Extract builderInstantiator interface to prepare for nullability chan…

…ges (#2988)

## Motivation and Context
#1725 exposed the need for easily configuring builder behavior between
client & server

## Description
- extract builderGenerator interface and attach it to `codegenContext`
to avoid loads of threading it up and down

## Testing
- codegen unit tests
- [x] codegen diff audit

## Checklist
<!--- If a checkbox below is not applicable, then please DELETE it
rather than leaving it unchecked -->
- [x] I have updated `CHANGELOG.next.toml` if I made changes to the
smithy-rs codegen or runtime crates
- [x] I have updated `CHANGELOG.next.toml` if I made changes to the AWS
SDK, generated SDK code, or SDK runtime crates

----

_By submitting this pull request, I confirm that you can use, modify,
copy, and redistribute this contribution, under the terms of your
choice._

codegen-client/src/main/kotlin/software/amazon/smithy/rust/codegen/client/smithy/ClientCodegenContext.kt

@@ -9,10 +9,12 @@ import software.amazon.smithy.model.Model
 import software.amazon.smithy.model.shapes.ServiceShape
 import software.amazon.smithy.model.shapes.ShapeId
 import software.amazon.smithy.rust.codegen.client.smithy.customize.ClientCodegenDecorator
+import software.amazon.smithy.rust.codegen.client.smithy.generators.ClientBuilderInstantiator
 import software.amazon.smithy.rust.codegen.core.smithy.CodegenContext
 import software.amazon.smithy.rust.codegen.core.smithy.CodegenTarget
 import software.amazon.smithy.rust.codegen.core.smithy.ModuleDocProvider
 import software.amazon.smithy.rust.codegen.core.smithy.RustSymbolProvider
+import software.amazon.smithy.rust.codegen.core.smithy.generators.BuilderInstantiator
 import software.amazon.smithy.rust.codegen.core.smithy.protocols.Protocol
 
 /**
@@ -36,4 +38,7 @@ data class ClientCodegenContext(
     model, symbolProvider, moduleDocProvider, serviceShape, protocol, settings, CodegenTarget.CLIENT,
 ) {
     val enableUserConfigurableRuntimePlugins: Boolean get() = settings.codegenConfig.enableUserConfigurableRuntimePlugins
+    override fun builderInstantiator(): BuilderInstantiator {
+        return ClientBuilderInstantiator(symbolProvider)
+    }
 }

codegen-client/src/main/kotlin/software/amazon/smithy/rust/codegen/client/smithy/generators/ClientBuilderInstantiator.kt

@@ -0,0 +1,41 @@
+/*
+ * Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package software.amazon.smithy.rust.codegen.client.smithy.generators
+
+import software.amazon.smithy.model.shapes.MemberShape
+import software.amazon.smithy.model.shapes.StructureShape
+import software.amazon.smithy.rust.codegen.client.smithy.ClientCodegenContext
+import software.amazon.smithy.rust.codegen.core.rustlang.Writable
+import software.amazon.smithy.rust.codegen.core.rustlang.map
+import software.amazon.smithy.rust.codegen.core.rustlang.rust
+import software.amazon.smithy.rust.codegen.core.rustlang.rustTemplate
+import software.amazon.smithy.rust.codegen.core.rustlang.writable
+import software.amazon.smithy.rust.codegen.core.smithy.RustSymbolProvider
+import software.amazon.smithy.rust.codegen.core.smithy.generators.BuilderGenerator
+import software.amazon.smithy.rust.codegen.core.smithy.generators.BuilderInstantiator
+
+fun ClientCodegenContext.builderInstantiator(): BuilderInstantiator = ClientBuilderInstantiator(symbolProvider)
+
+class ClientBuilderInstantiator(private val symbolProvider: RustSymbolProvider) : BuilderInstantiator {
+    override fun setField(builder: String, value: Writable, field: MemberShape): Writable {
+        return setFieldWithSetter(builder, value, field)
+    }
+
+    override fun finalizeBuilder(builder: String, shape: StructureShape, mapErr: Writable?): Writable = writable {
+        if (BuilderGenerator.hasFallibleBuilder(shape, symbolProvider)) {
+            rustTemplate(
+                "$builder.build()#{mapErr}?",
+                "mapErr" to (
+                    mapErr?.map {
+                        rust(".map_err(#T)", it)
+                    } ?: writable { }
+                    ),
+            )
+        } else {
+            rust("$builder.build()")
+        }
+    }
+}

codegen-client/src/main/kotlin/software/amazon/smithy/rust/codegen/client/smithy/protocols/ClientProtocolLoader.kt

@@ -63,9 +63,9 @@ private class ClientAwsJsonFactory(private val version: AwsJsonVersion) :
     ProtocolGeneratorFactory<OperationGenerator, ClientCodegenContext> {
     override fun protocol(codegenContext: ClientCodegenContext): Protocol =
         if (compatibleWithAwsQuery(codegenContext.serviceShape, version)) {
-            AwsQueryCompatible(codegenContext, AwsJson(codegenContext, version))
+            AwsQueryCompatible(codegenContext, AwsJson(codegenContext, version, codegenContext.builderInstantiator()))
         } else {
-            AwsJson(codegenContext, version)
+            AwsJson(codegenContext, version, codegenContext.builderInstantiator())
         }
 
     override fun buildProtocolGenerator(codegenContext: ClientCodegenContext): OperationGenerator =

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

@@ -8,6 +8,7 @@ package software.amazon.smithy.rust.codegen.core.smithy
 import software.amazon.smithy.model.Model
 import software.amazon.smithy.model.shapes.ServiceShape
 import software.amazon.smithy.model.shapes.ShapeId
+import software.amazon.smithy.rust.codegen.core.smithy.generators.BuilderInstantiator
 
 /**
  * [CodegenContext] contains code-generation context that is _common to all_  smithy-rs plugins.
@@ -17,7 +18,7 @@ import software.amazon.smithy.model.shapes.ShapeId
  * If your data is specific to the `rust-client-codegen` client plugin, put it in [ClientCodegenContext] instead.
  * If your data is specific to the `rust-server-codegen` server plugin, put it in [ServerCodegenContext] instead.
  */
-open class CodegenContext(
+abstract class CodegenContext(
     /**
      * The smithy model.
      *
@@ -89,4 +90,6 @@ open class CodegenContext(
     fun expectModuleDocProvider(): ModuleDocProvider = checkNotNull(moduleDocProvider) {
         "A ModuleDocProvider must be set on the CodegenContext"
     }
+
+    abstract fun builderInstantiator(): BuilderInstantiator
 }

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

@@ -0,0 +1,32 @@
+/*
+ * Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package software.amazon.smithy.rust.codegen.core.smithy.generators
+
+import software.amazon.smithy.model.shapes.MemberShape
+import software.amazon.smithy.model.shapes.StructureShape
+import software.amazon.smithy.rust.codegen.core.rustlang.Writable
+import software.amazon.smithy.rust.codegen.core.rustlang.rustTemplate
+import software.amazon.smithy.rust.codegen.core.rustlang.writable
+
+/** Abstraction for instantiating builders.
+ *
+ * Builder abstractions vary—clients MAY use `build_with_error_correction`, e.g., and builders can vary in fallibility.
+ * */
+interface BuilderInstantiator {
+    /** Set a field on a builder. */
+    fun setField(builder: String, value: Writable, field: MemberShape): Writable
+
+    /** Finalize a builder, turning it into a built object
+     *  - In the case of builders-of-builders, the value should be returned directly
+     *  - If an error is returned, you MUST use `mapErr` to convert the error type
+     */
+    fun finalizeBuilder(builder: String, shape: StructureShape, mapErr: Writable? = null): Writable
+
+    /** Set a field on a builder using the `$setterName` method. $value will be passed directly. */
+    fun setFieldWithSetter(builder: String, value: Writable, field: MemberShape) = writable {
+        rustTemplate("$builder = $builder.${field.setterName()}(#{value})", "value" to value)
+    }
+}

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

@@ -18,6 +18,7 @@ import software.amazon.smithy.rust.codegen.core.rustlang.rustBlockTemplate
 import software.amazon.smithy.rust.codegen.core.rustlang.rustTemplate
 import software.amazon.smithy.rust.codegen.core.smithy.CodegenContext
 import software.amazon.smithy.rust.codegen.core.smithy.RuntimeType
+import software.amazon.smithy.rust.codegen.core.smithy.generators.BuilderInstantiator
 import software.amazon.smithy.rust.codegen.core.smithy.generators.serializationError
 import software.amazon.smithy.rust.codegen.core.smithy.protocols.parse.JsonParserGenerator
 import software.amazon.smithy.rust.codegen.core.smithy.protocols.parse.StructuredDataParserGenerator
@@ -122,6 +123,7 @@ class AwsJsonSerializerGenerator(
 open class AwsJson(
     val codegenContext: CodegenContext,
     val awsJsonVersion: AwsJsonVersion,
+    val builderInstantiator: BuilderInstantiator,
 ) : Protocol {
     private val runtimeConfig = codegenContext.runtimeConfig
     private val errorScope = arrayOf(

codegen-core/src/main/kotlin/software/amazon/smithy/rust/codegen/core/smithy/protocols/parse/EventStreamUnmarshallerGenerator.kt

@@ -53,6 +53,7 @@ class EventStreamUnmarshallerGenerator(
     private val unionShape: UnionShape,
 ) {
     private val model = codegenContext.model
+    private val builderInstantiator = codegenContext.builderInstantiator()
     private val symbolProvider = codegenContext.symbolProvider
     private val codegenTarget = codegenContext.target
     private val runtimeConfig = codegenContext.runtimeConfig
@@ -339,6 +340,7 @@ class EventStreamUnmarshallerGenerator(
                     // TODO(EventStream): Errors on the operation can be disjoint with errors in the union,
                     //  so we need to generate a new top-level Error type for each event stream union.
                     when (codegenTarget) {
+                        // TODO(https://github.com/awslabs/smithy-rs/issues/1970) It should be possible to unify these branches now
                         CodegenTarget.CLIENT -> {
                             val target = model.expectShape(member.target, StructureShape::class.java)
                             val parser = protocol.structuredDataParser().errorParser(target)
@@ -352,9 +354,19 @@ class EventStreamUnmarshallerGenerator(
                                         })?;
                                     builder.set_meta(Some(generic));
                                     return Ok(#{UnmarshalledMessage}::Error(
-                                        #{OpError}::${member.target.name}(builder.build())
+                                        #{OpError}::${member.target.name}(
+                                            #{build}
+                                        )
                                     ))
                                     """,
+                                    "build" to builderInstantiator.finalizeBuilder(
+                                        "builder", target,
+                                        mapErr = {
+                                            rustTemplate(
+                                                """|err|#{Error}::unmarshalling(format!("{}", err))""", *codegenScope,
+                                            )
+                                        },
+                                    ),
                                     "parser" to parser,
                                     *codegenScope,
                                 )

codegen-core/src/main/kotlin/software/amazon/smithy/rust/codegen/core/smithy/protocols/parse/JsonParserGenerator.kt

@@ -59,13 +59,16 @@ import software.amazon.smithy.utils.StringUtils
  * Class describing a JSON parser section that can be used in a customization.
  */
 sealed class JsonParserSection(name: String) : Section(name) {
-    data class BeforeBoxingDeserializedMember(val shape: MemberShape) : JsonParserSection("BeforeBoxingDeserializedMember")
+    data class BeforeBoxingDeserializedMember(val shape: MemberShape) :
+        JsonParserSection("BeforeBoxingDeserializedMember")
 
-    data class AfterTimestampDeserializedMember(val shape: MemberShape) : JsonParserSection("AfterTimestampDeserializedMember")
+    data class AfterTimestampDeserializedMember(val shape: MemberShape) :
+        JsonParserSection("AfterTimestampDeserializedMember")
 
     data class AfterBlobDeserializedMember(val shape: MemberShape) : JsonParserSection("AfterBlobDeserializedMember")
 
-    data class AfterDocumentDeserializedMember(val shape: MemberShape) : JsonParserSection("AfterDocumentDeserializedMember")
+    data class AfterDocumentDeserializedMember(val shape: MemberShape) :
+        JsonParserSection("AfterDocumentDeserializedMember")
 }
 
 /**
@@ -100,6 +103,7 @@ class JsonParserGenerator(
     private val codegenTarget = codegenContext.target
     private val smithyJson = CargoDependency.smithyJson(runtimeConfig).toType()
     private val protocolFunctions = ProtocolFunctions(codegenContext)
+    private val builderInstantiator = codegenContext.builderInstantiator()
     private val codegenScope = arrayOf(
         "Error" to smithyJson.resolve("deserialize::error::DeserializeError"),
         "expect_blob_or_null" to smithyJson.resolve("deserialize::token::expect_blob_or_null"),
@@ -251,6 +255,7 @@ class JsonParserGenerator(
                                     deserializeMember(member)
                                 }
                             }
+
                             CodegenTarget.SERVER -> {
                                 if (symbolProvider.toSymbol(member).isOptional()) {
                                     withBlock("builder = builder.${member.setterName()}(", ");") {
@@ -508,12 +513,14 @@ class JsonParserGenerator(
                         "Builder" to symbolProvider.symbolForBuilder(shape),
                     )
                     deserializeStructInner(shape.members())
-                    // Only call `build()` if the builder is not fallible. Otherwise, return the builder.
-                    if (returnSymbolToParse.isUnconstrained) {
-                        rust("Ok(Some(builder))")
-                    } else {
-                        rust("Ok(Some(builder.build()))")
+                    val builder = builderInstantiator.finalizeBuilder(
+                        "builder", shape,
+                    ) {
+                        rustTemplate(
+                            """|err|#{Error}::custom_source("Response was invalid", err)""", *codegenScope,
+                        )
                     }
+                    rust("Ok(Some(#T))", builder)
                 }
             }
         }