Upgrade smithy to 1.27.2, correct query empty list serialization

.changelog/c3a62c73ab624737a829d8c85167835e.json

@@ -0,0 +1,31 @@
+{
+    "id": "c3a62c73-ab62-4737-a829-d8c85167835e",
+    "type": "dependency",
+    "description": "Upgrade smithy to 1.27.2 and correct empty query list serialization.",
+    "modules": [
+        "internal/protocoltest/awsrestjson",
+        "internal/protocoltest/ec2query",
+        "internal/protocoltest/jsonrpc",
+        "internal/protocoltest/jsonrpc10",
+        "internal/protocoltest/query",
+        "internal/protocoltest/restxml",
+        "service/autoscaling",
+        "service/cloudformation",
+        "service/cloudsearch",
+        "service/cloudwatch",
+        "service/docdb",
+        "service/ec2",
+        "service/elasticache",
+        "service/elasticbeanstalk",
+        "service/elasticloadbalancing",
+        "service/elasticloadbalancingv2",
+        "service/iam",
+        "service/neptune",
+        "service/rds",
+        "service/redshift",
+        "service/ses",
+        "service/sns",
+        "service/sqs",
+        "service/sts"
+    ]
+}

aws/protocol/query/array.go

@@ -36,20 +36,31 @@ type Array struct {
 	memberName string
 	// Elements are stored in values, so we keep track of the list size here.
 	size int32
+	// Empty lists are encoded as "<prefix>=", if we add a value later we will
+	// remove this encoding
+	emptyValue Value
 }
 
 func newArray(values url.Values, prefix string, flat bool, memberName string) *Array {
+	emptyValue := newValue(values, prefix, flat)
+	emptyValue.String("")
+
 	return &Array{
 		values:     values,
 		prefix:     prefix,
 		flat:       flat,
 		memberName: memberName,
+		emptyValue: emptyValue,
 	}
 }
 
 // Value adds a new element to the Query Array. Returns a Value type used to
 // encode the array element.
 func (a *Array) Value() Value {
+	if a.size == 0 {
+		delete(a.values, a.emptyValue.key)
+	}
+
 	// Query lists start a 1, so adjust the size first
 	a.size++
 	prefix := a.prefix

aws/protocol/query/encoder_test.go

@@ -3,8 +3,9 @@ package query
 import (
 	"bytes"
 	"fmt"
-	smithytesting "github.com/aws/smithy-go/testing"
 	"testing"
+
+	smithytesting "github.com/aws/smithy-go/testing"
 )
 
 func TestEncode(t *testing.T) {
@@ -35,6 +36,13 @@ func TestEncode(t *testing.T) {
 			},
 			Expect: []byte(`list.spam.1=spam&list.spam.2=eggs`),
 		},
+		"empty list": {
+			Encode: func(e *Encoder) error {
+				e.Object().Key("list").Array("spam")
+				return e.Encode()
+			},
+			Expect: []byte(`list=`),
+		},
 		"flat list": {
 			Encode: func(e *Encoder) error {
 				list := e.Object().FlatKey("list").Array("spam")
@@ -44,6 +52,13 @@ func TestEncode(t *testing.T) {
 			},
 			Expect: []byte(`list.1=spam&list.2=eggs`),
 		},
+		"empty flat list": {
+			Encode: func(e *Encoder) error {
+				e.Object().FlatKey("list").Array("spam")
+				return e.Encode()
+			},
+			Expect: []byte(`list=`),
+		},
 		"map": {
 			Encode: func(e *Encoder) error {
 				mapValue := e.Object().Key("map").Map("key", "value")

codegen/gradle.properties

@@ -1,2 +1,2 @@
-smithyVersion=1.25.2
+smithyVersion=1.27.2
 smithyGradleVersion=0.6.0

codegen/smithy-aws-go-codegen/src/main/java/software/amazon/smithy/aws/go/codegen/QueryShapeSerVisitor.java

@@ -75,9 +75,6 @@ protected void serializeCollection(GenerationContext context, CollectionShape sh
         MemberShape member = shape.getMember();
         Shape target = context.getModel().expectShape(member.getTarget());
 
-        // If the list is empty, exit early to avoid extra effort.
-        writer.write("if len(v) == 0 { return nil }");
-
         writer.write("array := value.Array($S)", getSerializedLocationName(member, "member"));
         writer.write("");