sizeof(HashTable));
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zend_hash_init_ex(CG(active_calls_in_constants), 128, NULL, NULL, 1, 0);
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zend_interned_strings_init();
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zend_startup_builtin_functions();
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zend_register_standard_constants();
@@ -962,7 +965,7 @@ void zend_register_standard_ini_entries(void) /* {{{ */
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}
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/* }}} */
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965-
static zend_class_entry *resolve_type_name(zend_string *type_name) {
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static zend_class_entry *resolve_type_name(zend_string *type_name) {
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zend_string *lc_type_name = zend_string_tolower(type_name);
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zend_class_entry *ce = zend_hash_find_ptr(CG(class_table), lc_type_name);
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@@ -1083,6 +1086,8 @@ void zend_shutdown(void) /* {{{ */
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10841087
zend_hash_destroy(GLOBAL_CONSTANTS_TABLE);
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free(GLOBAL_CONSTANTS_TABLE);
1089+
zend_hash_destroy(CG(active_calls_in_constants));
1090+
free(CG(active_calls_in_constants));
10861091
zend_shutdown_strtod();
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#ifdef ZTS

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