Rely on model rather than view to focus a point

Currently when we want to focus a point on a view (i.e. highlight a
line and ensure it's within the bounds of a view's box, we use the
LinesHeight method on the view to work out how many lines in total
there are.

This is bad because for example if we come back from editing a file,
the view will have no contents so LinesHeight == 0, but we might
be trying to select line 10 because there are actual ten things we
expect to be rendered already. This causes a crash when e.g. 10 is
greater than the height of the view.

So we need to pass in to our FocusPoint method the actual number of
items we want to render, rather than having the method rely on the
LinesHeight, so that the method knows to scroll a bit before setting
the cursor's y position.

Unfortunately this makes for some awkward code with our current setup.
We don't have a good interface type on these state objects so we now
need to explicitly obtain the len() of whatever array we're rendering.

In the case of the menu panel this is even more awkward because the items
list is just an interface{} and it's not easy to get the list of that, so
now when we instantiate a menu we need to pass in the count of items
as well.

The better solution would be to define an interface with a getItems
and getLength method and have all these item arrays become structs
implementing the interface, but I am too lazy to do this right now :)

11 files changed, 28 insertions, 21 deletions

diff --git a/pkg/gui/branches_panel.go b/pkg/gui/branches_panel.go
index 8ee1b451d..4ce53bebd 100644
--- a/pkg/gui/branches_panel.go
+++ b/pkg/gui/branches_panel.go
@@ -34,7 +34,7 @@ func (gui *Gui) handleBranchSelect(g *gocui.Gui, v *gocui.View) error {
 		return gui.renderString(g, "main", gui.Tr.SLocalize("NoBranchesThisRepo"))
 	}
 	branch := gui.getSelectedBranch()
-	if err := gui.focusPoint(0, gui.State.Panels.Branches.SelectedLine, v); err != nil {
+	if err := gui.focusPoint(0, gui.State.Panels.Branches.SelectedLine, len(gui.State.Branches), v); err != nil {
 		return err
 	}
 	go func() {
diff --git a/pkg/gui/commit_files_panel.go b/pkg/gui/commit_files_panel.go
index e8c20e0e7..2cdda6815 100644
--- a/pkg/gui/commit_files_panel.go
+++ b/pkg/gui/commit_files_panel.go
@@ -20,7 +20,7 @@ func (gui *Gui) handleCommitFileSelect(g *gocui.Gui, v *gocui.View) error {
 		return gui.renderString(g, "commitFiles", gui.Tr.SLocalize("NoCommiteFiles"))
 	}
 
-	if err := gui.focusPoint(0, gui.State.Panels.CommitFiles.SelectedLine, v); err != nil {
+	if err := gui.focusPoint(0, gui.State.Panels.CommitFiles.SelectedLine, len(gui.State.CommitFiles), v); err != nil {
 		return err
 	}
 	commitText, err := gui.GitCommand.ShowCommitFile(commitFile.Sha, commitFile.Name)
diff --git a/pkg/gui/commits_panel.go b/pkg/gui/commits_panel.go
index 627b35835..1bd8be4a1 100644
--- a/pkg/gui/commits_panel.go
+++ b/pkg/gui/commits_panel.go
@@ -36,7 +36,7 @@ func (gui *Gui) handleCommitSelect(g *gocui.Gui, v *gocui.View) error {
 		return gui.renderString(g, "main", gui.Tr.SLocalize("NoCommitsThisBranch"))
 	}
 
-	if err := gui.focusPoint(0, gui.State.Panels.Commits.SelectedLine, v); err != nil {
+	if err := gui.focusPoint(0, gui.State.Panels.Commits.SelectedLine, len(gui.State.Commits), v); err != nil {
 		return err
 	}
 	commitText, err := gui.GitCommand.Show(commit.Sha)
diff --git a/pkg/gui/files_panel.go b/pkg/gui/files_panel.go
index 45b3f4dd7..728ad2f97 100644
--- a/pkg/gui/files_panel.go
+++ b/pkg/gui/files_panel.go
@@ -63,7 +63,7 @@ func (gui *Gui) handleFileSelect(g *gocui.Gui, v *gocui.View, alreadySelected bo
 		return gui.renderString(g, "main", gui.Tr.SLocalize("NoChangedFiles"))
 	}
 
-	if err := gui.focusPoint(0, gui.State.Panels.Files.SelectedLine, v); err != nil {
+	if err := gui.focusPoint(0, gui.State.Panels.Files.SelectedLine, len(gui.State.Files), v); err != nil {
 		return err
 	}
 
diff --git a/pkg/gui/gui.go b/pkg/gui/gui.go
index d4ce0b3dc..07d51e2bc 100644
--- a/pkg/gui/gui.go
+++ b/pkg/gui/gui.go
@@ -135,6 +135,7 @@ type guiState struct {
 	Commits             []*commands.Commit
 	StashEntries        []*commands.StashEntry
 	CommitFiles         []*commands.CommitFile
+	MenuItemCount       int // can't store the actual list because it's of interface{} type
 	PreviousView        string
 	Platform            commands.Platform
 	Updating            bool
@@ -480,20 +481,25 @@ func (gui *Gui) layout(g *gocui.Gui) error {
 		}
 	}
 
-	listViews := map[*gocui.View]int{
-		filesView:    gui.State.Panels.Files.SelectedLine,
-		branchesView: gui.State.Panels.Branches.SelectedLine,
-		commitsView:  gui.State.Panels.Commits.SelectedLine,
-		stashView:    gui.State.Panels.Stash.SelectedLine,
+	type listViewState struct {
+		selectedLine int
+		lineCount    int
+	}
+
+	listViews := map[*gocui.View]listViewState{
+		filesView:    {selectedLine: gui.State.Panels.Files.SelectedLine, lineCount: len(gui.State.Files)},
+		branchesView: {selectedLine: gui.State.Panels.Branches.SelectedLine, lineCount: len(gui.State.Branches)},
+		commitsView:  {selectedLine: gui.State.Panels.Commits.SelectedLine, lineCount: len(gui.State.Commits)},
+		stashView:    {selectedLine: gui.State.Panels.Stash.SelectedLine, lineCount: len(gui.State.StashEntries)},
 	}
 
 	// menu view might not exist so we check to be safe
 	if menuView, err := gui.g.View("menu"); err == nil {
-		listViews[menuView] = gui.State.Panels.Menu.SelectedLine
+		listViews[menuView] = listViewState{selectedLine: gui.State.Panels.Menu.SelectedLine, lineCount: gui.State.MenuItemCount}
 	}
-	for view, selectedLine := range listViews {
+	for view, state := range listViews {
 		// check if the selected line is now out of view and if so refocus it
-		if err := gui.focusPoint(0, selectedLine, view); err != nil {
+		if err := gui.focusPoint(0, state.selectedLine, state.lineCount, view); err != nil {
 			return err
 		}
 	}
diff --git a/pkg/gui/menu_panel.go b/pkg/gui/menu_panel.go
index dbfa0cf01..d78a67199 100644
--- a/pkg/gui/menu_panel.go
+++ b/pkg/gui/menu_panel.go
@@ -10,7 +10,7 @@ import (
 // list panel functions
 
 func (gui *Gui) handleMenuSelect(g *gocui.Gui, v *gocui.View) error {
-	return gui.focusPoint(0, gui.State.Panels.Menu.SelectedLine, v)
+	return gui.focusPoint(0, gui.State.Panels.Menu.SelectedLine, gui.State.MenuItemCount, v)
 }
 
 func (gui *Gui) handleMenuNextLine(g *gocui.Gui, v *gocui.View) error {
@@ -51,8 +51,9 @@ func (gui *Gui) handleMenuClose(g *gocui.Gui, v *gocui.View) error {
 	return gui.returnFocus(g, v)
 }
 
-func (gui *Gui) createMenu(title string, items interface{}, handlePress func(int) error) error {
+func (gui *Gui) createMenu(title string, items interface{}, itemCount int, handlePress func(int) error) error {
 	isFocused := gui.g.CurrentView().Name() == "menu"
+	gui.State.MenuItemCount = itemCount
 	list, err := utils.RenderList(items, isFocused)
 	if err != nil {
 		return err
diff --git a/pkg/gui/options_menu_panel.go b/pkg/gui/options_menu_panel.go
index d217fb8f2..dfd354839 100644
--- a/pkg/gui/options_menu_panel.go
+++ b/pkg/gui/options_menu_panel.go
@@ -49,5 +49,5 @@ func (gui *Gui) handleCreateOptionsMenu(g *gocui.Gui, v *gocui.View) error {
 		return bindings[index].Handler(g, v)
 	}
 
-	return gui.createMenu(strings.Title(gui.Tr.SLocalize("menu")), bindings, handleMenuPress)
+	return gui.createMenu(strings.Title(gui.Tr.SLocalize("menu")), bindings, len(bindings), handleMenuPress)
 }
diff --git a/pkg/gui/rebase_options_panel.go b/pkg/gui/rebase_options_panel.go
index 337d81692..633574275 100644
--- a/pkg/gui/rebase_options_panel.go
+++ b/pkg/gui/rebase_options_panel.go
@@ -38,7 +38,7 @@ func (gui *Gui) handleCreateRebaseOptionsMenu(g *gocui.Gui, v *gocui.View) error
 		title = gui.Tr.SLocalize("RebaseOptionsTitle")
 	}
 
-	return gui.createMenu(title, options, handleMenuPress)
+	return gui.createMenu(title, options, len(options), handleMenuPress)
 }
 
 func (gui *Gui) genericMergeCommand(command string) error {
diff --git a/pkg/gui/recent_repos_panel.go b/pkg/gui/recent_repos_panel.go
index 3f92431ea..a9ea5d481 100644
--- a/pkg/gui/recent_repos_panel.go
+++ b/pkg/gui/recent_repos_panel.go
@@ -44,7 +44,7 @@ func (gui *Gui) handleCreateRecentReposMenu(g *gocui.Gui, v *gocui.View) error {
 		return gui.Errors.ErrSwitchRepo
 	}
 
-	return gui.createMenu(gui.Tr.SLocalize("RecentRepos"), recentRepos, handleMenuPress)
+	return gui.createMenu(gui.Tr.SLocalize("RecentRepos"), recentRepos, len(recentRepos), handleMenuPress)
 }
 
 // updateRecentRepoList registers the fact that we opened lazygit in this repo,
diff --git a/pkg/gui/stash_panel.go b/pkg/gui/stash_panel.go
index 05844f0ac..9c1851971 100644
--- a/pkg/gui/stash_panel.go
+++ b/pkg/gui/stash_panel.go
@@ -31,7 +31,7 @@ func (gui *Gui) handleStashEntrySelect(g *gocui.Gui, v *gocui.View) error {
 	if stashEntry == nil {
 		return gui.renderString(g, "main", gui.Tr.SLocalize("NoStashEntries"))
 	}
-	if err := gui.focusPoint(0, gui.State.Panels.Stash.SelectedLine, v); err != nil {
+	if err := gui.focusPoint(0, gui.State.Panels.Stash.SelectedLine, len(gui.State.StashEntries), v); err != nil {
 		return err
 	}
 	go func() {
diff --git a/pkg/gui/view_helpers.go b/pkg/gui/view_helpers.go
index a258ca7e8..c7ee8dc88 100644
--- a/pkg/gui/view_helpers.go
+++ b/pkg/gui/view_helpers.go
@@ -180,8 +180,8 @@ func (gui *Gui) resetOrigin(v *gocui.View) error {
 }
 
 // if the cursor down past the last item, move it to the last line
-func (gui *Gui) focusPoint(cx int, cy int, v *gocui.View) error {
-	if cy < 0 {
+func (gui *Gui) focusPoint(cx int, cy int, lineCount int, v *gocui.View) error {
+	if cy < 0 || cy > lineCount {
 		return nil
 	}
 	ox, oy := v.Origin()
@@ -191,7 +191,7 @@ func (gui *Gui) focusPoint(cx int, cy int, v *gocui.View) error {
 	// if line is above origin, move origin and set cursor to zero
 	// if line is below origin + height, move origin and set cursor to max
 	// otherwise set cursor to value - origin
-	if ly > v.LinesHeight() {
+	if ly > lineCount {
 		if err := v.SetCursor(cx, cy); err != nil {
 			return err
 		}