[codex] Implement D1 tab handling

examples/ted/TedApp.cs

@@ -47,6 +47,19 @@ public TedApp ()
             Value = Editor.ShowLineNumbers ? CheckState.Checked : CheckState.UnChecked
         };
 
+        CheckBox convertTabsToSpacesCheckBox = new ()
+        {
+            AllowCheckStateNone = false,
+            CanFocus = false,
+            Text = "_Convert Tabs To Spaces",
+            Value = Editor.ConvertTabsToSpaces ? CheckState.Checked : CheckState.UnChecked
+        };
+
+        convertTabsToSpacesCheckBox.ValueChanged += (_, e) =>
+        {
+            Editor.ConvertTabsToSpaces = e.NewValue == CheckState.Checked;
+        };
+
         ThemeDropDown = new DropDownList<ThemeName>
         {
             Value = ThemeName.DarkPlus,
@@ -81,29 +94,42 @@ public TedApp ()
 #pragma warning restore CS0618 // Type or member is obsolete
         };
 
-        TabWidthUpDown = new NumericUpDown<int>
+        IndentationSizeUpDown = new NumericUpDown<int>
         {
-            Value = Editor.TabWidth,
+            Value = Editor.IndentationSize,
             Increment = 1
         };
 
-        TabWidthUpDown.ValueChanged += (_, e) =>
+        IndentationSizeUpDown.ValueChanged += (_, e) =>
         {
-            if (Editor.TabWidth == e.NewValue)
+            if (Editor.IndentationSize == e.NewValue)
             {
                 return;
             }
 
-            Editor.TabWidth = e.NewValue;
+            Editor.IndentationSize = e.NewValue;
+        };
+
+        ShowTabsCheckBox = new CheckBox
+        {
+            AllowCheckStateNone = false,
+            CanFocus = false,
+            Title = "↹",
+            Value = Editor.ShowTabs ? CheckState.Checked : CheckState.UnChecked
+        };
+
+        ShowTabsCheckBox.ValueChanged += (_, e) =>
+        {
+            Editor.ShowTabs = e.NewValue == CheckState.Checked;
         };
 
         StatusBar statusBar =
             new ([
                 new Shortcut (KeyFor (Command.Quit), "Quit", Quit),
                 new Shortcut (Key.Empty, "Themes", null) { MouseHighlightStates = MouseState.None },
                 new Shortcut { Title = "Themes", CommandView = ThemeDropDown },
-                new Shortcut (Key.Empty, "Tab", null) { MouseHighlightStates = MouseState.None },
-                new Shortcut { Title = "Tab", CommandView = TabWidthUpDown },
+                new Shortcut { Text = "Indent Size", CommandView = IndentationSizeUpDown },
+                new Shortcut { CommandView = ShowTabsCheckBox },
                 new Shortcut (Key.Empty, "x, y", null, "Loc") { MouseHighlightStates = MouseState.None },
                 _fileNameShortcut = new Shortcut (Key.Empty, "<untitled>", Open)
                 {
@@ -145,6 +171,11 @@ public TedApp ()
                     },
                     CommandView = lineNumbersCheckBox,
                     HelpText = "Show line numbers"
+                },
+                new MenuItem
+                {
+                    CommandView = convertTabsToSpacesCheckBox,
+                    HelpText = "Insert spaces when Tab is pressed"
                 }
             ]),
             new MenuBarItem (Strings.menuHelp,
@@ -165,8 +196,11 @@ [new MenuItem ("_About", "Show About dialog", Action)])
     /// <summary>The syntax-highlighting theme selector shown in the status bar.</summary>
     public DropDownList<ThemeName> ThemeDropDown { get; }
 
-    /// <summary>The tab-width selector shown in the status bar.</summary>
-    public NumericUpDown<int> TabWidthUpDown { get; }
+    /// <summary>The indentation-size selector shown in the status bar.</summary>
+    public NumericUpDown<int> IndentationSizeUpDown { get; }
+
+    /// <summary>The status-bar checkbox that toggles visible tab glyphs.</summary>
+    public CheckBox ShowTabsCheckBox { get; }
 
     /// <summary>The path currently associated with <see cref="Editor" />, or <see langword="null" /> for an untitled buffer.</summary>
     public string? CurrentFilePath { get; private set; }

specs/03-public-api.md

@@ -0,0 +1,32 @@
+# Public API Notes
+
+This file tracks public API added during pre-alpha work. It is intentionally brief; `specs/00-plan.md`
+remains the source of truth for the target architecture.
+
+## D1 Tabs
+
+`Terminal.Gui.Views.Editor` exposes the AvaloniaEdit-aligned tab surface directly:
+
+- `int IndentationSize { get; set; } = 4` controls indentation stops in terminal cells. Values less than 1 are rejected.
+- `bool ConvertTabsToSpaces { get; set; }` controls what the Tab key inserts. It never rewrites existing document text.
+- `bool ShowTabs { get; set; }` renders a visible glyph in the first cell of each tab expansion.
+
+`Editor.TabWidth` was removed rather than shimmed because the project is still pre-alpha and `IndentationSize`
+is the planned AvaloniaEdit-compatible name.
+
+## Rendering Pipeline Slice
+
+The first rendering pipeline types live in `Terminal.Gui.Views.Rendering`:
+
+- `VisualLineBuilder`
+- `CellVisualLine`
+- `CellVisualLineElement`
+- `TextRunElement`
+- `TabElement`
+- `IVisualLineTransformer`
+- `IBackgroundRenderer`
+- `VisualLineBuildContext`
+
+`Editor.LineTransformers` and `Editor.BackgroundRenderers` expose the current extension points. This is the
+D1-enabling slice only: cache invalidation, folding markers, line-number background rendering, and the full B1/B2
+pipeline remain tracked in `specs/00-plan.md`.

specs/runs/test-codex-final.md

@@ -0,0 +1,47 @@
+# Codex D1 Tabs Final Report
+
+## What I did
+
+- Chose option (b): implemented the slice of the VisualLineBuilder pipeline needed for D1, then implemented tab handling on top of it.
+- Added `Terminal.Gui.Views.Rendering` types: `VisualLineBuilder`, `CellVisualLine`, `CellVisualLineElement`, `TextRunElement`, `TabElement`, `IVisualLineTransformer`, `IBackgroundRenderer`, and build context.
+- Replaced `Editor.TabWidth` with `Editor.IndentationSize`, and added `ConvertTabsToSpaces`, `ShowTabs`, `LineTransformers`, and `BackgroundRenderers`.
+- Moved visible line text drawing through grapheme-aware visual-line elements. `OnDrawingContent` no longer expands `\t` directly or walks rendered text char-by-char.
+- Implemented Tab, Shift+Tab, block indent/unindent, and indentation-aware Backspace.
+- Updated mouse tab hit-testing to snap to the nearest logical tab edge, with midpoint rounding before the tab.
+- Updated ted: status bar uses `Indent Size`, adds a `ShowTabs` checkbox, and Options has `_Convert Tabs To Spaces`.
+- Added/updated tests for visual-line tab expansion, grapheme widths, Tab insertion modes, block indent undo grouping, Shift+Tab, indentation Backspace, mouse snapping, ted UI, and tab round trip.
+- Added `specs/03-public-api.md` notes for the new `Editor` tab surface and rendering pipeline slice.
+
+## What I skipped
+
+- I did not implement all of B1 as specified in `specs/00-plan.md`: there is no visual-line cache/invalidation, no folding marker element, and no full background-renderer migration for line numbers.
+- I did not implement `IIndentationStrategy` / `DefaultIndentationStrategy`; that belongs to A3/D7 and is not present in this checkout.
+- I did not migrate line numbers from `OnDrawComplete` to an `IBackgroundRenderer`; that is B2 scope.
+
+## Why
+
+D1 explicitly depends on B1, and shipping another draw-loop tab shortcut would repeat the R1/R2 violation. I implemented the smallest B1-compatible line-element layer that lets tabs be represented as a `TabElement` and makes the D1 behavior testable without taking over the whole B1/B2 work item.
+
+## Validation
+
+- `dotnet build Terminal.Gui.Text.slnx`
+- `dotnet run --project tests/Terminal.Gui.Text.Tests`
+- `dotnet run --project tests/Terminal.Gui.Editor.Tests`
+- `dotnet run --project tests/Terminal.Gui.Editor.IntegrationTests`
+- `dotnet format Terminal.Gui.Text.slnx --verify-no-changes --exclude third_party/`
+
+`dotnet tool restore` succeeded. `dotnet jb cleanupcode Terminal.Gui.Text.slnx --profile="Full Cleanup"` failed because the JetBrains CLI did not recognize the solution cleanup profile from this `.slnx` checkout. Running without the profile against the `.slnx` reported no cleanup items. I ran cleanup against the touched projects directly, which used JetBrains' built-in reformat profile.
+
+PR CI result: macOS and Windows passed. Ubuntu failed in the existing ReSharper cleanupcode step because
+`dotnet jb cleanupcode Terminal.Gui.Text.slnx --profile="Built-in: Full Cleanup" --no-build --exclude="third_party/**/*"`
+returned exit code 3 with `No items were found to cleanup.` I confirmed the current `develop` CI fails the same way
+on run `25613103283`, so I decided I cannot make CI green from this PR without changing `.github/workflows/ci.yml`
+or the repository-wide cleanup setup, both of which are outside the allowed edit set for this task.
+
+## Total tokens spent
+
+Exact token usage is not exposed inside this Codex session. My best estimate from the transcript size is roughly 120k-160k tokens.
+
+## What I would do differently
+
+If this were a normal feature PR instead of an experiment, I would split the rendering pipeline into a separate B1 PR first, with cache invalidation and line-number/background migration handled in follow-up B2, then land D1 as a smaller PR on top.

src/Terminal.Gui.Editor/Editor.Commands.cs

@@ -110,6 +110,9 @@ private void CreateCommandsAndBindings ()
 
         ApplyKeyBindings (View.DefaultKeyBindings, DefaultKeyBindings);
 
+        KeyBindings.Remove (Key.Tab);
+        KeyBindings.Remove (Key.Tab.WithShift);
+
         MouseBindings.Add (MouseFlags.WheeledUp, Command.ScrollUp);
         MouseBindings.Add (MouseFlags.WheeledDown, Command.ScrollDown);
         MouseBindings.Add (MouseFlags.WheeledLeft, Command.ScrollLeft);
@@ -181,6 +184,10 @@ private void CreateCommandsAndBindings ()
         {
             ReplaceSelection (string.Empty);
         }
+        else if (TryDeleteIndentationLeft ())
+        {
+            return true;
+        }
         else if (_caretOffset > 0)
         {
             _document!.Remove (_caretOffset - 1, 1);

src/Terminal.Gui.Editor/Editor.Drawing.cs

@@ -3,6 +3,7 @@
 using Terminal.Gui.Drivers;
 using Terminal.Gui.Text.Document;
 using Terminal.Gui.ViewBase;
+using Terminal.Gui.Views.Rendering;
 using Attribute = Terminal.Gui.Drawing.Attribute;
 
 namespace Terminal.Gui.Views;
@@ -44,7 +45,7 @@ protected override bool OnDrawingContent (DrawContext? context)
             }
 
             DocumentLine line = _document.GetLineByNumber (lineIndex + 1);
-            var text = _document.GetText (line);
+            string text = _document.GetText (line);
 #pragma warning disable CS0618 // Type or member is obsolete — see note at top of OnDrawingContent.
             IReadOnlyList<StyledSegment>? segments = syntaxHighlighter?.Highlight (text, SyntaxLanguage);
 #pragma warning restore CS0618 // Type or member is obsolete
@@ -53,13 +54,12 @@ protected override bool OnDrawingContent (DrawContext? context)
 
             DrawLineContent (
                 row,
-                text,
+                line,
                 visibleStart,
                 visibleEnd,
                 segments,
                 normal,
                 selected,
-                line.Offset,
                 hasSelection,
                 selStart,
                 selEnd);
@@ -91,68 +91,32 @@ private void PrepareSyntaxHighlighter (ISyntaxHighlighter? syntaxHighlighter, in
 
     private void DrawLineContent (
         int row,
-        string text,
+        DocumentLine line,
         int visibleStart,
         int visibleEnd,
         IReadOnlyList<StyledSegment>? segments,
         Attribute normal,
         Attribute selected,
-        int lineOffset,
         bool hasSelection,
         int selStart,
         int selEnd)
     {
-        var visualColumn = 0;
-        var segmentIndex = 0;
-        var segmentEnd = segments is { Count: > 0 } ? segments[0].Text.Length : int.MaxValue;
-
-        for (var i = 0; i < text.Length; i++)
+        CellVisualLine visualLine = BuildVisualLine (
+            line,
+            segments,
+            normal,
+            selected,
+            hasSelection ? selStart : 0,
+            hasSelection ? selEnd : 0);
+
+        foreach (IBackgroundRenderer renderer in BackgroundRenderers)
         {
-            while (segments is not null && i >= segmentEnd && segmentIndex + 1 < segments.Count)
-            {
-                segmentIndex++;
-                segmentEnd += segments[segmentIndex].Text.Length;
-            }
-
-            Attribute attribute = segments is null
-                ? normal
-                : segments[segmentIndex].Attribute ?? normal;
-
-            if (hasSelection && lineOffset + i >= selStart && lineOffset + i < selEnd)
-            {
-                attribute = selected;
-            }
-
-            var c = text[i];
-            var width = GetVisualWidthForCharacter (c, visualColumn, TabWidth);
-            var charVisualStart = visualColumn;
-            var charVisualEnd = visualColumn + width;
-
-            if (charVisualEnd <= visibleStart)
-            {
-                visualColumn = charVisualEnd;
-
-                continue;
-            }
-
-            if (charVisualStart >= visibleEnd)
-            {
-                break;
-            }
-
-            var drawStart = Math.Max (charVisualStart, visibleStart);
-            var drawEnd = Math.Min (charVisualEnd, visibleEnd);
-
-            if (drawEnd > drawStart)
-            {
-                SetAttribute (attribute);
-                AddStr (
-                    drawStart - visibleStart,
-                    row,
-                    c == '\t' ? new (' ', drawEnd - drawStart) : c.ToString ());
-            }
+            renderer.Draw (this, visualLine, row, Viewport);
+        }
 
-            visualColumn = charVisualEnd;
+        foreach (CellVisualLineElement element in visualLine.Elements)
+        {
+            element.Draw (this, 0, row, visibleStart, visibleEnd);
         }
     }