Why it is "end" now when we're calling BEGIN() here?

Very good, how about also adding a comment here to explain all readons behind this rule, as you nicely did in the description?

This is nice but how about keeping the

[\~\!\@\#\^\&\|\`\?,()\[\]\.;\:\+\-\*\/\%\^\<\>\=] { ... }

which just defines all single-character tokens and adding the . { } afterwards?
In the . {} we may also add a debug explaining that the yytext[0] is unsupported.
Doing so at flex level can have its value too.

BEGIN is to switch to a new start condition: after this flex will only look for rules that are within the group DATE_OR_TIME_caller, in this case the INITIAL or empty start condition. That is, it will look all the rules that have *no* prefix, hence this is the end of the date/time “subparser”.

In other words, this is the rule of the '#' character that ends the date/time literal.

Yes, it is indeed way better because now i can return an actual scanning error and the error message that the end user sees is “Unexpected character literal: x”, that is much nicer than the “Query error” i was getting before.

Thank you.

The problem i had quoting the unexpected character is that, depending on the font settings, it can be very hard to spot what is the offending character when it is a symbol like ' or ". For example, in the following screenshot i have problems seeing the ' character in "'":

Having the character alone at the end removes that kind of problems:

Do you want me to keep the quotes around the character?

That's a good note.

How about doing the same as a compiler shows:

when there's a quote it shows just it, e.g:'

error: missing terminating " character

else, it shows like

error: unknown type name 'a'

So we could do:

const QString string(QString::fromUtf8(yytext, yyleng));
QString char(string.left(1));
if (char == QLatin1Char('\'') || char == QLatin1Char('"') || char == QLatin1Char('`')) {
} else {
  char = QString("\"%1\").arg(char);
}

setError(KDbParser::tr("Unexpected character %1 in date/time").arg(char));

So we could do:

const QString string(QString::fromUtf8(yytext, yyleng));
QString char(string.left(1));
if (char == QLatin1Char('\'') || char == QLatin1Char('"') || char == QLatin1Char('`')) {
} else {
 char = QString("\"%1\").arg(char);
}

I’ve put that code into a function so that i could reuse in both error conditions and changed the message to what you suggested.

{ in new line

Use clang-format if unsure:

Sorry, did not know i could run clang-format on flex sources. Will use it next time.

Do you have the correct .clang-format file, though? I tried clang-format with WebKit-based style but it resulted in massive changes to this file and other C++ sources i tried.

Thank you.