Yes and the proposed resolution changes handling of such cases in an
incompatible way that goes against the original intent and makes width
estimation less useful. This is a design change.

- Victor

On Sun, Sep 18, 2022 at 7:20 AM Corentin <corentin.jabot_at_[hidden]> wrote:

>
>
> On Sun, Sep 18, 2022, 16:09 Victor Zverovich <victor.zverovich_at_[hidden]>
> wrote:
>
>> Even a cursory look at the issue shows a number of undesirable changes
>> that go against the intent of P1868R1. For example,
>>
>> U+2E9A
>>
>
> This codepoint does not appear to be assigned.
>
>>
>> has display width of 2 on common terminals while the proposed resolution
>> changes it to 1.
>>
>> The part "it seems questionable to make an exception for those without
>> input from Unicode" is itself a questionable design change.
>>
>> - Victor
>>
>> On Thu, Sep 15, 2022 at 10:12 AM Corentin via SG16 <sg16_at_[hidden]>
>> wrote:
>>
>>>
>>>
>>> On Thu, Sep 15, 2022 at 5:59 PM Tom Honermann <tom_at_[hidden]> wrote:
>>>
>>>> Thank you for looking into this, Corentin. It would be great to have
>>>> some kind of principled approach to how estimated widths are assigned.
>>>>
>>>> I don't think this should be handled as an LWG issue though. This is a
>>>> design change, so should go through LEWG (and probably SG16 as well).
>>>>
>>>> I think it would be helpful to have a paper that includes screenshots
>>>> (of select characters, not all 8500+ characters!) to demonstrate how common
>>>> terminals display them today. The goal being to ensure that they are
>>>> handled consistently across platforms before we standardize them.
>>>>
>>>> A paper would also present the opportunity to attribute an estimated
>>>> width of 0 (or a negative width!) to some characters. Perhaps it is worth
>>>> asking whether an estimated width of 1 really makes sense for CR, LF, NL,
>>>> VT, etc... It looks like these changes still don't cover edge cases like ﷽
>>>> (U+FDFD ARABIC LIGATURE BISMILLAH AR-RAHMAN AR-RAHEEM).
>>>>
>>>
>>> I'm not trying to change the design, nor am I trying to make case-by
>>> case decisions, the original paper covered that.
>>> I think these are questions worth asking, sure, at least for control
>>> characters as, for an arbitrary non-cjk, non-emoji neither an information
>>> nor a specification exist.
>>> Note that however it's not straightforward
>>> * There is no spec so it's handled manually
>>> https://github.com/termux/wcwidth/blob/master/wcwidth.c#L497
>>> * C1 control characters may be mapped differently on EBCDIC platforms
>>> * Combining characters not preceded by a grapheme starter are in
>>> fact rendered
>>> * We already ignore non leading codepoints in graphemes
>>> * Negative width would be novel
>>>
>>> I do not intend to explore these further but I'd be happy to review such
>>> work :)
>>>
>>> However, the original paper intended for CJK characters and emojis to be
>>> covered, Unicode 14 and 15 added a number of such characters, I considered
>>> this a bug.
>>> But mostly, I consider specifying anything Unicode related in terms of
>>> partially-assigned ranges to be a bug reminiscent of the identifiers of old.
>>>
>>> Now, I expect SG16 will deal with this issue, but all the information is
>>> in the issue.
>>> The only design-ish question is whether we want to grandfather U+3248
>>> CIRCLED NUMBER TEN ON BLACK SQUARE..U+324F CIRCLED NUMBER EIGHTY ON BLACK
>>> SQUARE
>>> for backward compat reasons.
>>>
>>> Codepoints which would go from 1 to 2
>>> https://gist.github.com/cor3ntin/e5731f77574b146d806e39283e8c7cb7
>>> Screenshot of my terminal
>>> [image: image.png]
>>>
>>> Tom.
>>>> On 9/15/22 5:02 AM, Corentin via SG16 wrote:
>>>>
>>>>
>>>> Affected clause [format.string.std]
>>>>
>>>> Issue:
>>>> For the purpose of width estimation, format considers ranges of
>>>> codepoints initially derived from an implementation of wcwidth with
>>>> modifications.
>>>> (See https://wg21.link/p1868r1)
>>>>
>>>> This however present a number of challenges:
>>>>
>>>> - From a reading of the spec, it is not clear how these ranges were
>>>> selected.
>>>> - Poor forward compatibility with future Unicode versions. The list
>>>> will become less and less meaningful overtime or require active maintenance
>>>> at each Unicode release (which we have not done for Unicode 14 already)
>>>> - Some of these codepoints are unassigned or otherwise reserved,
>>>> which is another forward compatibility concern.
>>>>
>>>> Instead, we propose to
>>>>
>>>> - Rely on UAX-11 https://www.unicode.org/reports/tr11/ for most of
>>>> the codepoints)
>>>> - Grand-father specific and fully assigned, blocks of codepoints to
>>>> support additional pictograms per the original intent of the paper and
>>>> existing practices. We add the name of these blocks in the wording for
>>>> clarity.
>>>>
>>>> Note that per UAX-11
>>>>
>>>> - Most emojis are considered East_Asian_Width="W"
>>>> - By design, East_Asian_Width="W" includes specific unassigned
>>>> ranges, which should always be treated as Wide.
>>>>
>>>> This change:
>>>>
>>>> - Considers 8477 extra codepoints as having a width 2 (as of
>>>> Unicode 15) (mostly Tangut Ideographs)
>>>> - Change the width of 85 unassigned code points from 2 to 1
>>>> - Change the width of 8 codepoints (in the range U+3248 CIRCLED
>>>> NUMBER TEN ON BLACK SQUARE ..U+324F CIRCLED NUMBER EIGHTY ON BLACK SQUARE)
>>>> from 2 to 1, because it seems questionable to make an exception for those
>>>> without input from Unicode
>>>>
>>>>
>>>> Proposed wording:
>>>>
>>>> Modify [format.string.std]/p12
>>>>
>>>> For a string in a Unicode encoding, implementations should estimate the
>>>> width of a string as the sum of estimated widths of the first code points
>>>> in its extended grapheme clusters. The extended grapheme clusters of a
>>>> string are defined by UAX #29. The estimated width of the following code
>>>> points is 2:
>>>>
>>>> - U+1100 – U+115F
>>>> - U+2329 – U+232A
>>>> - U+2E80 – U+303E
>>>> - U+3040 – U+A4CF
>>>> - U+AC00 – U+D7A3
>>>> - U+F900 – U+FAFF
>>>> - U+FE10 – U+FE19
>>>> - U+FE30 – U+FE6F
>>>> - U+FF00 – U+FF60
>>>> - U+FFE0 – U+FFE6
>>>> - U+1F300 – U+1F64F
>>>> - U+1F900 – U+1F9FF
>>>> - U+20000 – U+2FFFD
>>>> - U+30000 – U+3FFFD
>>>> - *Any codepoint with the East_Asian_Width="W"
>>>> or East_Asian_Width="F" Derived Extracted Property as described by UAX #44*
>>>> -
>>>> *U+4DC0 - U+4DFF (Yijing Hexagram Symbols) *
>>>> - *U+1F300 - U+1F5FF (Miscellaneous Symbols and Pictographs)*
>>>> - *U+1F900 - U+1F9FF (Supplemental Symbols and Pictographs)*
>>>>
>>>> The estimated width of other code points is 1.
>>>>
>>>>
>>>> ---- END OF WORDING ----
>>>>
>>>> Annex: Differences introduced by this change
>>>>
>>>> // Missing from the standard (count: 8477)
>>>> // Used to be of width 1, becomes 2
>>>>
>>>> U+231A WATCH ..U+231B HOURGLASS
>>>> U+23E9 BLACK RIGHT-POINTING DOUBLE TRIANGLE ..U+23EC BLACK
>>>> DOWN-POINTING DOUBLE TRIANGLE
>>>> U+23F0 ALARM CLOCK
>>>> U+23F3 HOURGLASS WITH FLOWING SAND
>>>> U+25FD WHITE MEDIUM SMALL SQUARE ..U+25FE BLACK MEDIUM SMALL SQUARE
>>>> U+2614 UMBRELLA WITH RAIN DROPS ..U+2615 HOT BEVERAGE
>>>> U+2648 ARIES ..U+2653 PISCES
>>>> U+267F WHEELCHAIR SYMBOL
>>>> U+2693 ANCHOR
>>>> U+26A1 HIGH VOLTAGE SIGN
>>>> U+26AA MEDIUM WHITE CIRCLE ..U+26AB MEDIUM BLACK CIRCLE
>>>> U+26BD SOCCER BALL ..U+26BE BASEBALL
>>>> U+26C4 SNOWMAN WITHOUT SNOW ..U+26C5 SUN BEHIND CLOUD
>>>> U+26CE OPHIUCHUS
>>>> U+26D4 NO ENTRY
>>>> U+26EA CHURCH
>>>> U+26F2 FOUNTAIN ..U+26F3 FLAG IN HOLE
>>>> U+26F5 SAILBOAT
>>>> U+26FA TENT
>>>> U+26FD FUEL PUMP
>>>> U+2705 WHITE HEAVY CHECK MARK
>>>> U+270A RAISED FIST ..U+270B RAISED HAND
>>>> U+2728 SPARKLES
>>>> U+274C CROSS MARK
>>>> U+274E NEGATIVE SQUARED CROSS MARK
>>>> U+2753 BLACK QUESTION MARK ORNAMENT ..U+2755 WHITE EXCLAMATION MARK
>>>> ORNAMENT
>>>> U+2757 HEAVY EXCLAMATION MARK SYMBOL
>>>> U+2795 HEAVY PLUS SIGN ..U+2797 HEAVY DIVISION SIGN
>>>> U+27B0 CURLY LOOP
>>>> U+27BF DOUBLE CURLY LOOP
>>>> U+2B1B BLACK LARGE SQUARE ..U+2B1C WHITE LARGE SQUARE
>>>> U+2B50 WHITE MEDIUM STAR
>>>> U+2B55 HEAVY LARGE CIRCLE
>>>> U+A960 HANGUL CHOSEONG TIKEUT-MIEUM ..U+A97C HANGUL CHOSEONG
>>>> SSANGYEORINHIEUH
>>>> U+16FE0 TANGUT ITERATION MARK ..U+16FE4 KHITAN SMALL SCRIPT FILLER
>>>> U+16FF0 VIETNAMESE ALTERNATE READING MARK CA ..U+16FF1 VIETNAMESE
>>>> ALTERNATE READING MARK NHAY
>>>> U+17000 TANGUT IDEOGRAPH-# ..U+187F7 TANGUT IDEOGRAPH-#
>>>> U+18800 TANGUT COMPONENT-001 ..U+18CD5 KHITAN SMALL SCRIPT CHARACTER-#
>>>> U+18D00 TANGUT IDEOGRAPH-# ..U+18D08 TANGUT IDEOGRAPH-#
>>>> U+1AFF0 KATAKANA LETTER MINNAN TONE-2 ..U+1AFF3 KATAKANA LETTER MINNAN
>>>> TONE-5
>>>> U+1AFF5 KATAKANA LETTER MINNAN TONE-7 ..U+1AFFB KATAKANA LETTER MINNAN
>>>> NASALIZED TONE-5
>>>> U+1AFFD KATAKANA LETTER MINNAN NASALIZED TONE-7 ..U+1AFFE KATAKANA
>>>> LETTER MINNAN NASALIZED TONE-8
>>>> U+1B000 KATAKANA LETTER ARCHAIC E ..U+1B122 KATAKANA LETTER ARCHAIC WU
>>>> U+1B132 HIRAGANA LETTER SMALL KO
>>>> U+1B150 HIRAGANA LETTER SMALL WI ..U+1B152 HIRAGANA LETTER SMALL WO
>>>> U+1B155 KATAKANA LETTER SMALL KO
>>>> U+1B164 KATAKANA LETTER SMALL WI ..U+1B167 KATAKANA LETTER SMALL N
>>>> U+1B170 NUSHU CHARACTER-# ..U+1B2FB NUSHU CHARACTER-#
>>>> U+1F004 MAHJONG TILE RED DRAGON
>>>> U+1F0CF PLAYING CARD BLACK JOKER
>>>> U+1F18E NEGATIVE SQUARED AB
>>>> U+1F191 SQUARED CL ..U+1F19A SQUARED VS
>>>> U+1F200 SQUARE HIRAGANA HOKA ..U+1F202 SQUARED KATAKANA SA
>>>> U+1F210 SQUARED CJK UNIFIED IDEOGRAPH-624B ..U+1F23B SQUARED CJK
>>>> UNIFIED IDEOGRAPH-914D
>>>> U+1F240 TORTOISE SHELL BRACKETED CJK UNIFIED IDEOGRAPH-672C ..U+1F248
>>>> TORTOISE SHELL BRACKETED CJK UNIFIED IDEOGRAPH-6557
>>>> U+1F250 CIRCLED IDEOGRAPH ADVANTAGE ..U+1F251 CIRCLED IDEOGRAPH ACCEPT
>>>> U+1F260 ROUNDED SYMBOL FOR FU ..U+1F265 ROUNDED SYMBOL FOR CAI
>>>> U+1F680 ROCKET ..U+1F6C5 LEFT LUGGAGE
>>>> U+1F6CC SLEEPING ACCOMMODATION
>>>> U+1F6D0 PLACE OF WORSHIP ..U+1F6D2 SHOPPING TROLLEY
>>>> U+1F6D5 HINDU TEMPLE ..U+1F6D7 ELEVATOR
>>>> U+1F6DC WIRELESS ..U+1F6DF RING BUOY
>>>> U+1F6EB AIRPLANE DEPARTURE ..U+1F6EC AIRPLANE ARRIVING
>>>> U+1F6F4 SCOOTER ..U+1F6FC ROLLER SKATE
>>>> U+1F7E0 LARGE ORANGE CIRCLE ..U+1F7EB LARGE BROWN SQUARE
>>>> U+1F7F0 HEAVY EQUALS SIGN
>>>> U+1FA70 BALLET SHOES ..U+1FA7C CRUTCH
>>>> U+1FA80 YO-YO ..U+1FA88 FLUTE
>>>> U+1FA90 RINGED PLANET ..U+1FABD WING
>>>> U+1FABF GOOSE ..U+1FAC5 PERSON WITH CROWN
>>>> U+1FACE MOOSE ..U+1FADB PEA POD
>>>> U+1FAE0 MELTING FACE ..U+1FAE8 SHAKING FACE
>>>> U+1FAF0 HAND WITH INDEX FINGER AND THUMB CROSSED ..U+1FAF8 RIGHTWARDS
>>>> PUSHING HAND
>>>>
>>>> // Reserved (count: 85) - Become used to be of width 2, becomes 1
>>>>
>>>> U+2E9A
>>>> U+2EF4 ..U+2EFF
>>>> U+2FD6 ..U+2FEF
>>>> U+2FFC ..U+2FFF
>>>> U+3040
>>>> U+3097 ..U+3098
>>>> U+3100 ..U+3104
>>>> U+3130
>>>> U+318F
>>>> U+31E4 ..U+31EF
>>>> U+321F
>>>> U+A48D ..U+A48F
>>>> U+A4C7 ..U+A4CF
>>>> U+FE53
>>>> U+FE67
>>>> U+FE6C ..U+FE6F
>>>> U+FF00
>>>>
>>>> // Used to be of width 2, becomes 1
>>>> U+3248 CIRCLED NUMBER TEN ON BLACK SQUARE ..U+324F CIRCLED NUMBER
>>>> EIGHTY ON BLACK SQUARE
>>>>
>>>>
>>>>
>>>> --
>>> SG16 mailing list
>>> SG16_at_[hidden]
>>> https://lists.isocpp.org/mailman/listinfo.cgi/sg16
>>>
>>