Language: User-defined constants (const, define()) and class constants

[PurHur]

Problem

Web apps use const VERSION = '1.0';, define('DEBUG', true);, and class constants for config. The compiler lowers classes and globals but user-defined constants are incomplete:

• Top-level const NAME = … may not reach the VM constant table
• define('NAME', value) runtime registration is missing or partial
• Class const inside compileClassBody is not handled alongside properties (Language: Class methods and property access in JIT #58 / Language: Visibility, constructors, and destructors #145)

examples/003-MiniWebApp/config.php is a plain return [...] array today; constants become important once config moves to define() / class constants.

Goal

const APP_NAME = 'MiniWeb';
define('MAX_UPLOAD', 1024);
class Config { public const ENV = 'prod'; }
echo APP_NAME, Config::ENV;

VM + JIT + AOT: immutable fetches; define() registers before use in same request.

Implementation hints

Compiler (lib/Compiler.php)

Construct	Lowering
Stmt\Const_	Add to compilation unit constant table at compile time
define()	Builtin or opcode TYPE_DEFINE with name + value
Class const	Extend compileClassBody — store in class metadata, TYPE_CLASS_CONST_FETCH

VM (lib/VM.php)

• Global constant table keyed by name (case-sensitive)
• Class constant table on class entry
• define() checks defined() / duplicate semantics (Zend subset)

JIT / AOT

• Inline literal constants where opcode is TYPE_CONST_FETCH with known value
• JIT: emit global as LLVM global or immediate

Lint

• Register unsupported const forms in UnsupportedRegistry until implemented

Tests

• test/compliance/cases/const_global.phpt
• test/compliance/cases/define_runtime.phpt
• test/compliance/cases/class_const.phpt
• script/capability-matrix.php if builtins added

Acceptance criteria

docker run --rm -v "$(pwd):/compiler" -w /compiler php-compiler:22.04-dev \
  php bin/vm.php -r 'const X=42; define("Y",1); echo X+Y;'

Prints 43. JIT parity when #98 LLVM group runs.

Verification (local / Docker only)

./script/ci-local.sh --filter const_

No GitHub Actions.

Dependencies

• Language: Class methods and property access in JIT #58 / Language: Visibility, constructors, and destructors #145 for class constants
• Language: Magic constants __DIR__, __FILE__, __LINE__ for multi-file apps #85 __DIR__ if config uses path constants
• Not blocking Reference app: examples/003-MiniWebApp (router, templates, forms) #67 v1 (array config is fine)

Links

• 🗺️ ROADMAP: Compile a small PHP web application (living document) #78 ROADMAP Phase 1 Language
• lib/Compiler.php, lib/VM.php, lib/OpCode.php