wrong month format in caption of gantt diagram

[pashutkin]

Description
Wrong month formatting is used for table captions of gantt diagram. Some languages/locales use different word for standalone month name and month as a part of date string.
English word "January" is used for both standalone month name (January'70) and part of date string (The 1st of January 1970).
But Ukrainian, Czech, Greek, Croatian, Russian, Polish, Finnish, Catalan languages have different words. For example, in Greek: "Ιανουάριος 1970" as standalone month and "1 Ιανουαρίου 1970" as a part of date string.

The problem is in Month.java: TextStyle.FULL_STANDALONE and TextStyle.FULL can't be used interchangeably. Specifically it might not be decided on longest criteria.
I would consider to use two separate methods for standalone and partial usage of month name.

To Reproduce
Steps to reproduce the behavior:

@startgantt
language en
project starts on 1970-01-01
[test] lasts 15 days
@endgantt

@startgantt
language el
project starts on 1970-01-01
[test] lasts 15 days
@endgantt

@startgantt
language fi
project starts on 1970-01-01
[test] lasts 15 days
@endgantt

@startgantt
language ru
project starts on 1970-01-01
[test] lasts 15 days
@endgantt

Expected behavior
Correspondingly, captions have to be:
en: January 1970 — correct
el: Ιανουάριος 1970 instead of Ιανουαρίου 1970
fi: Tammikuu 1970 instead of Tammikuuta 1970
ru: Январь 1970 instead of Января 1970

Screenshots

Additional context
To illustrate the difference of month representation one may run following code in java:

        for (var language : java.util.List.of("en", "de", "uk","cs","el","hr","ru","pl","fi","ca")) {
            var locale = java.util.Locale.forLanguageTag(language);
            String month = new java.text.SimpleDateFormat("LLLL yyyy", locale).format(new java.util.Date(0));
            String date = java.text.SimpleDateFormat.getDateInstance(java.text.DateFormat.LONG, locale).format(new java.util.Date(0));
            String fullStandaloneName = java.time.Month.JANUARY.getDisplayName(java.time.format.TextStyle.FULL_STANDALONE, locale);
            String fullName = java.time.Month.JANUARY.getDisplayName(java.time.format.TextStyle.FULL, locale);
            int comparison = fullStandaloneName.length() - fullName.length();
            System.out.printf("""
                    Locale "%1$s" / %2$s
                        FULL_STANDALONE = "%3$s", usage: "%4$s"
                        FULL = "%5$s", usage: "%6$s"
                        FULL_STANDALONE.length() - FULL.length() = %7$d
                    %n""", locale, locale.getDisplayName(), fullStandaloneName, month, fullName, date, comparison);
        }

[arnaudroques]

Thanks for the report and for the detailed explanations, it really helps!

The difference between FULL_STANDALONE and FULL was not clear to us :-)

Still, we are not sure to have fixed the issue in last commit.

Is this better better this way ?

plantuml/src/net/sourceforge/plantuml/project/time/Month.java

Line 70 in 87caaeb

return javaTimeMonth.getDisplayName(TextStyle.FULL_STANDALONE, locale);

[pashutkin]

Yes. Makes sense. At least as long as the method longName is used only for rendering month name without 'day' part.

Thank you very much!