Add user config gui.showNumstatInFilesView

When enabled, it adds "+n -m" after each file in the Files panel to show how
many lines were added and deleted, as with `git diff --numstat` on the command
line.

pkg/gui/presentation/files.go

@@ -22,12 +22,13 @@ func RenderFileTree(
 	tree filetree.IFileTree,
 	submoduleConfigs []*models.SubmoduleConfig,
 	showFileIcons bool,
+	showNumstat bool,
 ) []string {
 	collapsedPaths := tree.CollapsedPaths()
 	return renderAux(tree.GetRoot().Raw(), collapsedPaths, -1, -1, func(node *filetree.Node[models.File], treeDepth int, visualDepth int, isCollapsed bool) string {
 		fileNode := filetree.NewFileNode(node)
 
-		return getFileLine(isCollapsed, fileNode.GetHasUnstagedChanges(), fileNode.GetHasStagedChanges(), treeDepth, visualDepth, showFileIcons, submoduleConfigs, node)
+		return getFileLine(isCollapsed, fileNode.GetHasUnstagedChanges(), fileNode.GetHasStagedChanges(), treeDepth, visualDepth, showNumstat, showFileIcons, submoduleConfigs, node)
 	})
 }
 
@@ -111,6 +112,7 @@ func getFileLine(
 	hasStagedChanges bool,
 	treeDepth int,
 	visualDepth int,
+	showNumstat,
 	showFileIcons bool,
 	submoduleConfigs []*models.SubmoduleConfig,
 	node *filetree.Node[models.File],
@@ -165,6 +167,12 @@ func getFileLine(
 		output += theme.DefaultTextColor.Sprint(" (submodule)")
 	}
 
+	if file != nil && showNumstat {
+		if lineChanges := formatLineChanges(file.LinesAdded, file.LinesDeleted); lineChanges != "" {
+			output += " " + lineChanges
+		}
+	}
+
 	return output
 }
 
@@ -186,6 +194,23 @@ func formatFileStatus(file *models.File, restColor style.TextStyle) string {
 	return firstCharCl.Sprint(firstChar) + secondCharCl.Sprint(secondChar)
 }
 
+func formatLineChanges(linesAdded, linesDeleted int) string {
+	output := ""
+
+	if linesAdded != 0 {
+		output += style.FgGreen.Sprintf("+%d", linesAdded)
+	}
+
+	if linesDeleted != 0 {
+		if output != "" {
+			output += " "
+		}
+		output += style.FgRed.Sprintf("-%d", linesDeleted)
+	}
+
+	return output
+}
+
 func getCommitFileLine(
 	isCollapsed bool,
 	treeDepth int,

pkg/gui/presentation/files_test.go

@@ -19,11 +19,12 @@ func toStringSlice(str string) []string {
 
 func TestRenderFileTree(t *testing.T) {
 	scenarios := []struct {
-		name           string
-		root           *filetree.FileNode
-		files          []*models.File
-		collapsedPaths []string
-		expected       []string
+		name            string
+		root            *filetree.FileNode
+		files           []*models.File
+		collapsedPaths  []string
+		showLineChanges bool
+		expected        []string
 	}{
 		{
 			name:     "nil node",
@@ -37,6 +38,22 @@ func TestRenderFileTree(t *testing.T) {
 			},
 			expected: []string{" M test"},
 		},
+		{
+			name: "numstat",
+			files: []*models.File{
+				{Name: "test", ShortStatus: " M", HasStagedChanges: true, LinesAdded: 1, LinesDeleted: 1},
+				{Name: "test2", ShortStatus: " M", HasStagedChanges: true, LinesAdded: 1},
+				{Name: "test3", ShortStatus: " M", HasStagedChanges: true, LinesDeleted: 1},
+				{Name: "test4", ShortStatus: " M", HasStagedChanges: true, LinesAdded: 0, LinesDeleted: 0},
+			},
+			showLineChanges: true,
+			expected: []string{
+				" M test +1 -1",
+				" M test2 +1",
+				" M test3 -1",
+				" M test4",
+			},
+		},
 		{
 			name: "big example",
 			files: []*models.File{
@@ -72,7 +89,7 @@ M  file1
 			for _, path := range s.collapsedPaths {
 				viewModel.ToggleCollapsed(path)
 			}
-			result := RenderFileTree(viewModel, nil, false)
+			result := RenderFileTree(viewModel, nil, false, s.showLineChanges)
 			assert.EqualValues(t, s.expected, result)
 		})
 	}