JIT: Self-host spine link — Struct::getElementType on __string__ pointer params

[PurHur]

Problem

make bootstrap-selfhost-lib-spine-smoke / native link of compiler_lib_spine_smoke fails on harness when expanding real JIT lowering on string builtins:

Call to undefined method Struct::getElementType()

Stack points at generated code in lib/JIT/Builtin/Type/String_.php (e.g. strlen / __string__alloc paths) calling:

$string->typeOf()->getElementType()->getName()

on LLVM values whose typeOf() is already a pointer (__string__*), not a struct wrapper — getElementType() is invalid on Struct in PHPLLVM for that shape.

This blocks:

• CI: Default BOOTSTRAP_LIB_SPINE_VM_SMOKE_GATE=1 in ci-local (#1846 follow-up) #1867 / PR CI: default BOOTSTRAP_LIB_SPINE_VM_SMOKE_GATE=1 in ci-local (#1867) #1875 — default BOOTSTRAP_LIB_SPINE_VM_SMOKE_GATE=1 in ci-local
• North Star 2 presenter step 4 (DevEx: make north-star2-verify presenter gate (self-host M0–M4) #1865) spine link stage
• Growing M2 spine beyond stubbed ExternalMethod for hot string paths

Goal

Spine bundle links under AOT with real String_ JIT lowering (no Struct::getElementType fatal).

Implementation hints

Area	Files	Approach
Root cause	lib/JIT/Builtin/Type/String_.php	Audit all typeOf()->getElementType() on params; use Context::getStringFromType() / struct name from pointer element type
Pattern	lib/JIT/JitValueBox.php, lib/JIT/Context.php	Existing helpers resolve __string__ / __value__ without double getElementType
Regression	test/selfhost/compiler_lib_spine_smoke/	Must link in make bootstrap-selfhost-lib-spine-smoke
Policy	lib/JIT/SelfHostBuiltinPolicy.php	Keep stub until fix proven; then allowlist symbol batch

Repro (Docker)

make docker-build-22
docker run --rm -v "$(pwd):/compiler" -w /compiler php-compiler:22.04-dev \
  bash -lc 'make bootstrap-selfhost-lib-spine-smoke 2>&1 | tail -40'

Acceptance criteria

• BOOTSTRAP_LIB_SPINE_SMOKE=1 make bootstrap-selfhost-lib-spine-smoke exits 0 in php-compiler:22.04-dev
• No Struct::getElementType fatal from String_.php during link
• ./script/ci-local.sh still green (full gate after CI: Default BOOTSTRAP_LIB_SPINE_VM_SMOKE_GATE=1 in ci-local (#1846 follow-up) #1867 flip)
• CI: Default BOOTSTRAP_LIB_SPINE_VM_SMOKE_GATE=1 in ci-local (#1846 follow-up) #1867 / CI: default BOOTSTRAP_LIB_SPINE_VM_SMOKE_GATE=1 in ci-local (#1867) #1875 unblocked for default-on spine VM smoke gate

Dependencies

• Epic: Self-host critical path — compiler compiles itself (M3→M5) #1492 epic · Self-host M2: land final 3 ext/standard Vm* units in compiler_lib_spine_smoke (578→586) #1821 ✅ Vm* spine · Self-host: Single source of truth for M2 spine unit counts (584/585/586/588 drift) #1872 ✅ count SSOT
• CI: Default BOOTSTRAP_LIB_SPINE_VM_SMOKE_GATE=1 in ci-local (#1846 follow-up) #1867 — CI default-on (follow-up)
• Orthogonal: Infrastructure: LLVM 9 → 14+ upgrade and CI matrix #174 LLVM version (toolchain, not this bug)

Verification (local / Docker only)

make bootstrap-selfhost-lib-spine-smoke
BOOTSTRAP_LIB_SPINE_VM_SMOKE=1 make bootstrap-selfhost-lib-spine-vm-smoke

No GitHub Actions.

Links

• ROADMAP 🗺️ ROADMAP: Self-host + web-capable PHP subset (living) #78 Phase 5 Self-host
• Open PR CI: default BOOTSTRAP_LIB_SPINE_VM_SMOKE_GATE=1 in ci-local (#1867) #1875 (blocked on this)

[PurHur]

PR #1884 fixes the `Struct::getElementType()` fatal in `String_.php` by adding `Context::structFieldIndex()` and updating yay macros + generated builtins.

Verified in Docker (`php-compiler:22.04-dev`):

• `bootstrap-selfhost-lib-spine-smoke-link.sh` no longer hits `getElementType` on struct types; compile proceeds into spine JIT lowering.
• Full spine link still ends in an LLVM segfault on this harness (pre-existing / separate).

This unblocks re-running PR #1875 (`BOOTSTRAP_LIB_SPINE_VM_SMOKE_GATE` default-on) once spine link is green end-to-end.

[PurHur]

PM: Implementation PR #1884 open (batch 80). Merge #1884 first → unblocks #1875 / #1867. Re-verify: make bootstrap-selfhost-lib-spine-smoke in php-compiler:22.04-dev.