Use usage template in subcommand help

to remove (confusing) difference between templates.

Closes #1879

Author: meatballhat

app_test.go

@@ -2047,7 +2047,7 @@ func TestApp_Run_CommandSubcommandHelpName(t *testing.T) {
 		t.Errorf("expected %q in output: %q", expected, output)
 	}
 
-	expected = "base foo command [command options] [arguments...]"
+	expected = "base foo [command options] [arguments...]"
 	if !strings.Contains(output, expected) {
 		t.Errorf("expected %q in output: %q", expected, output)
 	}

godoc-current.txt

@@ -136,7 +136,10 @@ var SubcommandHelpTemplate = `NAME:
    {{template "helpNameTemplate" .}}
 
 USAGE:
-   {{if .UsageText}}{{wrap .UsageText 3}}{{else}}{{.HelpName}} {{if .VisibleFlags}}command [command options]{{end}}{{if .ArgsUsage}} {{.ArgsUsage}}{{else}}{{if .Args}} [arguments...]{{end}}{{end}}{{end}}{{if .Description}}
+   {{template "usageTemplate" .}}{{if .Category}}
+
+CATEGORY:
+   {{.Category}}{{end}}{{if .Description}}
 
 DESCRIPTION:
    {{template "descriptionTemplate" .}}{{end}}{{if .VisibleCommands}}

help.go

@@ -54,7 +54,7 @@ var helpCommand = &Command{
 			cCtx = cCtx.parentContext
 		}
 
-		// Case 4. $ app hello foo
+		// Case 4. $ app help foo
 		// foo is the command for which help needs to be shown
 		if argsPresent {
 			return ShowCommandHelp(cCtx, firstArg)

template.go

@@ -83,7 +83,10 @@ var SubcommandHelpTemplate = `NAME:
    {{template "helpNameTemplate" .}}
 
 USAGE:
-   {{if .UsageText}}{{wrap .UsageText 3}}{{else}}{{.HelpName}} {{if .VisibleFlags}}command [command options]{{end}}{{if .ArgsUsage}} {{.ArgsUsage}}{{else}}{{if .Args}} [arguments...]{{end}}{{end}}{{end}}{{if .Description}}
+   {{template "usageTemplate" .}}{{if .Category}}
+
+CATEGORY:
+   {{.Category}}{{end}}{{if .Description}}
 
 DESCRIPTION:
    {{template "descriptionTemplate" .}}{{end}}{{if .VisibleCommands}}

testdata/godoc-v2.x.txt

@@ -35,7 +35,7 @@ var AppHelpTemplate = `NAME:
    {{template "helpNameTemplate" .}}
 
 USAGE:
-   {{if .UsageText}}{{wrap .UsageText 3}}{{else}}{{.HelpName}} {{if .VisibleFlags}}[global options]{{end}}{{if .Commands}} command [command options]{{end}} {{if .ArgsUsage}}{{.ArgsUsage}}{{else}}{{if .Args}}[arguments...]{{end}}{{end}}{{end}}{{if .Version}}{{if not .HideVersion}}
+   {{if .UsageText}}{{wrap .UsageText 3}}{{else}}{{.HelpName}} {{if .VisibleFlags}}[global options]{{end}}{{if .Commands}} command [command options]{{end}}{{if .ArgsUsage}} {{.ArgsUsage}}{{else}}{{if .Args}} [arguments...]{{end}}{{end}}{{end}}{{if .Version}}{{if not .HideVersion}}
 
 VERSION:
    {{.Version}}{{end}}{{end}}{{if .Description}}
@@ -136,7 +136,10 @@ var SubcommandHelpTemplate = `NAME:
    {{template "helpNameTemplate" .}}
 
 USAGE:
-   {{if .UsageText}}{{wrap .UsageText 3}}{{else}}{{.HelpName}} {{if .VisibleFlags}}command [command options]{{end}} {{if .ArgsUsage}}{{.ArgsUsage}}{{else}}{{if .Args}}[arguments...]{{end}}{{end}}{{end}}{{if .Description}}
+   {{template "usageTemplate" .}}{{if .Category}}
+
+CATEGORY:
+   {{.Category}}{{end}}{{if .Description}}
 
 DESCRIPTION:
    {{template "descriptionTemplate" .}}{{end}}{{if .VisibleCommands}}