Add test that demonstrates problem with showing filtered history of file with renames

The test shows that selecting a commit before the rename shows an empty diff,
and selecting the rename itself shows an added file rather than a rename.

pkg/integration/components/shell.go

@@ -235,6 +235,10 @@ func (self *Shell) DeleteFileAndAdd(fileName string) *Shell {
 		GitAdd(fileName)
 }
 
+func (self *Shell) RenameFileInGit(oldName string, newName string) *Shell {
+	return self.RunCommand([]string{"git", "mv", oldName, newName})
+}
+
 // creates commits 01, 02, 03, ..., n with a new file in each
 // The reason for padding with zeroes is so that it's easier to do string
 // matches on the commit messages when there are many of them

pkg/integration/tests/filter_by_path/show_diffs_for_renamed_file.go

@@ -0,0 +1,128 @@
+package filter_by_path
+
+import (
+	"github.com/jesseduffield/lazygit/pkg/config"
+	. "github.com/jesseduffield/lazygit/pkg/integration/components"
+)
+
+var ShowDiffsForRenamedFile = NewIntegrationTest(NewIntegrationTestArgs{
+	Description:  "Filter commits by file path for a file that was renamed, and verify that it shows the diffs correctly",
+	ExtraCmdArgs: []string{},
+	Skip:         false,
+	SetupConfig: func(config *config.AppConfig) {
+	},
+	SetupRepo: func(shell *Shell) {
+		shell.CreateFileAndAdd("oldFile", "a\nb\nc\n")
+		shell.Commit("add old file")
+		shell.UpdateFileAndAdd("oldFile", "x\nb\nc\n")
+		shell.Commit("update old file")
+		shell.CreateFileAndAdd("unrelatedFile", "content of unrelated file\n")
+		shell.Commit("add unrelated file")
+		shell.RenameFileInGit("oldFile", "newFile")
+		shell.Commit("rename file")
+		shell.UpdateFileAndAdd("newFile", "y\nb\nc\n")
+		shell.UpdateFileAndAdd("unrelatedFile", "updated content of unrelated file\n")
+		shell.Commit("update both files")
+	},
+	Run: func(t *TestDriver, keys config.KeybindingConfig) {
+		t.Views().Commits().
+			Focus().
+			Lines(
+				Contains("update both files").IsSelected(),
+				Contains("rename file"),
+				Contains("add unrelated file"),
+				Contains("update old file"),
+				Contains("add old file"),
+			).
+			PressEnter()
+
+		t.Views().CommitFiles().
+			IsFocused().
+			Lines(
+				Equals("▼ /").IsSelected(),
+				Equals("  M newFile"),
+				Equals("  M unrelatedFile"),
+			).
+			SelectNextItem().
+			Press(keys.Universal.FilteringMenu)
+
+		t.ExpectPopup().Menu().Title(Equals("Filtering")).
+			Select(Contains("Filter by 'newFile'")).Confirm()
+
+		t.Views().Commits().
+			IsFocused().
+			Lines(
+				Contains("update both files").IsSelected(),
+				Contains("rename file"),
+				Contains("update old file"),
+				Contains("add old file"),
+			)
+
+		t.Views().Main().ContainsLines(
+			Equals("    update both files"),
+			Equals("---"),
+			Equals(" newFile | 2 +-"),
+			Equals(" 1 file changed, 1 insertion(+), 1 deletion(-)"),
+			Equals(""),
+			Equals("diff --git a/newFile b/newFile"),
+			Contains("index"),
+			Equals("--- a/newFile"),
+			Equals("+++ b/newFile"),
+			Equals("@@ -1,3 +1,3 @@"),
+			Equals("-x"),
+			Equals("+y"),
+			Equals(" b"),
+			Equals(" c"),
+		)
+
+		t.Views().Commits().SelectNextItem()
+
+		t.Views().Main().ContainsLines(
+			Equals("    rename file"),
+			Equals("---"),
+			/* EXPECTED:
+			Equals(" oldFile => newFile | 0"),
+			Equals(" 1 file changed, 0 insertions(+), 0 deletions(-)"),
+			Equals(""),
+			Equals("diff --git a/oldFile b/newFile"),
+			Equals("similarity index 100%"),
+			Equals("rename from oldFile"),
+			Equals("rename to newFile"),
+			ACTUAL: */
+			Equals(" newFile | 3 +++"),
+			Equals(" 1 file changed, 3 insertions(+)"),
+			Equals(""),
+			Equals("diff --git a/newFile b/newFile"),
+			Equals("new file mode 100644"),
+			Contains("index"),
+			Equals("--- /dev/null"),
+			Equals("+++ b/newFile"),
+			Equals("@@ -0,0 +1,3 @@"),
+			Equals("+x"),
+			Equals("+b"),
+			Equals("+c"),
+		)
+
+		t.Views().Commits().SelectNextItem()
+
+		/* EXPECTED:
+		t.Views().Main().ContainsLines(
+			Equals("    update old file"),
+			Equals("---"),
+			Equals(" oldFile | 2 +-"),
+			Equals(" 1 file changed, 1 insertion(+), 1 deletion(-)"),
+			Equals(""),
+			Equals("diff --git a/oldFile b/oldFile"),
+			Contains("index"),
+			Equals("--- a/oldFile"),
+			Equals("+++ b/oldFile"),
+			Equals("@@ -1,3 +1,3 @@"),
+			Equals("-a"),
+			Equals("+x"),
+			Equals(" b"),
+			Equals(" c"),
+		)
+		ACTUAL: */
+		t.Views().Main().IsEmpty()
+	},
+})

pkg/integration/tests/test_list.go

@@ -235,6 +235,7 @@ var tests = []*components.IntegrationTest{
 	filter_by_path.CliArg,
 	filter_by_path.KeepSameCommitSelectedOnExit,
 	filter_by_path.SelectFile,
+	filter_by_path.ShowDiffsForRenamedFile,
 	filter_by_path.TypeFile,
 	interactive_rebase.AdvancedInteractiveRebase,
 	interactive_rebase.AmendCommitWithConflict,