Runtime: Undefined array/superglobal key — Zend notice parity

[PurHur]

Problem

Shipped examples/001-SimpleWeb/example.php does:

$name = $_GET['name'];

On stock PHP 8 with E_ALL, a request without name emits:

Warning: Undefined array key "name"

The compiler may throw, return null, or behave inconsistently across VM / JIT / AOT for missing hashtable keys — especially superglobals populated by lib/Web/Superglobals.php.

MiniWebApp routing (#67, #210) and forms need predictable behavior before ?? (#99) is implemented everywhere.

Goal

Define, document, and test missing-key semantics for $_GET, $_POST, and ordinary arrays so web apps can rely on the same policy as PHP 8.x (or a deliberate subset documented in README).

Scope

• Audit lib/VM.php / JIT dim-fetch paths for array/superglobal reads
• PHPT under test/real/cases/: missing $_GET['key'] with default error_reporting
• Document chosen policy in docs/ or next to DevEx: Builtin capability matrix (VM / JIT / AOT per function) #176 capability notes
• After Language: Null coalescing operator (??) in compiler pipeline #99 lands: update 001-SimpleWeb to $name = $_GET['name'] ?? 'Guest'; (optional follow-up PR)

Acceptance criteria

docker run --rm -v "$(pwd):/compiler" -w /compiler php-compiler:22.04-dev \
  ./phpc run examples/001-SimpleWeb/example.php

Behavior is documented and covered by a PHPT (pass or explicit XFAIL with issue link until fixed).

With ?? implemented (#99), the same script with ?? 'Guest' runs without notices on both Zend and compiler.

Verification (local only)

No GitHub Actions required. Use Docker command above and ./script/ci-local.sh --filter undefined.

Dependencies

• Language: Null coalescing operator (??) in compiler pipeline #99 null coalescing (recommended app pattern)
• Web: Dynamic isset/empty on $_GET and $_POST keys in JIT #70 dynamic isset/empty on superglobals
• JIT: Dynamic hashtable read/write for $_GET[$key] and $_POST[$key] #86 / Web: Runtime-populated superglobals for JIT and AOT (per-request $_GET/$_POST) #49 JIT superglobal slices

Links

• examples/001-SimpleWeb/example.php, lib/Web/Superglobals.php
• 🗺️ ROADMAP: Self-host + web-capable PHP subset (living) #78 ROADMAP Phase 1, Docs: examples/README — phpc/vm/aot run matrix per example folder #262 examples run matrix

[PurHur]

Fixed in #364: VM/JIT/AOT undefined array key warnings with null read semantics; documented in docs/runtime-semantics.md.