Add support for ~/.config/lazygit without setting XDG_CONFIG_HOME

Currently lazygit looks for its config file in `XDG_CONFIG_HOME` if it's
available, but if not it falls back to the defaults defined by the
[xdg](https://github.com/adrg/xdg) package. Unfortunately the defaults
the package falls back to isn't what CLI applications commonly fall back
to on macOS. Specifically, it looks in `~/Library/Application Support`
instead of `~/.config`.

This updates the app config logic to:

- Look for `~/.config/lazygit` first if `XDG_CONFIG_HOME` is not set
  and we're on macOS.
- Fallback to the existing `xdg` package location if the configuration
  file exists there.
- Default to `~/.config/lazygit/config.yml` if `XDG_CONFIG_HOME` is not
  set, we're on macOS, and there is no existing configuration file.

This change did feel a bit like having to thread a needle and I didn't
see any existing tests for this behavior (which is reasonable, since it's
complicated and OS dependent) so I did test a few variations of the
configuration locally by building with this change included and running
a `brew` installed lazygit.

It seemed to work properly, falling back to the existing location when
`XDG_CONFIG_HOME` isn't set, using `~/.config/lazygit` when `config.yml`
is present, and creating `~/.config/lazygit/config.yml` when it's not.

I think this should resolve jesseduffield#1341

pkg/config/app_config.go

@@ -349,13 +349,34 @@ func findConfigFile(filename string) (exists bool, path string) {
 		return true, legacyConfigPath
 	}
 
+	// if on macOs, default to looking in ~/.config/lazygit first since that's
+	// the most common location for CLI apps to store configuration when
+	// `XDG_CONFIG_HOME` is not set. The `xdg` package uses `~/Library/Application\ Support`
+	// as the default directory for macOS, so we have to handle this case manually.
+	if overrideXdgConfigHome && os.Getenv("XDG_CONFIG_HOME") == "" {
+		homeConfigFilePath, err := findHomeConfigFile(filename)
+		if err == nil {
+			return true, homeConfigFilePath
+		}
+	}
+
 	// look for lazygit/filename in XDG_CONFIG_HOME and XDG_CONFIG_DIRS
 	configFilepath, err := xdg.SearchConfigFile(filepath.Join("lazygit", filename))
 	if err == nil {
 		return true, configFilepath
 	}
 
-	return false, filepath.Join(xdg.ConfigHome, "lazygit", filename)
+	configHome := xdg.ConfigHome
+	// If we're on macOS and XDG_CONFIG_HOME is not set, we use
+	// ~/.config/lazygit instead of the default `~/Library/Application\ Support`
+	// directory the `xdg` package uses.
+	if overrideXdgConfigHome && os.Getenv("XDG_CONFIG_HOME") == "" {
+		if homeDir, err := os.UserHomeDir(); err == nil {
+			return false, filepath.Join(homeDir, ".config", "lazygit", filename)
+		}
+	}
+
+	return false, filepath.Join(configHome, "lazygit", filename)
 }
 
 var ConfigFilename = "config.yml"
@@ -494,3 +515,17 @@ func LogPath() (string, error) {
 
 	return stateFilePath("development.log")
 }
+
+func findHomeConfigFile(filename string) (string, error) {
+	home, err := os.UserHomeDir()
+	if err != nil {
+		return "", err
+	}
+
+	path := filepath.Join(home, ".config", "lazygit", filename)
+	if _, err = os.Stat(path); err != nil {
+		return "", err
+	}
+
+	return path, nil
+}

pkg/config/xdg.go

@@ -0,0 +1,5 @@
+//go:build !darwin
+
+package config
+
+const overrideXdgConfigHome = false

pkg/config/xdg_darwin.go

@@ -0,0 +1,5 @@
+//go:build darwin
+
+package config
+
+const overrideXdgConfigHome = true