Serialize zero values

Removes logic from RustWriter that was used to not serialize
zero values, ie. 0 for numbers and false for booleans, if
that was also the default value for the member. With this change,
the only time the default value for a member is not serialized is
if the member is also `@clientOptional`.

The Blob type was also updated to implement std::Default, since
SymbolVisitor treats `""` as a RustDefault.

It _seems_ like this logic was originally added to fix issues with
[S3](#102) which
are technically modeling issues and have since been fixed.
However, this change impacts all the protocols and will cause
many members to now be sent over the wire that previously weren't.

codegen-core/src/main/kotlin/software/amazon/smithy/rust/codegen/core/smithy/SymbolVisitor.kt

@@ -38,6 +38,7 @@ import software.amazon.smithy.model.shapes.StringShape
 import software.amazon.smithy.model.shapes.StructureShape
 import software.amazon.smithy.model.shapes.TimestampShape
 import software.amazon.smithy.model.shapes.UnionShape
+import software.amazon.smithy.model.traits.ClientOptionalTrait
 import software.amazon.smithy.model.traits.DefaultTrait
 import software.amazon.smithy.model.traits.EnumTrait
 import software.amazon.smithy.model.traits.ErrorTrait
@@ -269,7 +270,9 @@ open class SymbolVisitor(
     override fun memberShape(shape: MemberShape): Symbol {
         val target = model.expectShape(shape.target)
         val defaultValue = shape.getMemberTrait(model, DefaultTrait::class.java).orNull()?.let { trait ->
-            if (target.isDocumentShape || target.isTimestampShape) {
+            if (shape.hasTrait<ClientOptionalTrait>()) {
+                Default.NoDefault
+            } else if (target.isDocumentShape || target.isTimestampShape) {
                 Default.NonZeroDefault(trait.toNode())
             } else {
                 when (val value = trait.toNode()) {

codegen-core/src/main/kotlin/software/amazon/smithy/rust/codegen/core/smithy/protocols/serialize/JsonSerializerGenerator.kt

@@ -178,7 +178,6 @@ class JsonSerializerGenerator(
         "JsonValueWriter" to RuntimeType.smithyJson(runtimeConfig).resolve("serialize::JsonValueWriter"),
         "ByteSlab" to RuntimeType.ByteSlab,
     )
-    private val serializerUtil = SerializerUtil(model)
 
     /**
      * Reusable structure serializer implementation that can be used to generate serializing code for
@@ -378,10 +377,8 @@ class JsonSerializerGenerator(
                 )
             }
 
-            with(serializerUtil) {
-                ignoreZeroValues(context.shape, context.valueExpression) {
-                    serializeMemberValue(context, targetShape)
-                }
+            rustBlock("") {
+                serializeMemberValue(context, targetShape)
             }
         }
     }

codegen-core/src/main/kotlin/software/amazon/smithy/rust/codegen/core/smithy/protocols/serialize/QuerySerializerGenerator.kt

@@ -96,7 +96,6 @@ abstract class QuerySerializerGenerator(private val codegenContext: CodegenConte
     private val serializerError = runtimeConfig.serializationError()
     private val smithyTypes = RuntimeType.smithyTypes(runtimeConfig)
     private val smithyQuery = RuntimeType.smithyQuery(runtimeConfig)
-    private val serdeUtil = SerializerUtil(model)
     private val protocolFunctions = ProtocolFunctions(codegenContext)
     private val codegenScope = arrayOf(
         "String" to RuntimeType.String,
@@ -208,10 +207,8 @@ abstract class QuerySerializerGenerator(private val codegenContext: CodegenConte
                 }
             }
         } else {
-            with(serdeUtil) {
-                ignoreZeroValues(context.shape, context.valueExpression) {
-                    serializeMemberValue(context, targetShape)
-                }
+            rustBlock("") {
+                serializeMemberValue(context, targetShape)
             }
         }
     }

codegen-core/src/main/kotlin/software/amazon/smithy/rust/codegen/core/smithy/protocols/serialize/XmlBindingTraitSerializerGenerator.kt

@@ -73,7 +73,6 @@ class XmlBindingTraitSerializerGenerator(
 
     private val xmlIndex = XmlNameIndex.of(model)
     private val rootNamespace = codegenContext.serviceShape.getTrait<XmlNamespaceTrait>()
-    private val util = SerializerUtil(model)
 
     sealed class Ctx {
         abstract val input: String
@@ -517,15 +516,8 @@ class XmlBindingTraitSerializerGenerator(
                 inner(Ctx.updateInput(ctx, tmp))
             }
         } else {
-            with(util) {
-                val valueExpression = if (ctx.input.startsWith("&")) {
-                    ValueExpression.Reference(ctx.input)
-                } else {
-                    ValueExpression.Value(ctx.input)
-                }
-                ignoreZeroValues(member, valueExpression) {
-                    inner(ctx)
-                }
+            rustBlock("") {
+                inner(ctx)
             }
         }
     }

rust-runtime/aws-smithy-types/src/blob.rs

@@ -31,6 +31,14 @@ impl AsRef<[u8]> for Blob {
     }
 }
 
+impl Default for Blob {
+    fn default() -> Self {
+        Blob {
+            inner: Vec::new()
+        }
+    }
+}
+
 #[cfg(all(aws_sdk_unstable, feature = "serde-serialize"))]
 mod serde_serialize {
     use super::*;