Copy the selected diff lines from the focused main view

The main view shows a diff renderer's picture of a diff, and that is not
what you want on your clipboard: a renderer may drop the +/- column, move
the line numbers into a gutter, group a hunk's deletions before its
additions, or leave lines out altogether. So copying takes the lines from
the diff itself, locating them by the identity of the selected rows.

Only the panel that produced the diff can produce it again, though: the
working tree's staged or unstaged side, a commit's, a stash entry's. The
new seam is there for that. It asks per file, so that copying three lines
of a commit's diff doesn't fetch the whole of it, and it will grow the
actions on a selection as staging and patch building arrive.

The clipboard gets the run of diff lines from the first selected line of
a file to the last, so that lines the renderer hid come along and the
result still reads as a diff. Headers count as selected lines too. A hunk
header names the first line of its hunk, so it is looked for the way a
line of the file is. A file header names no line at all, and a rendering
may draw it over any number of rows, so a selection touching one of them
takes the whole header.

As in the patch explorers, a selection that is all additions or all
deletions loses its +/- column, ready to be pasted into code. One that
reaches into a header keeps the columns, and what comes out is a patch
fragment rather than lines of code.

Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>

docs-master/keybindings/Keybindings_en.md

@@ -226,6 +226,7 @@ _This file is auto-generated. To update, make the changes in the pkg/i18n direct
 | `` a `` | Toggle hunk selection | Toggle line-by-line vs. hunk selection mode. |
 | `` v `` | Toggle range select |  |
 | `` e `` | Edit file | Open file in external editor. |
+| `` <ctrl+o> `` | Copy selected text to clipboard |  |
 | `` <left>, h `` | Go to previous hunk |  |
 | `` <right>, l `` | Go to next hunk |  |
 | `` N `` | Go to previous file |  |
@@ -338,6 +339,7 @@ _This file is auto-generated. To update, make the changes in the pkg/i18n direct
 | `` a `` | Toggle hunk selection | Toggle line-by-line vs. hunk selection mode. |
 | `` v `` | Toggle range select |  |
 | `` e `` | Edit file | Open file in external editor. |
+| `` <ctrl+o> `` | Copy selected text to clipboard |  |
 | `` <left>, h `` | Go to previous hunk |  |
 | `` <right>, l `` | Go to next hunk |  |
 | `` N `` | Go to previous file |  |

docs-master/keybindings/Keybindings_ja.md

@@ -195,6 +195,7 @@ _This file is auto-generated. To update, make the changes in the pkg/i18n direct
 | `` a `` | ハンクの選択を切り替える | Toggle line-by-line vs. hunk selection mode. |
 | `` v `` | 範囲選択を切り替え |  |
 | `` e `` | ファイルを編集 | 外部エディタでファイルを開きます。 |
+| `` <ctrl+o> `` | 選択したテキストをクリップボードにコピー |  |
 | `` <left>, h `` | 前のハンクに移動 |  |
 | `` <right>, l `` | 次のハンクに移動 |  |
 | `` N `` | Go to previous file |  |
@@ -315,6 +316,7 @@ _This file is auto-generated. To update, make the changes in the pkg/i18n direct
 | `` a `` | ハンクの選択を切り替える | Toggle line-by-line vs. hunk selection mode. |
 | `` v `` | 範囲選択を切り替え |  |
 | `` e `` | ファイルを編集 | 外部エディタでファイルを開きます。 |
+| `` <ctrl+o> `` | 選択したテキストをクリップボードにコピー |  |
 | `` <left>, h `` | 前のハンクに移動 |  |
 | `` <right>, l `` | 次のハンクに移動 |  |
 | `` N `` | Go to previous file |  |

docs-master/keybindings/Keybindings_ko.md

@@ -87,6 +87,7 @@ _This file is auto-generated. To update, make the changes in the pkg/i18n direct
 | `` a `` | Toggle hunk selection | Toggle line-by-line vs. hunk selection mode. |
 | `` v `` | 드래그 선택 전환 |  |
 | `` e `` | 파일 편집 | Open file in external editor. |
+| `` <ctrl+o> `` | 선택한 텍스트를 클립보드에 복사 |  |
 | `` <left>, h `` | 이전 hunk를 선택 |  |
 | `` <right>, l `` | 다음 hunk를 선택 |  |
 | `` N `` | Go to previous file |  |
@@ -172,6 +173,7 @@ _This file is auto-generated. To update, make the changes in the pkg/i18n direct
 | `` a `` | Toggle hunk selection | Toggle line-by-line vs. hunk selection mode. |
 | `` v `` | 드래그 선택 전환 |  |
 | `` e `` | 파일 편집 | Open file in external editor. |
+| `` <ctrl+o> `` | 선택한 텍스트를 클립보드에 복사 |  |
 | `` <left>, h `` | 이전 hunk를 선택 |  |
 | `` <right>, l `` | 다음 hunk를 선택 |  |
 | `` N `` | Go to previous file |  |

docs-master/keybindings/Keybindings_nl.md

@@ -234,6 +234,7 @@ _This file is auto-generated. To update, make the changes in the pkg/i18n direct
 | `` a `` | Wissel tussen hunk selectie aan of uit | Wissel tussen regel-voor-regel of hunk selectie modus. |
 | `` v `` | Toggle drag selecteer |  |
 | `` e `` | Verander bestand | Open bestand in externe editor. |
+| `` <ctrl+o> `` | Copy selected text to clipboard |  |
 | `` <left>, h `` | Selecteer de vorige hunk |  |
 | `` <right>, l `` | Selecteer de volgende hunk |  |
 | `` N `` | Go to previous file |  |
@@ -316,6 +317,7 @@ _This file is auto-generated. To update, make the changes in the pkg/i18n direct
 | `` a `` | Wissel tussen hunk selectie aan of uit | Wissel tussen regel-voor-regel of hunk selectie modus. |
 | `` v `` | Toggle drag selecteer |  |
 | `` e `` | Verander bestand | Open bestand in externe editor. |
+| `` <ctrl+o> `` | Copy selected text to clipboard |  |
 | `` <left>, h `` | Selecteer de vorige hunk |  |
 | `` <right>, l `` | Selecteer de volgende hunk |  |
 | `` N `` | Go to previous file |  |

docs-master/keybindings/Keybindings_pl.md

@@ -102,6 +102,7 @@ _This file is auto-generated. To update, make the changes in the pkg/i18n direct
 | `` a `` | Toggle hunk selection | Toggle line-by-line vs. hunk selection mode. |
 | `` v `` | Przełącz zaznaczenie zakresu |  |
 | `` e `` | Edytuj plik | Otwórz plik w zewnętrznym edytorze. |
+| `` <ctrl+o> `` | Kopiuj zaznaczony tekst do schowka |  |
 | `` <left>, h `` | Idź do poprzedniego fragmentu |  |
 | `` <right>, l `` | Idź do następnego fragmentu |  |
 | `` N `` | Go to previous file |  |
@@ -211,6 +212,7 @@ _This file is auto-generated. To update, make the changes in the pkg/i18n direct
 | `` a `` | Toggle hunk selection | Toggle line-by-line vs. hunk selection mode. |
 | `` v `` | Przełącz zaznaczenie zakresu |  |
 | `` e `` | Edytuj plik | Otwórz plik w zewnętrznym edytorze. |
+| `` <ctrl+o> `` | Kopiuj zaznaczony tekst do schowka |  |
 | `` <left>, h `` | Idź do poprzedniego fragmentu |  |
 | `` <right>, l `` | Idź do następnego fragmentu |  |
 | `` N `` | Go to previous file |  |

docs-master/keybindings/Keybindings_pt.md

@@ -238,6 +238,7 @@ _This file is auto-generated. To update, make the changes in the pkg/i18n direct
 | `` a `` | Toggle hunk selection | Ativa/desativa modo linha por linha vs. modo de seleção por partes. |
 | `` v `` | Toggle range select |  |
 | `` e `` | Editar arquivo | Abrir arquivo no editor externo. |
+| `` <ctrl+o> `` | Copiar texto selecionado para área de transferência |  |
 | `` <left>, h `` | Ir para o local anterior |  |
 | `` <right>, l `` | Ir para o próximo trecho |  |
 | `` N `` | Go to previous file |  |
@@ -347,6 +348,7 @@ _This file is auto-generated. To update, make the changes in the pkg/i18n direct
 | `` a `` | Toggle hunk selection | Ativa/desativa modo linha por linha vs. modo de seleção por partes. |
 | `` v `` | Toggle range select |  |
 | `` e `` | Editar arquivo | Abrir arquivo no editor externo. |
+| `` <ctrl+o> `` | Copiar texto selecionado para área de transferência |  |
 | `` <left>, h `` | Ir para o local anterior |  |
 | `` <right>, l `` | Ir para o próximo trecho |  |
 | `` N `` | Go to previous file |  |

docs-master/keybindings/Keybindings_ru.md

@@ -77,6 +77,7 @@ _This file is auto-generated. To update, make the changes in the pkg/i18n direct
 | `` a `` | Toggle hunk selection | Toggle line-by-line vs. hunk selection mode. |
 | `` v `` | Переключить выборку перетаскивания |  |
 | `` e `` | Редактировать файл | Open file in external editor. |
+| `` <ctrl+o> `` | Скопировать выделенный текст в буфер обмена |  |
 | `` <left>, h `` | Выбрать предыдущую часть |  |
 | `` <right>, l `` | Выбрать следующую часть |  |
 | `` N `` | Go to previous file |  |
@@ -116,6 +117,7 @@ _This file is auto-generated. To update, make the changes in the pkg/i18n direct
 | `` a `` | Toggle hunk selection | Toggle line-by-line vs. hunk selection mode. |
 | `` v `` | Переключить выборку перетаскивания |  |
 | `` e `` | Редактировать файл | Open file in external editor. |
+| `` <ctrl+o> `` | Скопировать выделенный текст в буфер обмена |  |
 | `` <left>, h `` | Выбрать предыдущую часть |  |
 | `` <right>, l `` | Выбрать следующую часть |  |
 | `` N `` | Go to previous file |  |

docs-master/keybindings/Keybindings_zh-CN.md

@@ -289,6 +289,7 @@ _This file is auto-generated. To update, make the changes in the pkg/i18n direct
 | `` a `` | 切换代码块选择 | 切换逐行选择与代码块选择模式。 |
 | `` v `` | 切换拖动选择 |  |
 | `` e `` | 编辑文件 | 使用外部编辑器打开文件 |
+| `` <ctrl+o> `` | 复制选中文本到剪贴板 |  |
 | `` <left>, h `` | 选择上一个区块 |  |
 | `` <right>, l `` | 选择下一个区块 |  |
 | `` N `` | Go to previous file |  |
@@ -344,6 +345,7 @@ _This file is auto-generated. To update, make the changes in the pkg/i18n direct
 | `` a `` | 切换代码块选择 | 切换逐行选择与代码块选择模式。 |
 | `` v `` | 切换拖动选择 |  |
 | `` e `` | 编辑文件 | 使用外部编辑器打开文件 |
+| `` <ctrl+o> `` | 复制选中文本到剪贴板 |  |
 | `` <left>, h `` | 选择上一个区块 |  |
 | `` <right>, l `` | 选择下一个区块 |  |
 | `` N `` | Go to previous file |  |

docs-master/keybindings/Keybindings_zh-TW.md

@@ -78,6 +78,7 @@ _This file is auto-generated. To update, make the changes in the pkg/i18n direct
 | `` a `` | 切換程式碼塊選擇 | 切換逐行選擇與程式碼塊選擇模式。 |
 | `` v `` | 切換拖曳選擇 |  |
 | `` e `` | 編輯檔案 | 使用外部編輯器開啟 |
+| `` <ctrl+o> `` | 複製所選文本至剪貼簿 |  |
 | `` <left>, h `` | 選擇上一段 |  |
 | `` <right>, l `` | 選擇下一段 |  |
 | `` N `` | Go to previous file |  |
@@ -366,6 +367,7 @@ _This file is auto-generated. To update, make the changes in the pkg/i18n direct
 | `` a `` | 切換程式碼塊選擇 | 切換逐行選擇與程式碼塊選擇模式。 |
 | `` v `` | 切換拖曳選擇 |  |
 | `` e `` | 編輯檔案 | 使用外部編輯器開啟 |
+| `` <ctrl+o> `` | 複製所選文本至剪貼簿 |  |
 | `` <left>, h `` | 選擇上一段 |  |
 | `` <right>, l `` | 選擇下一段 |  |
 | `` N `` | Go to previous file |  |

pkg/gocui/view.go

@@ -1484,9 +1484,9 @@ func (v *View) CopyContent(from *View) {
 
 	// A background task may be streaming output into the source view's buffer
 	// via Write, so read it under its own lock. The source is always a
-	// different view than the destination (see the sole caller,
-	// moveMainContextToTop), and no other code holds two view write locks at
-	// once, so this can't deadlock.
+	// different view than the destination — its callers hand content from one
+	// view to another — and no other code holds two view write locks at once, so
+	// this can't deadlock.
 	from.writeMutex.Lock()
 	defer from.writeMutex.Unlock()
 

pkg/gui/context/base_context.go

@@ -13,14 +13,15 @@ type BaseContext struct {
 	windowName      string
 	onGetOptionsMap func() map[string]string
 
-	keybindingsFns      []types.KeybindingsFn
-	mouseKeybindingsFns []types.MouseKeybindingsFn
-	onDoubleClickFn     func() error
-	onClickFn           func(opts gocui.ViewMouseBindingOpts) error
-	onRenderToMainFn    func()
-	onFocusFns          []onFocusFn
-	onFocusLostFns      []onFocusLostFn
-	onQuitFns           []func()
+	keybindingsFns            []types.KeybindingsFn
+	mouseKeybindingsFns       []types.MouseKeybindingsFn
+	onDoubleClickFn           func() error
+	onClickFn                 func(opts gocui.ViewMouseBindingOpts) error
+	focusedMainViewDiffSource types.FocusedMainViewDiffSource
+	onRenderToMainFn          func()
+	onFocusFns                []onFocusFn
+	onFocusLostFns            []onFocusLostFn
+	onQuitFns                 []func()
 
 	focusable                   bool
 	transient                   bool
@@ -159,6 +160,7 @@ func (self *BaseContext) ClearAllAttachedControllerFunctions() {
 	self.onQuitFns = nil
 	self.onDoubleClickFn = nil
 	self.onClickFn = nil
+	self.focusedMainViewDiffSource = nil
 	self.onRenderToMainFn = nil
 }
 
@@ -180,6 +182,15 @@ func (self *BaseContext) AddOnClickFn(fn func(opts gocui.ViewMouseBindingOpts) e
 	}
 }
 
+func (self *BaseContext) AddFocusedMainViewDiffSource(source types.FocusedMainViewDiffSource) {
+	if source != nil {
+		if self.focusedMainViewDiffSource != nil {
+			panic("only one controller is allowed to set the focused main view diff source")
+		}
+		self.focusedMainViewDiffSource = source
+	}
+}
+
 func (self *BaseContext) GetOnDoubleClick() func() error {
 	return self.onDoubleClickFn
 }
@@ -188,6 +199,10 @@ func (self *BaseContext) GetOnClick() func(opts gocui.ViewMouseBindingOpts) erro
 	return self.onClickFn
 }
 
+func (self *BaseContext) GetFocusedMainViewDiffSource() types.FocusedMainViewDiffSource {
+	return self.focusedMainViewDiffSource
+}
+
 func (self *BaseContext) AddOnRenderToMainFn(fn func()) {
 	if fn != nil {
 		if self.onRenderToMainFn != nil {

pkg/gui/context/commit_files_context.go

@@ -85,10 +85,16 @@ func (self *CommitFilesContext) RefForAdjustingLineNumberInDiff() string {
 }
 
 func (self *CommitFilesContext) GetFromAndToForDiff() (string, string) {
-	if refs := self.GetRefRange(); refs != nil {
-		return refs.From.ParentRefName(), refs.To.RefName()
+	return FromAndToForDiff(self.GetRef(), self.GetRefRange())
+}
+
+// FromAndToForDiff gives the two ends to diff for a ref, or for a range of them: a
+// range runs from the parent of its first ref to its last, a single ref from its own
+// parent to itself.
+func FromAndToForDiff(ref models.Ref, refRange *types.RefRange) (string, string) {
+	if refRange != nil {
+		return refRange.From.ParentRefName(), refRange.To.RefName()
 	}
-	ref := self.GetRef()
 	return ref.ParentRefName(), ref.RefName()
 }
 

pkg/gui/controllers/attach.go

@@ -8,6 +8,7 @@ func AttachControllers(context types.Context, controllers ...types.IController)
 		context.AddMouseKeybindingsFn(controller.GetMouseKeybindings)
 		context.AddOnDoubleClickFn(controller.GetOnDoubleClick())
 		context.AddOnClickFn(controller.GetOnClick())
+		context.AddFocusedMainViewDiffSource(controller.GetFocusedMainViewDiffSource())
 		context.AddOnRenderToMainFn(controller.GetOnRenderToMain())
 		context.AddOnFocusFn(controller.GetOnFocus())
 		context.AddOnFocusLostFn(controller.GetOnFocusLost())

pkg/gui/controllers/base_controller.go

@@ -23,6 +23,10 @@ func (self *baseController) GetOnClick() func(opts gocui.ViewMouseBindingOpts) e
 	return nil
 }
 
+func (self *baseController) GetFocusedMainViewDiffSource() types.FocusedMainViewDiffSource {
+	return nil
+}
+
 func (self *baseController) GetOnRenderToMain() func() {
 	return nil
 }

pkg/gui/controllers/commits_files_controller.go

@@ -191,6 +191,18 @@ func (self *CommitFilesController) GetOnRenderToMain() func() {
 	}
 }
 
+func (self *CommitFilesController) GetFocusedMainViewDiffSource() types.FocusedMainViewDiffSource {
+	return self
+}
+
+// PlainDiff hands out the commit's diff for the given files. Both panes show the same
+// diff here — the secondary one shows the custom patch built from it, which is not a
+// diff of the commit — so which pane asks makes no difference.
+func (self *CommitFilesController) PlainDiff(_ types.DiffPaneContext, paths []string) string {
+	from, to := self.context().GetFromAndToForDiff()
+	return self.c.Helpers().Diff.PlainDiffBetweenRefs(from, to, paths)
+}
+
 func (self *CommitFilesController) copyDiffToClipboard(paths []string, toastMessage string) error {
 	from, to := self.context().GetFromAndToForDiff()
 	from, reverse := self.c.Modes().Diffing.GetFromAndReverseArgsForDiff(from)

pkg/gui/controllers/files_controller.go

@@ -21,6 +21,9 @@ type FilesController struct {
 	baseController
 	*ListControllerTrait[*filetree.FileNode]
 	c *ControllerCommon
+
+	// what this panel offers on the diff it shows in the focused main view
+	diffActions *WorkingTreeDiffActions
 }
 
 var _ types.IController = &FilesController{}
@@ -36,6 +39,7 @@ func NewFilesController(
 			c.Contexts().Files.GetSelected,
 			c.Contexts().Files.GetSelectedItems,
 		),
+		diffActions: NewWorkingTreeDiffActions(c),
 	}
 }
 
@@ -366,42 +370,44 @@ func (self *FilesController) renderNonTextualConflict(node *filetree.FileNode) {
 func (self *FilesController) renderWorkingTreeDiff(node *filetree.FileNode) {
 	self.c.Helpers().MergeConflicts.ResetMergeState()
 
-	split := self.c.UserConfig().Gui.SplitDiff == "always" || (node.GetHasUnstagedChanges() && node.GetHasStagedChanges())
-	mainShowsStaged := !split && node.GetHasStagedChanges()
+	// The unstaged side of a file's diff is shown in the main pane and the staged side
+	// in the secondary one, each only where there is a side to show — so a side is
+	// always in the same place, whatever the file happens to have. A file with nothing
+	// unstaged therefore shows its staged changes in the secondary pane, which then has
+	// the whole section to itself. Configured to always split, both panes are shown
+	// whether or not there is anything on either side.
+	alwaysSplit := self.c.UserConfig().Gui.SplitDiff == "always"
+	showStaged := node.GetHasStagedChanges() || alwaysSplit
+	showUnstaged := node.GetHasUnstagedChanges() || alwaysSplit || !showStaged
 
 	paths := self.pathsForDiff(node)
-	cmdObj := self.c.Git().WorkingTree.WorktreeFileDiffCmdObj(node, false, mainShowsStaged, paths)
-	title := self.c.Tr.UnstagedChanges
-	if mainShowsStaged {
-		title = self.c.Tr.StagedChanges
-	}
-	refreshOpts := types.RefreshMainOpts{
-		Pair: self.c.MainViewPairs().Normal,
-		Main: &types.ViewUpdateOpts{
+	refreshOpts := types.RefreshMainOpts{Pair: self.c.MainViewPairs().Normal}
+
+	if showUnstaged {
+		cmdObj := self.c.Git().WorkingTree.WorktreeFileDiffCmdObj(node, false, false, paths)
+		refreshOpts.Main = &types.ViewUpdateOpts{
 			Task:     types.NewRunDiffRendererTask(cmdObj.GetCmd()),
 			SubTitle: self.c.Helpers().Diff.IgnoringWhitespaceSubTitle(),
-			Title:    title,
-		},
-	}
-
-	if split {
-		cmdObj := self.c.Git().WorkingTree.WorktreeFileDiffCmdObj(node, false, true, paths)
-
-		title := self.c.Tr.StagedChanges
-		if mainShowsStaged {
-			title = self.c.Tr.UnstagedChanges
+			Title:    self.c.Tr.UnstagedChanges,
 		}
+	}
 
+	if showStaged {
+		cmdObj := self.c.Git().WorkingTree.WorktreeFileDiffCmdObj(node, false, true, paths)
 		refreshOpts.Secondary = &types.ViewUpdateOpts{
-			Title:    title,
-			SubTitle: self.c.Helpers().Diff.IgnoringWhitespaceSubTitle(),
 			Task:     types.NewRunDiffRendererTask(cmdObj.GetCmd()),
+			SubTitle: self.c.Helpers().Diff.IgnoringWhitespaceSubTitle(),
+			Title:    self.c.Tr.StagedChanges,
 		}
 	}
 
 	self.c.RenderToMainViews(refreshOpts)
 }
 
+func (self *FilesController) GetFocusedMainViewDiffSource() types.FocusedMainViewDiffSource {
+	return self.diffActions
+}
+
 func (self *FilesController) GetOnDoubleClick() func() error {
 	return self.withItemGraceful(func(node *filetree.FileNode) error {
 		return self.press([]*filetree.FileNode{node})

pkg/gui/controllers/helpers/diff_helper.go

@@ -83,6 +83,19 @@ func (self *DiffHelper) GetUpdateTaskForRenderingCommitsDiff(commit *models.Comm
 	return types.NewRunDiffRendererTask(cmdObj.GetCmd())
 }
 
+// PlainDiffBetweenRefs returns the diff of the given files between two refs as git
+// writes it, without colour or a diff renderer's involvement — what a panel showing
+// a commit's diff hands out as the diff behind its rendering (see
+// types.FocusedMainViewDiffSource). It honours diffing mode, so that the diff is of
+// the same two ends the main view is showing.
+func (self *DiffHelper) PlainDiffBetweenRefs(from string, to string, paths []string) string {
+	from, reverse := self.c.Modes().Diffing.GetFromAndReverseArgsForDiff(from)
+	// An error means there is no diff to be had, which for our purposes is the same
+	// as an empty one.
+	diff, _ := self.c.Git().WorkingTree.ShowFileDiffCmdObj(from, to, reverse, paths, true).RunWithOutput()
+	return diff
+}
+
 func (self *DiffHelper) FilterPathsForCommit(commit *models.Commit) []string {
 	filterPath := self.c.Modes().Filtering.GetPath()
 	if filterPath != "" {

pkg/gui/controllers/helpers/diff_line_plain_text.go

@@ -0,0 +1,172 @@
+package helpers
+
+import (
+	"path/filepath"
+	"slices"
+	"strings"
+
+	"github.com/jesseduffield/lazygit/pkg/gocui"
+	"github.com/jesseduffield/lazygit/pkg/gui/types"
+)
+
+// Reading a rendering back to the diff it came from. What a diff view shows is a diff
+// renderer's picture of a diff, and a picture is not what you want on your clipboard,
+// or in a patch — so the lines of interest are located by identity in the diff itself,
+// which the panel that rendered it hands out (types.FocusedMainViewDiffSource).
+
+// PlainDiffOfSelection returns the text of the rows selected in view, in two parts.
+//
+// aboveDiff is what the selection covers above the diff, as it reads on screen; see
+// textAboveDiff. fromDiff is the diff behind the rest: per file the selection touches,
+// the run of diff lines from the first of its selected lines to the last, with the
+// files in the order the selection meets them.
+//
+// A run, rather than the matched lines alone, so that what comes out reads as a diff:
+// the lines between two selected ones come along even when the rendering didn't show
+// them (difftastic leaves out whitespace-only changes) or showed them in another order
+// (a side-by-side rendering groups the deletions of a hunk before its additions).
+//
+// Headers are selected lines like any other. A hunk header names the first line of its
+// hunk, in the rendering as in the diff, so it is looked for the way a line of the file
+// is; a file header names no line at all and a rendering may spread it over as many
+// rows as it likes, so a selection touching one of them takes the whole header.
+//
+// plainDiff fetches the diff of the given repo-relative files, and is asked only for
+// the files the selection touches, so that copying three lines of a commit's diff
+// doesn't fetch the whole of it. fromDiff is "" when no selected row could be found in
+// the diff, e.g. because the selection covers nothing but a renderer's decoration.
+func (self *DiffLineHelper) PlainDiffOfSelection(
+	view *gocui.View, first int, last int, plainDiff func(paths []string) string,
+) (aboveDiff string, fromDiff string) {
+	worktreePath := self.c.Git().RepoPaths.WorktreePath()
+	aboveDiff = self.textAboveDiff(view, first, last)
+
+	// The files in the order they are shown, and per file what the selection covers of
+	// its diff.
+	paths := []string{}
+	selection := map[string]*selectedDiffLines{}
+	for _, info := range self.DiffLinesInViewRange(view, first, last) {
+		// A row that is neither a line of the file nor a header — the "\ No newline at
+		// end of file" marker — names nothing to look for. It comes along anyway when it
+		// falls within a run.
+		if info.Type == types.DiffLineOther {
+			continue
+		}
+		selected, ok := selection[info.Path]
+		if !ok {
+			paths = append(paths, info.Path)
+			selected = &selectedDiffLines{lines: map[patchLine]bool{}}
+			selection[info.Path] = selected
+		}
+		if info.Type == types.DiffLineFileHeader {
+			selected.header = true
+		} else {
+			selected.lines[patchLineOf(info)] = true
+		}
+	}
+
+	relPaths := repoRelativePaths(worktreePath, paths)
+	if len(relPaths) == 0 {
+		return aboveDiff, ""
+	}
+
+	diffLines := strings.Split(strings.TrimSuffix(plainDiff(relPaths), "\n"), "\n")
+	runs := map[string][2]int{}
+	for i, parsed := range parseAllDiffLinesFromBuffer(diffLines) {
+		if !parsed.ok {
+			continue
+		}
+		info := diffLineInfoIn(worktreePath, parsed.parsed)
+		selected := selection[info.Path]
+		if selected == nil || !selected.covers(info) {
+			continue
+		}
+		if run, ok := runs[info.Path]; ok {
+			runs[info.Path] = [2]int{run[0], i}
+		} else {
+			runs[info.Path] = [2]int{i, i}
+		}
+	}
+
+	text := strings.Builder{}
+	for _, path := range paths {
+		run, ok := runs[path]
+		if !ok {
+			continue
+		}
+		for _, line := range diffLines[run[0] : run[1]+1] {
+			text.WriteString(line)
+			text.WriteString("\n")
+		}
+	}
+	return aboveDiff, text.String()
+}
+
+// textAboveDiff returns the text of the selected rows that sit above the diff, as they
+// read on screen. What a diff view shows before its first file — a commit's message and
+// git's summary of it — is part of no file's diff, so there is nothing to look those
+// rows up in and the rendering is all we have of them.
+//
+// It is "" for a view that shows no file at all: with no diff on screen there is
+// nothing for the text to be above, and a rendering we couldn't read as a diff is
+// exactly what we don't want on the clipboard.
+func (self *DiffLineHelper) textAboveDiff(view *gocui.View, first int, last int) string {
+	firstRow, ok := view.BufferLineForViewLine(first)
+	if !ok {
+		return ""
+	}
+	lastRow, ok := view.BufferLineForViewLine(last)
+	if !ok {
+		return ""
+	}
+
+	startOfDiff := slices.IndexFunc(self.filePaths(view), func(path string) bool { return path != "" })
+	if startOfDiff == -1 {
+		return ""
+	}
+
+	lastRow = min(lastRow, startOfDiff-1)
+	if lastRow < firstRow {
+		return ""
+	}
+	return strings.Join(view.BufferLines()[firstRow:lastRow+1], "\n") + "\n"
+}
+
+// selectedDiffLines is what a selection covers of one file's diff.
+type selectedDiffLines struct {
+	// The lines of the file to look for, hunk headers among them, by the identity that
+	// names them in any rendering of the diff.
+	lines map[patchLine]bool
+	// Whether the file's header is covered, in whole or in part.
+	header bool
+}
+
+// covers reports whether the given line of a file's diff is one the selection holds.
+//
+// A file header is answered for by kind rather than looked for: the two ways a row's
+// identity is recovered disagree about what to call it — a parse of the diff says the
+// file's first line, a renderer's record says the file has no line — and a rendering
+// may show the header as one row or as ten. So a selection that touches it holds every
+// line of it.
+func (self *selectedDiffLines) covers(info types.DiffLineInfo) bool {
+	if info.Type == types.DiffLineFileHeader {
+		return self.header
+	}
+	return self.lines[patchLineOf(info)]
+}
+
+// repoRelativePaths turns the absolute paths a diff line's identity carries into the
+// repo-relative ones git speaks, dropping any that lies outside the worktree — a diff
+// renderer states the path however it likes, and one we can't place is one we can't
+// ask git about.
+func repoRelativePaths(worktreePath string, paths []string) []string {
+	relPaths := make([]string, 0, len(paths))
+	for _, path := range paths {
+		relPath, err := filepath.Rel(worktreePath, path)
+		if err != nil || strings.HasPrefix(relPath, "..") {
+			continue
+		}
+		relPaths = append(relPaths, filepath.ToSlash(relPath))
+	}
+	return relPaths
+}

pkg/gui/controllers/helpers/diff_line_queries.go

@@ -11,6 +11,30 @@ import (
 // cursor and a click speak. They are all built on the identities recovered in
 // diff_line_helper.go, which is where the answering stops and the recovering starts.
 
+// DiffLinesInViewRange returns the identity of every diff line shown by the rows in
+// the inclusive view-line range [first, last] of view's rendered diff, in display
+// order. Rows whose identity can't be recovered are left out, as are the wrapped
+// segments of a row already counted.
+//
+// A row can show more than one diff line — a side-by-side rendering puts a deletion
+// beside the addition replacing it — and all of them are reported: what the user
+// pointed at is the row, so everything on it is selected.
+func (self *DiffLineHelper) DiffLinesInViewRange(view *gocui.View, first int, last int) []types.DiffLineInfo {
+	identities := self.resolveDiffLineIdentities(view.DiffLineContents())
+
+	infos := []types.DiffLineInfo{}
+	previousBufferLine := -1
+	for viewLine := first; viewLine <= last; viewLine++ {
+		bufferLine, ok := view.BufferLineForViewLine(viewLine)
+		if !ok || bufferLine == previousBufferLine || bufferLine >= len(identities) {
+			continue
+		}
+		previousBufferLine = bufferLine
+		infos = append(infos, identities[bufferLine]...)
+	}
+	return infos
+}
+
 // changeLines resolves view's rendered diff to one flag per buffer line: whether
 // that row is a change line (an addition or a deletion), as opposed to context, a
 // header, or a row whose identity couldn't be recovered. Those are the rows a

pkg/gui/controllers/helpers/window_arrangement_helper.go

@@ -60,7 +60,7 @@ type WindowArrangementArgs struct {
 	ContentHeightForWindow func(window string) int
 	// Whether the main panel is split (as is the case e.g. when a file has both
 	// staged and unstaged changes)
-	SplitMainPanel bool
+	MainPanes types.MainPanes
 	// The current screen mode (normal, half, full)
 	ScreenMode types.ScreenMode
 	// The content shown on the bottom left of the screen when showing a loader
@@ -103,7 +103,7 @@ func (self *WindowArrangementHelper) GetWindowDimensions(informationStr string,
 		ContentHeightForWindow: func(window string) int {
 			return self.windowHelper.GetContextForWindow(window).TotalContentHeight()
 		},
-		SplitMainPanel:   repoState.GetSplitMainPanel(),
+		MainPanes:        repoState.GetMainPanes(),
 		ScreenMode:       repoState.GetScreenMode(),
 		AppStatus:        appStatus,
 		InformationStr:   informationStr,
@@ -215,36 +215,27 @@ func MergeMaps[K comparable, V any](maps ...map[K]V) map[K]V {
 }
 
 func mainSectionChildren(args WindowArrangementArgs) []*boxlayout.Box {
-	// if we're not in split mode we can just show the one main panel. Likewise if
-	// the main panel is focused and we're in full-screen mode
-	if !args.SplitMainPanel || (args.ScreenMode == types.SCREEN_FULL && args.CurrentWindow == "main") {
-		return []*boxlayout.Box{
-			{
-				Window: "main",
-				Weight: 1,
-			},
+	mainPane := &boxlayout.Box{Window: "main", Weight: 1}
+	secondaryPane := &boxlayout.Box{Window: "secondary", Weight: 1}
+
+	switch args.MainPanes {
+	case types.MainPaneOnly:
+		return []*boxlayout.Box{mainPane}
+	case types.SecondaryPaneOnly:
+		return []*boxlayout.Box{secondaryPane}
+	case types.BothMainPanes:
+		// In full-screen mode the focused one takes the whole section anyway.
+		if args.ScreenMode == types.SCREEN_FULL {
+			if args.CurrentWindow == "main" {
+				return []*boxlayout.Box{mainPane}
+			}
+			if args.CurrentWindow == "secondary" {
+				return []*boxlayout.Box{secondaryPane}
+			}
 		}
 	}
 
-	if args.CurrentWindow == "secondary" && args.ScreenMode == types.SCREEN_FULL {
-		return []*boxlayout.Box{
-			{
-				Window: "secondary",
-				Weight: 1,
-			},
-		}
-	}
-
-	return []*boxlayout.Box{
-		{
-			Window: "main",
-			Weight: 1,
-		},
-		{
-			Window: "secondary",
-			Weight: 1,
-		},
-	}
+	return []*boxlayout.Box{mainPane, secondaryPane}
 }
 
 func getMidSectionWeights(args WindowArrangementArgs) (int, int) {
@@ -382,7 +373,7 @@ func infoSectionChildren(args WindowArrangementArgs) []*boxlayout.Box {
 }
 
 func splitMainPanelSideBySide(args WindowArrangementArgs) bool {
-	if !args.SplitMainPanel {
+	if args.MainPanes != types.BothMainPanes {
 		return false
 	}
 

pkg/gui/controllers/helpers/window_arrangement_helper_test.go

@@ -35,7 +35,7 @@ func TestGetWindowDimensions(t *testing.T) {
 			// Each panel shows its first tab by default; for the special-cased
 			// panels (status, stash) the view name matches the window name.
 			ActiveViewForWindow: func(window string) string { return window },
-			SplitMainPanel:      false,
+			MainPanes:           types.MainPaneOnly,
 			ScreenMode:          types.SCREEN_NORMAL,
 			AppStatus:           "",
 			InformationStr:      "information",

pkg/gui/controllers/main_view_controller.go

@@ -79,6 +79,13 @@ func (self *MainViewController) GetKeybindings(opts types.KeybindingsOpts) []*ty
 			GetDisabledReason: self.diffSelectionDisabledReason,
 			Tooltip:           self.c.Tr.EditFileTooltip,
 		},
+		{
+			Keys:              opts.GetKeys(opts.Config.Universal.CopyToClipboard),
+			Handler:           self.copySelection,
+			Description:       self.c.Tr.CopySelectedTextToClipboard,
+			DescriptionFunc:   self.diffSelectionDescriptionText(self.c.Tr.CopySelectedTextToClipboard),
+			GetDisabledReason: self.diffSelectionDisabledReason,
+		},
 		{
 			Keys:              opts.GetKeys(opts.Config.Main.PrevHunk),
 			Handler:           self.prevChangeBlock,
@@ -248,6 +255,63 @@ func (self *MainViewController) diffMainViewType() types.DiffMainViewType {
 	return types.DiffMainViewTypeNone
 }
 
+// diffSource returns the panel beneath the focused main view, as the thing that can
+// hand out the diff it rendered there. nil when this pane isn't on the stack, or the
+// panel beneath shows no diff.
+func (self *MainViewController) diffSource() types.FocusedMainViewDiffSource {
+	if !self.c.Context().IsInStack(self.context) {
+		return nil
+	}
+	sidePanel := self.c.Context().NextInStack(self.context)
+	if sidePanel == nil {
+		return nil
+	}
+	return sidePanel.GetFocusedMainViewDiffSource()
+}
+
+// copySelection copies the selected diff lines to the clipboard — not as the diff
+// renderer drew them, but as they read in the diff itself, which is both what you meant
+// to copy and the only form a renderer can't have mangled. A selection that is all
+// additions or all deletions loses its +/- column, so that it can be pasted straight
+// into code.
+//
+// The rows above the diff (a commit's message, git's summary of it) belong to no file,
+// so they are copied as they stand on screen.
+func (self *MainViewController) copySelection() error {
+	text := self.textOfSelection()
+	if text == "" {
+		self.c.ErrorToast(self.c.Tr.SelectionNotFoundInDiffToast)
+		return nil
+	}
+
+	self.c.LogAction(self.c.Tr.Actions.CopySelectedTextToClipboard)
+	if err := self.c.OS().CopyToClipboard(text); err != nil {
+		return err
+	}
+	self.c.Toast(self.c.Tr.SelectedDiffLinesCopiedToast)
+	return nil
+}
+
+// textOfSelection is what copying the selection puts on the clipboard. It is "" when
+// none of the selected rows could be placed in the diff, which is what a rendering's
+// own decoration comes to.
+func (self *MainViewController) textOfSelection() string {
+	source := self.diffSource()
+	if source == nil {
+		return ""
+	}
+	view := self.context.GetView()
+	first, last := view.SelectedLineRange()
+	aboveDiff, fromDiff := self.c.Helpers().DiffLine.PlainDiffOfSelection(view, first, last,
+		func(paths []string) string { return source.PlainDiff(self.context, paths) })
+	if aboveDiff == "" {
+		// Only text that is all diff has a +/- column to lose: a line of a commit message
+		// may begin with a '-' without being a deletion of anything.
+		fromDiff = dropDiffPrefix(fromDiff)
+	}
+	return aboveDiff + fromDiff
+}
+
 // diffSelectState returns this pane's diff selection mode state.
 func (self *MainViewController) diffSelectState() *types.DiffSelectState {
 	return self.context.DiffSelectState()

pkg/gui/controllers/reflog_commits_controller.go

@@ -37,6 +37,20 @@ func (self *ReflogCommitsController) context() *context.ReflogCommitsContext {
 	return self.c.Contexts().ReflogCommits
 }
 
+func (self *ReflogCommitsController) GetFocusedMainViewDiffSource() types.FocusedMainViewDiffSource {
+	return self
+}
+
+// PlainDiff hands out the reflog entry's diff for the given files — the same diff its
+// main view shows, only without the entry's message and stat above it.
+func (self *ReflogCommitsController) PlainDiff(_ types.DiffPaneContext, paths []string) string {
+	commit := self.context().GetSelected()
+	if commit == nil {
+		return ""
+	}
+	return self.c.Helpers().Diff.PlainDiffBetweenRefs(commit.ParentRefName(), commit.RefName(), paths)
+}
+
 func (self *ReflogCommitsController) GetOnRenderToMain() func() {
 	return func() {
 		self.c.Helpers().Diff.WithDiffModeCheck(func() {

pkg/gui/controllers/switch_to_diff_files_controller.go

@@ -4,6 +4,7 @@ import (
 	"path/filepath"
 
 	"github.com/jesseduffield/lazygit/pkg/commands/models"
+	"github.com/jesseduffield/lazygit/pkg/gui/context"
 	"github.com/jesseduffield/lazygit/pkg/gui/types"
 )
 
@@ -64,6 +65,22 @@ func (self *SwitchToDiffFilesController) GetOnDoubleClick() func() error {
 	}
 }
 
+func (self *SwitchToDiffFilesController) GetFocusedMainViewDiffSource() types.FocusedMainViewDiffSource {
+	return self
+}
+
+// PlainDiff hands out the diff of the panel's selected commit (or range of them) for
+// the given files — the same diff its main view shows, only without the commit's
+// message and stat above it.
+func (self *SwitchToDiffFilesController) PlainDiff(_ types.DiffPaneContext, paths []string) string {
+	ref := self.context.GetSelectedRef()
+	if ref == nil {
+		return ""
+	}
+	from, to := context.FromAndToForDiff(ref, self.context.GetSelectedRefRangeForDiffFiles())
+	return self.c.Helpers().Diff.PlainDiffBetweenRefs(from, to, paths)
+}
+
 func (self *SwitchToDiffFilesController) enter() error {
 	ref := self.context.GetSelectedRef()
 	refsRange := self.context.GetSelectedRefRangeForDiffFiles()

pkg/gui/controllers/switch_to_focused_main_view_controller.go

@@ -70,7 +70,13 @@ func (self *SwitchToFocusedMainViewController) onClickSecondary(opts gocui.ViewM
 }
 
 func (self *SwitchToFocusedMainViewController) handleFocusMainView() error {
-	return self.focusMainView(self.c.Contexts().Normal, -1)
+	// Usually the main pane, but the content can be in the secondary one alone: a file
+	// with nothing but staged changes shows them there.
+	mainViewContext := self.c.Contexts().Normal
+	if self.c.State().GetRepoState().GetMainPanes() == types.SecondaryPaneOnly {
+		mainViewContext = self.c.Contexts().NormalSecondary
+	}
+	return self.focusMainView(mainViewContext, -1)
 }
 
 func (self *SwitchToFocusedMainViewController) focusMainView(mainViewContext *context.MainContext, clickedLineIdx int) error {

pkg/gui/controllers/working_tree_diff_actions.go

@@ -0,0 +1,44 @@
+package controllers
+
+import (
+	"github.com/jesseduffield/lazygit/pkg/gui/context"
+	"github.com/jesseduffield/lazygit/pkg/gui/types"
+)
+
+// WorkingTreeDiffActions implements what the files panel offers on the diff it renders
+// into the focused main view: the diff itself, for the commands that need to read lines
+// out of it rather than off the screen.
+type WorkingTreeDiffActions struct {
+	c *ControllerCommon
+}
+
+var _ types.FocusedMainViewDiffSource = &WorkingTreeDiffActions{}
+
+func NewWorkingTreeDiffActions(c *ControllerCommon) *WorkingTreeDiffActions {
+	return &WorkingTreeDiffActions{c: c}
+}
+
+func (self *WorkingTreeDiffActions) context() *context.WorkingTreeContext {
+	return self.c.Contexts().Files
+}
+
+// PlainDiff hands out the working tree's diff for the given files, taken from the
+// side of the index that the asking pane shows.
+func (self *WorkingTreeDiffActions) PlainDiff(pane types.DiffPaneContext, paths []string) string {
+	node := self.context().GetSelected()
+	if node == nil {
+		return ""
+	}
+	// An error means there is no diff to be had, which for our purposes is the same as
+	// an empty one.
+	diff, _ := self.c.Git().WorkingTree.
+		WorktreeFileDiffCmdObj(node, true, self.showsStagedSide(pane), paths).
+		RunWithOutput()
+	return diff
+}
+
+// showsStagedSide reports whether the given main pane is the one showing the staged
+// side of a file's diff, which is always the lower one.
+func (self *WorkingTreeDiffActions) showsStagedSide(pane types.DiffPaneContext) bool {
+	return pane.GetKey() == self.c.Contexts().NormalSecondary.GetKey()
+}

pkg/gui/global_handlers.go

@@ -22,12 +22,7 @@ func (gui *Gui) scrollDownView(view *gocui.View) {
 }
 
 func (gui *Gui) scrollUpMain() error {
-	var view *gocui.View
-	if gui.c.Context().Current().GetWindowName() == "secondary" {
-		view = gui.secondaryView()
-	} else {
-		view = gui.mainView()
-	}
+	view := gui.mainSectionView()
 
 	if view.Name() == "mergeConflicts" {
 		// although we have this same logic in the controller, this method can be invoked
@@ -43,12 +38,7 @@ func (gui *Gui) scrollUpMain() error {
 }
 
 func (gui *Gui) scrollDownMain() error {
-	var view *gocui.View
-	if gui.c.Context().Current().GetWindowName() == "secondary" {
-		view = gui.secondaryView()
-	} else {
-		view = gui.mainView()
-	}
+	view := gui.mainSectionView()
 
 	if view.Name() == "mergeConflicts" {
 		gui.State.Contexts.MergeConflicts.SetUserScrolling(true)
@@ -59,6 +49,17 @@ func (gui *Gui) scrollDownMain() error {
 	return nil
 }
 
+// mainSectionView returns the view that the keys for scrolling the main section act
+// on: the pane the focus is in when it is in one of them, and otherwise the pane the
+// section is showing — which is the lower one whenever it has the section to itself.
+func (gui *Gui) mainSectionView() *gocui.View {
+	if gui.c.Context().Current().GetWindowName() == "secondary" ||
+		gui.State.MainPanes == types.SecondaryPaneOnly {
+		return gui.secondaryView()
+	}
+	return gui.mainView()
+}
+
 func (gui *Gui) mainView() *gocui.View {
 	viewName := gui.helpers.Window.GetViewNameForWindow("main")
 	view, _ := gui.g.View(viewName)

pkg/gui/gui.go

@@ -101,6 +101,10 @@ type Gui struct {
 	// this tells us whether our views have been initially set up
 	ViewsSetup bool
 
+	// the label for the key that focuses the main view, worn by whichever of the two
+	// main panes that key focuses (see showFocusMainViewJumpLabelOn)
+	focusMainViewJumpLabel string
+
 	Views types.Views
 
 	// Log of the commands/actions logged in the Command Log panel.
@@ -231,7 +235,7 @@ type GuiRepoState struct {
 	Model *types.Model
 	Modes *types.Modes
 
-	SplitMainPanel bool
+	MainPanes types.MainPanes
 
 	SearchState *types.SearchState
 	// Lets us not load everything at once. Written and read from refresh
@@ -321,12 +325,12 @@ func (self *GuiRepoState) GetSearchState() *types.SearchState {
 	return self.SearchState
 }
 
-func (self *GuiRepoState) SetSplitMainPanel(value bool) {
-	self.SplitMainPanel = value
+func (self *GuiRepoState) SetMainPanes(value types.MainPanes) {
+	self.MainPanes = value
 }
 
-func (self *GuiRepoState) GetSplitMainPanel() bool {
-	return self.SplitMainPanel
+func (self *GuiRepoState) GetMainPanes() types.MainPanes {
+	return self.MainPanes
 }
 
 func (gui *Gui) onSwitchToNewRepo(startArgs appTypes.StartArgs, contextKey types.ContextKey) error {

pkg/gui/main_panels.go

@@ -110,8 +110,13 @@ func (gui *Gui) allMainContextPairs() []types.MainContextPair {
 func (gui *Gui) refreshMainViews(opts types.RefreshMainOpts) {
 	gui.moveMainContextPairToTop(opts.Pair)
 
+	panes := mainPanesFor(opts)
+	gui.handOverMainSection(opts.Pair, panes)
+
 	if opts.Main != nil {
 		gui.RefreshMainView(opts.Main, opts.Pair.Main)
+	} else {
+		gui.clearMainView(opts.Pair.Main)
 	}
 
 	if opts.Secondary != nil {
@@ -134,7 +139,50 @@ func (gui *Gui) refreshMainViews(opts types.RefreshMainOpts) {
 		}
 	}
 
-	gui.splitMainPanel(opts.Secondary != nil)
+	gui.setMainPanes(panes)
+}
+
+// handOverMainSection carries the content of the main section from the pane that has
+// been showing it on its own to the pane about to, when a render moves the section's
+// content from one to the other — a file's changes going from unstaged to staged, say.
+//
+// The section is one region of the screen to the user, so a change of which pane holds
+// it has to look like that region re-rendering rather than blanking and filling in
+// again: the incoming pane shows what the outgoing one was showing, where it was
+// showing it, until its own render has read enough to be swapped in. It renders from
+// the top when it does, the content it took over not being its own (see
+// clearMainView).
+func (gui *Gui) handOverMainSection(pair types.MainContextPair, panes types.MainPanes) {
+	// The lower pane is always the same view, being the only one a render can leave
+	// holding the section on its own; the upper one is whichever view of the main
+	// window this render is for, which moveMainContextPairToTop has just given a copy
+	// of what that window was showing.
+	upper, lower := pair.Main.GetView(), gui.Views.Secondary
+
+	var from, to *gocui.View
+	switch {
+	case gui.State.MainPanes == types.MainPaneOnly && panes == types.SecondaryPaneOnly:
+		from, to = upper, lower
+	case gui.State.MainPanes == types.SecondaryPaneOnly && panes == types.MainPaneOnly:
+		from, to = lower, upper
+	default:
+		return
+	}
+
+	gui.g.CopyContent(from, to)
+}
+
+// mainPanesFor says which panes the given render occupies: the one it has content for,
+// or both when it has content for both.
+func mainPanesFor(opts types.RefreshMainOpts) types.MainPanes {
+	switch {
+	case opts.Secondary == nil:
+		return types.MainPaneOnly
+	case opts.Main == nil:
+		return types.SecondaryPaneOnly
+	default:
+		return types.BothMainPanes
+	}
 }
 
 // clampDiffSelectionToContent brings the focused main view's selection back onto the
@@ -162,10 +210,19 @@ func (gui *Gui) clampDiffSelectionToContent(view *gocui.View) {
 }
 
 // clearMainView empties a pane that is being given nothing to show, selection and all.
+//
+// An emptied pane is showing nothing, so it also goes back to the top and stops
+// claiming the render it was showing: whatever it is given next is content the user
+// hasn't seen there, and is shown from the top like any other.
 func (gui *Gui) clearMainView(mainContext types.Context) {
-	mainContext.GetView().Clear()
+	view := mainContext.GetView()
+	view.Clear()
+	view.SetOrigin(0, 0)
 	mainContext.SetHasSelectableContent(false)
 	gui.State.ContextMgr.UpdateSelectionHighlights()
+	if manager := gui.getViewBufferManagerForView(view); manager != nil {
+		manager.ForgetRenderedContent()
+	}
 }
 
 // updateDiffSelectionVisibility works out whether a main pane holds anything for a
@@ -289,8 +346,24 @@ func (gui *Gui) mainContextForView(view *gocui.View) *context.MainContext {
 	return nil
 }
 
-func (gui *Gui) splitMainPanel(splitMainPanel bool) {
-	gui.State.SplitMainPanel = splitMainPanel
+func (gui *Gui) setMainPanes(panes types.MainPanes) {
+	gui.State.MainPanes = panes
+
+	// The label for the key that focuses the main view belongs on the pane that key
+	// focuses, which is the secondary one while it is the only one shown.
+	if panes == types.SecondaryPaneOnly {
+		gui.showFocusMainViewJumpLabelOn(gui.Views.Secondary)
+	} else {
+		gui.showFocusMainViewJumpLabelOn(gui.Views.Main)
+	}
+}
+
+// showFocusMainViewJumpLabelOn puts the main view's jump label on the given pane and
+// takes it off the other one, so that only the pane the key focuses wears it.
+func (gui *Gui) showFocusMainViewJumpLabelOn(view *gocui.View) {
+	gui.Views.Main.TitlePrefix = ""
+	gui.Views.Secondary.TitlePrefix = ""
+	view.TitlePrefix = gui.focusMainViewJumpLabel
 }
 
 // reApplySearch runs a search the view holds again over the content a render has just

pkg/gui/types/common.go

@@ -461,8 +461,8 @@ type IRepoStateAccessor interface {
 	SetScreenMode(ScreenMode)
 	InSearchPrompt() bool
 	GetSearchState() *SearchState
-	SetSplitMainPanel(bool)
-	GetSplitMainPanel() bool
+	SetMainPanes(MainPanes)
+	GetMainPanes() MainPanes
 	GetMergeOrRebaseStartedInLazygit() bool
 	SetMergeOrRebaseStartedInLazygit(bool)
 }

pkg/gui/types/context.go

@@ -106,6 +106,10 @@ type IBaseContext interface {
 	// Adding on to the above, this is so that a list-specific handler can register
 	// a hook for doing additional click handling
 	AddOnClickFn(func(opts gocui.ViewMouseBindingOpts) error)
+	// Likewise for the focused main view, which acts on the diff of whichever panel
+	// is beneath it and so has to reach that panel's controller. nil for a panel
+	// that shows no diff.
+	AddFocusedMainViewDiffSource(FocusedMainViewDiffSource)
 
 	AddOnRenderToMainFn(func())
 	AddOnFocusFn(func(OnFocusOpts))
@@ -220,6 +224,21 @@ type DiffPaneContext interface {
 	DiffSelectState() *DiffSelectState
 }
 
+// FocusedMainViewDiffSource is how a side panel hands out the diff behind what it
+// renders into the focused main view: the diff of the given files as git writes it,
+// with no colour and no diff renderer in the way. What the main view shows is that
+// same diff after a renderer has had it, which may have restructured, reordered or
+// dropped parts of it — so anything that needs the diff itself, rather than a picture
+// of it, asks the panel that produced it.
+//
+// paths are repo-relative, and are asked for rather than assumed so that a few lines
+// of a commit's diff can be had without fetching the whole thing. pane says which of
+// the two main panes is asking, since a panel can show a different diff in each — the
+// files panel shows the unstaged changes in one and the staged ones in the other.
+type FocusedMainViewDiffSource interface {
+	PlainDiff(pane DiffPaneContext, paths []string) string
+}
+
 type IListContext interface {
 	Context
 
@@ -315,6 +334,11 @@ type HasKeybindings interface {
 	// HandleFocus has already been called (so the main view is up to date). Should return nil if it
 	// decides not to do anything with the click.
 	GetOnClick() func(opts gocui.ViewMouseBindingOpts) error
+
+	// Implement this in a side-panel controller to hand out the diff behind what your
+	// panel renders into the focused main view, for the commands that act on a
+	// selection in it. nil for a controller whose panel shows no diff.
+	GetFocusedMainViewDiffSource() FocusedMainViewDiffSource
 }
 
 type IController interface {

pkg/gui/types/diff_line_info.go

@@ -40,3 +40,11 @@ type DiffLineInfo struct {
 func (self DiffLineInfo) IsChange() bool {
 	return self.Type == DiffLineAdded || self.Type == DiffLineDeleted
 }
+
+// IsContent reports whether the row is a line of the file itself — a change or a
+// context line — as opposed to a header or a marker. Those are the rows that have a
+// position in the file, and so can be looked for in another rendering of the same
+// diff, or in the diff itself.
+func (self DiffLineInfo) IsContent() bool {
+	return self.IsChange() || self.Type == DiffLineContext
+}

pkg/gui/types/rendering.go

@@ -13,6 +13,19 @@ func NewMainContextPair(main Context, secondary Context) MainContextPair {
 	return MainContextPair{Main: main, Secondary: secondary}
 }
 
+// MainPanes says which of the two panes of the main section are shown. Most content
+// takes the main pane alone; content with two sides to it — the working tree's
+// unstaged and staged changes, a commit's diff and the patch built from it — takes
+// both; and content whose only side is the second one takes the secondary pane alone,
+// so that it has the whole section rather than sitting under an empty pane.
+type MainPanes int
+
+const (
+	MainPaneOnly MainPanes = iota
+	BothMainPanes
+	SecondaryPaneOnly
+)
+
 type MainViewPairs struct {
 	Normal         MainContextPair
 	MergeConflicts MainContextPair

pkg/gui/views.go

@@ -283,11 +283,11 @@ func (gui *Gui) configureViewProperties() {
 		}
 	}
 
+	gui.focusMainViewJumpLabel = ""
 	if gui.c.UserConfig().Gui.ShowPanelJumps {
-		gui.Views.Main.TitlePrefix = keyToTitlePrefix(gui.c.UserConfig().Keybinding.Universal.FocusMainView)
-	} else {
-		gui.Views.Main.TitlePrefix = ""
+		gui.focusMainViewJumpLabel = keyToTitlePrefix(gui.c.UserConfig().Keybinding.Universal.FocusMainView)
 	}
+	gui.showFocusMainViewJumpLabelOn(gui.Views.Main)
 
 	// Index the tab strips by view so we can both set them on views that are
 	// part of a multi-tab panel and clear them on views that no longer are

pkg/i18n/english.go

@@ -736,6 +736,8 @@ type TranslationSet struct {
 	CopyPathToClipboard                   string
 	CommitPrefixPatternError              string
 	CopySelectedTextToClipboard           string
+	SelectedDiffLinesCopiedToast          string
+	SelectionNotFoundInDiffToast          string
 	NoFilesStagedTitle                    string
 	NoFilesStagedPrompt                   string
 	BranchNotFoundTitle                   string
@@ -1925,6 +1927,8 @@ func EnglishTranslationSet() *TranslationSet {
 		CopyTagToClipboard:                       "Copy tag to clipboard",
 		CopyPathToClipboard:                      "Copy path to clipboard",
 		CopySelectedTextToClipboard:              "Copy selected text to clipboard",
+		SelectedDiffLinesCopiedToast:             "Selected diff lines copied to clipboard",
+		SelectionNotFoundInDiffToast:             "Nothing in the selection could be found in the diff",
 		CommitPrefixPatternError:                 "Error in commitPrefix pattern",
 		NoFilesStagedTitle:                       "No files staged",
 		NoFilesStagedPrompt:                      "You have not staged any files. Commit all files?",

pkg/integration/components/view_driver.go

@@ -88,6 +88,17 @@ func (self *ViewDriver) IsImmediatelyBelow(upper *ViewDriver) *ViewDriver {
 	return self
 }
 
+// TitlePrefix asserts on the label a view wears in front of its title, which is the
+// key that jumps to it.
+func (self *ViewDriver) TitlePrefix(expected *TextMatcher) *ViewDriver {
+	self.t.assertWithRetries(func() (bool, string) {
+		actual := self.getView().TitlePrefix
+		return expected.context(fmt.Sprintf("%s title prefix", self.context)).test(actual)
+	})
+
+	return self
+}
+
 func (self *ViewDriver) Clear() *ViewDriver {
 	// clearing multiple times in case there's multiple lines
 	//  (the clear button only clears a single line at a time)

pkg/integration/tests/conflicts/resolve_without_trailing_lf.go

@@ -54,6 +54,6 @@ var ResolveWithoutTrailingLf = NewIntegrationTest(NewIntegrationTestArgs{
 				Contains("M  file").IsSelected(),
 			)
 
-		t.Views().Main().Content(Contains("-a1\n+a2\n").DoesNotContain("-no eol"))
+		t.Views().Secondary().Content(Contains("-a1\n+a2\n").DoesNotContain("-no eol"))
 	},
 })

pkg/integration/tests/diff/diff_and_apply_patch.go

@@ -73,6 +73,7 @@ var DiffAndApplyPatch = NewIntegrationTest(NewIntegrationTestArgs{
 			Focus().
 			SelectedLine(Contains("file1"))
 
-		t.Views().Main().Content(Contains("+second line"))
+		// The patch was applied to the index, so the file's changes are all staged.
+		t.Views().Secondary().Content(Contains("+second line"))
 	},
 })

pkg/integration/tests/file/directory_diff_with_renamed_files.go

@@ -32,7 +32,7 @@ var DirectoryDiffWithRenamedFiles = NewIntegrationTest(NewIntegrationTestArgs{
 				Equals("  R  dir/nested/file3 → file3"),
 			)
 
-		t.Views().Main().ContainsLines(
+		t.Views().Secondary().ContainsLines(
 			Equals("diff --git a/file1 b/dir/file1"),
 			Equals("similarity index 100%"),
 			Equals("rename from file1"),
@@ -51,7 +51,7 @@ var DirectoryDiffWithRenamedFiles = NewIntegrationTest(NewIntegrationTestArgs{
 			SelectNextItem().
 			SelectedLine(Equals("  ▼ dir"))
 
-		t.Views().Main().
+		t.Views().Secondary().
 			ContainsLines(
 				Equals("diff --git a/file1 b/dir/file1"),
 				Equals("similarity index 100%"),
@@ -75,7 +75,7 @@ var DirectoryDiffWithRenamedFiles = NewIntegrationTest(NewIntegrationTestArgs{
 				Equals("  R  file1 → file1"),
 			)
 
-		t.Views().Main().
+		t.Views().Secondary().
 			ContainsLines(
 				Equals("diff --git a/file1 b/dir/file1"),
 				Equals("similarity index 100%"),

pkg/integration/tests/file/pane_shown_again_starts_at_the_top.go

@@ -0,0 +1,61 @@
+package file
+
+import (
+	"fmt"
+	"strings"
+
+	"github.com/jesseduffield/lazygit/pkg/config"
+	. "github.com/jesseduffield/lazygit/pkg/integration/components"
+)
+
+var PaneShownAgainStartsAtTheTop = NewIntegrationTest(NewIntegrationTestArgs{
+	Description:  "A pane that was emptied while it wasn't shown starts at the top when it comes back, rather than where it was left",
+	ExtraCmdArgs: []string{},
+	Skip:         false,
+	Width:        120,
+	Height:       30,
+	SetupConfig:  func(cfg *config.AppConfig) {},
+	SetupRepo: func(shell *Shell) {
+		lines := make([]string, 40)
+		for i := range lines {
+			lines[i] = fmt.Sprintf("line%02d", i+1)
+		}
+		shell.CreateFileAndAdd("file1", strings.Join(lines, "\n")+"\n")
+		shell.CreateFileAndAdd("file2", "one\n")
+		shell.Commit("one")
+
+		// More staged changes in file1 than fit in the pane they are shown in, so that
+		// there is a position in it to lose, plus an unstaged change to give the file a
+		// second pane.
+		for i := range lines {
+			lines[i] = strings.ToUpper(lines[i])
+		}
+		shell.UpdateFileAndAdd("file1", strings.Join(lines, "\n")+"\n")
+		shell.UpdateFile("file1", strings.Join(lines, "\n")+"unstaged\n")
+
+		shell.UpdateFile("file2", "two\n")
+	},
+	Run: func(t *TestDriver, keys config.KeybindingConfig) {
+		t.Views().Files().
+			IsFocused().
+			NavigateToLine(Contains("file1"))
+
+		t.Views().Secondary().
+			IsVisible().
+			Title(Equals("Staged changes")).
+			ScrollWheelDown().
+			ScrollWheelDown().
+			OriginYAtLeast(1)
+
+		// A file with nothing staged leaves that pane with nothing to show, so it goes
+		// away and is emptied.
+		t.Views().Files().NavigateToLine(Contains("file2"))
+		t.Views().Secondary().IsInvisible()
+
+		t.Views().Files().NavigateToLine(Contains("file1"))
+		t.Views().Secondary().
+			IsVisible().
+			Content(Contains("+LINE40")).
+			OriginY(0)
+	},
+})

pkg/integration/tests/file/pane_taking_over_starts_at_the_top.go

@@ -0,0 +1,85 @@
+package file
+
+import (
+	"fmt"
+	"strings"
+
+	"github.com/jesseduffield/lazygit/pkg/config"
+	. "github.com/jesseduffield/lazygit/pkg/integration/components"
+)
+
+// changedLines is a file's worth of numbered lines, prefixed so that each file's diff
+// can be told from the other's on screen.
+func changedLines(prefix string) string {
+	lines := make([]string, 40)
+	for i := range lines {
+		lines[i] = fmt.Sprintf("%s%02d", prefix, i+1)
+	}
+	return strings.Join(lines, "\n") + "\n"
+}
+
+var PaneTakingOverStartsAtTheTop = NewIntegrationTest(NewIntegrationTestArgs{
+	Description:  "A pane taking the main section over shows its diff from the top, rather than at the offset it was left at",
+	ExtraCmdArgs: []string{},
+	Skip:         false,
+	Width:        120,
+	Height:       30,
+	SetupConfig:  func(cfg *config.AppConfig) {},
+	SetupRepo: func(shell *Shell) {
+		shell.CreateFileAndAdd("file1", changedLines("one"))
+		shell.CreateFileAndAdd("file2", changedLines("two"))
+		shell.Commit("one")
+
+		// One file's changes are unstaged and the other's are staged, so each is shown
+		// in a pane of its own — and selecting one after the other hands the section
+		// from one pane to the other. Both diffs are longer than the section, so either
+		// pane can be scrolled.
+		shell.UpdateFile("file1", changedLines("ONE"))
+		shell.UpdateFileAndAdd("file2", changedLines("TWO"))
+	},
+	Run: func(t *TestDriver, keys config.KeybindingConfig) {
+		t.Views().Files().
+			IsFocused().
+			NavigateToLine(Contains("file1"))
+
+		t.Views().Secondary().IsInvisible()
+		t.Views().Main().
+			IsVisible().
+			Title(Equals("Unstaged changes")).
+			ScrollWheelDown().
+			ScrollWheelDown().
+			OriginYAtLeast(1)
+
+		t.Views().Files().NavigateToLine(Contains("file2"))
+
+		t.Views().Main().IsInvisible()
+		t.Views().Secondary().
+			IsVisible().
+			Title(Equals("Staged changes")).
+			Content(Contains("+TWO40")).
+			OriginY(0).
+			ScrollWheelDown().
+			ScrollWheelDown().
+			OriginYAtLeast(1)
+
+		// Back to the pane that was left scrolled: what it is given is a diff the user
+		// hasn't seen there, so it starts at the top like any other.
+		t.Views().Files().NavigateToLine(Contains("file1"))
+
+		t.Views().Secondary().IsInvisible()
+		t.Views().Main().
+			IsVisible().
+			Title(Equals("Unstaged changes")).
+			Content(Contains("+ONE40")).
+			OriginY(0)
+
+		t.Views().Files().NavigateToLine(Contains("file2"))
+
+		t.Views().Main().IsInvisible()
+		t.Views().Secondary().
+			IsVisible().
+			Title(Equals("Staged changes")).
+			Content(Contains("+TWO40")).
+			OriginY(0)
+	},
+})

pkg/integration/tests/file/rename_similarity_threshold_change.go

@@ -34,7 +34,7 @@ var RenameSimilarityThresholdChange = NewIntegrationTest(NewIntegrationTestArgs{
 			).
 			Press(keys.Universal.FocusMainView).
 			Tap(func() {
-				t.Views().Main().
+				t.Views().Secondary().
 					Press(keys.Universal.IncreaseRenameSimilarityThreshold)
 				t.ExpectToast(Equals("Changed rename similarity threshold to 50%"))
 			}).

pkg/integration/tests/file/staged_changes_in_lower_pane.go

@@ -0,0 +1,81 @@
+package file
+
+import (
+	"fmt"
+	"strings"
+
+	"github.com/jesseduffield/lazygit/pkg/config"
+	. "github.com/jesseduffield/lazygit/pkg/integration/components"
+)
+
+var StagedChangesInLowerPane = NewIntegrationTest(NewIntegrationTestArgs{
+	Description:  "A file's staged changes are shown in the lower pane whether or not it also has unstaged ones",
+	ExtraCmdArgs: []string{},
+	Skip:         false,
+	SetupConfig:  func(cfg *config.AppConfig) {},
+	SetupRepo: func(shell *Shell) {
+		shell.CreateFileAndAdd("both", "one\n")
+		shell.CreateFileAndAdd("indexOnly", "one\n")
+		shell.CreateFileAndAdd("worktreeOnly", "one\n")
+		shell.Commit("one")
+
+		shell.UpdateFileAndAdd("both", "one\nstaged\n")
+		shell.UpdateFile("both", "one\nstaged\nunstaged\n")
+		// More staged lines than fit in the pane, so that it can be scrolled.
+		staged := make([]string, 40)
+		for i := range staged {
+			staged[i] = fmt.Sprintf("staged%02d", i+1)
+		}
+		shell.UpdateFileAndAdd("indexOnly", "one\n"+strings.Join(staged, "\n")+"\n")
+		shell.UpdateFile("worktreeOnly", "one\nunstaged\n")
+	},
+	Run: func(t *TestDriver, keys config.KeybindingConfig) {
+		t.Views().Files().
+			IsFocused().
+			NavigateToLine(Contains("both"))
+
+		// With changes on both sides, each side has its own pane.
+		t.Views().Main().
+			Title(Equals("Unstaged changes")).
+			Content(Contains("+unstaged"))
+		t.Views().Secondary().
+			Title(Equals("Staged changes")).
+			Content(Contains("+staged"))
+
+		// With nothing unstaged, the staged side keeps its pane, which then has the
+		// whole space to itself.
+		t.Views().Files().NavigateToLine(Contains("indexOnly"))
+
+		t.Views().Main().IsInvisible()
+		t.Views().Secondary().
+			IsVisible().
+			Title(Equals("Staged changes")).
+			Content(Contains("+staged01")).
+			// The key that focuses the diff wears its label, wherever the diff is.
+			TitlePrefix(Equals("[0]")).
+			OriginY(0)
+
+		// And the keys for scrolling the diff scroll the pane it is in.
+		t.GlobalPress(keys.Universal.ScrollDownMain)
+		t.Views().Secondary().OriginYAtLeast(1)
+		t.GlobalPress(keys.Universal.ScrollUpMain)
+		t.Views().Secondary().OriginY(0)
+
+		// And focusing the diff focuses the pane it is in.
+		t.Views().Files().Press(keys.Universal.FocusMainView)
+		t.Views().Secondary().IsFocused()
+		t.Views().Secondary().PressEscape()
+
+		// With nothing staged, only the upper pane is shown.
+		t.Views().Files().
+			IsFocused().
+			NavigateToLine(Contains("worktreeOnly"))
+
+		t.Views().Secondary().IsInvisible()
+		t.Views().Main().
+			IsVisible().
+			Title(Equals("Unstaged changes")).
+			Content(Contains("+unstaged")).
+			TitlePrefix(Equals("[0]"))
+	},
+})

pkg/integration/tests/main_view/copy_rows_that_are_no_diff_line.go

@@ -0,0 +1,56 @@
+package main_view
+
+import (
+	"github.com/jesseduffield/lazygit/pkg/config"
+	. "github.com/jesseduffield/lazygit/pkg/integration/components"
+)
+
+var CopyRowsThatAreNoDiffLine = NewIntegrationTest(NewIntegrationTestArgs{
+	Description:  "Copying rows that stand for no line of the diff says so rather than copying nothing",
+	ExtraCmdArgs: []string{},
+	Skip:         false,
+	SetupConfig: func(cfg *config.AppConfig) {
+		cfg.GetUserConfig().Gui.UseHunkModeInStagingView = false
+		cfg.GetUserConfig().OS.CopyToClipboardCmd = "printf '%s' {{text}} > clipboard"
+		// A renderer that states which line of the file each row of its diff shows, and
+		// ends with a row of its own that shows none. It ignores its input and prints
+		// this one.
+		cfg.GetUserConfig().Git.DiffRenderers = []config.DiffRendererConfig{
+			{Command: `printf '\033]1717;1\007'; ` +
+				`printf '\033]1717;1;f;;;file1\007file1\n'; ` +
+				`printf '\033]1717;1;c;1;;file1\007 one\n'; ` +
+				`printf '\033]1717;1;d;2;2;file1\007-two\n'; ` +
+				`printf '\033]1717;1;a;2;;file1\007+TWO\n'; ` +
+				`printf '\033]1717;1;c;3;;file1\007 three\n'; ` +
+				`printf -- '--- that was the diff ---\n'; ` +
+				`cat >/dev/null`},
+		}
+	},
+	SetupRepo: func(shell *Shell) {
+		shell.CreateFileAndAdd("file1", "one\ntwo\nthree\n")
+		shell.Commit("one")
+
+		shell.UpdateFile("file1", "one\nTWO\nthree\n")
+	},
+	Run: func(t *TestDriver, keys config.KeybindingConfig) {
+		t.Views().Files().
+			IsFocused().
+			Press(keys.Universal.FocusMainView)
+
+		t.Views().Main().
+			IsFocused().
+			SelectedLines(
+				Contains("-two"),
+			).
+			SelectNextItem().
+			SelectNextItem().
+			SelectNextItem().
+			SelectedLines(
+				Contains("that was the diff"),
+			).
+			Press(keys.Universal.CopyToClipboard)
+
+		t.ExpectToast(Equals("Nothing in the selection could be found in the diff"))
+		t.FileSystem().PathNotPresent("clipboard")
+	},
+})

pkg/integration/tests/main_view/copy_selected_diff_lines.go

@@ -0,0 +1,141 @@
+package main_view
+
+import (
+	"github.com/jesseduffield/lazygit/pkg/config"
+	. "github.com/jesseduffield/lazygit/pkg/integration/components"
+)
+
+// The clipboard is emulated by a file, so that this works on CI too. A copy says so
+// with a toast, which the harness wants acknowledged before the next keypress.
+func expectClipboard(t *TestDriver, matcher *TextMatcher) {
+	defer t.Shell().DeleteFile("clipboard")
+
+	t.ExpectToast(Equals("Selected diff lines copied to clipboard"))
+	t.FileSystem().FileContent("clipboard", matcher)
+}
+
+var CopySelectedDiffLines = NewIntegrationTest(NewIntegrationTestArgs{
+	Description:  "Copy the selected diff lines from the focused main view, as the diff reads rather than as the renderer drew it",
+	ExtraCmdArgs: []string{},
+	Skip:         false,
+	SetupConfig: func(cfg *config.AppConfig) {
+		cfg.GetUserConfig().Gui.UseHunkModeInStagingView = true
+		// Emulate the clipboard by writing to a file.
+		cfg.GetUserConfig().OS.CopyToClipboardCmd = "printf '%s' {{text}} > clipboard"
+		// A renderer that decorates every line of a diff's body, so that what is on
+		// screen is not what the diff says. It reads the +/- column, so it wants its
+		// input uncoloured.
+		cfg.GetUserConfig().Git.DiffRenderers = []config.DiffRendererConfig{
+			{
+				Command:  `awk '/^@@/ { body = 1 } body && /^[-+ ]/ { print $0 " <<<"; next } { print }'`,
+				ColorArg: "never",
+			},
+		}
+	},
+	SetupRepo: func(shell *Shell) {
+		shell.CreateFileAndAdd("file1", "one\ntwo\nthree\n")
+		shell.Commit("one")
+		shell.UpdateFileAndAdd("file1", "one\nTWO\nthree\n")
+		shell.Commit("two")
+
+		shell.UpdateFile("file1", "one\nTWO\nADD1\nADD2\nthree\n")
+	},
+	Run: func(t *TestDriver, keys config.KeybindingConfig) {
+		t.Views().Files().
+			IsFocused().
+			Press(keys.Universal.FocusMainView)
+
+		t.Views().Main().
+			IsFocused().
+			SelectedLines(
+				Contains("+ADD1 <<<"),
+				Contains("+ADD2 <<<"),
+			).
+			Press(keys.Universal.CopyToClipboard)
+
+		// The renderer's decoration is nowhere in what was copied, and a selection that
+		// is all additions loses its '+' column, ready to be pasted into code.
+		expectClipboard(t, Equals("ADD1\nADD2\n"))
+
+		// A selection reaching up into the hunk header takes the header with it, and what
+		// comes out is a patch fragment rather than lines of code, so the columns stay.
+		t.Views().Main().
+			IsFocused().
+			Press(keys.Main.ToggleSelectHunk).
+			SelectedLines(
+				Contains("+ADD1 <<<"),
+			).
+			Press(keys.Universal.ToggleRangeSelect).
+			Press(keys.Universal.PrevItem).
+			Press(keys.Universal.PrevItem).
+			Press(keys.Universal.PrevItem).
+			SelectedLines(
+				Contains("@@ -1,3 +1,5 @@"),
+				Contains(" one <<<"),
+				Contains(" TWO <<<"),
+				Contains("+ADD1 <<<"),
+			).
+			Press(keys.Universal.CopyToClipboard)
+
+		expectClipboard(t, Equals("@@ -1,3 +1,5 @@\n one\n TWO\n+ADD1\n"))
+
+		// A file header is taken whole, however much of it is selected: the rendering may
+		// show it as any number of rows, none of which is a line of the file.
+		t.Views().Main().
+			IsFocused().
+			Press(keys.Universal.PrevItem).
+			SelectedLines(
+				Contains("+++ b/file1"),
+				Contains("@@ -1,3 +1,5 @@"),
+				Contains(" one <<<"),
+				Contains(" TWO <<<"),
+				Contains("+ADD1 <<<"),
+			).
+			Press(keys.Universal.CopyToClipboard)
+
+		expectClipboard(t, MatchesRegexp(
+			`\Adiff --git a/file1 b/file1\nindex [0-9a-f]+\.\.[0-9a-f]+ 100644\n`+
+				`--- a/file1\n\+\+\+ b/file1\n@@ -1,3 \+1,5 @@\n one\n TWO\n\+ADD1\n\z`))
+
+		// A commit's diff is copied the same way, through the panel that produced it.
+		t.Views().Commits().
+			Focus().
+			NavigateToLine(Contains("two")).
+			Press(keys.Universal.FocusMainView)
+
+		t.Views().Main().
+			IsFocused().
+			SelectedLines(
+				Contains("-two <<<"),
+				Contains("+TWO <<<"),
+			).
+			Press(keys.Universal.CopyToClipboard)
+
+		// Both kinds of line are in the selection, so the columns stay: what comes out
+		// is the diff itself.
+		expectClipboard(t, Equals("-two\n+TWO\n"))
+
+		// What a diff view shows above the diff is part of no file's diff, a commit's
+		// message among it, so a selection of those rows is copied as it stands on screen.
+		t.Views().Main().
+			IsFocused().
+			Press(keys.Main.ToggleSelectHunk).
+			NavigateToLine(Contains("    two")).
+			Press(keys.Universal.CopyToClipboard)
+
+		expectClipboard(t, Equals("    two\n"))
+
+		// A selection reaching from there into the diff takes the screen's rows down to
+		// the first file and the diff's own from there on.
+		t.Views().Main().
+			IsFocused().
+			Press(keys.Universal.ToggleRangeSelect).
+			NavigateToLine(Contains("-two <<<")).
+			Press(keys.Universal.CopyToClipboard)
+
+		expectClipboard(t, MatchesRegexp(
+			`\A {4}two\n---\n file1 \|[^\n]*\n 1 file changed[^\n]*\n\n`+
+				`diff --git a/file1 b/file1\nindex [0-9a-f]+\.\.[0-9a-f]+ 100644\n`+
+				`--- a/file1\n\+\+\+ b/file1\n@@ -1,3 \+1,3 @@\n one\n-two\n\z`))
+	},
+})

pkg/integration/tests/main_view/select_line_when_whole_file_is_one_hunk.go

@@ -26,7 +26,7 @@ var SelectLineWhenWholeFileIsOneHunk = NewIntegrationTest(NewIntegrationTestArgs
 
 		// Every line of the file is an addition, so widening to the change block would
 		// select the file entire; hunk mode gives way to a single line.
-		t.Views().Main().
+		t.Views().Secondary().
 			IsFocused().
 			SelectedLines(
 				Contains("+one"),

pkg/integration/tests/patch_building/apply.go

@@ -58,7 +58,7 @@ var Apply = NewIntegrationTest(NewIntegrationTestArgs{
 				Contains("file1").IsSelected(),
 			)
 
-		t.Views().Main().
+		t.Views().Secondary().
 			Content(Contains("second line"))
 	},
 })

pkg/integration/tests/patch_building/apply_in_reverse.go

@@ -45,7 +45,7 @@ var ApplyInReverse = NewIntegrationTest(NewIntegrationTestArgs{
 				Contains("D").Contains("file1").IsSelected(),
 			)
 
-		t.Views().Main().
+		t.Views().Secondary().
 			Content(Contains("-file1 content"))
 	},
 })

pkg/integration/tests/patch_building/apply_in_reverse_with_conflict.go

@@ -88,7 +88,7 @@ var ApplyInReverseWithConflict = NewIntegrationTest(NewIntegrationTestArgs{
 				Equals("  M  file2"),
 			)
 
-		t.Views().Main().
+		t.Views().Secondary().
 			ContainsLines(
 				Contains(" file1 content"),
 				Contains("-more file1 content"),

pkg/integration/tests/patch_building/apply_with_modified_file_no_conflict.go

@@ -63,7 +63,7 @@ var ApplyWithModifiedFileNoConflict = NewIntegrationTest(NewIntegrationTestArgs{
 				Equals("M  file1").IsSelected(),
 			)
 
-		t.Views().Main().
+		t.Views().Secondary().
 			Content(Contains("-1\n+11\n 2\n 3\n+4"))
 	},
 })

pkg/integration/tests/patch_building/move_range_to_index.go

@@ -62,12 +62,12 @@ var MoveRangeToIndex = NewIntegrationTest(NewIntegrationTestArgs{
 				Equals("  A  file2"),
 			)
 
-		t.Views().Main().
+		t.Views().Secondary().
 			Content(Contains("second line"))
 
 		t.Views().Files().Focus().NavigateToLine(Contains("file2"))
 
-		t.Views().Main().
+		t.Views().Secondary().
 			Content(Contains("file two content"))
 	},
 })

pkg/integration/tests/patch_building/move_to_index.go

@@ -62,7 +62,7 @@ var MoveToIndex = NewIntegrationTest(NewIntegrationTestArgs{
 		t.Views().Files().
 			Focus()
 
-		t.Views().Main().
+		t.Views().Secondary().
 			Content(Contains("file1 content"))
 	},
 })

pkg/integration/tests/patch_building/move_to_index_part_of_adjacent_added_lines.go

@@ -63,7 +63,7 @@ var MoveToIndexPartOfAdjacentAddedLines = NewIntegrationTest(NewIntegrationTestA
 				Contains("M").Contains("file1"),
 			)
 
-		t.Views().Main().
+		t.Views().Secondary().
 			Content(Contains("+1st line\n 2nd line"))
 	},
 })

pkg/integration/tests/patch_building/move_to_index_partial.go

@@ -85,7 +85,7 @@ var MoveToIndexPartial = NewIntegrationTest(NewIntegrationTestArgs{
 		t.Views().Files().
 			Focus()
 
-		t.Views().Main().
+		t.Views().Secondary().
 			ContainsLines(
 				Contains(`-first line`),
 				Contains(`+first line2`),

pkg/integration/tests/submodule/add.go

@@ -50,7 +50,7 @@ var Add = NewIntegrationTest(NewIntegrationTestArgs{
 			).
 			SelectNextItem().
 			Tap(func() {
-				t.Views().Main().Content(
+				t.Views().Secondary().Content(
 					Contains("[submodule \"my_submodule\"]").
 						Contains("path = my_submodule_path").
 						Contains("url = ../other_repo"),
@@ -58,7 +58,7 @@ var Add = NewIntegrationTest(NewIntegrationTestArgs{
 			}).
 			SelectNextItem().
 			Tap(func() {
-				t.Views().Main().Content(
+				t.Views().Secondary().Content(
 					Contains("Submodule my_submodule_path").
 						Contains("(new submodule)"),
 				)

pkg/integration/tests/submodule/remove.go

@@ -41,7 +41,7 @@ var Remove = NewIntegrationTest(NewIntegrationTestArgs{
 			).
 			SelectNextItem()
 
-		t.Views().Main().Content(
+		t.Views().Secondary().Content(
 			Contains("-[submodule \"my_submodule_name\"]").
 				Contains("-   path = my_submodule_path").
 				Contains("-   url = ../my_submodule_name"),

pkg/integration/tests/submodule/remove_nested.go

@@ -46,7 +46,7 @@ var RemoveNested = NewIntegrationTest(NewIntegrationTestArgs{
 			).
 			NavigateToLine(Contains(".gitmodules"))
 
-		t.Views().Main().Content(
+		t.Views().Secondary().Content(
 			Contains("-[submodule \"innerSubName\"]").
 				Contains("-   path = modules/innerSubPath").
 				Contains("-   url = ../innerSubmodule"),

pkg/integration/tests/test_list.go

@@ -252,6 +252,8 @@ var tests = []*components.IntegrationTest{
 	file.ExcludeWithoutInfoDir,
 	file.Gitignore,
 	file.GitignoreSpecialCharacters,
+	file.PaneShownAgainStartsAtTheTop,
+	file.PaneTakingOverStartsAtTheTop,
 	file.RememberCommitMessageAfterFail,
 	file.RenameSimilarityThresholdChange,
 	file.RenamedFiles,
@@ -260,6 +262,7 @@ var tests = []*components.IntegrationTest{
 	file.StageChildrenRangeSelect,
 	file.StageDeletedRangeSelect,
 	file.StageRangeSelect,
+	file.StagedChangesInLowerPane,
 	filter_and_search.FilterByFileStatus,
 	filter_and_search.FilterCommitFiles,
 	filter_and_search.FilterCommitFilesToggleDirectory,
@@ -364,6 +367,8 @@ var tests = []*components.IntegrationTest{
 	interactive_rebase.SwapWithConflict,
 	interactive_rebase.ViewFilesOfTodoEntries,
 	main_view.ClickSelectsDiffLine,
+	main_view.CopyRowsThatAreNoDiffLine,
+	main_view.CopySelectedDiffLines,
 	main_view.DragRangeWithAutoscroll,
 	main_view.DragSelectsDiffLineRange,
 	main_view.EditSelectedDiffLine,

pkg/tasks/tasks.go

@@ -251,6 +251,17 @@ func (self *ViewBufferManager) GetTaskKey() string {
 	return self.taskKey
 }
 
+// ForgetRenderedContent records that the view no longer shows the render whose key it
+// is holding, because it has been emptied. The key says what the view is showing, and
+// the next task is compared against it to tell whether that task renders something
+// new. A view with nothing in it is showing nothing, so whatever comes next is new.
+func (self *ViewBufferManager) ForgetRenderedContent() {
+	self.taskIDMutex.Lock()
+	defer self.taskIDMutex.Unlock()
+
+	self.taskKey = ""
+}
+
 func NewViewBufferManager(
 	log *logrus.Entry,
 	writer io.Writer,

pkg/tasks/tasks_test.go

@@ -610,6 +610,50 @@ func TestKeepScrollPositionForNextTask(t *testing.T) {
 	assert.EqualValues(t, 0, beforeStartCount.Load())
 }
 
+// A view that has been emptied is showing nothing, so the render it was showing is no
+// longer the one to compare the next task against: running the same command again is
+// putting content into the view that isn't there any more, and starts from the top.
+func TestForgetRenderedContent(t *testing.T) {
+	resetOrigin, getResetOriginCallCount := getCounter()
+
+	manager := NewViewBufferManager(
+		utils.NewDummyLog(),
+		io.Discard,
+		func() {}, // beforeStart
+		func() {}, // refreshView
+		func() {}, // onEndOfInput
+		resetOrigin,
+		func() {}, // beginRender
+		func() {}, // swapInRender
+		func() gocui.Task { return gocui.NewFakeTask() },
+		// no UI thread in the test; run the view mutations inline
+		func(f func()) error { f(); return nil },
+	)
+
+	runTaskToCompletion := func(key string) {
+		start := func() (Cmd, io.Reader) {
+			// not actually starting this because it's not necessary
+			return ExecCmd{Cmd: exec.Command("blah")}, &BlankLineReader{totalLinesToYield: 3}
+		}
+		done := make(chan struct{})
+		_ = manager.NewTask(
+			manager.NewCmdTask(start, "", LinesToRead{100, 50, nil}, func() { close(done) }), key)
+		<-done
+	}
+
+	runTaskToCompletion("cmd1")
+	assert.Equal(t, 1, getResetOriginCallCount())
+
+	// Rendering the same command's output again leaves the view where it is, that being
+	// what it already shows.
+	runTaskToCompletion("cmd1")
+	assert.Equal(t, 1, getResetOriginCallCount())
+
+	manager.ForgetRenderedContent()
+	runTaskToCompletion("cmd1")
+	assert.Equal(t, 2, getResetOriginCallCount(), "an emptied view is shown its content afresh")
+}
+
 func TestNewCmdTaskRefresh(t *testing.T) {
 	type scenario struct {
 		name                        string