Rerender fewer views when their width changes

In d5b4f7bb3e and 58a83b0862 we introduced a combined mechanism for rerendering
views when either their width changes (needed for the branches view which
truncates long branch names), or the screen mode (needed for those views that
display more information in half or full screen mode, e.g. the commits view).

This was a bad idea, because it unnecessarily rerenders too many views when just
their width changes, which causes a noticable lag. This is a problem, for
example, when selecting a file in the files panel that has only unstaged
changes, and then going to one that has both staged and unstaged changes; this
splits the main view, causing the side panels to become a bit narrower, and
rerendering all those views took almost 500ms on my machine. Another similar
example is entering or leaving staging mode.

Fix this by being more specific about which views need rerendering under what
conditions; this improves the time it takes to rerender in the above scenarios
from 450-500s down to about 20ms.

This reintroduces the code that was removed in 58a83b0862, but in a slightly
different way.

8 files changed, 48 insertions, 11 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/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/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/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/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