Web: Output buffering (ob_start, ob_get_clean, ob_end_flush)

[PurHur]

Problem

Layout/template patterns wrap page body:

ob_start();
include 'view.php';
$body = ob_get_clean();
include 'layout.php';

bin/serve.php uses native PHP ob_start() for the host wrapper only. Compiled PHP has no output buffering; every echo goes straight to stdout/CGI. MiniWebApp (#67) and template includes (#54, #275 extract) need a capture buffer.

Goal

Minimal OB stack (single level is enough for v1) on VM; document JIT/AOT gap until echo hooks exist in LLVM path.

Implementation hints

1. VM context (lib/VM.php or dedicated OutputBuffer.php):
   • Stack of growable strings (or list of chunks)
   • ob_start() pushes buffer; TYPE_ECHO / TYPE_PRINT append when active
   • ob_get_clean() returns string and pops; ob_end_flush() echoes buffer and pops
   • ob_get_level() returns stack depth
2. Nested ob_start (v2): second level optional; v1 may error on double-start like Zend
3. Include interaction: include inside OB (Language: include/require in JIT and AOT (multi-file applications) #54) must route echoes into active buffer
4. Serve/CGI: flush top buffer before sending headers in bin/serve.php wrapper (host PHP) — compiled OB is separate from host ob_start() in serve.php
5. JIT/AOT: defer — document VM-only in docs/capabilities.md; lint registry flags ob_start until JIT lands

Files

File	Change
ext/standard/ob_start.php (etc.)	VM builtins
lib/VM.php	Hook echo when ob_get_level() > 0
test/compliance/cases/stdlib/ob_start.phpt	Capture + layout pattern
lib/Lint/UnsupportedRegistry.php	Until implemented

Scope

• VM: ob_start, ob_get_clean, ob_end_flush, ob_get_level
• PHPT: nested echo captured, layout pattern with two includes
• Capability matrix row
• JIT/AOT: stretch goal (string buffer in runtime or skip)

Acceptance criteria

./phpc run -r 'ob_start(); echo "body"; $b=ob_get_clean(); echo "wrap:", $b;'
# wrap:body

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

Verification (local / Docker only)

No .github/workflows/* changes.

Dependencies

• Language: include/require in JIT and AOT (multi-file applications) #54 include/require (echo inside included file)
• Stdlib: extract() and compact() for PHP template includes #275 extract/compact templates (consumer)
• Web: Output buffering (ob_start, ob_get_clean, ob_end_flush) #118 blocks clean layout for Reference: MiniWebApp lint-first skeleton (examples/003-MiniWebApp) #246 skeleton

Links

• bin/serve.php (host OB only today)
• 🗺️ ROADMAP: Self-host + web-capable PHP subset (living) #78 ROADMAP Phase 2 (stdlib)
• Reference app: examples/003-MiniWebApp (router, templates, forms) #67 MiniWebApp templates