[Polyfill] mbstring polyfill does not have its iconv dependency declared

[theofidry]

Symfony version(s) affected

All versions of symfony/polyfill-mbstring

Description

From the description of Mbstring:

Partial mbstring implementation in PHP, iconv based, UTF-8 centric.

And indeed the class uses a few ext-iconv functions, for instance: https://github.com/symfony/polyfill-mbstring/blob/1.x/Mbstring.php#L116

The package is quite old (~8yo) so I do not know if this was a conscious decision at that time, a lack of support from Composer or if this is actually wanted. But my understanding is that the package currently depends on ext-iconv but does not declare it. As a result you can end up with the following failure:

Uncaught Error: Call to undefined function Symfony\Po  
  lyfill\Mbstring\iconv_substr() in /path/to/project/vendor/symfony/  
  polyfill-mbstring/Mbstring.php:660

How to reproduce

I did not try to reproduce it on its own as I think the issue is understandable enough. But I think currently this can be done by:

• having an project using GitHub Actions with a ubuntu-latest image
• using the PHP binary coming with the image
• having the project using symfony/polyfill-mbstring and using the mb_substr() function

I encountered this issue while debugging something entirely unrelated in https://github.com/box-project/box/actions/runs/6591562359/job/17910413036?pr=1089.

Possible Solution

Add ext-iconv to the require of the composer.json

Additional Context

No response

[nicolas-grekas]

This is (was) on purpose, because there's also a polyfill for iconv.
Not listing the iconv polyfill is also on purpose, because it's a heavy one.
See composer/composer#11669 for possible next steps.
Nothing we can do here (also because it's the wrong repo ;) )

[nicolas-grekas]

For box, you might want to require the iconv-polyfill.

[theofidry]

For box, you might want to require the iconv-polyfill.

Yeah I mean it's not a problem in itself, I just wanted to make sure it was not an issue that just went under the radar for whatever reason.