config: return error on extra command line arguments (#3397)

agent/config/builder.go

@@ -79,6 +79,12 @@ type Builder struct {
 // NewBuilder returns a new configuration builder based on the given command
 // line flags.
 func NewBuilder(flags Flags) (*Builder, error) {
+	// We expect all flags to be parsed and flags.Args to be empty.
+	// Therefore, we bail if we find unparsed args.
+	if len(flags.Args) > 0 {
+		return nil, fmt.Errorf("config: Unknown extra arguments: %v", flags.Args)
+	}
+
 	newSource := func(name string, v interface{}) Source {
 		b, err := json.MarshalIndent(v, "", "    ")
 		if err != nil {

agent/config/flags.go

@@ -22,17 +22,9 @@ type Flags struct {
 
 	// HCL contains an arbitrary config in hcl format.
 	HCL []string
-}
 
-// ParseFlag parses the arguments into a Flags struct.
-func ParseFlags(args []string) (Flags, error) {
-	var f Flags
-	fs := flag.NewFlagSet("agent", flag.ContinueOnError)
-	AddFlags(fs, &f)
-	if err := fs.Parse(args); err != nil {
-		return Flags{}, err
-	}
-	return f, nil
+	// Args contains the remaining unparsed flags.
+	Args []string
 }
 
 // AddFlags adds the command line flags for the agent.

agent/config/flags_test.go

@@ -1,6 +1,7 @@
 package config
 
 import (
+	"flag"
 	"reflect"
 	"strings"
 	"testing"
@@ -35,10 +36,6 @@ func TestParseFlags(t *testing.T) {
 			args:  []string{`-bootstrap=false`},
 			flags: Flags{Config: Config{Bootstrap: pBool(false)}},
 		},
-		{
-			args:  []string{`-bootstrap`, `true`},
-			flags: Flags{Config: Config{Bootstrap: pBool(true)}},
-		},
 		{
 			args:  []string{`-config-file`, `a`, `-config-dir`, `b`, `-config-file`, `c`, `-config-dir`, `d`},
 			flags: Flags{ConfigFiles: []string{"a", "b", "c", "d"}},
@@ -59,14 +56,22 @@ func TestParseFlags(t *testing.T) {
 			args:  []string{`-node-meta`, `a:b`, `-node-meta`, `c:d`},
 			flags: Flags{Config: Config{NodeMeta: map[string]string{"a": "b", "c": "d"}}},
 		},
+		{
+			args:  []string{`-bootstrap`, `true`},
+			flags: Flags{Config: Config{Bootstrap: pBool(true)}, Args: []string{"true"}},
+		},
 	}
 
 	for _, tt := range tests {
 		t.Run(strings.Join(tt.args, " "), func(t *testing.T) {
-			flags, err := ParseFlags(tt.args)
+			flags := Flags{}
+			fs := flag.NewFlagSet("", flag.ContinueOnError)
+			AddFlags(fs, &flags)
+			err := fs.Parse(tt.args)
 			if got, want := err, tt.err; !reflect.DeepEqual(got, want) {
 				t.Fatalf("got error %v want %v", got, want)
 			}
+			flags.Args = fs.Args()
 			if !verify.Values(t, "flag", flags, tt.flags) {
 				t.FailNow()
 			}