prevent unparsed flags (#15)

aconfig.go

@@ -2,6 +2,7 @@ package aconfig
 
 import (
 	"encoding/json"
+	"errors"
 	"flag"
 	"fmt"
 	"os"
@@ -41,6 +42,7 @@ type loaderConfig struct {
 	EnvPrefix  string
 	FlagPrefix string
 
+	FailOnNotParsedFlags  bool
 	ShouldStopOnFileError bool
 	Files                 []string
 }
@@ -108,6 +110,14 @@ func (l *Loader) WithEnvPrefix(prefix string) *Loader {
 	return l
 }
 
+// FailOnNotParsedFlags to not forget parse flags explicitly.
+// Use `l.FlagSet().Parse(os.Args[1:])` in your code for this.
+//
+func (l *Loader) FailOnNotParsedFlags() *Loader {
+	l.config.FailOnNotParsedFlags = true
+	return l
+}
+
 // StopOnFileError to stop configuration loading on file error.
 func (l *Loader) StopOnFileError() *Loader {
 	l.config.ShouldStopOnFileError = true
@@ -267,9 +277,10 @@ func (l *Loader) loadEnvironment() error {
 
 func (l *Loader) loadFlags() error {
 	if !l.flagSet.Parsed() {
-		if err := l.flagSet.Parse(os.Args[1:]); err != nil {
-			return err
+		if l.config.FailOnNotParsedFlags {
+			return errors.New("aconfig: flags must be parsed")
 		}
+		return nil
 	}
 
 	actualFlags := map[string]*flag.Flag{}

aconfig_test.go

@@ -397,6 +397,17 @@ func TestBadDefauts(t *testing.T) {
 	}{})
 }
 
+func TestNotParsedFlags(t *testing.T) {
+	loader := LoaderFor(&TestConfig{}).
+		FailOnNotParsedFlags().
+		Build()
+
+	var cfg TestConfig
+	if err := loader.Load(&cfg); err == nil {
+		t.Fatal(err)
+	}
+}
+
 func TestBadFiles(t *testing.T) {
 	f := func(filepath string) {
 		t.Helper()