Fix help text for positional args with default and env var

usage.go

@@ -260,7 +260,7 @@ func (p *Parser) WriteHelpForSubcommand(w io.Writer, subcommand ...string) error
 	if len(positionals) > 0 {
 		fmt.Fprint(w, "\nPositional arguments:\n")
 		for _, spec := range positionals {
-			print(w, spec.placeholder, spec.help)
+			print(w, spec.placeholder, spec.help, withDefault(spec.defaultString), withEnv(spec.env))
 		}
 	}
 

usage_test.go

@@ -1015,3 +1015,72 @@ Commands:
 	p.WriteHelp(&help)
 	assert.Equal(t, expectedHelp[1:], help.String())
 }
+
+func TestHelpShowsPositionalWithDefault(t *testing.T) {
+	expectedHelp := `
+Usage: example [NUMBER]
+
+Positional arguments:
+  NUMBER                 this is a positional with a default [default: foo]
+
+Options:
+  --help, -h             display this help and exit
+`
+
+	var args struct {
+		Number string `arg:"positional" default:"foo" help:"this is a positional with a default"`
+	}
+
+	p, err := NewParser(Config{Program: "example"}, &args)
+	require.NoError(t, err)
+
+	var help bytes.Buffer
+	p.WriteHelp(&help)
+	assert.Equal(t, expectedHelp[1:], help.String())
+}
+
+func TestHelpShowsPositionalWithEnv(t *testing.T) {
+	expectedHelp := `
+Usage: example [NUMBER]
+
+Positional arguments:
+  NUMBER                 this is a positional with an env variable [env: NUMBER]
+
+Options:
+  --help, -h             display this help and exit
+`
+
+	var args struct {
+		Number string `arg:"positional,env:NUMBER" help:"this is a positional with an env variable"`
+	}
+
+	p, err := NewParser(Config{Program: "example"}, &args)
+	require.NoError(t, err)
+
+	var help bytes.Buffer
+	p.WriteHelp(&help)
+	assert.Equal(t, expectedHelp[1:], help.String())
+}
+
+func TestHelpShowsPositionalWithDefaultAndEnv(t *testing.T) {
+	expectedHelp := `
+Usage: example [NUMBER]
+
+Positional arguments:
+  NUMBER                 this is a positional with a default and an env variable [default: foo, env: NUMBER]
+
+Options:
+  --help, -h             display this help and exit
+`
+
+	var args struct {
+		Number string `arg:"positional,env:NUMBER" default:"foo" help:"this is a positional with a default and an env variable"`
+	}
+
+	p, err := NewParser(Config{Program: "example"}, &args)
+	require.NoError(t, err)
+
+	var help bytes.Buffer
+	p.WriteHelp(&help)
+	assert.Equal(t, expectedHelp[1:], help.String())
+}