Allow no commands for RunnerOf (#62)

acmd.go

@@ -108,6 +108,9 @@ type Config struct {
 	// VerboseHelp if "./app help -v" is passed, default is false.
 	VerboseHelp bool
 
+	// AllowNoCommands set to true will not panic on empty list of commands.
+	AllowNoCommands bool
+
 	_ struct{} // enforce explicit field names.
 }
 
@@ -124,7 +127,7 @@ func HasHelpFlag(flags []string) bool {
 
 // RunnerOf creates a Runner.
 func RunnerOf(cmds []Command, cfg Config) *Runner {
-	if len(cmds) == 0 {
+	if len(cmds) == 0 && !cfg.AllowNoCommands {
 		panic("acmd: cannot run without commands")
 	}
 

acmd_test.go

@@ -155,6 +155,12 @@ func TestRunnerPanicWithoutCommands(t *testing.T) {
 	RunnerOf(nil, Config{})
 }
 
+func TestRunner_AllowNoCommands(t *testing.T) {
+	RunnerOf(nil, Config{
+		AllowNoCommands: true,
+	})
+}
+
 func TestRunnerJustExit(t *testing.T) {
 	var exitDone bool
 	doExitOld := func(_ int) {
@@ -248,15 +254,21 @@ func TestRunnerInit(t *testing.T) {
 			wantErrStr: `duplicate command "a"`,
 		},
 		{
-			cmds:       []Command{{Name: "aaa", ExecFunc: nopFunc}, {Name: "b", Alias: "aaa", ExecFunc: nopFunc}},
+			cmds: []Command{{Name: "aaa", ExecFunc: nopFunc}, {
+				Name: "b", Alias: "aaa", ExecFunc: nopFunc,
+			}},
 			wantErrStr: `duplicate command alias "aaa"`,
 		},
 		{
-			cmds:       []Command{{Name: "aaa", Alias: "a", ExecFunc: nopFunc}, {Name: "bbb", Alias: "a", ExecFunc: nopFunc}},
+			cmds: []Command{{Name: "aaa", Alias: "a", ExecFunc: nopFunc}, {
+				Name: "bbb", Alias: "a", ExecFunc: nopFunc,
+			}},
 			wantErrStr: `duplicate command alias "a"`,
 		},
 		{
-			cmds:       []Command{{Name: "a", ExecFunc: nopFunc}, {Name: "b", Alias: "a", ExecFunc: nopFunc}},
+			cmds: []Command{{Name: "a", ExecFunc: nopFunc}, {
+				Name: "b", Alias: "a", ExecFunc: nopFunc,
+			}},
 			wantErrStr: `duplicate command alias "a"`,
 		},
 	}