Fix checking out a file from a range selection of commits (#4423)

- **PR Description**

When selecting a range of commits by selecting the top one and then
pressing shift-down to create a range, and then pressing enter and
checking out one of the files by pressing `c`, you would get the file
checked out with its state at the bottom end of the range, which is not
what you want; it is expected to check out the file at the state that
the diff shows it changes to. (And if the file was only created in the
middle of that range, trying to check it out would result in an error.)
Fix this by paying attention to a "from-to" range selection, and
checking out the file at the "to" state.

Related to #4420.

pkg/gui/controllers/commits_files_controller.go

@@ -292,7 +292,8 @@ func (self *CommitFilesController) openCopyMenu() error {
 
 func (self *CommitFilesController) checkout(node *filetree.CommitFileNode) error {
 	self.c.LogAction(self.c.Tr.Actions.CheckoutFile)
-	if err := self.c.Git().WorkingTree.CheckoutFile(self.context().GetRef().RefName(), node.GetPath()); err != nil {
+	_, to := self.context().GetFromAndToForDiff()
+	if err := self.c.Git().WorkingTree.CheckoutFile(to, node.GetPath()); err != nil {
 		return err
 	}
 

pkg/integration/tests/commit/checkout_file_from_commit.go

@@ -0,0 +1,55 @@
+package commit
+
+import (
+	"github.com/jesseduffield/lazygit/pkg/config"
+	. "github.com/jesseduffield/lazygit/pkg/integration/components"
+)
+
+var CheckoutFileFromCommit = NewIntegrationTest(NewIntegrationTestArgs{
+	Description:  "Checkout a file from a commit",
+	ExtraCmdArgs: []string{},
+	Skip:         false,
+	SetupConfig:  func(config *config.AppConfig) {},
+	SetupRepo: func(shell *Shell) {
+		shell.CreateFileAndAdd("file.txt", "one\n")
+		shell.Commit("one")
+		shell.CreateFileAndAdd("file.txt", "two\n")
+		shell.Commit("two")
+		shell.CreateFileAndAdd("file.txt", "three\n")
+		shell.Commit("three")
+		shell.CreateFileAndAdd("file.txt", "four\n")
+		shell.Commit("four")
+	},
+	Run: func(t *TestDriver, keys config.KeybindingConfig) {
+		t.Views().Commits().
+			Focus().
+			Lines(
+				Contains("four").IsSelected(),
+				Contains("three"),
+				Contains("two"),
+				Contains("one"),
+			).
+			NavigateToLine(Contains("three")).
+			Tap(func() {
+				t.Views().Main().ContainsLines(
+					Contains("-two"),
+					Contains("+three"),
+				)
+			}).
+			PressEnter()
+
+		t.Views().CommitFiles().
+			IsFocused().
+			Lines(
+				Equals("M file.txt"),
+			).
+			Press(keys.CommitFiles.CheckoutCommitFile)
+
+		t.Views().Files().
+			Lines(
+				Equals("M  file.txt"),
+			)
+
+		t.FileSystem().FileContent("file.txt", Equals("three\n"))
+	},
+})

pkg/integration/tests/commit/checkout_file_from_range_selection_of_commits.go

@@ -0,0 +1,56 @@
+package commit
+
+import (
+	"github.com/jesseduffield/lazygit/pkg/config"
+	. "github.com/jesseduffield/lazygit/pkg/integration/components"
+)
+
+var CheckoutFileFromRangeSelectionOfCommits = NewIntegrationTest(NewIntegrationTestArgs{
+	Description:  "Checkout a file from a range selection of commits",
+	ExtraCmdArgs: []string{},
+	Skip:         false,
+	SetupConfig:  func(config *config.AppConfig) {},
+	SetupRepo: func(shell *Shell) {
+		shell.CreateFileAndAdd("file.txt", "one\n")
+		shell.Commit("one")
+		shell.CreateFileAndAdd("file.txt", "two\n")
+		shell.Commit("two")
+		shell.CreateFileAndAdd("file.txt", "three\n")
+		shell.Commit("three")
+		shell.CreateFileAndAdd("file.txt", "four\n")
+		shell.Commit("four")
+	},
+	Run: func(t *TestDriver, keys config.KeybindingConfig) {
+		t.Views().Commits().
+			Focus().
+			Lines(
+				Contains("four").IsSelected(),
+				Contains("three"),
+				Contains("two"),
+				Contains("one"),
+			).
+			NavigateToLine(Contains("three")).
+			Press(keys.Universal.RangeSelectDown).
+			Tap(func() {
+				t.Views().Main().ContainsLines(
+					Contains("-one"),
+					Contains("+three"),
+				)
+			}).
+			PressEnter()
+
+		t.Views().CommitFiles().
+			IsFocused().
+			Lines(
+				Equals("M file.txt"),
+			).
+			Press(keys.CommitFiles.CheckoutCommitFile)
+
+		t.Views().Files().
+			Lines(
+				Equals("M  file.txt"),
+			)
+
+		t.FileSystem().FileContent("file.txt", Equals("three\n"))
+	},
+})

pkg/integration/tests/test_list.go

@@ -89,6 +89,8 @@ var tests = []*components.IntegrationTest{
 	commit.AmendWhenThereAreConflictsAndContinue,
 	commit.AutoWrapMessage,
 	commit.Checkout,
+	commit.CheckoutFileFromCommit,
+	commit.CheckoutFileFromRangeSelectionOfCommits,
 	commit.Commit,
 	commit.CommitMultiline,
 	commit.CommitSkipHooks,