Fix #5302: Create .git/info directory before writing exclude file (#5325)

Fixes #5302

## Problem

When `.git/info` directory does not exist (can happen with bare clones,
manual deletion, or certain Git configurations), selecting "Add to
.git/info/exclude" fails with:

```
open <repo-path>/.git/info/exclude: no such file or directory
```

The `Exclude` function used `os.OpenFile` with `os.O_CREATE` which
creates the file but not its parent directory.

## Fix

Added `os.MkdirAll` to create the `.git/info` directory (with 0755
permissions) before attempting to open the exclude file. `MkdirAll` is a
no-op if the directory already exists, so existing behavior is
unchanged.

## Test

Added integration test `file/exclude_without_info_dir` that:
1. Removes `.git/info` directory during repo setup
2. Attempts to exclude a file via the menu
3. Verifies `.git/info/exclude` is created with the correct content

Test fails without the fix, passes with it.

Tested locally on macOS ARM (Apple Silicon). Unit tests and integration
test pass.

pkg/commands/git_commands/working_tree.go

@@ -246,7 +246,11 @@ func (self *WorkingTreeCommands) Ignore(filename string) error {
 
 // Exclude adds a file to the .git/info/exclude for the repo
 func (self *WorkingTreeCommands) Exclude(filename string) error {
-	excludeFile := filepath.Join(self.repoPaths.repoGitDirPath, "info", "exclude")
+	infoDir := filepath.Join(self.repoPaths.repoGitDirPath, "info")
+	if err := os.MkdirAll(infoDir, 0o755); err != nil {
+		return err
+	}
+	excludeFile := filepath.Join(infoDir, "exclude")
 	return self.os.AppendLineToFile(excludeFile, escapeFilename(filename))
 }
 

pkg/integration/tests/file/exclude_without_info_dir.go

@@ -0,0 +1,32 @@
+package file
+
+import (
+	"github.com/jesseduffield/lazygit/pkg/config"
+	. "github.com/jesseduffield/lazygit/pkg/integration/components"
+)
+
+var ExcludeWithoutInfoDir = NewIntegrationTest(NewIntegrationTestArgs{
+	Description:  "Exclude a file when .git/info directory does not exist",
+	ExtraCmdArgs: []string{},
+	Skip:         false,
+	SetupConfig: func(config *config.AppConfig) {
+	},
+	SetupRepo: func(shell *Shell) {
+		// Remove .git/info directory to reproduce #5302
+		shell.RunCommand([]string{"rm", "-rf", ".git/info"})
+		shell.CreateFile("toExclude", "")
+	},
+	Run: func(t *TestDriver, keys config.KeybindingConfig) {
+		t.Views().Files().
+			IsFocused().
+			Focus().
+			NavigateToLine(Contains("toExclude")).
+			Press(keys.Files.IgnoreFile).
+			Tap(func() {
+				t.ExpectPopup().Menu().Title(Equals("Ignore or exclude file")).Select(Contains("Add to .git/info/exclude")).Confirm()
+
+				// Should succeed without error, creating .git/info/ directory automatically
+				t.FileSystem().FileContent(".git/info/exclude", Contains("/toExclude"))
+			})
+	},
+})

pkg/integration/tests/test_list.go

@@ -221,6 +221,7 @@ var tests = []*components.IntegrationTest{
 	file.DiscardUnstagedRangeSelect,
 	file.DiscardVariousChanges,
 	file.DiscardVariousChangesRangeSelect,
+	file.ExcludeWithoutInfoDir,
 	file.Gitignore,
 	file.GitignoreSpecialCharacters,
 	file.RememberCommitMessageAfterFail,