Compiler: Return type declarations on user functions (VM + JIT)

[PurHur]

Problem

Modern PHP web code uses declared return types on functions and methods:

function slug(string $s): string { return strtolower($s); }
private function renderHome(): void { /* … */ }

#55 tracks emitting non-void values in JIT; this issue adds reading and enforcing : return types from php-cfg in the compiler (VM checks, JIT typed returns, AOT metadata).

examples/003-MiniWebApp/src/Router.php already uses : void on dispatch() and private render* methods — they will fail type checks once #145 methods compile unless returns are wired here.

Goal

• VM: coerce/check return value at TYPE_RETURN against declared type (respect Language: declare(strict_types=1) enforcement in VM #156 strict_types when enabled)
• JIT: LLVM return value uses declared scalar types where possible
• AOT: same metadata as JIT
• Explicit (): void — reject non-null returns

Implementation hints

Area	Files	Notes
Compiler	lib/Compiler.php compileFunction, compileClassBody	Read Func::returnType / method return type from PHPCfg
VM	lib/VM.php TYPE_RETURN	TypeError on mismatch when strict_types=1
JIT	lib/JIT.php return lowering	Pair with #55 — void vs value returns
Lint	lib/Lint/UnsupportedRegistry.php	Until done, map unsupported return kinds
Tests	test/compliance/cases/return_type_*.phpt	valid string return, void, strict failure

MiniWebApp

After #145 lands, Router::dispatch(): void must not require stripping return types from the reference app.

Acceptance criteria

docker run --rm -v "$(pwd):/compiler" -w /compiler php-compiler:22.04-dev \
  php bin/vm.php -r 'declare(strict_types=1); function f(): int { return "x"; } f();'

Throws TypeError in VM (message parity optional v1).

docker run --rm -v "$(pwd):/compiler" -w /compiler php-compiler:22.04-dev \
  php bin/vm.php -r 'function g(): string { return "ok"; } echo g();'

Prints ok.

Verification (local / Docker only)

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

Dependencies

• Language: JIT support for non-void function return types #55 non-void JIT return emission
• Language: declare(strict_types=1) enforcement in VM #156 strict_types enforcement
• Language: Class methods and property access in JIT #58 / Language: Visibility, constructors, and destructors #145 method return types
• Blocks: Reference app: examples/003-MiniWebApp (router, templates, forms) #67 Router methods with : void

Related

• 🗺️ ROADMAP: Compile a small PHP web application (living document) #78 ROADMAP Phase 1 Language
• examples/003-MiniWebApp/src/Router.php