SUMMARY
KFileExtractor stops part-way through extracting text from non-UTF text files, including HTML files, leading to weird unexpected indexing behavior from Baloo (see bug 410680 comments).

STEPS TO REPRODUCE
1. Do the mystery incantation to see qDebug() output.
2. Create a text file with iso-8859-1 encoding and a special non-ASCII character like © in it, e.g. using KWrite's File > Save As with Encoding
2b. Save an HTML file with a different encoding.

3. Either run KFileMetadata's "dump" test utility with ~/kde/build/frameworks/kfilemetadata/bin/dump -f path/to/myiso8859file.txt , or watch the output of `balooctl monitor`.


OBSERVED RESULT
You may see the debug output
KFileMetaData::PlainTextExtractor::extract: Invalid encoding. Ignoring "/path/to/myiso8859file.txt"

If Baloo indexes the location where you saved the file, only words up to the line with the non-Unicode character will be indexed.

EXPECTED RESULT

It's tricky, but it's entirely possible to detect the encoding of any text file and correctly index its contents instead of bailing. For an HTML file, it's arguably wrong to ignore a charset=ISO-8859-1" specification at the top.

It seems plaintextextractor.cpp just uses a standard QTextCodec::codecForLocale(), and if codec->toUnicode() returns invalidChars, it just bails half-way through; I don't know what would happen if it kept going.

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: 
KDE Plasma Version: 5.22.4
KDE Frameworks Version: 5.84.0
Qt Version: 5.15.2 (Wayland)

ADDITIONAL INFORMATION
The command `balooctl failed` needs to report these files as failing or incompletely indexed, that's a Baloo bug.

I documented this in a new https://community.kde.org/Baloo#Indexing_limitations section.