Fix inconsistent display width for emoji outside East Asian Wide ranges - #4896
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edugomz wants to merge 9 commits into
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Fix inconsistent display width for emoji outside East Asian Wide ranges#4896edugomz wants to merge 9 commits into
edugomz wants to merge 9 commits into
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fmt::detail::display_width_of() only treated East Asian Wide/Fullwidth
code points and two hand-picked emoji ranges as two columns wide, so
emoji outside those ranges (e.g. the Dingbats block: cross mark U+274C,
white heavy check mark U+2705) were measured as one column even though
most terminals render them double-width. This produced visibly
inconsistent padding under {:^N} compared to CJK text (fixes fmtlib#4851).
Replaced the ad hoc boolean expression with a sorted table of ranges
(East Asian Wide/Fullwidth plus the full Emoji_Presentation set from
Unicode's emoji-data.txt) looked up via binary search, and added
regression tests covering the original report plus edge cases:
multiple emoji, mixed emoji/CJK/ASCII content, precision truncation,
alignment/fill variants, newly covered emoji ranges, and regional
indicator (flag) pairs.
vitaut
requested changes
Aug 25, 2026
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The standard width rules are not just East_Asian_Width=W/F; [format.string.std] also explicitly includes 1F300–1F5FF and 1F900–1F9FF.
vitaut
reviewed
Aug 25, 2026
Closed
…nges to match [format.string.std]
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Fixes #4851
Continues #4865 with the requested changes addressed:
East_Asian_Width=W/Fdata instead ofEmoji_Presentation, so regional indicators (flag halves) aren't individually double-counted - 🇺🇸 still measures 2 columns, not 4display_width_of()remainsFMT_CONSTEXPRTesting
Regression tests added to
test/format-test.cc: the #4851 example, multiple/mixed emoji, precision truncation, alignment, newly-covered ranges, and a regional indicator (flag) pair.