Builders of builders

CHANGELOG.next.toml

@@ -92,3 +92,127 @@ references = ["smithy-rs#1935"]
 meta = { "breaking" = true, "tada" = false, "bug" = false }
 author = "jdisanti"
 
+[[smithy-rs]]
+message = """
+[Constraint traits](https://awslabs.github.io/smithy/2.0/spec/constraint-traits.html) in server SDKs are beginning to be supported. The following are now supported:
+
+* The `length` trait on `string` shapes.
+* The `length` trait on `map` shapes.
+
+Upon receiving a request that violates the modeled constraints, the server SDK will reject it with a message indicating why.
+
+Unsupported (constraint trait, target shape) combinations will now fail at code generation time, whereas previously they were just ignored. This is a breaking change to raise awareness in service owners of their server SDKs behaving differently than what was modeled. To continue generating a server SDK with unsupported constraint traits, set `codegenConfig.ignoreUnsupportedConstraints` to `true` in your `smithy-build.json`.
+"""
+references = ["smithy-rs#1199", "smithy-rs#1342", "smithy-rs#1401"]
+meta = { "breaking" = true, "tada" = true, "bug" = false, "target" = "server" }
+author = "david-perez"
+
+[[smithy-rs]]
+message = """
+Server SDKs now generate "constrained types" for constrained shapes. Constrained types are [newtypes](https://rust-unofficial.github.io/patterns/patterns/behavioural/newtype.html) that encapsulate the modeled constraints. They constitute a [widespread pattern to guarantee domain invariants](https://www.lpalmieri.com/posts/2020-12-11-zero-to-production-6-domain-modelling/) and promote correctness in your business logic. So, for example, the model:
+
+```smithy
+@length(min: 1, max: 69)
+string NiceString
+```
+
+will now render a `struct NiceString(String)`. Instantiating a `NiceString` is a fallible operation:
+
+```rust
+let data: String = ... ;
+let nice_string = NiceString::try_from(data).expect("data is not nice");
+```
+
+A failed attempt to instantiate a constrained type will yield a `ConstraintViolation` error type you may want to handle. This type's API is subject to change.
+
+Constrained types _guarantee_, by virtue of the type system, that your service's operation outputs adhere to the modeled constraints. To learn more about the motivation for constrained types and how they work, see [the RFC](https://github.com/awslabs/smithy-rs/pull/1199).
+
+If you'd like to opt-out of generating constrained types, you can set `codegenConfig.publicConstrainedTypes` to `false`. Note that if you do, the generated server SDK will still honor your operation input's modeled constraints upon receiving a request, but will not help you in writing business logic code that adheres to the constraints, and _will not prevent you from returning responses containing operation outputs that violate said constraints_.
+"""
+references = ["smithy-rs#1342", "smithy-rs#1119"]
+meta = { "breaking" = true, "tada" = true, "bug" = false, "target" = "server" }
+author = "david-perez"
+
+[[smithy-rs]]
+message = """
+Structure builders in server SDKs have undergone significant changes.
+
+The API surface has been reduced. It is now simpler and closely follows what you would get when using the [`derive_builder`](https://docs.rs/derive_builder/latest/derive_builder/) crate:
+
+1. Builders no longer have `set_*` methods taking in `Option<T>`. You must use the unprefixed method, named exactly after the structure's field name, and taking in a value _whose type matches exactly that of the structure's field_.
+2. Builders no longer have convenience methods to pass in an element for a field whose type is a vector or a map. You must pass in the entire contents of the collection up front.
+3. Builders no longer implement [`PartialEq`](https://doc.rust-lang.org/std/cmp/trait.PartialEq.html).
+
+Bug fixes:
+
+4. Builders now always fail to build if a value for a `required` member is not provided. Previously, builders were falling back to a default value (e.g. `""` for `String`s) for some shapes. This was a bug.
+
+Additions:
+
+5. A structure `Structure` with builder `Builder` now implements `TryFrom<Builder> for Structure` or `From<Builder> for Structure`, depending on whether the structure [is constrained](https://awslabs.github.io/smithy/2.0/spec/constraint-traits.html) or not, respectively.
+
+To illustrate how to migrate to the new API, consider the example model below.
+
+```smithy
+structure Pokemon {
+    @required
+    name: String,
+    @required
+    description: String,
+    @required
+    evolvesTo: PokemonList
+}
+
+list PokemonList {
+    member: Pokemon
+}
+```
+
+In the Rust code below, note the references calling out the changes described in the numbered list above.
+
+Before:
+
+```rust
+let eevee_builder = Pokemon::builder()
+    // (1) `set_description` takes in `Some<String>`.
+    .set_description(Some("Su código genético es muy inestable. Puede evolucionar en diversas razas de Pokémon.".to_owned()))
+    // (2) Convenience method to add one element to the `evolvesTo` list.
+    .evolves_to(vaporeon)
+    .evolves_to(jolteon)
+    .evolves_to(flareon);
+
+// (3) Builder types can be compared.
+assert_ne!(eevee_builder, Pokemon::builder());
+
+// (4) Builds fine even though we didn't provide a value for `name`, which is `required`!
+let _eevee = eevee_builder.build();
+```
+
+After:
+
+```rust
+let eevee_builder = Pokemon::builder()
+    // (1) `set_description` no longer exists. Use `description`, which directly takes in `String`.
+    .description("Su código genético es muy inestable. Puede evolucionar en diversas razas de Pokémon.".to_owned())
+    // (2) Convenience methods removed; provide the entire collection up front.
+    .evolves_to(vec![vaporeon, jolteon, flareon]);
+
+// (3) Binary operation `==` cannot be applied to `pokemon::Builder`.
+// assert_ne!(eevee_builder, Pokemon::builder());
+
+// (4) `required` member `name` was not set.
+// (5) Builder type can be fallibly converted to the structure using `TryFrom` or `TryInto`.
+let _error = Pokemon::try_from(eevee_builder).expect_err("name was not provided");
+```
+"""
+references = ["smithy-rs#1714", "smithy-rs#1342"]
+meta = { "breaking" = true, "tada" = true, "bug" = true, "target" = "server" }
+author = "david-perez"
+
+[[smithy-rs]]
+message = """
+Server SDKs now correctly reject operation inputs that don't set values for `required` structure members. Previously, in some scenarios, server SDKs would accept the request and set a default value for the member (e.g. `""` for a `String`), even when the member shape did not have [Smithy IDL v2's `default` trait](https://awslabs.github.io/smithy/2.0/spec/type-refinement-traits.html#smithy-api-default-trait) attached. The `default` trait is [still unsupported](https://github.com/awslabs/smithy-rs/issues/1860).
+"""
+references = ["smithy-rs#1714", "smithy-rs#1342", "smithy-rs#1860"]
+meta = { "breaking" = true, "tada" = false, "bug" = true, "target" = "server" }
+author = "david-perez"

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

@@ -6,20 +6,34 @@
 package software.amazon.smithy.rust.codegen.client.smithy.generators
 
 import software.amazon.smithy.codegen.core.Symbol
+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.rust
 import software.amazon.smithy.rust.codegen.core.rustlang.writable
 import software.amazon.smithy.rust.codegen.core.smithy.CodegenContext
+import software.amazon.smithy.rust.codegen.core.smithy.generators.BuilderGenerator
 import software.amazon.smithy.rust.codegen.core.smithy.generators.Instantiator
+import software.amazon.smithy.rust.codegen.core.smithy.generators.setterName
 
 private fun enumFromStringFn(enumSymbol: Symbol, data: String): Writable = writable {
     rust("#T::from($data)", enumSymbol)
 }
 
+class ClientBuilderKindBehavior(val codegenContext: CodegenContext) : Instantiator.BuilderKindBehavior {
+    override fun hasFallibleBuilder(shape: StructureShape): Boolean =
+        BuilderGenerator.hasFallibleBuilder(shape, codegenContext.symbolProvider)
+
+    override fun setterName(memberShape: MemberShape): String = memberShape.setterName()
+
+    override fun doesSetterTakeInOption(memberShape: MemberShape): Boolean = true
+}
+
 fun clientInstantiator(codegenContext: CodegenContext) =
     Instantiator(
         codegenContext.symbolProvider,
         codegenContext.model,
         codegenContext.runtimeConfig,
+        ClientBuilderKindBehavior(codegenContext),
         ::enumFromStringFn,
     )

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

@@ -26,7 +26,7 @@ import software.amazon.smithy.rust.codegen.core.smithy.RuntimeType
 import software.amazon.smithy.rust.codegen.core.smithy.customize.OperationCustomization
 import software.amazon.smithy.rust.codegen.core.smithy.customize.OperationSection
 import software.amazon.smithy.rust.codegen.core.smithy.customize.writeCustomizations
-import software.amazon.smithy.rust.codegen.core.smithy.generators.StructureGenerator
+import software.amazon.smithy.rust.codegen.core.smithy.generators.BuilderGenerator
 import software.amazon.smithy.rust.codegen.core.smithy.generators.builderSymbol
 import software.amazon.smithy.rust.codegen.core.smithy.generators.error.errorSymbol
 import software.amazon.smithy.rust.codegen.core.smithy.generators.http.ResponseBindingGenerator
@@ -332,7 +332,7 @@ class HttpBoundProtocolTraitImplGenerator(
             }
         }
 
-        val err = if (StructureGenerator.hasFallibleBuilder(outputShape, symbolProvider)) {
+        val err = if (BuilderGenerator.hasFallibleBuilder(outputShape, symbolProvider)) {
             ".map_err(${format(errorSymbol)}::unhandled)?"
         } else ""