🔗 feat(link-styling): add per-profile underline style and hover/active colours for OSC 8 hyperlinks

[kud]

Overview

Add per-profile customisation for OSC 8 hyperlinks beyond colour. Previously iTerm2 only allowed users to set a single link colour per profile. This PR introduces:

• Link underline style picker — per-profile selection of underline styles (Single / Double / Dashed / Curly / Dotted) for OSC 8 hyperlinks. Previously hardcoded to dashed-single.
• Hover colour — optional per-profile colour applied when Cmd+hovering over a link (KEY_LINK_HOVER_COLOR, opt-in with checkbox).
• Active colour — optional per-profile colour applied whilst Cmd+clicking a link (KEY_LINK_ACTIVE_COLOR, opt-in with checkbox).

Changes

Profile Keys & Defaults (5 new)

• ITAddressBookMgr.h — added KEY_LINK_UNDERLINE_STYLE, KEY_LINK_HOVER_COLOR, KEY_LINK_HOVER_COLOR_ENABLED, KEY_LINK_ACTIVE_COLOR, KEY_LINK_ACTIVE_COLOR_ENABLED
• iTermProfilePreferences.m — registered defaults, help text, type registration

Colour Map & Rendering

• iTermColorMap.h/.m — added kColorMapLinkHover and kColorMapLinkActive (extended colour slots 2 and 3)
• iTermColorPresets.m — included new colour keys in preset serialisation list
• iTermAttributedStringBuilder.m — unified hover colour check across Metal and non-Metal paths

Metal Rendering

• iTermMetalPerFrameStateConfiguration.h/.m — added underlineStyle field and hover/active colour flags
• iTermMetalPerFrameStateRow.h/.m — per-row snapshot of active link range (mirrors existing hover tracking)
• iTermMetalPerFrameState.m — bounds-checked underline style substitution with three-way colour priority (active > hover > default)

Session & View Logic

• PTYSession.m/.swift — colour table wiring and terminalOnlyKeys configuration
• PTYTextView+ARC.m / PTYTextView.m — set/clear active link range on Cmd+mouseDown/mouseUp
• iTermTextDrawingHelper.h/.m — activeLinkRange property and activeLinkRangeOnLine: method

UI

• ProfilesColorsPreferencesViewController.m — IBOutlets and control registration for the style picker and colour wells (xib wiring required — see Known Gaps below)

Tests

• ModernTests/LinkColourMapAndActiveRangeTests.swift — 21 unit tests covering colour priority, range tracking, and style substitution

Validation

To test the feature:

1. Open Profiles → Colours tab
2. (After XIB wiring is complete) Select a link underline style from the popup
3. Hover over a link with Cmd held — the selected underline style should appear
4. Enable "Hover" colour and pick a colour — Cmd+hover should show that colour instead of the default
5. Enable "Active" colour and Cmd+click (hold briefly) on a link — the active colour should appear whilst clicking

The three-way colour priority ensures: active colour (when clicking) > hover colour (when hovering) > default link colour.

Known Gaps

The Interfaces/PreferencePanel.xib changes are not included in this commit. The xib requires Xcode Interface Builder to wire:

• One NSPopUpButton for the underline style selector
• Two NSColorWell controls for hover and active colours
• Two NSButton checkboxes to enable/disable hover and active colours

All IBOutlet declarations and defineControl: registrations are in place in ProfilesColorsPreferencesViewController.m — only the visual controls in the xib file are pending.

Notes

• Underline style substitution is bounds-checked to ensure invalid values fall back to the default dashed-single style
• The colour priority system means active colour always takes precedence over hover, preventing visual confusion during click events
• Both hover and active colours are opt-in (off by default) to preserve existing behaviour unless explicitly enabled per profile

[kud]

Still working on it.

Draft: not ready to present it to reviewers, but gives information that I'm working on a feature.

[gnachman]

There are a number of underlines. In addition to the ones set by SGR control sequence, they are also used for annotations, semantic history, and OSC 8 hyperlinks. There could be others I'm forgetting. Customizing colors is simple enough but customizing the shapes is riskier - you could easily end up with ambiguous cases. I believe there's a special code path for semantic history on already-underlined text that shows a mixed sold/dash underline.