Show an error when checking out a file would overwrite local modifications

pkg/gui/controllers/commits_files_controller.go

@@ -12,6 +12,7 @@ import (
 	"github.com/jesseduffield/lazygit/pkg/commands/patch"
 	"github.com/jesseduffield/lazygit/pkg/constants"
 	"github.com/jesseduffield/lazygit/pkg/gui/context"
+	"github.com/jesseduffield/lazygit/pkg/gui/controllers/helpers"
 	"github.com/jesseduffield/lazygit/pkg/gui/filetree"
 	"github.com/jesseduffield/lazygit/pkg/gui/keybindings"
 	"github.com/jesseduffield/lazygit/pkg/gui/types"
@@ -283,6 +284,12 @@ func (self *CommitFilesController) openCopyMenu() error {
 }
 
 func (self *CommitFilesController) checkout(node *filetree.CommitFileNode) error {
+	hasModifiedFiles := helpers.AnyTrackedFilesInPathExceptSubmodules(node.GetPath(),
+		self.c.Model().Files, self.c.Model().Submodules)
+	if hasModifiedFiles {
+		return errors.New(self.c.Tr.CannotCheckoutWithModifiedFilesErr)
+	}
+
 	self.c.LogAction(self.c.Tr.Actions.CheckoutFile)
 	_, to := self.context().GetFromAndToForDiff()
 	if err := self.c.Git().WorkingTree.CheckoutFile(to, node.GetPath()); err != nil {

pkg/gui/controllers/helpers/working_tree_helper.go

@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"os"
 	"regexp"
+	"strings"
 
 	"github.com/jesseduffield/lazygit/pkg/commands/git_commands"
 	"github.com/jesseduffield/lazygit/pkg/commands/models"
@@ -71,6 +72,23 @@ func AnyTrackedFilesExceptSubmodules(files []*models.File, submoduleConfigs []*m
 	return lo.SomeBy(files, func(f *models.File) bool { return f.Tracked && !f.IsSubmodule(submoduleConfigs) })
 }
 
+func isContainedInPath(candidate string, path string) bool {
+	return (
+	// If the path is the repo root (appears as "/" in the UI), then all candidates are contained in it
+	path == "." ||
+		// Exact match; will only be true for files
+		candidate == path ||
+		// Match for files within a directory. We need to match the trailing slash to avoid
+		// matching files with longer names.
+		strings.HasPrefix(candidate, path+"/"))
+}
+
+func AnyTrackedFilesInPathExceptSubmodules(path string, files []*models.File, submoduleConfigs []*models.SubmoduleConfig) bool {
+	return lo.SomeBy(files, func(f *models.File) bool {
+		return f.Tracked && isContainedInPath(f.GetPath(), path) && !f.IsSubmodule(submoduleConfigs)
+	})
+}
+
 func (self *WorkingTreeHelper) IsWorkingTreeDirtyExceptSubmodules() bool {
 	return IsWorkingTreeDirtyExceptSubmodules(self.c.Model().Files, self.c.Model().Submodules)
 }

pkg/i18n/english.go

@@ -425,6 +425,7 @@ type TranslationSet struct {
 	ViewItemFiles                         string
 	CommitFilesTitle                      string
 	CheckoutCommitFileTooltip             string
+	CannotCheckoutWithModifiedFilesErr    string
 	CanOnlyDiscardFromLocalCommits        string
 	Remove                                string
 	DiscardOldFileChangeTooltip           string
@@ -1525,6 +1526,7 @@ func EnglishTranslationSet() *TranslationSet {
 		ViewItemFiles:                        "View files",
 		CommitFilesTitle:                     "Commit files",
 		CheckoutCommitFileTooltip:            "Checkout file. This replaces the file in your working tree with the version from the selected commit.",
+		CannotCheckoutWithModifiedFilesErr:   "You have local modifications for the file(s) you are trying to check out. You need to stash or discard these first.",
 		CanOnlyDiscardFromLocalCommits:       "Changes can only be discarded from local commits",
 		Remove:                               "Remove",
 		DiscardOldFileChangeTooltip:          "Discard this commit's changes to this file. This runs an interactive rebase in the background, so you may get a merge conflict if a later commit also changes this file.",

pkg/integration/tests/commit/checkout_file_with_local_modifications.go

@@ -0,0 +1,40 @@
+package commit
+
+import (
+	"github.com/jesseduffield/lazygit/pkg/config"
+	. "github.com/jesseduffield/lazygit/pkg/integration/components"
+)
+
+var CheckoutFileWithLocalModifications = NewIntegrationTest(NewIntegrationTestArgs{
+	Description:  "Checkout a file from a commit that has local modifications",
+	ExtraCmdArgs: []string{},
+	Skip:         false,
+	SetupConfig:  func(config *config.AppConfig) {},
+	SetupRepo: func(shell *Shell) {
+		shell.CreateFileAndAdd("dir/file1.txt", "file1\n")
+		shell.CreateFileAndAdd("dir/file2.txt", "file2\n")
+		shell.Commit("one")
+		shell.UpdateFile("dir/file1.txt", "file1\nfile1 change\n")
+	},
+	Run: func(t *TestDriver, keys config.KeybindingConfig) {
+		t.Views().Commits().
+			Focus().
+			Lines(
+				Contains("one").IsSelected(),
+			).
+			PressEnter()
+
+		t.Views().CommitFiles().
+			IsFocused().
+			Lines(
+				Equals("▼ dir").IsSelected(),
+				Equals("  A file1.txt"),
+				Equals("  A file2.txt"),
+			).
+			Press(keys.CommitFiles.CheckoutCommitFile)
+
+		t.ExpectPopup().Alert().Title(Equals("Error")).
+			Content(Contains("local modifications")).
+			Confirm()
+	},
+})

pkg/integration/tests/test_list.go

@@ -107,6 +107,7 @@ var tests = []*components.IntegrationTest{
 	commit.Checkout,
 	commit.CheckoutFileFromCommit,
 	commit.CheckoutFileFromRangeSelectionOfCommits,
+	commit.CheckoutFileWithLocalModifications,
 	commit.Commit,
 	commit.CommitMultiline,
 	commit.CommitSkipHooks,