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To: Nikita Popov <nikita.ppv@gmail.com>
CC: "internals@lists.php.net" <internals@lists.php.net>
Thread-Topic: [PHP-DEV] [RFC] Configurable callback to dump results of
 expressions in `php -a`
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Date: Sun, 3 Jan 2021 16:11:35 +0000
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Subject: Re: [PHP-DEV] [RFC] Configurable callback to dump results of
 expressions in `php -a`
From: tysonandre775@hotmail.com (tyson andre)

> Reading through the linked earlier mail, you have quite a few additional =
hooks in mind, which might need a significant amount of additional userland=
 code (such as a parser implementation) to usefully implement. At that poin=
t I'm wondering what the benefit of this hybrid approach is, relatively to =
a userland implementation like psysh.=0A=
>=0A=
> That is: =0A=
> a) Assuming all the hooks have been implemented, what additional function=
ality is the interactive shell implementation itself actually providing?=0A=
> b) Is it possible to go the other way around, and expose that additional =
functionality to userland instead? You do mention fatal error tolerance as =
one distinguishing feature -- is there anything beyond that?=0A=
=0A=
For https://wiki.php.net/rfc/readline_interactive_shell_result_function in =
particular,=0A=
compared to `php -a` in php 8.0, a subsequent RFC would provide additional =
functionality using these hooks: it would add default hooks to print a shor=
t representation of results of expressions to the interactive shell impleme=
ntation (that could be turned off or replaced to dump objects)=0A=
=0A=
- The benefit is that dumping the result of expressions improves the defaul=
t experience.=0A=
  psysh wouldn't be installed by default when a new developer is learning p=
hp through the php manual, or when sshed into a remote server.=0A=
- The reason to allow hooking it is because some objects wouldn't have a us=
er-friendly representation for var_dump/var_export (e.g. recursive data str=
uctures)=0A=
- Even if the code size is large, it may be doable by making the userland i=
mplementation part of ext/phpi/ (--enable-phpi), which is disabled by defau=
lt and can be installed in separate packages created by operating system pa=
ckage maintainers (and shrunk by using minifiers)=0A=
=0A=
Compared to psysh, the main distinguishing feature is definitely the abilit=
y to detect/tolerate fatal errors when compiling snippets or inheriting cla=
sses, and fewer dependencies to include to integrate an interactive shell w=
ith utilities for a project.=0A=
I don't think it should be exposed to regular processes or web servers, tho=
ugh, due to possible memory corruption or leaks after zend_error_noreturn (=
e.g. class inheritance errors after autoloading), etc.).=0A=
=0A=
- It would possibly be an improvement to throw an error instead of causing =
a fatal error for common mistakes in interactive shell sessions such as dup=
licate functions/parameters but I'm not sure how likely that is, especially=
 since classes and functions currently get added as the file is being compi=
led.=0A=
=0A=
Integrating userland shells like `psysh` deeply into `php -a` may wish to a=
void readline entirely and call a callback instead of printing `php>` and d=
irectly processing input like those projects already do.=0A=
Two hooks may help with enabling that approach, which can be added in `auto=
_prepend_file`=0A=
=0A=
1. A hook to call a callback instead of printing "php >" and C readline rea=
ding stdin.=0A=
    e.g. `readline_replace_interactive_shell_initializer(function () { ... =
read and process stdin in a loop })`=0A=
2. Adding a hook to call a function every time an uncatchable fatal error w=
as encountered, e.g. to resume the userland shell.=0A=
    e.g. `readline_replace_interactive_fatal_error_handler(function ($errco=
de, $errmsg, $file, $line, $errcount): bool { /* process or exit */ })`=0A=
=0A=
Thanks,=0A=
- Tyson=