Stdlib: sprintf()/printf() positional arguments — %1$s reordering (ext/standard/sprintf.c parity)

[PurHur]

Category

stdlib

Problem

Zend sprintf() / printf() support positional arguments in the format string (%2$s, %1$d, …) so callers can reorder values without changing argument order. This compiler rejects those specifiers at runtime:

LogicException: sprintf() unsupported conversion specifier %2 in this compiler build

(ext/standard/VmSprintf.php).

php-src reference

• php/php-src ext/standard/sprintf.c — php_sprintf() positional arg parsing (%n$ forms)
• php/php-src ext/standard/formatted_print.c — shared formatter helpers

Repro (failure today)

<?php
echo sprintf('%2$s %1$s', 'world', 'hello'), "\n";

./script/docker-exec.sh -- bash -lc 'source script/php-env.sh && php bin/vm.php repro.php'
/usr/bin/php repro.php   # Zend: hello world

This compiler: fatal in VmSprintf::format().

Additional cases for done-when:

printf('%1$d-%2$d', 10, 20);   // 10-20
sprintf('%2$.2f %1$s', 'pi', 3.14159); // 3.14 pi

Scope (this repo)

Module	Path
VM formatter	ext/standard/VmSprintf.php — parse %n$ prefix, remap arg index
Builtin wrappers	ext/standard/sprintf_.php, printf if registered
JIT/AOT	ext/standard/JitSprintf.php — delegate or document VM-only v1
Tests	test/compliance/cases/stdlib/sprintf_positional.phpt
Matrix	script/capability-matrix.php note on positional support

Done when

• Repro prints hello world on VM matching Zend
• Positional + width/precision specifiers (%2$.2f) match Zend on compliance fixtures
• Invalid positional index raises Zend-compatible warning/error (not silent wrong output)
• ./script/ci-fast.sh --filter sprintf_positional green

Related

• Epic: Self-host critical path — compiler compiles itself (M3→M5) #1492 — bootstrap/vendor code uses sprintf with positional forms in places
• Distinct from Stdlib: number_format() — numeric string coercion (ext/standard/number_format.c parity) #3596 (numeric-string coercion in number_format)

[PurHur]

claim: PHP Compiler STD Lib — starting this run

[PurHur]

Merged via #8227.

Verification (Docker):

• `php bin/vm.php test/repro/sprintf_positional_3631.php` → `hello world` / `10-20` / `3.14 pi`
• `php bin/jit.php test/repro/sprintf_positional_3631.php` → same
• `vendor/bin/phpunit --filter sprintf_positional` → OK (4 tests)
• `vendor/bin/phpunit --filter "sprintf.phpt|sprintf_conversions" test/compliance/` → OK (7 tests)

php-src reference: `ext/standard/sprintf.c` (%n$ positional forms). PHP implementation: `ext/standard/VmSprintf.php` + `lib/JIT/Builtin/StringFormatJit.php`.