pull errors out of package scope and store sentinel errors on the gui struct

pkg/gui/gui.go

@@ -25,11 +25,29 @@ import (
 // OverlappingEdges determines if panel edges overlap
 var OverlappingEdges = false
 
-// ErrSubProcess tells us we're switching to a subprocess so we need to
-// close the Gui until it is finished
-var (
-	ErrSubProcess = errors.New("running subprocess")
-)
+// SentinelErrors are the errors that have special meaning and need to be checked
+// by calling functions. The less of these, the better
+type SentinelErrors struct {
+	ErrSubProcess error
+	ErrNoFiles    error
+}
+
+// GenerateSentinelErrors makes the sentinel errors for the gui. We're defining it here
+// because we can't do package-scoped errors with localization, and also because
+// it seems like package-scoped variables are bad in general
+// https://dave.cheney.net/2017/06/11/go-without-package-scoped-variables
+// In the future it would be good to implement some of the recommendations of
+// that article. For now, if we don't need an error to be a sentinel, we will just
+// define it inline. This has implications for error messages that pop up everywhere
+// in that we'll be duplicating the default values. We may need to look at
+// having a default localisation bundle defined, and just using keys-only when
+// localising things in the code.
+func (gui *Gui) GenerateSentinelErrors() {
+	gui.Errors = SentinelErrors{
+		ErrSubProcess: errors.New("running subprocess"),
+		ErrNoFiles:    errors.New(gui.Tr.SLocalize("NoChangedFiles", "No changed files")),
+	}
+}
 
 // Gui wraps the gocui Gui object which handles rendering and events
 type Gui struct {
@@ -41,6 +59,7 @@ type Gui struct {
 	SubProcess *exec.Cmd
 	State      guiState
 	Tr         *i18n.Localizer
+	Errors     SentinelErrors
 }
 
 type guiState struct {
@@ -70,17 +89,21 @@ func NewGui(log *logrus.Logger, gitCommand *commands.GitCommand, oSCommand *comm
 		Conflicts:     make([]commands.Conflict, 0),
 		EditHistory:   stack.New(),
 		Platform:      *oSCommand.Platform,
-		Version:       "test version", // TODO: send version in
+		Version:       version,
 	}
 
-	return &Gui{
+	gui := &Gui{
 		Log:        log,
 		GitCommand: gitCommand,
 		OSCommand:  oSCommand,
 		Version:    version,
 		State:      initialState,
 		Tr:         tr,
-	}, nil
+	}
+
+	gui.GenerateSentinelErrors()
+
+	return gui, nil
 }
 
 func (gui *Gui) scrollUpMain(g *gocui.Gui, v *gocui.View) error {
@@ -313,7 +336,7 @@ func (gui *Gui) RunWithSubprocesses() {
 		if err := gui.Run(); err != nil {
 			if err == gocui.ErrQuit {
 				break
-			} else if err == ErrSubProcess {
+			} else if err == gui.Errors.ErrSubProcess {
 				gui.SubProcess.Stdin = os.Stdin
 				gui.SubProcess.Stdout = os.Stdout
 				gui.SubProcess.Stderr = os.Stderr