Language: throw expressions (PHP 8.0) — parse and lowering in expression context

[PurHur]

Category

language

Problem

PHP 8.0 throw expressions allow throw anywhere an expression is valid (ternary arms, null-coalesce, short-circuit, parentheses). This compiler’s php-cfg pass does not handle PhpParser\Node\Expr\Throw_ inside expression trees — parse fails before compile.

This is syntax/lowering, distinct from #195 (builtin Exception class registration for catch).

php-src reference

• php/php-src Zend/zend_compile.c — zend_compile_throw() used from expression compile paths
• php/php-src Zend/zend_language_parser.y — expr includes T_THROW expr

Repro (failure today)

<?php
// ternary arm
echo (false ? 1 : throw new LogicException('x'));

./script/docker-exec.sh -- bash -lc 'source script/php-env.sh && php bin/vm.php repro.php'

Zend PHP 8+: uncaught LogicException: x (non-zero exit)

This compiler:

RuntimeException: Unknown Expr Type Expr_Throw
  in vendor/ircmaxell/php-cfg/lib/PHPCfg/Parser.php

Also fails for: ($x ?? throw new Exception('missing')), true && throw new Exception('x').

Scope (this repo)

Layer	Path	Notes
php-cfg	vendor/ircmaxell/php-cfg/lib/PHPCfg/Parser.php	parseExprNode() / parseExpr_Throw
Patch	patches/php-cfg-*.patch	if vendor fix required
Compiler	lib/Compiler.php	lower throw-expr to TYPE_THROW with value operand
VM/JIT	lib/VM.php, lib/JIT.php	reuse existing throw opcodes
Tests	test/compliance/cases/language/throw_expression.phpt	ternary + coalesce cases

Done when

• Ternary and null-coalesce repros compile and throw at runtime (after Language: throw expressions and Exception object propagation #195 lands, use LogicException or user class)
• Short-circuit && / \|\| throw arm matches Zend evaluation order
• ./script/ci-fast.sh --filter throw_expression green
• docs/capabilities-syntax.md notes throw-expressions VM/JIT/AOT status

Verification

./script/docker-exec.sh -- bash -lc 'source script/php-env.sh && ./script/ci-fast.sh --filter throw_expression'

Dependencies

• Language: throw expressions and Exception object propagation #195 — object throw/catch for end-to-end Exception/LogicException (can land parser first with user classes)
• Language: try/catch/finally lowering #57 — try/catch lowering (already landed)

Links

• North star Epic: Self-host critical path — compiler compiles itself (M3→M5) #1492 · Wave trackers Language features wave 2: JIT/syntax gaps tracker (#1222–#1235) #1238, Self-host: Unsupported expression CFG batch tracker (post-#2254 triage) #2301

[PurHur]

claim: cursor-agent-lane-c — starting this run