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Date: Sun, 23 Oct 2022 15:43:54 +0200
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Subject: Newcomer, PHP pre-processing, Magic Constants __FILE__ and __LINE__
 override with #line like in C
From: ludovic@pouzenc.fr (Ludovic Pouzenc)

Hi,

I'm a newcomer here. I came from https://wiki.php.net/rfc/howto.

*TL;DR:* I want to know if a proposal of a #line parsing to alter 
__FILE__ and __LINE__ in PHP like it exists in C could be a good idea.

I've searched about __LINE__ and __FILE__ in mailing archives and wiki, 
I don't really find things matching. I hope it's not because "__" are 
stripped before search. "Magic constants" didn't help neither. Let me 
know if I am rethinking and old thing already imagined here in the past.

*Background / use case:* I think at first about webservices, maybe the 
useful also with browser/human-facing use cases.

With PHP, it's hard to get high responsiveness under load if user code 
start by loading a composer's autoload.php, then (lazy) loads a whole 
framework with 10+ dependencies, then execute 1 SQL request, 1 
json_encode() then output and exit. Even with "Slim" framework that 
should be minimal, using only the route feature, I see "strace" counting 
200+ file-related syscalls per request with recent 
linux/debian/apache/php-fpm.

It's not so hard to get it better with other langages : when they are 
compiled, or when framework loading happens at server start and to at 
each request.

Web projects have more and more a "compilation" phase for minimising JS, 
for proprocessing scss to css, it is possible to hook it some PHP 
processing too.

In my university, I started using a purpose-written PHP Preprocessor to 
minimize runtime dependency loading. It only understands #include like 
in C. From a src/mywebservice/v1/some-endpoint.php it will generate and 
build/mywebservice/v1/some-endpoint.php with all #include 
"some/path/somedep.php" replaced by the file's contents.

So the generated some-endpoint.php have no run-time dependency at all: 
no autoload, no include(), no require(). I think it evens maximize the 
gains with APC caching.

The preprocessor also generate things like #line 2 
"some/path/somedep.php" where an #include was encountered, then a thing 
like #line 47 "src/mywebservice/v1/some-endpoint.php" right after the 
end of the inclusion. In C, a great concrete example of #line importance 
is working with a flex/bison parser generator.

If PHP parser interpret #line as in C, __FILE__ and __LINE__ Magic 
Constants will be changed to source file and line, instead of generated 
file and line. It could greatly improve development write-then-rerun 
cycle. (missing ";" at line NN , other PHP Errors, Exception details/traces)

I hope it could unlock many use cases where "big" PHP frameworks get 
really hard time to try to compete with other languages equivalents.

Do you think it's an idea that is suitable to discuss, improve and 
submit as an RFC ?

Regards,

-- 

Ludovic Pouzenc
www.pouzenc.fr