Language: Traits, abstract classes, and interfaces

[PurHur]

Category

language

Problem (May 2026 refresh)

Simple trait use, abstract classes, and interfaces compile on VM today:

./script/docker-exec.sh -- bash -lc 'source script/php-env.sh
php bin/vm.php -r "trait T { public function f(): int { return 1; } } class C { use T; } echo (new C)->f();"
php bin/vm.php -r "abstract class A { abstract public function f(): int; } class C extends A { public function f(): int { return 1; } } echo (new C)->f();"
php bin/vm.php -r "interface I { public function f(): int; } class C implements I { public function f(): int { return 1; } } echo (new C)->f();"
'

All print 1 on master. Remaining Zend parity:

1. TraitUseAdaptation — insteadof / as fails at parse (Language: TraitUseAdaptation — insteadof / as alias (Zend compile parity) #3238)
2. implements enforcement — missing method not fatal at compile time
3. instanceof interface — verify bool against Zend (Compiler: Class inheritance (extends) and interfaces #101 overlap)
4. JIT/AOT trait + abstract dispatch — VM-only today for some paths
5. Horizontal trait conflicts — fatal when two traits define same method without adaptation
6. Abstract instantiation — new AbstractClass must fatal

php-src reference

• Zend/zend_compile.c — zend_compile_traits, abstract flag, interface table
• Zend/zend_inheritance.c — trait flattening, abstract method checks
• Zend/zend_execute.c — instanceof, interface ce checks
• Zend/zend_language_parser.y — trait adaptation grammar (Language: TraitUseAdaptation — insteadof / as alias (Zend compile parity) #3238)

Repro — gaps

Trait adaptation (parse failure → #3238)

trait T { public function f(): int { return 1; } public function g(): int { return 2; } }
class C { use T { f as renamed; g insteadof f; } }

This compiler: parse error T_INSTEADOF
Zend: prints 12

Missing interface method (compile-time)

interface I { public function m(): void; }
class C implements I { }

Zend: compile error Class C contains 1 abstract method
This compiler: verify — file issue sub-task if silent

Abstract instantiate

abstract class A { public function f(): int { return 1; } }
new A();

Zend: fatal Cannot instantiate abstract class
This compiler: verify and match

Scope (this repo)

Layer	Files	Notes
Parser	trait adaptation patch	#3238
Compiler	lib/Compiler.php compileClassLike	Abstract + interface tables
VM	lib/VM.php	Trait merge, instanceof interface, abstract guard
JIT	lib/JIT.php	After VM PHPT green
Tests	test/compliance/cases/trait_use.phpt, abstract_class.phpt, interface_implements.phpt

Done when

• Simple use T; + abstract + interface repros remain green on VM
• Missing interface method → compile error (Zend message subset)
• new Abstract → fatal on VM
• Trait conflict without adaptation → compile error
• Language: TraitUseAdaptation — insteadof / as alias (Zend compile parity) #3238 trait adaptation tracked separately; link closed when landed
• ./script/ci-fast.sh --filter TraitUse green
• JIT/AOT: trait method call on @group llvm (or document VM fallback)

Verification

./script/docker-exec.sh -- bash -lc 'source script/php-env.sh && ./script/ci-fast.sh --filter TraitUse'
./script/docker-exec.sh -- bash -lc 'source script/php-env.sh && vendor/bin/phpunit --filter trait'

Dependencies

• Compiler: Class inheritance (extends) and interfaces #101 extends + interface instanceof (coordinate, avoid duplicate work)
• Language: TraitUseAdaptation — insteadof / as alias (Zend compile parity) #3238 trait adaptation syntax
• Language: Class methods and property access in JIT #58 / Language: Visibility, constructors, and destructors #145 method dispatch + visibility

Links

• Language: TraitUse and unsupported class body elements (self-host subset) #2314 simple trait use (VM ✅)
• Epic: Self-host critical path — compiler compiles itself (M3→M5) #1492 self-host may need interface declarations on spine
• 🗺️ ROADMAP: Self-host + web-capable PHP subset (living) #78 ROADMAP Phase 2

[PurHur]

Implementation hints — batch 99 (2026-05-25)

Prerequisite audit

Before trait flattening, confirm #101 extends assert status in lib/Compiler.php — search:

rg "assert.*extends|implements" lib/Compiler.php

If extends already compiles on master, update #101 body and use this issue for traits + abstract only.

Trait flattening sketch

class C { use T1, T2; }
  → build merged method table at compile time
  → conflict: same method name from two traits without alias → compile error

Step	File	Action
1	lib/Compiler.php	Parse Stmt_TraitUse; copy methods into class symbol
2	lib/VM.php	Method lookup checks class table then traits (flattened)
3	lib/Lint/UnsupportedRegistry.php	Remove trait-related unsupported nodes when VM accepts
4	Tests	trait_use_method.phpt, trait_conflict_fail.phpt

Schedule

Not blocking NS1 (#1044 ✅) or self-host M3 (#1492). Schedule after #145 visibility is stable on 003-scale apps.

Verify (local / Docker)

./script/ci-fast.sh --filter ComplianceTest
docker run --rm -v "$(pwd):/compiler" -w /compiler php-compiler:22.04-dev ./script/ci-fast.sh