PHP Warning: Constant already defined when processing multiple sources with __halt_compiler()

Description

Whenever PHP processes more then one __halt_compiler() statement in one session, it emits this cryptic warning:

PHP Warning:  Constant  already defined in ...

Note the empty constant name.

There are several ways to trigger this. Here's one:

# echo '<?php __halt_compiler();' >inc.php
# php -a
php > include('inc.php');
php > include('inc.php');
PHP Warning:  Constant  already defined in /tmp/inc.php on line 1

Here's another:

# php -r "eval('?><?php __halt_compiler();'); eval('?><?php __halt_compiler();');"

PHP Version

PHP 8.4.5 (cli) (built: Mar 12 2025 16:58:15) (NTS)
Copyright (c) The PHP Group
Zend Engine v4.4.5, Copyright (c) Zend Technologies

Operating System

No response

Confirm this with 8.0.30:

php -v
PHP 8.0.30-master-850_prod-centos (cli) (built: Nov  2 2023 08:51:55) ( NTS )
Copyright (c) The PHP Group
Zend Engine v4.0.30-dev, Copyright (c) Zend Technologies

php -r "eval('?><?php __halt_compiler();'); eval('?><?php __halt_compiler();');"

Warning: Constant  already defined in Command line code(1) : eval()'d code on line 1

Thanks for the report.

This is because __halt_compiler() also declares the __COMPILER_HALT_OFFSET__ constant:
https://www.php.net/manual/en/function.halt-compiler.php

This design is really just dubious, so I'm not sure this can be fixed without replacing the constant with a function, like compiler_halt_get_last_offset(). So, I'm tending towards closing this as a #wontfix.

Why not just avoid declaring __COMPILER_HALT_OFFSET__ if it's already declared? Any approach is better then the current obscure warning.

Any approach is better then the current obscure warning.

Not necessarily. If you expect __COMPILER_HALT_OFFSET__ to be something else, then no warning is not better.

I'd honestly expect __COMPILER_HALT_OFFSET__ to work like __FILE__ - i.e. you'd get the offset of the current file. (Which you might then assign to a variable or something.)

Might be sensible. However, any such change here is breaking. As such, this will at least require some discussion.

I'd honestly expect __COMPILER_HALT_OFFSET__ to work like __FILE__ - i.e. you'd get the offset of the current file.

Doesn't it already work like that?

# echo '<?php __halt_compiler();' >inc.php
# php -a
php > include('inc.php');
php > include('inc.php');
PHP Warning:  Constant  already defined in /tmp/inc.php on line 1
php > echo __COMPILER_HALT_OFFSET__;
PHP Warning:  Uncaught Error: Undefined constant "__COMPILER_HALT_OFFSET__"

Actually, yes, you are right. __COMPILER_HALT_OFFSET__ is mangled with the current file name. So, suppressing the warning might be feasible after all, given that __halt_compiler(); will always occur in the same place for a given file.

Fix "Constant already defined" warning with repeated inclusion of fil…

Navigation Menu

Repository navigation

PHP Warning: Constant already defined when processing multiple sources with __halt_compiler() #18850

Description

PHP Version

Operating System

Metadata

Assignees

Labels

Type

Projects

Milestone

Relationships

Development

PHP Warning: Constant already defined when processing multiple sources with __halt_compiler() #18850

Description

Description

PHP Version

Operating System

Activity

Sannis commented on Jun 23, 2025

iluuu1994 commented on Jun 23, 2025

ProgerXP commented on Jun 23, 2025

iluuu1994 commented on Jun 23, 2025

bwoebi commented on Jun 23, 2025

iluuu1994 commented on Jun 23, 2025

ProgerXP commented on Jun 23, 2025

iluuu1994 commented on Jun 23, 2025

Metadata

Metadata

Assignees

Labels

Type

Projects

Milestone

Relationships

Development

Issue actions