From 9e7b6c1099ac67632661c139bcf4774e60895874 Mon Sep 17 00:00:00 2001
From: Russell Cohen <rcoh@amazon.com>
Date: Mon, 2 Oct 2023 14:39:40 -0400
Subject: [PATCH] Add additional default semantics

---
 .../core/smithy/generators/BuilderGenerator.kt      |  2 ++
 .../core/smithy/generators/BuilderGeneratorTest.kt  | 13 +++++++++++++
 2 files changed, 15 insertions(+)

diff --git a/codegen-core/src/main/kotlin/software/amazon/smithy/rust/codegen/core/smithy/generators/BuilderGenerator.kt b/codegen-core/src/main/kotlin/software/amazon/smithy/rust/codegen/core/smithy/generators/BuilderGenerator.kt
index 80b9329d63..e1de17cfdc 100644
--- a/codegen-core/src/main/kotlin/software/amazon/smithy/rust/codegen/core/smithy/generators/BuilderGenerator.kt
+++ b/codegen-core/src/main/kotlin/software/amazon/smithy/rust/codegen/core/smithy/generators/BuilderGenerator.kt
@@ -416,6 +416,8 @@ class BuilderGenerator(
                                 ")?",
                             ) { missingRequiredField(memberName) }
                         }
+                    } else if (member.isRequired && default != null) {
+                        rust(".or_else(|| Some((#T)()))", default.expr)
                     }
                 }
             }
diff --git a/codegen-core/src/test/kotlin/software/amazon/smithy/rust/codegen/core/smithy/generators/BuilderGeneratorTest.kt b/codegen-core/src/test/kotlin/software/amazon/smithy/rust/codegen/core/smithy/generators/BuilderGeneratorTest.kt
index 2220a6f10f..0cf63123ae 100644
--- a/codegen-core/src/test/kotlin/software/amazon/smithy/rust/codegen/core/smithy/generators/BuilderGeneratorTest.kt
+++ b/codegen-core/src/test/kotlin/software/amazon/smithy/rust/codegen/core/smithy/generators/BuilderGeneratorTest.kt
@@ -177,12 +177,24 @@ internal class BuilderGeneratorTest {
               @default(true)
               @required
               defaultDocument: Document
+
+              @clientOptional
+              @required
+              @default([])
+              requiredButOptional: StringList
+
+              @default(1)
+              @clientOptional
+              @required
+              reqOptInt: OneDefault
+
             }
             list StringList {
                 member: String
             }
             @default(1)
             integer OneDefault
+
         """.asSmithyModel(smithyVersion = "2.0")
 
         val provider = testSymbolProvider(
@@ -207,6 +219,7 @@ internal class BuilderGeneratorTest {
                     assert_eq!(s.an_actually_required_field(), 5);
                     assert_eq!(s.no_default(), None);
                     assert_eq!(s.default_document().as_bool().unwrap(), true);
+                    assert_eq!(s.required_but_optional, Some(vec![]));
                     """,
                     "Struct" to provider.toSymbol(shape),
                 )