Add PHP pkg-config (pkgconf) .pc metadata file(s)

[petk]

Since PHP *nix Autotools build system already extensively relies on
pkgconf (pkg-config) command-line tool to find dependencies it should
also provide its .pc metadata file(s). 1

This adds an initial php.pc.in and php-embed.pc.in templates that are
created during the configuration and build phase. They are installed in
the provided system pkgconfig directory. For example:

/usr/lib/pkgconfig/php.pc
/usr/lib/pkgconfig/php-embed.pc
/usr/lib/pkgconfig/php-embed8.pc
/usr/lib/pkgconfig/php-embed8.4.pc
/usr/lib/x86_64-linux-gnu/pkgconfig/php.pc

Pkgconf 2 is a maintained continuation of the initial Freedesktop's
pkg-config project 3.

Extensions and applications embedding the PHP Embed SAPI can then
use also pkgconf to get the required PHP CFLAGS and/or LIBS.

For PHP extensions:

pkgconf --cflags php
pkgconf --libs php
pkgconf --modversion php
pkgconf --cflags php8.4

Applications embedding the PHP Embed SAPI:

pkgconf --libs php-embed
pkgconf --cflags php-embed
pkgconf --modversion php-embed
pkgconf --cflags php-embed8.4

Mapping of php-config and pkg-config usage:

php-config option	pkg-config
--prefix	pkg-config --variable=prefix php
--includes	pkg-config --cflags-only-I php
	pkg-config --cflags php
--ldflags	pkg-config --libs-only-L php
--libs	pkg-config --libs-only-l php
	pkg-config --libs-only-other php
	pkg-config --libs php
--extension-dir	pkg-config --variable=php_extension_dir php
--include-dir	pkg-config --variable=includedir php
--lib-dir	pkg-config --variable=libdir php-embed
--lib-embed	N/A
	pkg-config --libs php-embed (--shared)
	pkg-config --libs php-embed --static
--man-dir	N/A
--php-binary	N/A
--php-sapis	N/A
--ini-path	pkg-config --variable=php_ini_path php
--ini-dir	pkg-config --variable=php_ini_dir php
--configure-options	N/A
--version	pkg-config --modversion php
--vernum	pkg-config --variable=php_vernum php
	pkg-config --variable=php_zts php
	pkg-config --variable=php_debug php

[morrisonlevi]

I think we should add variables php_debug and php_zts as well. Extensions need to know this information to order to know what ABIs to build for.

[petk]

I think we should add variables php_debug and php_zts as well. Extensions need to know this information to order to know what ABIs to build for.

Yes, this list of variables needs to be expanded further. I've added php_debug=yes|no and php_zts=yes|no variables.

[morrisonlevi]

I think it needs the PHP_VERSION_ID as well. The php-config calls this --vernum. I may try building against this today to see if I can get it to work.

[petk]

I think it needs the PHP_VERSION_ID as well. The php-config calls this --vernum. I may try building against this today to see if I can get it to work.

This one is added as php_vernum. php_vernum=@PHP_VERSION_ID@.

[morrisonlevi]

I just built from source and this one didn't get expanded:

Cflags.private: @PHP_CFLAGS_PRIVATE@

Also, is it expected that it goes into ${prefix}/lib/php/pkgconf instead of ${prefix}/lib/pkgconf?

[petk]

I just built from source and this one didn't get expanded:

Cflags.private: @PHP_CFLAGS_PRIVATE@

Also, is it expected that it goes into ${prefix}/lib/php/pkgconf instead of ${prefix}/lib/pkgconf?

Fixed in the 3rd commit. Installation now puts it to pkgconf directory in libdir. For now, I've removed this Cflags.private part.

[Girgias]

@morrisonlevi could you have another look to see if this behaves like you expect it?

I have no knowledge about build systems/package dependency resolution for system libraries, but I think or we be good to use what seems to be industry standard.

[petk]

I've rebased the branch so it's easier to handle this PR. Here actually everything works but PHP has a bit of weird include flags handling at the moment. This pkg-config template files are (for now) done like the php-config script is done. I'll recheck all the pkg-config variables again what needs to be added.

As far as the PHP-8.4 is concerned I won't touch the include flags yet in this branch. Because they aren't done correctly. Neither the main PHP include directory is done correctly. This also goes for the php-config script. They are for now hard-coded in there as part of the PHP history, but they would need to be dynamic.

[petk]

I've also added a quick table for tracking options between php-config script and possible pkg-config alternatives in the PR's first post. The next appended commit adds some fixes and syncs of the .pc.in templates.

[petk]

Yes, this pkg-config stuff is complex, anyone here to test it :D?

Basically it works but the main issue with this will be in scenarios where different PHP versions are installed (where also php-config is prone to errors) or when installing PHP with program prefix/sufix (like php8.4), or when in extreme case both static and shared libphp embed is installed. The PHP Embed library still probably needs one more adjustment to totally match the php-config's php-config --lib-embed behavior. But I think we can adjust these .pc files on the go as needed, either through PHP 8.4 bug fixes or add more fine-tuned features in the next version...

[petk]

I got another idea about the php_zts and php_debug variables. Instead of these only a single pkg-config variable like php_features can be added:

--- a/scripts/php.pc.in
+++ b/scripts/php.pc.in
@@ -12,10 +12,7 @@ php_vernum=@PHP_VERSION_ID@
-# Whether PHP is built in debug mode (yes) or not (no).
-php_debug=@ZEND_DEBUG@
-# Whether PHP is built with thread safety (yes) or not (no).
-php_zts=@PHP_THREAD_SAFETY@
+php_features="@PHP_FEATURES@"

This php_features would be a space separated list of enabled features, for example:

php_features="DEBUG ZTS"

Then the php_features can be parsed manually by the build system where needed. And it can be a bit simpler extended in the future with more "features" if needed. For example, curl is using a similar approach and I think it works pretty ok.

Anyhow, I think that this won't be able to land in PHP 8.4 so, let's target next PHP version here then.

[cmb69]

Generally, this looks like a very good (and overdue) addition (we could get rid of php-config in the long run). Thank you!

I got another idea about the php_zts and php_debug variables. Instead of these only a single pkg-config variable like php_features can be added:

I think this is a good idea. (I would probably go with features only, though.)

[cmb69]

This might better be pkg-config metadata file or maybe just .pc, or something like this.

[cmb69]

Out of curiosity, what's the difference between these macros?

[cmb69]

Hmm, isn't this supposed to be the description of the package? So maybe instead

Suggested change

	Description: Build extension for a PHP general-purpose scripting language
	Description: A popular general-purpose scripting language that is especially suited to web development

[cmb69]

Do we need to add @PHP_LDFLAGS@ here?