Implemented new TextDiff feature "Show All Lines" (toggle)

* Added new ToggleButton in DiffView toolbar, visible when IsTextDiff, disabling the buttons "Increase/Decrease Number of Visible Lines" when on.

* Added new Preference property "UseFullTextDiff".

* Added StyledProperty "UseFullTextDiffProperty" in TextDiffView, with a DataTemplate binding to the corresponding preference property.

* When changed, UseFullTextDiffProperty is handled identically as UseSideBySideDiffProperty (via new helper method RefreshContent(), for unification with OnDataContextChanged()).

* Added new method DiffContext.ToggleFullTextDiff() for changing the preference property and reloading the diff content.

* Implemented the new feature by overriding the "unified" (number of context lines) for Commands.Diff() with a very high number.

NOTE: The number used (~1 billion) is supposed to be the highest one working on Mac, according to this forum comment: https://stackoverflow.com/questions/28727424/for-git-diff-is-there-a-uinfinity-option-to-show-the-whole-file#comment135202820_28846576

src/ViewModels/DiffContext.cs

@@ -78,6 +78,12 @@ namespace SourceGit.ViewModels
             LoadDiffContent();
         }
 
+        public void ToggleFullTextDiff()
+        {
+            Preference.Instance.UseFullTextDiff = !Preference.Instance.UseFullTextDiff;
+            LoadDiffContent();
+        }
+
         public void IncrUnified()
         {
             UnifiedLines = _unifiedLines + 1;
@@ -109,7 +115,12 @@ namespace SourceGit.ViewModels
 
             Task.Run(() =>
             {
-                var latest = new Commands.Diff(_repo, _option, _unifiedLines, _ignoreWhitespace).Result();
+                // NOTE: Here we override the UnifiedLines value (if UseFullTextDiff is on).
+                // There is no way to tell a git-diff to use "ALL lines of context",
+                // so instead we set a very high number for the "lines of context" parameter.
+                var numLines = Preference.Instance.UseFullTextDiff ? 999999999 : _unifiedLines;
+
+                var latest = new Commands.Diff(_repo, _option, numLines, _ignoreWhitespace).Result();
                 var rs = null as object;
 
                 if (latest.TextDiff != null)

src/ViewModels/Preference.cs

@@ -186,6 +186,12 @@ namespace SourceGit.ViewModels
             set => SetProperty(ref _showHiddenSymbolsInDiffView, value);
         }
 
+        public bool UseFullTextDiff
+        {
+            get => _useFullTextDiff;
+            set => SetProperty(ref _useFullTextDiff, value);
+        }
+
         public Models.ChangeViewMode UnstagedChangeViewMode
         {
             get => _unstagedChangeViewMode;
@@ -591,6 +597,7 @@ namespace SourceGit.ViewModels
         private bool _useSyntaxHighlighting = false;
         private bool _enableDiffViewWordWrap = false;
         private bool _showHiddenSymbolsInDiffView = false;
+        private bool _useFullTextDiff = false;
 
         private Models.ChangeViewMode _unstagedChangeViewMode = Models.ChangeViewMode.List;
         private Models.ChangeViewMode _stagedChangeViewMode = Models.ChangeViewMode.List;

src/Views/DiffView.axaml

@@ -34,11 +34,24 @@
 
           <!-- Toolbar Buttons -->
           <StackPanel Grid.Column="3" Margin="8,0,0,0" Orientation="Horizontal" VerticalAlignment="Center">
+            <ToggleButton Classes="line_path"
+                          Width="32" Height="18"
+                          Background="Transparent"
+                          Padding="9,6"
+                          Command="{Binding ToggleFullTextDiff}"
+                          IsChecked="{Binding Source={x:Static vm:Preference.Instance}, Path=UseFullTextDiff, Mode=OneWay}"
+                          IsVisible="{Binding IsTextDiff}"
+                          ToolTip.Tip="{DynamicResource Text.Diff.VisualLines.All}">
+              <Path Width="13" Height="13" Data="{StaticResource Icons.Lines.All}" Margin="0,3,0,0"/>
+            </ToggleButton>
             <Button Classes="icon_button" 
                     Width="32" 
                     Command="{Binding IncrUnified}" 
                     IsVisible="{Binding IsTextDiff}"
                     ToolTip.Tip="{DynamicResource Text.Diff.VisualLines.Incr}">
+              <Button.IsEnabled>
+                <Binding Source="{x:Static vm:Preference.Instance}" Path="UseFullTextDiff" Mode="OneWay" Converter="{x:Static BoolConverters.Not}"/>
+              </Button.IsEnabled>
               <Path Width="12" Height="12" Stretch="Uniform" Margin="0,6,0,0" Data="{StaticResource Icons.Lines.Incr}"/>
             </Button>
 
@@ -46,8 +59,13 @@
                     Width="32" 
                     Command="{Binding DecrUnified}" 
                     IsVisible="{Binding IsTextDiff}" 
-                    ToolTip.Tip="{DynamicResource Text.Diff.VisualLines.Decr}" 
+                    ToolTip.Tip="{DynamicResource Text.Diff.VisualLines.Decr}">
-                    IsEnabled="{Binding UnifiedLines, Converter={x:Static c:IntConverters.IsGreaterThanFour}}">
+              <Button.IsEnabled>
+                <MultiBinding Converter="{x:Static BoolConverters.And}">
+                  <Binding Path="UnifiedLines" Mode="OneWay" Converter="{x:Static c:IntConverters.IsGreaterThanFour}"/>
+                  <Binding Source="{x:Static vm:Preference.Instance}" Path="UseFullTextDiff" Mode="OneWay" Converter="{x:Static BoolConverters.Not}"/>
+                </MultiBinding>
+              </Button.IsEnabled>
               <Path Width="12" Height="12" Stretch="Uniform" Margin="0,6,0,0" Data="{StaticResource Icons.Lines.Decr}"/>
             </Button>
 
@@ -211,7 +229,9 @@
 
           <!-- Text Diff -->
           <DataTemplate DataType="m:TextDiff">
-            <v:TextDiffView UseSideBySideDiff="{Binding Source={x:Static vm:Preference.Instance}, Path=UseSideBySideDiff, Mode=OneWay}"/>
+            <v:TextDiffView 
+              UseSideBySideDiff="{Binding Source={x:Static vm:Preference.Instance}, Path=UseSideBySideDiff, Mode=OneWay}"
+              UseFullTextDiff="{Binding Source={x:Static vm:Preference.Instance}, Path=UseFullTextDiff, Mode=OneWay}"/>
           </DataTemplate>
 
           <!-- Empty or only EOL changes -->

src/Views/TextDiffView.axaml.cs

@@ -1205,6 +1205,15 @@ namespace SourceGit.Views
             set => SetValue(UseSideBySideDiffProperty, value);
         }
 
+        public static readonly StyledProperty<bool> UseFullTextDiffProperty =
+            AvaloniaProperty.Register<TextDiffView, bool>(nameof(UseFullTextDiff));
+
+        public bool UseFullTextDiff
+        {
+            get => GetValue(UseFullTextDiffProperty);
+            set => SetValue(UseFullTextDiffProperty, value);
+        }
+
         public static readonly StyledProperty<TextDiffViewChunk> SelectedChunkProperty =
             AvaloniaProperty.Register<TextDiffView, TextDiffViewChunk>(nameof(SelectedChunk));
 
@@ -1232,19 +1241,44 @@ namespace SourceGit.Views
             set => SetValue(EnableChunkSelectionProperty, value);
         }
 
+        private void RefreshContent(Models.TextDiff diff, bool keepScrollOffset = true)
+        {
+            if (SelectedChunk != null)
+                SetCurrentValue(SelectedChunkProperty, null);
+
+            if (diff == null)
+            {
+                Editor.Content = null;
+                GC.Collect();
+                return;
+            }
+
+            if (UseSideBySideDiff)
+            {
+                var previousContent = Editor.Content as ViewModels.TwoSideTextDiff;
+                Editor.Content = new ViewModels.TwoSideTextDiff(diff, keepScrollOffset ? previousContent : null);
+            }
+            else
+            {
+                if (!keepScrollOffset)
+                    diff.ScrollOffset = Vector.Zero;
+                Editor.Content = diff;
+            }
+
+            IsUnstagedChange = diff.Option.IsUnstaged;
+            EnableChunkSelection = diff.Option.WorkingCopyChange != null;
+        }
+
         static TextDiffView()
         {
             UseSideBySideDiffProperty.Changed.AddClassHandler<TextDiffView>((v, _) =>
             {
-                if (v.DataContext is Models.TextDiff diff)
+                v.RefreshContent(v.DataContext as Models.TextDiff, false);
-                {
+            });
-                    diff.ScrollOffset = Vector.Zero;
 
-                    if (v.UseSideBySideDiff)
+            UseFullTextDiffProperty.Changed.AddClassHandler<TextDiffView>((v, _) =>
-                        v.Editor.Content = new ViewModels.TwoSideTextDiff(diff);
+            {
-                    else
+                v.RefreshContent(v.DataContext as Models.TextDiff, false);
-                        v.Editor.Content = diff;
-                }
             });
 
             SelectedChunkProperty.Changed.AddClassHandler<TextDiffView>((v, _) =>
@@ -1271,25 +1305,7 @@ namespace SourceGit.Views
         protected override void OnDataContextChanged(EventArgs e)
         {
             base.OnDataContextChanged(e);
-
+            RefreshContent(DataContext as Models.TextDiff, true);
-            if (SelectedChunk != null)
-                SetCurrentValue(SelectedChunkProperty, null);
-
-            var diff = DataContext as Models.TextDiff;
-            if (diff == null)
-            {
-                Editor.Content = null;
-                GC.Collect();
-                return;
-            }
-
-            if (UseSideBySideDiff)
-                Editor.Content = new ViewModels.TwoSideTextDiff(diff, Editor.Content as ViewModels.TwoSideTextDiff);
-            else
-                Editor.Content = diff;
-
-            IsUnstagedChange = diff.Option.IsUnstaged;
-            EnableChunkSelection = diff.Option.WorkingCopyChange != null;
         }
 
         protected override void OnPointerExited(PointerEventArgs e)