please add proper tests for this functionality

No idea how

Because there are a couple of bug reports where often the response was like "No, can't be done" need this a closer look from @dhaumann and @cullmann

@loh.tar Slightly related: You may want to also have a look at this: https://phabricator.kde.org/source/ktexteditor/browse/master/src/script/data/commands/utils.js$271
In short, there is a command line command (F7) called 'rewrap' that rewraps the selection in a "smart" way. My idea when writing this once was:

1. there is a target wrap column, say 80
2. there is a soft violation wrap column, say 82
3. there is a minimum wrap column, say 70

Now, lets take the following example:

         1         2         3         4         5         6         7         8
1234567890123456789012345678901234567890123456789012345678901234567890123456789012345
the quick brown fox jumps of the lazy dog. The bla bla bla bla bla aRatherLongWord

Now, usually, aRatherLongWord would wrap to the next line, since it is longer that column 80. However, it leaves a "big gap" starting at column <70 (cf. 3. soft wrap above) in the end of the line, which is visually not so appealing ;) So in this case, we allow violation of the hard-wrap at 80, and instead allow a violation up to column 82 (cf. 2. above).

With this, you can for instance nicely rewrap a TeX document so that you can nicely read it without too big gaps at the end of a line.

However, to be honest, I don't even know whether I ever finished the implementation, so maybe rewrap even does something different...

Interesting. Didn't know that such function exist. Well, it may help to read the handbook...
Is there no GUI way to access such stuff? "Read the handbook" lala...

Well, word/text wrapping is a field which has many room for improvements.

• Adjust as block by inserting spaces at "smart" places to avoid ugly holes in the overall appearance
• Wrap/split the word, not only text at a space. IIRC Is that somewhere done in Kate, or was there a function in Sonnet which offer that(?)
• Your smart solution to allow in rare cases to extend the desired width
• Probably some more I didn't know
• Keep the indent: https://bugs.kde.org/show_bug.cgi?id=135737
• Keep the indent and the "semantic", e.g. "Is comment" or "Is citation (like in e-mails)" https://bugs.kde.org/show_bug.cgi?id=369049

As some of you know, I talk often about the latter two issues and I'm willing to fix that.
The first three are really nice but more like the candy after the necessary lunch.

also don't change the behavior of wordwrapping that is used by the view compared to what we would get by calling wordwrap on the document directly

It's somehow not the case. The document has no such function. It's similar to ViewPrivate::smartNewline() or ViewPrivate::killLine().

ViewPrivate::applyWordWrap() is (now) like a higher level functionality based on two lower level functions.

When everyone want this into the document, I can try to do it. Just give advice how exactly.
My only idea is to add a new function (e.g. wrapParagraph, reformatLines), which will result in an almost empty ViewPrivate::applyWordWrap().

I am ok with the change, but I would like to have one test case in

https://cgit.kde.org/ktexteditor.git/tree/autotests/src/katedocument_test.cpp

It must be nothing complex, just fill a document with a bit of text and apply the wrapping and check the result. The case should include the kind of input that profits by this change.

As it is a document function, nothing more fancy must be done than calling it with the right line pair.