fix(cmd): respect empty SummaryTrendStats value

Resolves: b91229a#r35621359

This changes current behavior on `master`, but as discussed above, it makes
sense to respect whatever the user specifies, so this can be considered a fix.

cmd/config.go

@@ -43,7 +43,6 @@ import (
 	"github.com/loadimpact/k6/stats/influxdb"
 	"github.com/loadimpact/k6/stats/kafka"
 	"github.com/loadimpact/k6/stats/statsd/common"
-	"github.com/loadimpact/k6/ui"
 )
 
 // configFlagSet returns a FlagSet with the default run configuration flags.
@@ -179,8 +178,15 @@ func readEnvConfig() (conf Config, err error) {
 		envconfig.Process("k6", &conf.Collectors.InfluxDB),
 		envconfig.Process("k6", &conf.Collectors.Kafka),
 	} {
+		// TODO(imiric): Remove this workaround once envconfig is updated to >=1.4.0, which
+		// would fix this issue: https://github.com/kelseyhightower/envconfig/pull/119
+		if len(conf.SummaryTrendStats) == 1 && conf.SummaryTrendStats[0] == "" {
+			conf.SummaryTrendStats = []string{}
+		}
+
 		return conf, err
 	}
+
 	return conf, nil
 }
 
@@ -305,16 +311,6 @@ func getConsolidatedConfig(fs afero.Fs, cliConf Config, runner lib.Runner) (conf
 	conf = conf.Apply(envConf).Apply(cliConf)
 	conf = applyDefault(conf)
 
-	// TODO(imiric): Move this validation where it makes sense in the configuration
-	// refactor of #883. Currently we validate CLI flags in cmd.getOptions. Yet
-	// there is no place where configuration is validated after applying all other
-	// sources, like environment variables (besides inline in the runCmd itself...).
-	// So this repeats the trend stats validation in case other sources overrode our
-	// default value.
-	if err = ui.ValidateSummary(conf.SummaryTrendStats); err != nil {
-		return conf, err
-	}
-
 	return conf, nil
 }
 
@@ -326,7 +322,7 @@ func applyDefault(conf Config) Config {
 	if conf.Options.SystemTags == nil {
 		conf = conf.Apply(Config{Options: lib.Options{SystemTags: lib.GetTagSet(lib.DefaultSystemTagList...)}})
 	}
-	if len(conf.Options.SummaryTrendStats) == 0 {
+	if conf.Options.SummaryTrendStats == nil {
 		conf = conf.Apply(Config{Options: lib.Options{SummaryTrendStats: lib.DefaultSummaryTrendStats}})
 	}
 	return conf

cmd/config_consolidation_test.go

@@ -410,7 +410,7 @@ func getConfigConsolidationTestCases() []configConsolidationTestCase {
 			assert.Equal(t, lib.DefaultSummaryTrendStats, c.Options.SummaryTrendStats)
 		}},
 		{opts{cli: []string{"--summary-trend-stats", `""`}}, exp{}, func(t *testing.T, c Config) {
-			assert.Equal(t, lib.DefaultSummaryTrendStats, c.Options.SummaryTrendStats)
+			assert.Equal(t, []string{}, c.Options.SummaryTrendStats)
 		}},
 		{
 			opts{runner: &lib.Options{SummaryTrendStats: []string{"avg", "p(90)", "count"}}},