feat: Throw on unknown key error

indexer/config/config.go

@@ -153,11 +153,18 @@ func LoadConfig(log log.Logger, path string) (Config, error) {
 	data = []byte(os.ExpandEnv(string(data)))
 	log.Debug("parsed config file", "data", string(data))
 
-	if _, err := toml.Decode(string(data), &cfg); err != nil {
+	md, err := toml.Decode(string(data), &cfg)
+	if err != nil {
 		log.Error("failed to decode config file", "err", err)
 		return cfg, err
 	}
 
+	if len(md.Undecoded()) > 0 {
+		log.Error("unknown fields in config file", "fields", md.Undecoded())
+		err = fmt.Errorf("unknown fields in config file: %v", md.Undecoded())
+		return cfg, err
+	}
+
 	if cfg.Chain.Preset == DevnetPresetId {
 		preset, err := DevnetPreset()
 		if err != nil {

indexer/config/config_test.go

@@ -257,3 +257,49 @@ func TestLocalDevnet(t *testing.T) {
 
 	require.Equal(t, devnetPreset.ChainConfig.L1Contracts, conf.Chain.L1Contracts)
 }
+
+func TestThrowsOnUnknownKeys(t *testing.T) {
+	logger := testlog.Logger(t, log.LvlInfo)
+	tmpfile, err := os.CreateTemp("", "test.toml")
+	require.NoError(t, err)
+	defer os.Remove(tmpfile.Name())
+	defer tmpfile.Close()
+
+	testData := `
+		[chain]
+    unknown_key = 420
+		preset = 420
+
+		[rpcs]
+		l1-rpc = "https://l1.example.com"
+		l2-rpc = "https://l2.example.com"
+
+		[db]
+	  another_unknownKey = 420
+		host = "127.0.0.1"
+		port = 5432
+		user = "postgres"
+		password = "postgres"
+	    name = "indexer"
+
+		[http]
+		host = "127.0.0.1"
+		port = 8080
+
+		[metrics]
+		host = "127.0.0.1"
+		port = 7300
+	`
+
+	data := []byte(testData)
+	err = os.WriteFile(tmpfile.Name(), data, 0644)
+	require.NoError(t, err)
+	defer os.Remove(tmpfile.Name())
+
+	err = tmpfile.Close()
+	require.NoError(t, err)
+
+	_, err = LoadConfig(logger, tmpfile.Name())
+	require.Error(t, err)
+	require.Contains(t, err.Error(), "unknown fields in config file")
+}