Merge pull request #6898 from dotCooCoo/feat/justify-cluster-gap

Type: letter spacing and Full Justify keep shaped clusters together

docs/target-app-parity.md

@@ -651,6 +651,7 @@ since 2026-10-01.
 - **Text styles redefined to the defaults:** New and Redefine Character Style and Paragraph Style capture every attribute of the selected text, including those at their defaults (Auto kerning, Roman baseline alignment, the default Hyphenation options, the Every-line Composer, no tab stops), and `charStyle.setAttrs` and `paraStyle.setAttrs` keep an attribute set to its default value. After a redefinition, text whose value still equals the old definition's takes the new value, a default included; local overrides stay, and text that still has the old value of an attribute the new definition leaves out goes back to the Normal style's value. The style panels show "+" only where the text differs from its style, including type with Auto alignment. Public reference: [Character and paragraph styles](https://web.archive.org/web/20260825113735/https://helpx.adobe.com/illustrator/using/character-paragraph-styles.html).
 - **Text styles dragged onto the panel's buttons:** a style dragged from the Character Styles or Paragraph Styles panel onto Create New Style is copied (`charStyle.duplicate`, `paraStyle.duplicate`, which name the copy `<name> copy`) and the copy is highlighted; dragged onto Delete it is deleted (`charStyle.delete`, `paraStyle.delete`); the Normal style is not deleted. Each drop is one undo step. Public reference: [Character and paragraph styles](https://web.archive.org/web/20261015081534/https://helpx.adobe.com/illustrator/using/character-paragraph-styles.html).
 - **Auto Leading outside the layout:** a paragraph's Justification… › Auto Leading (<https://helpx.adobe.com/illustrator/desktop/design-with-text/edit-format-text/adjust-word-and-letterspacing-in-justified-text.html>) also sets the Leading the Character panel shows for Auto type (blank where the selected paragraphs differ), the leading the Alt+↑/↓ nudge (`type.step`) steps from, each paragraph's own, and the lines Fill with Placeholder Text counts in area type. Evidence: `ParaStyle::effective_leading` (`crates/doc/src/text.rs` test `paragraph_effective_leading_follows_auto_leading`), `tests_prefs::auto_leading_steps_and_fills_from_the_paragraph_auto_leading`, `panels::character` test `leading_field_shows_the_paragraph_auto_leading`.
+- **Letter spacing and Full Justify between shaped clusters:** Desired Letter Spacing on any line, the letter spacing range of a justified line, and Single Word Justification's Full Justify add space only between shaped clusters, in horizontal, right-to-left and vertical type, so a combining mark stays on its letter and a Devanagari syllable's glyphs stay together. They add no space next to a zero-width format control (a soft hyphen, a bidi mark, embedding, override or isolate, a zero-width space, a joiner or non-joiner, a word joiner, a variation selector, a tag, the byte order mark), so a word wrapped in an override still reaches both edges of a justified line, and a Kinsoku push-in counts no gap at one either. A zero-width space is a line break opportunity but not a word separator ([CSS Text Level 3](https://www.w3.org/TR/css-text-3/#word-separator) does not list it), so a justified line gives it no share of its room. Desired Letter Spacing between the letters on either side of a zero-width space goes after the zero-width space, so a line that breaks there ends at its last letter, and the line breaker does not measure a gap after it. A line that Full Justify spreads and that ends in a drawn hyphen puts the same gap between its last letter and the hyphen. The cluster boundary is VectorCraft's own rule, based on the typographic character unit of [CSS Text Level 3](https://www.w3.org/TR/css-text-3/#typographic-character-unit). Tests `tests::justify::single_word_full_justify_keeps_combining_mark_with_base`, `desired_and_fitted_letter_spacing_skip_shaped_cluster`, `rtl_single_word_cluster_gap_follows_drawn_order`, `vertical_single_word_cluster_gap_follows_drawn_order`, `single_word_full_justify_keeps_conjunct_cluster`, `desired_letter_spacing_skips_bidi_format_controls`, `letter_spacing_and_full_justify_skip_joiners_and_soft_hyphens`, `format_controls_are_the_zero_width_default_ignorables`, `zero_width_space_takes_no_word_space_room`, `desired_letter_spacing_ends_a_line_broken_at_a_zero_width_space_without_a_gap`, `single_word_full_justify_spreads_up_to_the_drawn_hyphen` and `layout::wrapping_tests::kinsoku_shori_type_counts_no_gap_at_a_format_control`. Public reference: the help page (<https://helpx.adobe.com/illustrator/desktop/design-with-text/edit-format-text/adjust-word-and-letterspacing-in-justified-text.html>).
 - **The text style panel menus' Duplicate and Delete:** in the Character Styles and Paragraph Styles panel menus, Duplicate highlights the copy, as Create New Style highlights the new style, and Delete leaves no style highlighted, as the Delete button does, so Duplicate, Clear Overrides, Redefine and Style Options are disabled until another style is clicked. A highlighted style that is renamed in Style Options or deleted by a command is no longer highlighted either. The tests `panels::text_styles::tests::panel_menu_duplicate_and_delete_update_the_highlighted_style` and `a_highlighted_style_that_is_no_longer_listed_is_not_highlighted` cover this. Public reference: [Character and paragraph styles](https://web.archive.org/web/20261015081534/https://helpx.adobe.com/illustrator/using/character-paragraph-styles.html).
 - **Names of new styles and symbols:** `charStyle.new` and `paraStyle.new` trim the white space around the name they are given, as `charStyle.rename` and `paraStyle.rename` do, and refuse a name that is then empty; Duplicate names its copy from the trimmed name. `symbol.new` and `symbol.duplicate` trim the name as Symbol Options does, and `library.use` adds a library's text style under its trimmed name. Public reference: [Character and paragraph styles](https://web.archive.org/web/20260825113735/https://helpx.adobe.com/illustrator/using/character-paragraph-styles.html).
 - **Naming a new text style first:** Alt-click on New in the Character Styles or Paragraph Styles panel opens New Character Style or New Paragraph Style (`ui.newCharStyle`, `ui.newParaStyle`) with the name a plain click's style gets; OK makes the style from the text selected when the dialog opened, and Cancel adds none. Tests `panels::text_styles::tests::alt_clicking_new_character_style_asks_for_its_name` and `alt_clicking_new_paragraph_style_asks_for_its_name`. Public reference: [Default keyboard shortcuts](https://web.archive.org/web/20260726060015/https://helpx.adobe.com/illustrator/using/default-keyboard-shortcuts.html), which lists Alt-click for opening panel options and names Actions, Brushes, Swatches and Symbols as exceptions.