Runtime: set_exception_handler() / restore_exception_handler() (ext/standard parity)

[PurHur]

Category

stdlib / runtime

Problem

set_exception_handler() and restore_exception_handler() are not registered. Uncaught exceptions always reach the VM top-level handler; Zend allows a user callback (and a stack of previous handlers) before process exit.

Blocked by: builtin Exception / Throwable classes (#195) — handler receives Throwable objects.

php-src reference

• ext/standard/basic_functions.c — PHP_FUNCTION(set_exception_handler), restore_exception_handler
• Zend/zend_exceptions.c — zend_exception_get_default(), uncaught handler chain, zend_throw_exception_hook

Repro (today)

./script/docker-exec.sh -- bash -lc 'source script/php-env.sh && php bin/vm.php -r "var_dump(function_exists(\"set_exception_handler\"));"'
# bool(false)

<?php
set_exception_handler(function (Throwable $e): void {
    echo 'handled:', $e->getMessage(), "\n";
});
throw new Exception('x');

Zend PHP: handled:x (no fatal). This compiler: undefined function and/or non-existing class Exception.

Stack behavior (done-when detail)

set_exception_handler(fn() => print "a\n");
set_exception_handler(fn() => print "b\n");
restore_exception_handler();
throw new Exception('z');
// Zend: prints b, then on second restore a, then default handler

Scope (this repo)

Piece	Path
Builtin	ext/standard/set_exception_handler.php, restore_exception_handler.php
Registry	ext/standard/Module.php
VM	lib/VM/Context.php — handler stack; lib/VM.php uncaught path calls top handler
Prerequisite	#195 — register Exception, Throwable, Error
Web	lib/Web/ — optional: map uncaught to HTTP 500 after handler (#152)
Tests	test/compliance/cases/stdlib/exception_handler.phpt

Done when

• Language: throw expressions and Exception object propagation #195 landed (or stub Exception sufficient for repro)
• First repro prints handled:x on VM without process fatal
• restore_exception_handler() restores previous callback; nested set_* matches Zend order
• Handler returning false falls through to previous/default (Zend)
• ./script/ci-fast.sh --filter exception_handler green

Verification

./script/docker-exec.sh -- bash -lc 'source script/php-env.sh && vendor/bin/phpunit --filter exception_handler'

Related

• Language: throw expressions and Exception object propagation #195 throw/catch objects · Stdlib: error_log() — write message to SAPI/error log (ext/standard/basic_functions.c parity) #3380 error_log · Epic: Self-host critical path — compiler compiles itself (M3→M5) #1492 self-host exception paths

Labels

stdlib, implementation-ready, phase-4:stdlib, area:vm

[PurHur]

claim: agent-lane-c — starting this run (Runtime exception handler stack; #195 Exception builtins present on master)

[PurHur]

claim: cursor-agent-lane-c — continuing PR #3887 this run (rebase + verification)

[PurHur]

Verification (cursor-agent-lane-c continuation)

Continued PR #3887 — all #3146 done-when criteria green:

• function_exists('set_exception_handler') → bool(true)
• exception_handler.phpt — uncaught Throwable → handled:x, exit 0
• exception_handler_restore.phpt — nested set_* + restore_exception_handler() → a
• exception_handler_fallthrough.phpt — handler returning false falls through to previous

./script/docker-exec.sh -- bash -lc 'source script/php-env.sh && vendor/bin/phpunit --filter exception_handler'
# OK (3 tests, 6 assertions)

This run: fixed dispatch to walk the stack by index without popping handlers that return false (Zend parity).

PR: #3887

[PurHur]

claim: cursor-agent-lane-c — continuing PR #3887 this run (merge-ready verification)

[PurHur]

Verification (cursor-agent-lane-c — PR #3887 continuation)

Lane C had no new non-stdlib implementation-ready issues without an open PR; continued this run on #3146.

Done-when

• function_exists('set_exception_handler') → bool(true)
• Uncaught handler repro → handled:x
• Nested restore_exception_handler() → inner handler only (exception_handler_restore.phpt)
• Handler returning false falls through (exception_handler_fallthrough.phpt)
• String callback name (exception_handler_string_callback.phpt) — added this run

./script/docker-exec.sh -- bash -lc 'source script/php-env.sh && vendor/bin/phpunit --filter exception_handler'
# OK (4 tests, 8 assertions)

php-src reference

• ext/standard/basic_functions.c — set_exception_handler, restore_exception_handler
• Zend/zend_exceptions.c — uncaught handler chain (false return does not pop stack)

PR: #3887 (merge-ready)

[PurHur]

Merged (cursor-agent-lane-c): PR #3887 squash-merged after rebase onto master.

Done-when (all green)

• function_exists('set_exception_handler') → bool(true)
• Uncaught Throwable → handled:x (exit 0)
• Nested restore_exception_handler() → inner handler only
• Handler returning false falls through to previous handler
• String callback name supported

Verification

./script/docker-exec.sh -- bash -lc 'source script/php-env.sh && vendor/bin/phpunit --filter exception_handler'
# OK (4 tests, 8 assertions)

./script/docker-exec.sh -- bash -lc 'source script/php-env.sh && php bin/vm.php -r "var_dump(function_exists(\"set_exception_handler\"));"'
# bool(true)

php-src reference

• ext/standard/basic_functions.c — set_exception_handler, restore_exception_handler
• Zend/zend_exceptions.c — uncaught handler chain (false return does not pop stack)

PR: #3887