[Bug localedata/26120] New: column width of of some Korean JUNGSEONG/JONGSEONG characters wrong (should be 0)

["maiku.fabian at gmail dot com" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=26120

            Bug ID: 26120
           Summary: column width of  of some Korean JUNGSEONG/JONGSEONG
                    characters wrong (should be 0)
           Product: glibc
           Version: 2.31
            Status: NEW
          Severity: normal
          Priority: P2
         Component: localedata
          Assignee: unassigned at sourceware dot org
          Reporter: maiku.fabian at gmail dot com
                CC: libc-locales at sourceware dot org
  Target Milestone: ---

Robert Ross <rob.ross@ymail.com> writes:

> Thank you for maintaining glibc's "localedata/charmaps/UTF-8".  It is
> good that most "HANGUL JUNGSEONG" characters have zero width due to
> "<U1160>...<U11FF> 0" on line 48775 but strange that the newer "HANGUL
> JUNGSEONG" characters have width 1 since there is no
> "<UD7B0>...<UD7C6> 0".  Similarly most "HANGUL JONGSEONG" characters
> have width 0 due to line 48775 but the newer ones have width 1 since
> there is no "<UD7CB>...<UD7FB> 0".  Please correct this if it's an
> error or explain if it's not.

In https://www.unicode.org/Public/13.0.0/ucd/EastAsianWidth.txt all of these
have width "N".

http://www.unicode.org/reports/tr11/ says:

6.2 Combining Marks

> Combining marks have been classified and are given a property
> assignment based on their typical applicability. For example,
> combining marks typically applied to characters of class N, Na, or W
> are classified as A. Combining marks for purely non-East Asian scripts
> are marked as N, and nonspacing marks used only with wide characters
> are given a W. Even more so than for other characters, the
> East_Asian_Width property for combining marks is not the same as their
> display width.
> 
> In particular, nonspacing marks do not possess actual advance
> width. Therefore, even when displaying combining marks, the
> East_Asian_Width property cannot be related to the advance width of
> these characters. However, it can be useful in determining the
> encoding length in a legacy encoding, or the choice of font for the
> range of characters including that nonspacing mark. The width of the
> glyph image of a nonspacing mark should always be chosen as the
> appropriate one for the width of the base character.

See also: https://sourceware.org/bugzilla/show_bug.cgi?id=21750#c5

> We also agree that the Hangul Jamo U+1160‥U+11FF are sort
> of "combining characters" although they are not marked as such
> in the Unicode data. But they are fragments of Hangul characters
> which combine. So it seems correct to mark them as width 0.

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