Self-host M3: native compile unit probe on lib/Parser.php slice

[PurHur]

Problem

M3 unit probes today cover Compiler (#2216), JIT (#2332 ✅ script), and VM (#2354 ✅ script) — but not the CFG parse front-end (PHPCfg\Parser via lib/Compiler.php → vendor ircmaxell/php-cfg). Contributors cannot tell whether native link failures are in emit/lowering vs parseStmt/parseExpr paths that block self-host on real PHP 8 syntax.

There is no test/selfhost/parser_unit_probe/ tree or bootstrap-selfhost-parser-unit-probe.sh yet (title references CFG Parser slice, not a lib/Parser.php file).

Goal

1. test/selfhost/parser_unit_probe/main.php — smallest honest require_once chain that loads lib/Compiler.php and exercises a fixed parse-only or compile-to-CFG path on a tiny fixture (no full spine).
2. script/bootstrap-selfhost-parser-unit-probe.sh — native AOT link + run printing parser_unit_probe bundle OK (mirror Self-host M3: native compile-driver unit probe on lib/JIT.php slice #2332 / Self-host M3: native compile unit probe on lib/VM.php slice #2354).
3. Document in docs/bootstrap-selfhost.md M3 probes table + make bootstrap-selfhost-parser-unit-probe.
4. Follow-ups: CI gate (new issue after this lands), north-star3-verify step 5, default-on flip.

Implementation hints

Piece	Path	Notes
Probe tree	test/selfhost/parser_unit_probe/main.php	Start from compiler_minimal-scale deps; add lib/Compiler.php + lint helpers only
Vendor CFG	vendor/ircmaxell/php-cfg/lib/PHPCfg/Parser.php	Patched via script/apply-patches.sh — probe must run after patches
Emit driver	Reuse php bin/compile.php -l / bootstrap-selfhost-compile-smoke-probe.sh env	PHP_COMPILER_SELFHOST_AOT=1, BOOTSTRAP_M3_COMPILE_DRIVER_REAL_LOWERING=1 when strict
Allowlist	lib/JIT.php isM3CompileDriverRealLoweringName()	Expand per #1768 — do not duplicate batch tracker
Makefile	Makefile	bootstrap-selfhost-parser-unit-probe target
Test	test/unit/BootstrapParserUnitProbeTest.php	Assert script + expected stdout substring

Suggested slice (first PR)

• Fixture: test/selfhost/parser_unit_probe/fixture.php with one class, one method, one if — enough to hit parseStmt_* without full web stack.
• Link output: build/selfhost-parser-unit-probe (same pattern as jit/vm probes).
• If vendor PHPCfg\Parser cannot link yet, gate script with clear skip + link to Self-host: Unsupported expression CFG batch tracker (post-#2254 triage) #2301 / Self-host: Unknown Stmt Type lowering batch tracker (post-#2254 triage) #2276 triage buckets.

Unblock order

#1768 honest lowering batches → #1937 strict emit → #2216 compiler probe → this probe → #1520 stub retirement

Acceptance criteria

./script/bootstrap-selfhost-parser-unit-probe.sh
php bin/compile.php -l test/selfhost/parser_unit_probe/main.php

Harness (Runforge — do not use raw bind-mount docker run):

./script/docker-exec.sh -- bash -lc 'source script/php-env.sh && ./script/bootstrap-selfhost-parser-unit-probe.sh'

• Native binary prints parser_unit_probe bundle OK
• Skip message when LLVM 9 missing (same as other bootstrap probes)
• No .github/workflows/* changes

Dependencies

• Self-host M3: native compile-driver probe on lib/Compiler.php unit #2216 — compiler unit probe (sibling; may land first)
• Self-host M3: native compile-driver unit probe on lib/JIT.php slice #2332 ✅ / Self-host M3: native compile unit probe on lib/VM.php slice #2354 ✅ — pattern for probe scripts
• Self-host M3: compile-driver real lowering symbol batch tracker #1768 — symbol batch tracker
• Self-host M3: Native emit for compiler compile-smoke fixture (post-#1493) #1937 → CI: BOOTSTRAP_M3_COMPILE_SMOKE_STRICT_GATE opt-in in ci-local after #1937 #1968 — M3 strict emit ladder
• Dependencies: php-parser token map for PHP 8.2+ host runs #113 — host PHP parser tokens (orthogonal; VM path in Docker)

Links

• Epic Epic: Self-host critical path — compiler compiles itself (M3→M5) #1492 · Presenter Testing: make north-star3-verify — M3 native unit probe bundle #2360 (make north-star3-verify)
• ROADMAP 🗺️ ROADMAP: Self-host + web-capable PHP subset (living) #78 Phase 1 Language + Self-host probes
• CFG coordination Self-host: CFG lowering batch coordination (stmt/expr/op trackers) #2362

[PurHur]

Fourth M3 unit probe slice (Parser front-end). Follow-up: CI gate issue after script lands (mirror #2361 pattern). ROADMAP #78 updated.