PHP 8.3: Arbitrary static variable initializers

Related to https://github.com/PHPCompatibility/PHPCompatibility/issues/1589

Analysis

Summary of existing PHP 8.2 behavior based on the RFC:

// Constant expressions can be assigned in this context (exact meaning in Syntax Variations below).
function foo1() {
    static $i = 1;
}

// Can redeclare, with the last taking precedence.
function foo2() {
    static $i = 1;
    static $i = 2;
}

// getStaticVariables() is able to get the literal value.
var_dump((new ReflectionFunction('foo2'))->getStaticVariables()['i']); // int(2)

Updated behavior in PHP 8.3:

// Allows arbitrary expressions (exact meaning in Syntax Variations below).
function foo1() {
    static $i = min(1, 2);
}

// Re-declaring is now a fatal error.
function foo2() {
    static $i = min(1, 2);
    static $i = max(1, 2); // Fatal error: Duplicate declaration of static variable $i
}

// getStaticVariables() can get the expression's value or null if not initialized. However, since the above syntax
// is a fatal error in PHP 8.2, there is no observable difference, so we don't need to sniff getStaticVariables().
var_dump((new ReflectionFunction('foo2'))->getStaticVariables()['i']); // int(2)

Everything in the "Other semantics" section of the RFC has no impact on what we need to sniff. Either the syntax exists or it doesn't.

• Exceptions during initialization
• Destructor
• Recursion

Top 2000 Packages

Found quite a few usages in the top 2000 packages ("static $" in a function). See results.

Detection in PHP 8.2

• function () { static $i; } Without assignment: valid.
• function () { static $i = 1; } Constant expression: valid.
• function () { static $a = 1; static $a = 2; } Duplicate declaration: valid
• function () { static $i = min(1, 2); } Arbitrary expression: error

Detection in PHP 8.3

• function () { static $i; } Without assignment: valid.
• function () { static $i = 1; } Constant expression: valid.
• function () { static $a = 1; static $a = 2; } Duplicate declaration: error
• function () { static $i = min(1, 2); } Arbitrary expression: valid

Syntax Variations & Detectability

• Expressions valid in both versions
• Expressions valid only in PHP 8.3 - uncomment one at a time to test the fatal error in 8.2
• Static outside of functions
• Duplicate declaration - re-declaring is a fatal error since PHP 8.3.
• Interaction with ReflectionFunction::getStaticVariables() - when using syntax supported in both versions, no difference can be observed.
• More PHP 8.3 from @jrfnl
• Multi-declarations from @jrfnl
• function () { static $i; } ✅ Without assignment: can be handled by PHPCompatibility.
• function () { static $a = 1; static $a = 2; } ✅ Duplicate declaration in the same function: can be handled by PHPCompatibility.
• function () { static $i = 1; } ✅❌ Various expressions: I identified 52 expression types in the first 2 samples above. I will rely on @jrfnl's knowledge of the tool's capabilities.

References

• RFC: Arbitrary static variable initializers
• PR: Allow arbitrary expressions in static variable initializer
  • Commit: Allow arbitrary expressions in static variable initializer
• PHP Manual:
  • Migrating from PHP 8.2.x to PHP 8.3.x - New Features
  • Using static variables

The issue names no implementation files or tests. Start by reviewing the existing PHPCompatibility handling for static-variable declarations, then compare the linked PHP 8.2/8.3 examples and RFC; done means the relevant syntax differences are detected consistently, including arbitrary initializers and duplicate declarations.