Remove PCRE2_EXTRA_ALLOW_LOOKAROUND_BSK from pcre compile options

[mvorisek]

As recommended [1] by main pcre2 maintainer.

The PCRE2_EXTRA_ALLOW_LOOKAROUND_BSK compile option was introduced in dd61002. I belive it was done mainly to fix 1 failing test, not to support some strong usecase. \K in lookaround is not much useful [2]. We should compile pcre2 with default options and remove this semi-deprecated option [3].

[1] PCRE2Project/pcre2#736 (comment)
[2] PCRE2Project/pcre2#736 (comment)
[3] PCRE2Project/pcre2#736 (comment)

[nielsdos]

I'll need to spend some time this weekend reading the docs and understanding the implications (even if there is little BC concern).
One thing that may be necessary is to guard the flag with a macro-based version check. That's because it's still possible to use an older system libpcre2 version with php master.

[mvorisek]

One thing that may be necessary is to guard the flag with a macro-based version check. That's because it's still possible to use an older system libpcre2 version with php master.

I do not think so. The tests are adjusted and since this PR we do not simply pass the semi-deprecated flag.

[nielsdos]

Okay. I am fine with this, but please make the following changes to your PR:

• Add a note in the "backwards incompatibility" section in the UPGRADING file, explaining the change and also linking to the discussion.
• Squash all commits. Include in your commit description that you're dropping the semi-deprecated flag.

[mvorisek]

* Add a note in the "backwards incompatibility" section in the UPGRADING file, explaining the change and also linking to the discussion.

Done, feel free to reword it.

* Squash all commits. Include in your commit description that you're dropping the semi-deprecated flag.

Do you know you can squash merge PR using web UI?

[nielsdos]

Do you know you can squash merge PR using web UI?

Yes, but since I plan to manually merge it to have a single commit with the news as well, it's more convenient if there already is a single commit with a description.

[nielsdos]

Merged, thanks