Disallow creating custom patches when the diff context size is 0 (#4522)

- **PR Description**

This is very similar to what we are doing for staging or discarding
hunks in the Files panel (see #4235). Git doesn't allow applying patches
with a zero context size (unless you use the --unidiff-zero option,
which is discouraged).

Fixes #4521.

pkg/gui/controllers/commits_files_controller.go

@@ -2,6 +2,7 @@ package controllers
 
 import (
 	"errors"
+	"fmt"
 	"path/filepath"
 	"strings"
 
@@ -12,6 +13,7 @@ import (
 	"github.com/jesseduffield/lazygit/pkg/constants"
 	"github.com/jesseduffield/lazygit/pkg/gui/context"
 	"github.com/jesseduffield/lazygit/pkg/gui/filetree"
+	"github.com/jesseduffield/lazygit/pkg/gui/keybindings"
 	"github.com/jesseduffield/lazygit/pkg/gui/types"
 	"github.com/jesseduffield/lazygit/pkg/utils"
 	"github.com/samber/lo"
@@ -380,6 +382,11 @@ func (self *CommitFilesController) openDiffTool(node *filetree.CommitFileNode) e
 }
 
 func (self *CommitFilesController) toggleForPatch(selectedNodes []*filetree.CommitFileNode) error {
+	if self.c.AppState.DiffContextSize == 0 {
+		return fmt.Errorf(self.c.Tr.Actions.NotEnoughContextToStage,
+			keybindings.Label(self.c.UserConfig().Keybinding.Universal.IncreaseContextInDiffView))
+	}
+
 	toggle := func() error {
 		return self.c.WithWaitingStatus(self.c.Tr.UpdatingPatch, func(gocui.Task) error {
 			if !self.c.Git().Patch.PatchBuilder.Active() {
@@ -471,6 +478,11 @@ func (self *CommitFilesController) enterCommitFile(node *filetree.CommitFileNode
 		return self.handleToggleCommitFileDirCollapsed(node)
 	}
 
+	if self.c.AppState.DiffContextSize == 0 {
+		return fmt.Errorf(self.c.Tr.Actions.NotEnoughContextToStage,
+			keybindings.Label(self.c.UserConfig().Keybinding.Universal.IncreaseContextInDiffView))
+	}
+
 	enterTheFile := func() error {
 		if !self.c.Git().Patch.PatchBuilder.Active() {
 			if err := self.startPatchBuilder(); err != nil {

pkg/i18n/english.go

@@ -984,6 +984,7 @@ type Actions struct {
 	ResolveConflictByDeletingFile     string
 	NotEnoughContextToStage           string
 	NotEnoughContextToDiscard         string
+	NotEnoughContextForCustomPatch    string
 	IgnoreExcludeFile                 string
 	IgnoreFileErr                     string
 	ExcludeFile                       string
@@ -2031,6 +2032,7 @@ func EnglishTranslationSet() *TranslationSet {
 			ResolveConflictByDeletingFile:   "Resolve by deleting file",
 			NotEnoughContextToStage:         "Staging or unstaging changes is not possible with a diff context size of 0. Increase the context using '%s'.",
 			NotEnoughContextToDiscard:       "Discarding changes is not possible with a diff context size of 0. Increase the context using '%s'.",
+			NotEnoughContextForCustomPatch:  "Creating custom patches is not possible with a diff context size of 0. Increase the context using '%s'.",
 			IgnoreExcludeFile:               "Ignore or exclude file",
 			IgnoreFileErr:                   "Cannot ignore .gitignore",
 			ExcludeFile:                     "Exclude file",