Make app help behavior consistent with commands

help.go

@@ -49,13 +49,16 @@ type helpPrinterCustom func(w io.Writer, templ string, data interface{}, customF
 
 // HelpPrinter is a function that writes the help output. If not set explicitly,
 // this calls HelpPrinterCustom using only the default template functions.
+//
+// If custom logic for printing help is required, this function can be
+// overridden. If the ExtraInfo field is defined on an App, this function
+// should not be modified, as HelpPrinterCustom will be used directly in order
+// to capture the extra information.
 var HelpPrinter helpPrinter = printHelp
 
-// HelpPrinterCustom is a function that writes the help output. If not set
-// explicitly, a default is used.
-//
-// The customFuncs map will be combined with a default template.FuncMap to
-// allow using arbitrary functions in template rendering.
+// HelpPrinterCustom is a function that writes the help output. It is used as
+// the default implementation of HelpPrinter, and may be called directly if
+// the ExtraInfo field is set on an App.
 var HelpPrinterCustom helpPrinterCustom = printHelpCustom
 
 // VersionPrinter prints the version for the App
@@ -68,20 +71,24 @@ func ShowAppHelpAndExit(c *Context, exitCode int) {
 }
 
 // ShowAppHelp is an action that displays the help.
-func ShowAppHelp(c *Context) (err error) {
-	if c.App.CustomAppHelpTemplate == "" {
-		HelpPrinter(c.App.Writer, AppHelpTemplate, c.App)
-		return
+func ShowAppHelp(c *Context) error {
+	template := c.App.CustomAppHelpTemplate
+	if template == "" {
+		template = AppHelpTemplate
+	}
+
+	if c.App.ExtraInfo == nil {
+		HelpPrinter(c.App.Writer, template, c.App)
+		return nil
 	}
+
 	customAppData := func() map[string]interface{} {
-		if c.App.ExtraInfo == nil {
-			return nil
-		}
 		return map[string]interface{}{
 			"ExtraInfo": c.App.ExtraInfo,
 		}
 	}
-	HelpPrinterCustom(c.App.Writer, c.App.CustomAppHelpTemplate, c.App, customAppData())
+	HelpPrinterCustom(c.App.Writer, template, c.App, customAppData())
+
 	return nil
 }
 
@@ -242,6 +249,10 @@ func ShowCommandCompletions(ctx *Context, command string) {
 
 }
 
+// printHelpCustom is the default implementation of HelpPrinterCustom.
+//
+// The customFuncs map will be combined with a default template.FuncMap to
+// allow using arbitrary functions in template rendering.
 func printHelpCustom(out io.Writer, templ string, data interface{}, customFuncs map[string]interface{}) {
 	funcMap := template.FuncMap{
 		"join": strings.Join,

help_test.go

@@ -295,6 +295,7 @@ func TestShowCommandHelp_HelpPrinter(t *testing.T) {
 		})
 	}
 }
+
 func TestShowCommandHelp_HelpPrinterCustom(t *testing.T) {
 	doublecho := func(text string) string {
 		return text + " " + text
@@ -550,6 +551,144 @@ func TestShowAppHelp_HiddenCommand(t *testing.T) {
 	}
 }
 
+func TestShowAppHelp_HelpPrinter(t *testing.T) {
+	doublecho := func(text string) string {
+		return text + " " + text
+	}
+
+	tests := []struct {
+		name         string
+		template     string
+		printer      helpPrinter
+		wantTemplate string
+		wantOutput   string
+	}{
+		{
+			name:     "standard-command",
+			template: "",
+			printer: func(w io.Writer, templ string, data interface{}) {
+				fmt.Fprint(w, "yo")
+			},
+			wantTemplate: AppHelpTemplate,
+			wantOutput:   "yo",
+		},
+		{
+			name:     "custom-template-command",
+			template: "{{doublecho .Name}}",
+			printer: func(w io.Writer, templ string, data interface{}) {
+				// Pass a custom function to ensure it gets used
+				fm := map[string]interface{}{"doublecho": doublecho}
+				printHelpCustom(w, templ, data, fm)
+			},
+			wantTemplate: "{{doublecho .Name}}",
+			wantOutput:   "my-app my-app",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			defer func(old helpPrinter) {
+				HelpPrinter = old
+			}(HelpPrinter)
+			HelpPrinter = func(w io.Writer, templ string, data interface{}) {
+				if templ != tt.wantTemplate {
+					t.Errorf("want template:\n%s\ngot template:\n%s", tt.wantTemplate, templ)
+				}
+
+				tt.printer(w, templ, data)
+			}
+
+			var buf bytes.Buffer
+			app := &App{
+				Name:                  "my-app",
+				Writer:                &buf,
+				CustomAppHelpTemplate: tt.template,
+			}
+
+			err := app.Run([]string{"my-app", "help"})
+			if err != nil {
+				t.Fatal(err)
+			}
+
+			got := buf.String()
+			if got != tt.wantOutput {
+				t.Errorf("want output %q, got %q", tt.wantOutput, got)
+			}
+		})
+	}
+}
+
+func TestShowAppHelp_HelpPrinterCustom(t *testing.T) {
+	doublecho := func(text string) string {
+		return text + " " + text
+	}
+
+	tests := []struct {
+		name         string
+		template     string
+		printer      helpPrinterCustom
+		wantTemplate string
+		wantOutput   string
+	}{
+		{
+			name:     "standard-command",
+			template: "",
+			printer: func(w io.Writer, templ string, data interface{}, fm map[string]interface{}) {
+				fmt.Fprint(w, "yo")
+			},
+			wantTemplate: AppHelpTemplate,
+			wantOutput:   "yo",
+		},
+		{
+			name:     "custom-template-command",
+			template: "{{doublecho .Name}}",
+			printer: func(w io.Writer, templ string, data interface{}, _ map[string]interface{}) {
+				// Pass a custom function to ensure it gets used
+				fm := map[string]interface{}{"doublecho": doublecho}
+				printHelpCustom(w, templ, data, fm)
+			},
+			wantTemplate: "{{doublecho .Name}}",
+			wantOutput:   "my-app my-app",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			defer func(old helpPrinterCustom) {
+				HelpPrinterCustom = old
+			}(HelpPrinterCustom)
+			HelpPrinterCustom = func(w io.Writer, templ string, data interface{}, fm map[string]interface{}) {
+				if fm != nil {
+					t.Error("unexpected function map passed")
+				}
+
+				if templ != tt.wantTemplate {
+					t.Errorf("want template:\n%s\ngot template:\n%s", tt.wantTemplate, templ)
+				}
+
+				tt.printer(w, templ, data, fm)
+			}
+
+			var buf bytes.Buffer
+			app := &App{
+				Name:                  "my-app",
+				Writer:                &buf,
+				CustomAppHelpTemplate: tt.template,
+			}
+
+			err := app.Run([]string{"my-app", "help"})
+			if err != nil {
+				t.Fatal(err)
+			}
+
+			got := buf.String()
+			if got != tt.wantOutput {
+				t.Errorf("want output %q, got %q", tt.wantOutput, got)
+			}
+		})
+	}
+}
+
 func TestShowAppHelp_CustomAppTemplate(t *testing.T) {
 	app := &App{
 		Commands: []Command{