Allow to reset the templates to the default (#2229)

Follow-up to #1956.

This commit allows a program to reset any of the tree templates to their
default behaviour, as it was possible to do before the change of #1956.

Signed-off-by: Marc Khouzam <marc.khouzam@gmail.com>

command.go

@@ -315,6 +315,10 @@ func (c *Command) SetUsageFunc(f func(*Command) error) {
 
 // SetUsageTemplate sets usage template. Can be defined by Application.
 func (c *Command) SetUsageTemplate(s string) {
+	if s == "" {
+		c.usageTemplate = nil
+		return
+	}
 	c.usageTemplate = tmpl(s)
 }
 
@@ -351,11 +355,19 @@ func (c *Command) SetCompletionCommandGroupID(groupID string) {
 
 // SetHelpTemplate sets help template to be used. Application can use it to set custom template.
 func (c *Command) SetHelpTemplate(s string) {
+	if s == "" {
+		c.helpTemplate = nil
+		return
+	}
 	c.helpTemplate = tmpl(s)
 }
 
 // SetVersionTemplate sets version template to be used. Application can use it to set custom template.
 func (c *Command) SetVersionTemplate(s string) {
+	if s == "" {
+		c.versionTemplate = nil
+		return
+	}
 	c.versionTemplate = tmpl(s)
 }
 

command_test.go

@@ -1047,6 +1047,18 @@ func TestSetHelpTemplate(t *testing.T) {
 	if got != expected {
 		t.Errorf("Expected %q, got %q", expected, got)
 	}
+
+	// Reset the root command help template and make sure
+	// it falls back to the default
+	rootCmd.SetHelpTemplate("")
+	got, err = executeCommand(rootCmd, "--help")
+	if err != nil {
+		t.Errorf("Unexpected error: %v", err)
+	}
+
+	if !strings.Contains(got, "Usage:") {
+		t.Errorf("Expected to contain %q, got %q", "Usage:", got)
+	}
 }
 
 func TestHelpFlagExecuted(t *testing.T) {
@@ -1139,6 +1151,18 @@ func TestSetUsageTemplate(t *testing.T) {
 
 	expected = "WORKS " + childCmd.UseLine()
 	checkStringContains(t, got, expected)
+
+	// Reset the root command usage template and make sure
+	// it falls back to the default
+	rootCmd.SetUsageTemplate("")
+	got, err = executeCommand(rootCmd, "--invalid")
+	if err == nil {
+		t.Errorf("Expected error but did not get one")
+	}
+
+	if !strings.Contains(got, "Usage:") {
+		t.Errorf("Expected to contain %q, got %q", "Usage:", got)
+	}
 }
 
 func TestVersionFlagExecuted(t *testing.T) {