[koendehondt]

This PR replaces #71, which started from the wrong branch.

Adds VS Code-style multi-cursor editing to the Album text editor, as requested by #70.

Try it

AlbTextEditorExamples exampleMultiCursorEditing opens an editor with a cursor at the start of every line.

Gesture	Effect
Alt-click (Option-click on macOS)	Toggle a cursor at the clicked position
Ctrl+Alt+Up/Down (Cmd+Option+Up/Down on macOS)	Add a cursor above the top-most / below the bottom-most cursor
Shift+arrows, Shift+Alt+arrows, Shift+Home/End	Extend or shrink the selection at every cursor
Copy / Cut	One line per selection
Paste	One line per cursor when the line count matches, otherwise the whole text at every cursor
Escape	Keep only the primary cursor
Plain click, select all, mouse drag	A single cursor / selection

Changes

Cursors

• AlbTextEditor keeps its primary cursor and gains secondaryCursors. cursors returns all cursors sorted by position. New: addCursorAt:, removeSecondaryCursors, hasMultipleCursors.
• AlbTextEditorNavigator:
  • Moves (left/right, up/down, word, line start/end, moveBy:, moveWithin:) apply to every cursor.
  • moveTo: / moveToScreenPosition: collapse to a single cursor; addAt: keeps its existing meaning.
  • New addCursorAt:, removeCursorAt:, removeSecondaryCursors; removeAt: (sent by the history but previously missing) is implemented.
  • apply merges cursors at the same position. Removing the primary cursor promotes a secondary one; the last cursor is never removed.
• The inserter, deleter and paster act at every cursor. Enter keeps the indentation of each cursor's line. A multi-interval deletion is one undoable step. Cursor-movement undo/redo restores every cursor.

Selections

• AlbTextEditorSelecter: keyboard extensions build one command per cursor (private...For: methods) and move all cursors with a single navigator.
• Selections that meet merge; one cursor survives, at the selection edge (withMergingWithinSelection, triggered at the end of select once the editor selection is up to date).
• Typing, paste and deletion replace every selection. Explicit ranges (select all, drag, Shift-click) keep a single cursor.

Copy / paste

• New AlbTextEditor>>selectedTexts. copySelected copies one selection per line; cutSelected removes only the selected ranges. Previously, with several selections, they used the span from the first to the last selection, so cut deleted the unselected text in between.
• AlbTextEditorPaster>>paste distributes lines over cursors (VS Code rule; a trailing line ending does not count).

Rendering

• apply is two-phase: remove all cursors from their old segments, update the model, then re-add them, so cursors sharing a segment do not hide each other.
• Segment pieces track all their local cursors. AlbTextElement holds secondary cursor elements next to the editor's shared primary cursor element.

Shortcuts and mouse

• New AlbEditorAddCursorAboveShortcut / AlbEditorAddCursorBelowShortcut; Escape (AlbEditorDeselectAllShortcut) also removes secondary cursors; Alt/Option-click in AlbTextEditorMouseHandler.

Cleanup

• Removed the unused toRemoveCursors slot from AlbExtendSelectionCommand and commented-out code from privatePerformSelectAndDeselectCommands:.

Tests

• New AlbMultiCursorTest (46 tests), a BlSpaceTestCase: element-based tests run in the test space with space deferAndSettle: (newer Bloc forbids forceLayout on attached elements). The notation 'a|b|c' means the text abc with cursors at 1 and 2. Coverage:
  • cursor-set invariants
  • insertion and deletion
  • navigation
  • undo/redo
  • selections: extending, shrinking, merging, typing over
  • copy/paste/cut
  • rendering
  • shortcuts
  • two seeded random oracle tests
• AlbTextEditorHistoryTest: two redo regression tests for multi-index insertion. One of them wraps a selection in parentheses, then undoes and redoes, a pre-existing single-cursor bug.
• Tests touching the system clipboard restore it afterwards.
• Album-Tests: all multi-cursor and existing tests pass. AlbTextEditorByScripterTest (upstream) needs the Bloc-Simulation package, which the full Bloc baseline loads.

Dependency

Requires pharo-graphics/Bloc# (requested indices in BlTextStringsInserted, deletion in BlSelectionTree). Without it, the multi-index redo tests and two selection tests fail.

See pharo-graphics/Bloc#895

Limitations

• Cursors don't blink by default (AlbCursorElement>>defaultBlinking is false). When blinking is enabled with cursorElement beBlinking: true, only the primary cursor blinks; synchronized blinking will come in a separate PR.

[tinchodias]

Thanks