feat: suggests commands on abbreviation match failure

application.go

@@ -117,7 +117,11 @@ func (a *Application) Run(arguments []string) (err error) {
 	args := context.Args()
 	if args.Present() {
 		name := args.first()
-		context.Command = a.BestCommand(name)
+		context.Command, err = a.BestCommand(name)
+		if err != nil {
+			HandleExitCoder(err)
+			return err
+		}
 	}
 
 	if a.Before != nil {
@@ -175,10 +179,10 @@ func (a *Application) Command(name string) *Command {
 // BestCommand returns the named command on App or a command fuzzy matching if
 // there is only one. Returns nil if the command does not exist of if the fuzzy
 // matching find more than one.
-func (a *Application) BestCommand(name string) *Command {
+func (a *Application) BestCommand(name string) (*Command, error) {
 	name = strings.ToLower(name)
 	if c := a.Command(name); c != nil {
-		return c
+		return c, nil
 	}
 
 	// fuzzy match?
@@ -190,9 +194,15 @@ func (a *Application) BestCommand(name string) *Command {
 	}
 	if len(matches) == 1 {
 		matches[0].UserName = name
-		return matches[0]
+		return matches[0], nil
+	} else if len(matches) > 1 {
+		suggestions := ""
+		for _, m := range matches {
+			suggestions += fmt.Sprintf("\n    %s", m.FullName())
+		}
+		return nil, fmt.Errorf("Command \"%s\" is ambiguous.\nDid you mean one of these?\n%s", name, suggestions)
 	}
-	return nil
+	return nil, nil
 }
 
 // Category returns the named CommandCategory on App. Returns nil if the category does not exist

command_test.go

@@ -124,22 +124,22 @@ func TestCaseInsensitiveCommandNames(t *testing.T) {
 
 	app.setup()
 
-	if c := app.BestCommand("project:list"); c != projectList {
+	if c, _ := app.BestCommand("project:list"); c != projectList {
 		t.Fatalf("expected project:list, got %v", c)
 	}
-	if c := app.BestCommand("Project:lISt"); c != projectList {
+	if c, _ := app.BestCommand("Project:lISt"); c != projectList {
 		t.Fatalf("expected project:list, got %v", c)
 	}
-	if c := app.BestCommand("project:link"); c != projectLink {
+	if c, _ := app.BestCommand("project:link"); c != projectLink {
 		t.Fatalf("expected project:link, got %v", c)
 	}
-	if c := app.BestCommand("project:Link"); c != projectLink {
+	if c, _ := app.BestCommand("project:Link"); c != projectLink {
 		t.Fatalf("expected project:link, got %v", c)
 	}
-	if c := app.BestCommand("foo"); c != projectList {
+	if c, _ := app.BestCommand("foo"); c != projectList {
 		t.Fatalf("expected project:link, got %v", c)
 	}
-	if c := app.BestCommand("FoO"); c != projectList {
+	if c, _ := app.BestCommand("FoO"); c != projectList {
 		t.Fatalf("expected project:link, got %v", c)
 	}
 }
@@ -154,30 +154,36 @@ func TestFuzzyCommandNames(t *testing.T) {
 		projectLink,
 	}
 
-	c := app.BestCommand("project:list")
+	c, _ := app.BestCommand("project:list")
 	if c != projectList {
 		t.Fatalf("expected project:list, got %v", c)
 	}
-	c = app.BestCommand("project:link")
+	c, _ = app.BestCommand("project:link")
 	if c != projectLink {
 		t.Fatalf("expected project:link, got %v", c)
 	}
-	c = app.BestCommand("pro:list")
+	c, _ = app.BestCommand("pro:list")
 	if c != projectList {
 		t.Fatalf("expected project:list, got %v", c)
 	}
-	c = app.BestCommand("pro:lis")
+	c, _ = app.BestCommand("pro:lis")
 	if c != projectList {
 		t.Fatalf("expected project:list, got %v", c)
 	}
-	c = app.BestCommand("p:lis")
+	c, _ = app.BestCommand("p:lis")
 	if c != projectList {
 		t.Fatalf("expected project:list, got %v", c)
 	}
-	c = app.BestCommand("p:li")
+	c, err := app.BestCommand("p:li")
 	if c != nil {
 		t.Fatalf("expected no matches, got %v", c)
 	}
+	if err == nil {
+		t.Fatal("expected an error message, got none")
+	}
+	if !strings.Contains(err.Error(), `Command "p:li" is ambiguous`) {
+		t.Fatalf("error message does not match, got %v", err.Error())
+	}
 }
 
 func TestCommandWithNoNames(t *testing.T) {

help.go

@@ -147,7 +147,7 @@ func ShowAppHelp(c *Context) error {
 
 // ShowCommandHelp prints help for the given command
 func ShowCommandHelp(ctx *Context, command string) error {
-	if c := ctx.App.BestCommand(command); c != nil {
+	if c, _ := ctx.App.BestCommand(command); c != nil {
 		if c.DescriptionFunc != nil {
 			c.Description = c.DescriptionFunc(c, ctx.App)
 		}