Category Archives: Common

During Akademy there was finally enough time to finalize the porting of KTextEditor to KSyntaxHighlighting.

Thanks to the help of Dominik and Volker, the needed extensions to the KSyntaxHighlighting framework were done in no time ;=)

Thanks for that!

The branch for the integration was merged to master yesterday, unit tests look OK and I am using that state now for my normal coding work. Beside minor glitches that should now be corrected, no issues came up until now.

But as with all changes, for sure some regressions slipped in.

If you notice strange behavior of the highlighting in master, please report the issues on bugs.kde.org or on our mailing list (or even better: provide a fix on phabricator).

For sure there are potential further cleanups and now that we have only one implementation of the highlighting infrastructure, we will be able to move forward with extensions of it much easier.

We contacted the QtCreator people, to see if we might be able to share a common implementation, as they have an own one at the moment. Hopefully that works out in a nice way and our KDE syntax-highlighting framework gets an even broader user base!

After a long time of constant distraction by my daily work, I finally found again a bit time to take care of KTextEditor/Kate/… issues.

One thing that really started to be an itch I wanted to scratch is some rendering fault that occur with ‘special’ font sizes.

Given I wanted to do again a bit work on the macOS port, I was really annoyed that on my screen the only application with text rendering issues was “my” one :/

I assume a lot of people have sometimes seen stuff like that in KTextEditor based applications like Kate or KDevelop:

These small white lines really stick out like a sore thumb 🙁 It looked like some off-by-one rounding issue, surely one should be able to find it…

I tried to track down where in our rendering in KTextEditor we do create these artifacts, but I never found any place that looks like a possible cause.

After a bit more tinkering it became obvious that actually it would be more or less impossible for the KTextEditor code to mess up the painting in such a way, as we normally draw one line more or less as one thing using QTextLayout that handles the painting of the selection background, too.

Using QtCreator as an non-KTextEditor based application that uses the Qt layouting & rendering it was possible to get similar effects on macOS (or X11):

:=) Good thing that Qt is open source. A quick look into the qtextlayout.cpp and a qt5 compile later, I was able to trace the issue down to some qFloor calls for painting the selections.

I hope my patch is correct and will be accepted (QTBUG-66036 / Gerrit 219804) or at least helps others to do the correct fix.

At least for the syntaxhighlighter example shipped with Qt I was able to reproduce the issue before my patch but not afterwards.

Would Qt not be open-source, I would have been at the end of the line after seeing no “error” in our codebase in KTextEditor.

With Qt as some open-source project, it is a completely different story.

Besides, the Qt documentation for “how to build it” and “how to contribute” on the Qt Wiki are well enough to understand that I was able to nicely compile the stuff from scratch on macOS and provide the Gerrit review request in no time.

The KTextEditor Framework uses the syntax highlighting files provided by the KSyntaxHighlighting Framework since the KDE Frameworks release 5.28.

The KSyntaxHighlighting Framework implements Kate’s highlighting system and meanwhile is used in quite some applications (e.g. LabPlot, KDE PIM). What is quite nice is that the KSyntaxHighlighting framework is nicely unit tested. And while we do not have tests for all highlighting files, we still provide some quality assurance through a compile time checker.

How does it work? Well – in former times, Kate loaded all highlighting .xml files from disk (through the KTextEditor framework). This lead to a slow startup over time, since there are >250 .xml files that needed a stat system call at startup.

With the KSyntaxHighlighting Framework, all these xml files are compiled into a Qt resource (qrc file), that then is included into the KSyntaxHighlighting library.

In order to create the Qt resource file, we need to iterate over all available xml files anyways. So what happens is that we take this opportunity and also scan the highlighting files for common mistakes.

As of today, we are checking the following:

RegExpr: A warning is raised, if a regular expression has syntax errors.

DetectChars: A warning is raised, if the char=”x” attribute contains more or less than one character, e.g. when char=”xyz”, or char=”\\” (no escaping required), or similar.

Detect2Chars: Same as DetectChars, just for char=”x” and char1=”y”.

Keyword lists: A warning is raised, if a keyword entry contains leading or trailing spaces. Additional trimming just takes time.

Keyword lists: A warning is raised if a keyword list is unused.

Keyword lists: A warning is raised if multiple keyword lists use the same me (=identifier).

Keyword lists: A warning is raised if a non-existing keyword list is used.

Contexts: A warning is raised, if a non-existing context is referenced.

Contexts: A warning is raised, if a context is unused.

Contexts: A warning is raised, if multiple contexts have the same name (identifier clash).

Attributes: A warning is raised, if non-existing itemData is used.

Attributes: A warning is raised, if multiple itemDatas use the same name (identifier clash).

Attributes: A warning is raised, if an itemData is unused.

This list helps us nicely to catch many mistakes at compile time even before running unit tests.

Update (2017-12-17): All above issues are fixed for all highlighting files starting with the KSyntaxHighlighting 5.42 framework, to be released in January 2018.