Nested server structure member shapes targeting simple shapes with default trait

CHANGELOG.next.toml

@@ -222,3 +222,10 @@ message = "Fluent builder methods on the client are now marked as deprecated whe
 references = ["aws-sdk-rust#740"]
 meta = { "breaking" = false, "tada" = true, "bug" = true, "target" = "client"}
 author = "Velfi"
+
+[[smithy-rs]]
+message = """Fix bug whereby nested server structure member shapes targeting simple shapes with `@default`
+produced Rust code that did not compile"""
+references = ["smithy-rs#2352", "smithy-rs#2343"]
+meta = { "breaking" = false, "tada" = false, "bug" = true, "target" = "server"}
+author = "82marbag"

codegen-server/src/main/kotlin/software/amazon/smithy/rust/codegen/server/smithy/Constraints.kt

@@ -83,7 +83,7 @@ fun Shape.isDirectlyConstrained(symbolProvider: SymbolProvider): Boolean = when
         //  The only reason why the functions in this file have
         //  to take in a `SymbolProvider` is because non-`required` blob streaming members are interpreted as
         //  `required`, so we can't use `member.isOptional` here.
-        this.members().map { symbolProvider.toSymbol(it) }.any { !it.isOptional() }
+        this.members().any { !symbolProvider.toSymbol(it).isOptional() && !it.hasNonNullDefault() }
     }
 
     is MapShape -> this.hasTrait<LengthTrait>()

codegen-server/src/test/kotlin/software/amazon/smithy/rust/codegen/server/smithy/ConstraintsTest.kt

@@ -8,6 +8,7 @@ package software.amazon.smithy.rust.codegen.server.smithy
 import io.kotest.inspectors.forAll
 import io.kotest.matchers.shouldBe
 import org.junit.jupiter.api.Test
+import software.amazon.smithy.model.shapes.BooleanShape
 import software.amazon.smithy.model.shapes.ListShape
 import software.amazon.smithy.model.shapes.MapShape
 import software.amazon.smithy.model.shapes.MemberShape
@@ -81,7 +82,12 @@ class ConstraintsTest {
             @length(min: 1, max: 5)
             mapAPrecedence: MapA
         }
-        """.asSmithyModel()
+
+        structure StructWithInnerDefault {
+            @default(false)
+            inner: PrimitiveBoolean
+        }
+        """.asSmithyModel(smithyVersion = "2")
     private val symbolProvider = serverTestSymbolProvider(model)
 
     private val testInputOutput = model.lookup<StructureShape>("test#TestInputOutput")
@@ -93,6 +99,8 @@ class ConstraintsTest {
     private val structA = model.lookup<StructureShape>("test#StructureA")
     private val structAInt = model.lookup<MemberShape>("test#StructureA\$int")
     private val structAString = model.lookup<MemberShape>("test#StructureA\$string")
+    private val structWithInnerDefault = model.lookup<StructureShape>("test#StructWithInnerDefault")
+    private val primitiveBoolean = model.lookup<BooleanShape>("smithy.api#PrimitiveBoolean")
 
     @Test
     fun `it should detect supported constrained traits as constrained`() {
@@ -119,4 +127,10 @@ class ConstraintsTest {
         mapB.canReachConstrainedShape(model, symbolProvider) shouldBe true
         recursiveShape.canReachConstrainedShape(model, symbolProvider) shouldBe true
     }
+
+    @Test
+    fun `it should not consider shapes with the default trait as constrained`() {
+        structWithInnerDefault.canReachConstrainedShape(model, symbolProvider) shouldBe false
+        primitiveBoolean.isDirectlyConstrained(symbolProvider) shouldBe false
+    }
 }

codegen-server/src/test/kotlin/software/amazon/smithy/rust/codegen/server/smithy/generators/ServerBuilderConstraintViolationsTest.kt

@@ -0,0 +1,49 @@
+/*
+ * Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package software.amazon.smithy.rust.codegen.server.smithy.generators
+
+import org.junit.jupiter.api.Test
+import software.amazon.smithy.rust.codegen.core.testutil.asSmithyModel
+import software.amazon.smithy.rust.codegen.server.smithy.testutil.serverIntegrationTest
+
+class ServerBuilderConstraintViolationsTest {
+
+    // This test exists not to regress on [this](https://github.com/awslabs/smithy-rs/issues/2343) issue.
+    // We generated constraint violation variants, pointing to a structure (StructWithInnerDefault below),
+    // but the structure was not constrained, because the structure's member have a default value
+    // and default values are validated at generation time from the model.
+    @Test
+    fun `it should not generate constraint violations for members with a default value`() {
+        val model = """
+            namespace test
+
+            use aws.protocols#restJson1
+            use smithy.framework#ValidationException
+
+            @restJson1
+            service SimpleService {
+                operations: [Operation]
+            }
+
+            @http(uri: "/operation", method: "POST")
+            operation Operation {
+                input: OperationInput
+                errors: [ValidationException]
+            }
+
+            structure OperationInput {
+                @required
+                requiredStructureWithInnerDefault: StructWithInnerDefault
+            }
+
+            structure StructWithInnerDefault {
+                @default(false)
+                inner: PrimitiveBoolean
+            }
+        """.asSmithyModel(smithyVersion = "2")
+        serverIntegrationTest(model)
+    }
+}