Allow context changes while building a custom patch

The focused diff addresses patch lines by identity, so changing how much
context is rendered cannot invalidate an active patch. Remove the
explorer era refusal and prove that another line can still be toggled
correctly after the rerender.

Co-Authored-By: GitHub Copilot <copilot@github.com>

pkg/gui/controllers/context_lines_controller.go

@@ -1,7 +1,6 @@
 package controllers
 
 import (
-	"errors"
 	"fmt"
 	"math"
 
@@ -50,10 +49,6 @@ func (self *ContextLinesController) Context() types.Context {
 }
 
 func (self *ContextLinesController) Increase() error {
-	if err := self.checkCanChangeContext(); err != nil {
-		return err
-	}
-
 	if self.c.UserConfig().Git.DiffContextSize < math.MaxUint64 {
 		self.c.UserConfig().Git.DiffContextSize++
 	}
@@ -61,10 +56,6 @@ func (self *ContextLinesController) Increase() error {
 }
 
 func (self *ContextLinesController) Decrease() error {
-	if err := self.checkCanChangeContext(); err != nil {
-		return err
-	}
-
 	if self.c.UserConfig().Git.DiffContextSize > 0 {
 		self.c.UserConfig().Git.DiffContextSize--
 	}
@@ -83,11 +74,3 @@ func (self *ContextLinesController) applyChange() error {
 	currentContext.HandleRenderToMain()
 	return nil
 }
-
-func (self *ContextLinesController) checkCanChangeContext() error {
-	if self.c.Git().Patch.PatchBuilder.Active() {
-		return errors.New(self.c.Tr.CantChangeContextSizeError)
-	}
-
-	return nil
-}

pkg/i18n/english.go

@@ -863,7 +863,6 @@ type TranslationSet struct {
 	SortOrderPrompt                          string
 	SortCommits                              string
 	SortCommitsTooltip                       string
-	CantChangeContextSizeError               string
 	CantChangeRenameThresholdError           string
 	OpenCommitInBrowser                      string
 	ViewBisectOptions                        string
@@ -2043,7 +2042,6 @@ func EnglishTranslationSet() *TranslationSet {
 		SortBasedOnReflog:                        "(based on reflog)",
 		SortCommits:                              "Commit sort order",
 		SortCommitsTooltip:                       "Change the sort order of the commits in the commit log.\n\nThe default can be changed in the config file with the key 'git.log.sortOrder'.",
-		CantChangeContextSizeError:               "Cannot change context while in patch building mode because we were too lazy to support it when releasing the feature. If you really want it, please let us know!",
 		CantChangeRenameThresholdError:           "Cannot change the rename similarity threshold while in patch building mode, because the custom patch can't cope with a rename turning into a delete and add underneath it.",
 		OpenCommitInBrowser:                      "Open commit in browser",
 		ViewBisectOptions:                        "View bisect options",

pkg/integration/tests/main_view/change_context_size_while_building_patch.go

@@ -0,0 +1,54 @@
+package main_view
+
+import (
+	"github.com/jesseduffield/lazygit/pkg/config"
+	. "github.com/jesseduffield/lazygit/pkg/integration/components"
+)
+
+var ChangeContextSizeWhileBuildingPatch = NewIntegrationTest(NewIntegrationTestArgs{
+	Description:  "Change diff context size while building a custom patch, then add another line",
+	ExtraCmdArgs: []string{},
+	Skip:         false,
+	SetupConfig: func(config *config.AppConfig) {
+		config.GetUserConfig().Gui.UseHunkModeInStagingView = false
+		config.GetUserConfig().Git.DiffContextSize = 1
+	},
+	SetupRepo: func(shell *Shell) {
+		shell.CreateFileAndAdd("file1", "one\ntwo\nthree\nfour\nfive\nsix\nseven\neight\nnine\nten\n")
+		shell.Commit("first commit")
+		shell.UpdateFileAndAdd("file1", "ONE\ntwo\nthree\nfour\nfive\nsix\nseven\neight\nnine\nTEN\n")
+		shell.Commit("second commit")
+	},
+	Run: func(t *TestDriver, keys config.KeybindingConfig) {
+		t.Views().Commits().
+			Focus().
+			Lines(
+				Contains("second commit").IsSelected(),
+				Contains("first commit"),
+			).
+			PressEnter()
+
+		t.Views().CommitFiles().
+			IsFocused().
+			Press(keys.Universal.FocusMainView)
+
+		t.Views().Main().
+			IsFocused().
+			SelectedLines(Contains("-one")).
+			PressPrimaryAction().
+			Press(keys.Universal.IncreaseContextInDiffView).
+			Tap(func() {
+				t.ExpectToast(Equals("Changed diff context size to 2"))
+			}).
+			NavigateToLine(Contains("-ten")).
+			PressPrimaryAction()
+
+		t.Views().Secondary().Content(
+			Contains("-one").Contains("-ten"),
+		)
+		t.Views().Main().MarkedLines(
+			Contains("-one"),
+			Contains("-ten"),
+		)
+	},
+})

pkg/integration/tests/test_list.go

@@ -376,6 +376,7 @@ var tests = []*components.IntegrationTest{
 	main_view.BuildPatchFromAReflogEntry,
 	main_view.BuildPatchFromAWholeCommitsDiff,
 	main_view.BuildPatchWithMixedSelections,
+	main_view.ChangeContextSizeWhileBuildingPatch,
 	main_view.ChangeScreenModeInFocusedDiff,
 	main_view.ClickSelectsDiffLine,
 	main_view.CommitFromMainView,