feat: add rough separation of concerns

In the earlier version, the same function updated the repo and reported
the result.  In this version, we separate updating from reporting.  I am
not sure whether this is the best way to do it.  To be continued...

.golangci.yml

@@ -1,4 +1,6 @@
 linters-settings:
+  copyloopvar:
+    check-alias: true
   depguard:
       rules:
         main:

cli/app.go

@@ -98,34 +98,46 @@ func (app *App) Unmarshal(configFile string, isDefault bool) *Wanted {
 	return &wanted
 }
 
-// MirrorRepos runs git push --mirror on a group of repositories.
-func (app *App) MirrorRepos(wanted *Wanted) {
+// MirrorRepos runs git push --mirror on a group of repositories and returns
+// a slice of results.
+func (app *App) MirrorRepos(wanted *Wanted) []Publisher {
 	if app.NoOp() || len(wanted.Repos) == 0 {
-		return
+		return nil
 	}
 	wanted.Repos = slices.DeleteFunc(wanted.Repos, func(r *Repo) bool {
 		return r == nil || r.Dir == ""
 	})
 	var wg sync.WaitGroup
 	wg.Add(len(wanted.Repos))
-	for _, repo := range wanted.Repos {
-		go func(r *Repo) {
+	results := make([]Publisher, len(wanted.Repos))
+	for i, r := range wanted.Repos {
+		go func(i int, r *Repo) {
 			defer wg.Done()
-			updateRepo(r)
-		}(repo)
+			res := updateRepo(r)
+			results[i] = res
+		}(i, r)
 	}
 	wg.Wait()
+	return results
+}
+
+func (app *App) DisplayResults(results []Publisher) {
+	if app.NoOp() || len(results) == 0 {
+		return
+	}
+	for _, r := range results {
+		r.Publish()
+	}
 }
 
-func updateRepo(r *Repo) {
+func updateRepo(r *Repo) Publisher {
 	args := []string{"push", "--mirror", r.Remote}
 	cmd := exec.Command("git", args...)
 	cmd.Dir = r.Dir
 	cmdString := fmt.Sprintf("`git %s` (in %s)", strings.Join(args, " "), cmd.Dir)
 	err := cmd.Run()
 	if err != nil {
-		fmt.Fprintf(os.Stderr, "%s: problem with %s: %s\n", appName, cmdString, err)
-		return
+		return Failure{msg: fmt.Sprintf("%s: problem with %s: %s", appName, cmdString, err)}
 	}
-	fmt.Printf("%s: %s\n", appName, cmdString)
+	return Success{msg: fmt.Sprintf("%s: %s", appName, cmdString)}
 }

cli/result.go

@@ -0,0 +1,27 @@
+package cli
+
+import (
+	"fmt"
+	"os"
+)
+
+// Publisher is the interface that wraps the Publish method.
+type Publisher interface {
+	Publish()
+}
+
+type Success struct {
+	msg string
+}
+
+type Failure struct {
+	msg string
+}
+
+func (s Success) Publish() {
+	fmt.Fprintln(os.Stdout, s.msg)
+}
+
+func (f Failure) Publish() {
+	fmt.Fprintln(os.Stderr, f.msg)
+}

cli/run.go

@@ -20,6 +20,7 @@ func Run(args []string) int {
 	app := &App{ExitValue: exitSuccess}
 	configFile, isDefault := app.ParseFlags(args)
 	wanted := app.Unmarshal(configFile, isDefault)
-	app.MirrorRepos(wanted)
+	results := app.MirrorRepos(wanted)
+	app.DisplayResults(results)
 	return app.ExitValue
 }