Improve render performance (#3686)

- **PR Description**

Fix a performance regression that I introduced with v0.41: when entering
or leaving staging mode for a file, or when switching from a file that
has only unstaged changes to one that has both staged and unstaged
changes, there was a noticeable lag of about 500ms on my machine. With
the improvements in this PR we get this back down to about 20ms.

14 files changed, 98 insertions, 26 deletions

diff --git a/pkg/gui/context/base_context.go b/pkg/gui/context/base_context.go
index dfcced021..ca04a2fa9 100644
--- a/pkg/gui/context/base_context.go
+++ b/pkg/gui/context/base_context.go
@@ -23,7 +23,7 @@ type BaseContext struct {
 	focusable                   bool
 	transient                   bool
 	hasControlledBounds         bool
-	needsRerenderOnWidthChange  bool
+	needsRerenderOnWidthChange  types.NeedsRerenderOnWidthChangeLevel
 	needsRerenderOnHeightChange bool
 	highlightOnFocus            bool
 
@@ -46,7 +46,7 @@ type NewBaseContextOpts struct {
 	Transient                   bool
 	HasUncontrolledBounds       bool // negating for the sake of making false the default
 	HighlightOnFocus            bool
-	NeedsRerenderOnWidthChange  bool
+	NeedsRerenderOnWidthChange  types.NeedsRerenderOnWidthChangeLevel
 	NeedsRerenderOnHeightChange bool
 
 	OnGetOptionsMap func() map[string]string
@@ -201,7 +201,7 @@ func (self *BaseContext) HasControlledBounds() bool {
 	return self.hasControlledBounds
 }
 
-func (self *BaseContext) NeedsRerenderOnWidthChange() bool {
+func (self *BaseContext) NeedsRerenderOnWidthChange() types.NeedsRerenderOnWidthChangeLevel {
 	return self.needsRerenderOnWidthChange
 }
 
diff --git a/pkg/gui/context/branches_context.go b/pkg/gui/context/branches_context.go
index d2647ef84..d289f2729 100644
--- a/pkg/gui/context/branches_context.go
+++ b/pkg/gui/context/branches_context.go
@@ -46,7 +46,7 @@ func NewBranchesContext(c *ContextCommon) *BranchesContext {
 				Key:                        LOCAL_BRANCHES_CONTEXT_KEY,
 				Kind:                       types.SIDE_CONTEXT,
 				Focusable:                  true,
-				NeedsRerenderOnWidthChange: true,
+				NeedsRerenderOnWidthChange: types.NEEDS_RERENDER_ON_WIDTH_CHANGE_WHEN_WIDTH_CHANGES,
 			})),
 			ListRenderer: ListRenderer{
 				list:              viewModel,
diff --git a/pkg/gui/context/local_commits_context.go b/pkg/gui/context/local_commits_context.go
index ab42cfb70..fcb9b00ca 100644
--- a/pkg/gui/context/local_commits_context.go
+++ b/pkg/gui/context/local_commits_context.go
@@ -77,7 +77,7 @@ func NewLocalCommitsContext(c *ContextCommon) *LocalCommitsContext {
 				Key:                         LOCAL_COMMITS_CONTEXT_KEY,
 				Kind:                        types.SIDE_CONTEXT,
 				Focusable:                   true,
-				NeedsRerenderOnWidthChange:  true,
+				NeedsRerenderOnWidthChange:  types.NEEDS_RERENDER_ON_WIDTH_CHANGE_WHEN_SCREEN_MODE_CHANGES,
 				NeedsRerenderOnHeightChange: true,
 			})),
 			ListRenderer: ListRenderer{
diff --git a/pkg/gui/context/reflog_commits_context.go b/pkg/gui/context/reflog_commits_context.go
index 57ca7c4dc..cec54988d 100644
--- a/pkg/gui/context/reflog_commits_context.go
+++ b/pkg/gui/context/reflog_commits_context.go
@@ -48,7 +48,7 @@ func NewReflogCommitsContext(c *ContextCommon) *ReflogCommitsContext {
 				Key:                        REFLOG_COMMITS_CONTEXT_KEY,
 				Kind:                       types.SIDE_CONTEXT,
 				Focusable:                  true,
-				NeedsRerenderOnWidthChange: true,
+				NeedsRerenderOnWidthChange: types.NEEDS_RERENDER_ON_WIDTH_CHANGE_WHEN_SCREEN_MODE_CHANGES,
 			})),
 			ListRenderer: ListRenderer{
 				list:              viewModel,
diff --git a/pkg/gui/context/remote_branches_context.go b/pkg/gui/context/remote_branches_context.go
index fff80e076..892953f82 100644
--- a/pkg/gui/context/remote_branches_context.go
+++ b/pkg/gui/context/remote_branches_context.go
@@ -43,7 +43,6 @@ func NewRemoteBranchesContext(
 				Kind:                        types.SIDE_CONTEXT,
 				Focusable:                   true,
 				Transient:                   true,
-				NeedsRerenderOnWidthChange:  true,
 				NeedsRerenderOnHeightChange: true,
 			})),
 			ListRenderer: ListRenderer{
diff --git a/pkg/gui/context/sub_commits_context.go b/pkg/gui/context/sub_commits_context.go
index ab0d2784a..ddbb380c5 100644
--- a/pkg/gui/context/sub_commits_context.go
+++ b/pkg/gui/context/sub_commits_context.go
@@ -121,7 +121,7 @@ func NewSubCommitsContext(
 				Kind:                        types.SIDE_CONTEXT,
 				Focusable:                   true,
 				Transient:                   true,
-				NeedsRerenderOnWidthChange:  true,
+				NeedsRerenderOnWidthChange:  types.NEEDS_RERENDER_ON_WIDTH_CHANGE_WHEN_SCREEN_MODE_CHANGES,
 				NeedsRerenderOnHeightChange: true,
 			})),
 			ListRenderer: ListRenderer{
diff --git a/pkg/gui/controllers/helpers/window_arrangement_helper.go b/pkg/gui/controllers/helpers/window_arrangement_helper.go
index 0eb7cdb4a..322cd1bd6 100644
--- a/pkg/gui/controllers/helpers/window_arrangement_helper.go
+++ b/pkg/gui/controllers/helpers/window_arrangement_helper.go
@@ -8,7 +8,6 @@ import (
 	"github.com/jesseduffield/lazygit/pkg/config"
 	"github.com/jesseduffield/lazygit/pkg/gui/types"
 	"github.com/jesseduffield/lazygit/pkg/utils"
-	"github.com/mattn/go-runewidth"
 	"golang.org/x/exp/slices"
 )
 
@@ -272,7 +271,7 @@ func infoSectionChildren(args WindowArrangementArgs) []*boxlayout.Box {
 		return []*boxlayout.Box{
 			{
 				Window: "searchPrefix",
-				Size:   runewidth.StringWidth(args.SearchPrefix),
+				Size:   utils.StringWidth(args.SearchPrefix),
 			},
 			{
 				Window: "search",
@@ -325,7 +324,7 @@ func infoSectionChildren(args WindowArrangementArgs) []*boxlayout.Box {
 		// app status appears very briefly in demos and dislodges the caption,
 		// so better not to show it at all
 		if args.AppStatus != "" {
-			result = append(result, &boxlayout.Box{Window: "appStatus", Size: runewidth.StringWidth(args.AppStatus)})
+			result = append(result, &boxlayout.Box{Window: "appStatus", Size: utils.StringWidth(args.AppStatus)})
 		}
 	}
 
@@ -338,7 +337,7 @@ func infoSectionChildren(args WindowArrangementArgs) []*boxlayout.Box {
 			&boxlayout.Box{
 				Window: "information",
 				// unlike appStatus, informationStr has various colors so we need to decolorise before taking the length
-				Size: runewidth.StringWidth(utils.Decolorise(args.InformationStr)),
+				Size: utils.StringWidth(utils.Decolorise(args.InformationStr)),
 			})
 	}
 
diff --git a/pkg/gui/controllers/screen_mode_actions.go b/pkg/gui/controllers/screen_mode_actions.go
index 1db27f2e2..2d0026793 100644
--- a/pkg/gui/controllers/screen_mode_actions.go
+++ b/pkg/gui/controllers/screen_mode_actions.go
@@ -1,6 +1,7 @@
 package controllers
 
 import (
+	"github.com/jesseduffield/gocui"
 	"github.com/jesseduffield/lazygit/pkg/gui/types"
 )
 
@@ -16,7 +17,7 @@ func (self *ScreenModeActions) Next() error {
 		),
 	)
 
-	return nil
+	return self.rerenderViewsWithScreenModeDependentContent()
 }
 
 func (self *ScreenModeActions) Prev() error {
@@ -27,9 +28,33 @@ func (self *ScreenModeActions) Prev() error {
 		),
 	)
 
+	return self.rerenderViewsWithScreenModeDependentContent()
+}
+
+// these views need to be re-rendered when the screen mode changes. The commits view,
+// for example, will show authorship information in half and full screen mode.
+func (self *ScreenModeActions) rerenderViewsWithScreenModeDependentContent() error {
+	for _, context := range self.c.Context().AllList() {
+		if context.NeedsRerenderOnWidthChange() == types.NEEDS_RERENDER_ON_WIDTH_CHANGE_WHEN_SCREEN_MODE_CHANGES {
+			if err := self.rerenderView(context.GetView()); err != nil {
+				return err
+			}
+		}
+	}
+
 	return nil
 }
 
+func (self *ScreenModeActions) rerenderView(view *gocui.View) error {
+	context, ok := self.c.Helpers().View.ContextForView(view.Name())
+	if !ok {
+		self.c.Log.Errorf("no context found for view %s", view.Name())
+		return nil
+	}
+
+	return context.HandleRender()
+}
+
 func nextIntInCycle(sl []types.WindowMaximisation, current types.WindowMaximisation) types.WindowMaximisation {
 	for i, val := range sl {
 		if val == current {
diff --git a/pkg/gui/information_panel.go b/pkg/gui/information_panel.go
index 00867fb92..3eac1e77c 100644
--- a/pkg/gui/information_panel.go
+++ b/pkg/gui/information_panel.go
@@ -6,7 +6,6 @@ import (
 	"github.com/jesseduffield/lazygit/pkg/constants"
 	"github.com/jesseduffield/lazygit/pkg/gui/style"
 	"github.com/jesseduffield/lazygit/pkg/utils"
-	"github.com/mattn/go-runewidth"
 )
 
 func (gui *Gui) informationStr() string {
@@ -34,7 +33,7 @@ func (gui *Gui) handleInfoClick() error {
 	width, _ := view.Size()
 
 	if activeMode, ok := gui.helpers.Mode.GetActiveMode(); ok {
-		if width-cx > runewidth.StringWidth(gui.c.Tr.ResetInParentheses) {
+		if width-cx > utils.StringWidth(gui.c.Tr.ResetInParentheses) {
 			return nil
 		}
 		return activeMode.Reset()
@@ -43,10 +42,10 @@ func (gui *Gui) handleInfoClick() error {
 	var title, url string
 
 	// if we're not in an active mode we show the donate button
-	if cx <= runewidth.StringWidth(gui.c.Tr.Donate) {
+	if cx <= utils.StringWidth(gui.c.Tr.Donate) {
 		url = constants.Links.Donate
 		title = gui.c.Tr.Donate
-	} else if cx <= runewidth.StringWidth(gui.c.Tr.Donate)+1+runewidth.StringWidth(gui.c.Tr.AskQuestion) {
+	} else if cx <= utils.StringWidth(gui.c.Tr.Donate)+1+utils.StringWidth(gui.c.Tr.AskQuestion) {
 		url = constants.Links.Discussions
 		title = gui.c.Tr.AskQuestion
 	}
diff --git a/pkg/gui/layout.go b/pkg/gui/layout.go
index 4e2b49477..2123731e4 100644
--- a/pkg/gui/layout.go
+++ b/pkg/gui/layout.go
@@ -73,7 +73,7 @@ func (gui *Gui) layout(g *gocui.Gui) error {
 		}
 
 		mustRerender := false
-		if context.NeedsRerenderOnWidthChange() {
+		if context.NeedsRerenderOnWidthChange() == types.NEEDS_RERENDER_ON_WIDTH_CHANGE_WHEN_WIDTH_CHANGES {
 			// view.Width() returns the width -1 for some reason
 			oldWidth := view.Width() + 1
 			newWidth := dimensionsObj.X1 - dimensionsObj.X0 + 2*frameOffset
diff --git a/pkg/gui/presentation/branches.go b/pkg/gui/presentation/branches.go
index b4c4a75c7..b75dfc95b 100644
--- a/pkg/gui/presentation/branches.go
+++ b/pkg/gui/presentation/branches.go
@@ -56,7 +56,7 @@ func getBranchDisplayStrings(
 	// Recency is always three characters, plus one for the space
 	availableWidth := viewWidth - 4
 	if len(branchStatus) > 0 {
-		availableWidth -= runewidth.StringWidth(utils.Decolorise(branchStatus)) + 1
+		availableWidth -= utils.StringWidth(utils.Decolorise(branchStatus)) + 1
 	}
 	if icons.IsIconEnabled() {
 		availableWidth -= 2 // one for the icon, one for the space
@@ -65,7 +65,7 @@ func getBranchDisplayStrings(
 		availableWidth -= utils.COMMIT_HASH_SHORT_SIZE + 1
 	}
 	if checkedOutByWorkTree {
-		availableWidth -= runewidth.StringWidth(worktreeIcon) + 1
+		availableWidth -= utils.StringWidth(worktreeIcon) + 1
 	}
 
 	displayName := b.Name
@@ -79,7 +79,7 @@ func getBranchDisplayStrings(
 	}
 
 	// Don't bother shortening branch names that are already 3 characters or less
-	if runewidth.StringWidth(displayName) > max(availableWidth, 3) {
+	if utils.StringWidth(displayName) > max(availableWidth, 3) {
 		// Never shorten the branch name to less then 3 characters
 		len := max(availableWidth, 4)
 		displayName = runewidth.Truncate(displayName, len, "…")
diff --git a/pkg/gui/types/context.go b/pkg/gui/types/context.go
index 003035fc2..70458c16f 100644
--- a/pkg/gui/types/context.go
+++ b/pkg/gui/types/context.go
@@ -39,6 +39,18 @@ type ParentContexter interface {
 	GetParentContext() (Context, bool)
 }
 
+type NeedsRerenderOnWidthChangeLevel int
+
+const (
+	// view doesn't render differently when its width changes
+	NEEDS_RERENDER_ON_WIDTH_CHANGE_NONE NeedsRerenderOnWidthChangeLevel = iota
+	// view renders differently when its width changes. An example is a view
+	// that truncates long lines to the view width, e.g. the branches view
+	NEEDS_RERENDER_ON_WIDTH_CHANGE_WHEN_WIDTH_CHANGES
+	// view renders differently only when the screen mode changes
+	NEEDS_RERENDER_ON_WIDTH_CHANGE_WHEN_SCREEN_MODE_CHANGES
+)
+
 type IBaseContext interface {
 	HasKeybindings
 	ParentContexter
@@ -60,8 +72,8 @@ type IBaseContext interface {
 	// determined independently.
 	HasControlledBounds() bool
 
-	// true if the view needs to be rerendered when its width changes
-	NeedsRerenderOnWidthChange() bool
+	// to what extent the view needs to be rerendered when its width changes
+	NeedsRerenderOnWidthChange() NeedsRerenderOnWidthChangeLevel
 
 	// true if the view needs to be rerendered when its height changes
 	NeedsRerenderOnHeightChange() bool
diff --git a/pkg/utils/formatting.go b/pkg/utils/formatting.go
index a6bbc5670..b7817346a 100644
--- a/pkg/utils/formatting.go
+++ b/pkg/utils/formatting.go
@@ -3,6 +3,7 @@ package utils
 import (
 	"fmt"
 	"strings"
+	"unicode"
 
 	"github.com/mattn/go-runewidth"
 	"github.com/samber/lo"
@@ -21,10 +22,22 @@ type ColumnConfig struct {
 	Alignment Alignment
 }
 
+func StringWidth(s string) int {
+	// We are intentionally not using a range loop here, because that would
+	// convert the characters to runes, which is unnecessary work in this case.
+	for i := 0; i < len(s); i++ {
+		if s[i] > unicode.MaxASCII {
+			return runewidth.StringWidth(s)
+		}
+	}
+
+	return len(s)
+}
+
 // WithPadding pads a string as much as you want
 func WithPadding(str string, padding int, alignment Alignment) string {
 	uncoloredStr := Decolorise(str)
-	width := runewidth.StringWidth(uncoloredStr)
+	width := StringWidth(uncoloredStr)
 	if padding < width {
 		return str
 	}
@@ -144,7 +157,7 @@ func getPadWidths(stringArrays [][]string) []int {
 		return MaxFn(stringArrays, func(stringArray []string) int {
 			uncoloredStr := Decolorise(stringArray[i])
 
-			return runewidth.StringWidth(uncoloredStr)
+			return StringWidth(uncoloredStr)
 		})
 	})
 }
@@ -161,7 +174,7 @@ func MaxFn[T any](items []T, fn func(T) int) int {
 
 // TruncateWithEllipsis returns a string, truncated to a certain length, with an ellipsis
 func TruncateWithEllipsis(str string, limit int) string {
-	if runewidth.StringWidth(str) > limit && limit <= 2 {
+	if StringWidth(str) > limit && limit <= 2 {
 		return strings.Repeat(".", limit)
 	}
 	return runewidth.Truncate(str, limit, "…")
diff --git a/pkg/utils/formatting_test.go b/pkg/utils/formatting_test.go
index 5b56a9b33..ac2adee5f 100644
--- a/pkg/utils/formatting_test.go
+++ b/pkg/utils/formatting_test.go
@@ -4,6 +4,7 @@ import (
 	"strings"
 	"testing"
 
+	"github.com/mattn/go-runewidth"
 	"github.com/stretchr/testify/assert"
 )
 
@@ -250,3 +251,27 @@ func TestRenderDisplayStrings(t *testing.T) {
 		assert.EqualValues(t, test.expectedColumnPositions, columnPositions)
 	}
 }
+
+func BenchmarkStringWidthAsciiOriginal(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		runewidth.StringWidth("some ASCII string")
+	}
+}
+
+func BenchmarkStringWidthAsciiOptimized(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		StringWidth("some ASCII string")
+	}
+}
+
+func BenchmarkStringWidthNonAsciiOriginal(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		runewidth.StringWidth("some non-ASCII string 🍉")
+	}
+}
+
+func BenchmarkStringWidthNonAsciiOptimized(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		StringWidth("some non-ASCII string 🍉")
+	}
+}