Migrate from QRegExp to QRegularExpression for Qt6 compatibility

[softins]

Short description of changes

Migrate QRegExp to QRegularExpression for compatibility with both Qt5 and Qt6

Context: Fixes an issue?

Prerequisite for supporting Qt6. The code for src/util.cpp was taken from the comment by @ngocdh at
#1999 (comment)

Should ease further work towards Qt6, particularly the draft PR in #1999

Does this change need documentation? What needs to be documented and how?

No

Status of this Pull Request

Tested on Qt5 to ensure backward compatibility. Not tested on Qt6, but should be identical by design.

What is missing until this pull request can be merged?

Ready to merge.

Checklist

• I've verified that this Pull Request follows the general code principles
• I tested my code and it does what I want
• My code follows the style guide
• I waited some time after this Pull Request was opened and all GitHub checks completed without errors.
• I've filled all the content above

[softins]

Also took the opportunity to improve the URL regex so that it didn't swallow up terminating punctuation characters (such as full stop) into the hyperlink. It was based on the tested behaviour of clients such as Outlook which automatically convert plain text URLs into hyperlinks, and exclude certain terminating characters from the link when doing so (not just based on white space).

[pljones]

@jamulussoftware/maindevelopers anyone object to this being merged?

[atsampson]

@softins, in the URL regexp change, why is the negative lookahead assertion (the (<?...) bit) duplicated? The regexp seems to work fine with just one instance of it...

[softins]

@softins, in the URL regexp change, why is the negative lookahead assertion (the (<?...) bit) duplicated? The regexp seems to work fine with just one instance of it...

It's not duplicated. One of them matches a single character class, and the other matches a ? followed by the character class. Negative look-behind assertions must be of fixed length, so I couldn't make the matching of the ? variable.

The behaviour with ? was what I observed in outlook's URL highlighting when I sent myself a plaintext email containing different kinds of URL with punctuation chars immediately following.

Maybe I should add an explanatory comment...

[pljones]

Maybe I should add an explanatory comment...

You'd have to step through the full regexp if you do. That would help in future, though.

[softins]

The regex could probably be improved; it did cause me a bit of head scratching! I would be open to suggestions. The intent is to exclude from the end of the URL characters that may well be legal within the URL.

I searched without success for a standard, official regex to do it. There were many different home-grown suggestions for validating a standalone URL, but not for identifying the extent of a URL within a surrounding string.

[softins]

Anyone else want to review or comment? Otherwise I'll admin-merge it.

[atsampson]

Looks good to me!