config: Return error from optFns in LoadDefaultConfig (aws#1562)

Adds handling of return error in LoadDefaultConfig when processing functional options for LoadOptions.

.changelog/450d4ca924cb43e1aaa66310a96b90d1.json

@@ -0,0 +1,8 @@
+{
+    "id": "450d4ca9-24cb-43e1-aaa6-6310a96b90d1",
+    "type": "bugfix",
+    "description": "Fixes LoadDefaultConfig handling of errors returned by passed in functional options. Previously errors returned from the LoadOptions passed into LoadDefaultConfig were incorrectly ignored. [#1562](https://github.com/aws/aws-sdk-go-v2/pull/1562). Thanks to [Pinglei Guo](https://github.com/pingleig) for submitting this PR.",
+    "modules": [
+        "config"
+    ]
+}

config/config.go

@@ -181,7 +181,9 @@ func (cs configs) ResolveConfig(f func(configs []interface{}) error) error {
 func LoadDefaultConfig(ctx context.Context, optFns ...func(*LoadOptions) error) (cfg aws.Config, err error) {
 	var options LoadOptions
 	for _, optFn := range optFns {
-		optFn(&options)
+		if err := optFn(&options); err != nil {
+			return aws.Config{}, err
+		}
 	}
 
 	// assign Load Options to configs

config/config_test.go

@@ -2,6 +2,7 @@ package config
 
 import (
 	"context"
+	"fmt"
 	"testing"
 
 	"github.com/aws/aws-sdk-go-v2/aws"
@@ -135,3 +136,13 @@ func TestConfigs_ResolveAWSConfig(t *testing.T) {
 		t.Errorf("expect config sources match, got diff: \n %s", diff)
 	}
 }
+
+func TestLoadDefaultConfig(t *testing.T) {
+	optWithErr := func(_ *LoadOptions) error {
+		return fmt.Errorf("some error")
+	}
+	_, err := LoadDefaultConfig(context.TODO(), optWithErr)
+	if err == nil {
+		t.Fatal("expect error when optFn returns error, got nil")
+	}
+}