fix(ir_lower): resolve a constructor signature through its owner class

[Guikingone]

Closes #868.

Cause

A private method is not inherited, so ClassInfo::methods deliberately carries no __construct entry on a descendant of a class with a private constructor. types::constructor_owner exists to walk to the ancestor that still owns it, and #796 routed the checker and new codegen through it.

Two IR-lowering sites — both named in the issue — kept reading class_info.methods.get("__construct") directly, so such a descendant looked like it had no constructor at all:

Site	Symptom
object_construction::constructor_signature	no signature → omitted defaults never padded → fixed_new rejects the arity: constructor call to Child::__construct with 0 args for 1 params
reflection_new_instance::constructor_signature_for_class_name	no signature → ReflectionClass::newInstance() pads nothing and runs no constructor, leaving promoted properties at their zero values

<?php
class Owner {
    private function __construct(private int $n = 1) {}
    public static function makeChild(): Child { return new Child(); }
    public function n(): int { return $this->n; }
}
class Child extends Owner {}
echo Owner::makeChild()->n();   // php: 1 — elephc: backend error

Fix

Both sites resolve through constructor_owner. An inherited public or protected constructor is unaffected: the walk stops at the instantiated class itself whenever its own map has the entry, and a descendant that replaces the constructor keeps its own for the same reason.

Tests

Six tests in tests/codegen/oop/relative_types.rs, next to the existing constructor_owner coverage:

• regression — padding an inherited private constructor's defaults on the named path (the fixture above)
• regression — test_reflection_new_instance_resolves_an_inherited_private_constructor: measured 6 with the owner walk, 0 without it, and verified to fail on the unpatched lowering
• an explicitly passed argument still winning over the default
• the reflection control with a public inherited constructor (it passes either way, since a public constructor is copied into the descendant's map)
• an inherited public constructor still padding (unchanged path)
• a descendant that declares its own constructor keeping it (unchanged path)

The reflection regression fixture depends on a separate elephc gap: newInstance() does not yet enforce constructor visibility, where php-src raises Error: Call to private Owner::__construct(). Its docblock says so, and says that closing that gap should turn the fixture into a rejection test rather than delete it — the lookup it pins is what decides which class's constructor the visibility check would then be asked about.

--test codegen_tests oop (810), relative_types (26), --test error_tests (1518) and cargo test --lib pass; cargo build is warning-free. One unrelated flake, elephc-pcntl's priority_failure_warnings_name_the_operation_and_errno, fails only under the parallel suite and passes in isolation — it lives in another crate that this change cannot reach.

Scope

The new static() form in the issue's reproduction is blocked earlier by #797, which rejects a new static() whose constructor has omitted defaults even for a public constructor with no inheritance at all:

<?php
class Plain {
    public function __construct(public int $n = 1) {}
    public static function make(): static { return new static(); }
}
Plain::make();   // dynamic object construction for Plain without EIR-lowered candidates

That path is out of scope here exactly as the issue states ("Not #797 … This is the named/fixed_new owner path after #796"). The dynamic thunk builder in ir_lower::function::lower_dynamic_constructor_thunk has the same methods lookup and will need the same treatment when #797 lands; it is left alone here because no shape can exercise it while #797 stands.

🤖 Generated with Claude Code

https://claude.ai/code/session_01KSAAWPyNBq6dP2b5puN3wr

[greptile-apps]

Greptile Summary

Resolves constructor signatures through constructor_owner in fixed object construction and reflection lowering, allowing private ancestor constructors to supply omitted defaults.

• Adds regression coverage for private-ancestor defaults and controls for explicit arguments, public inheritance, and constructor overrides.
• Both previous findings are fixed: reflection now has a distinguishing regression fixture, and the stopping-condition docblock is corrected.
• No file changes exist since the previous review SHA, and no new actionable findings were identified.

Confidence Score: 5/5

The PR appears safe to merge, with both previous findings addressed and no new blocking findings.

The private-ancestor reflection fixture now distinguishes owner lookup from direct lookup, and the public-inheritance docblock correctly states that traversal stops when the constructor entry exists. The stopping-condition thread was resolved without an explanatory reply; the code confirms its correction. There are no file changes since the previous review.

Important Files Changed

Filename	Overview
src/ir_lower/expr/object_construction.rs	Resolves fixed-class constructor metadata through the owner lookup so inherited private-constructor defaults can be padded.
src/ir_lower/expr/reflection_new_instance.rs	Uses the same owner lookup for known-class reflection constructor signatures.
tests/codegen/oop/relative_types.rs	Adds six regression and control tests, including the previously missing reflection fallback regression, and corrects the stopping-condition documentation.

_{Reviews (4): Last reviewed commit: "test(oop): add the reflection regression..." | Re-trigger Greptile}

[nahime0]

lgtm