Fix bug with enum code generation (#4137)

Author: landonxjames

.changelog/unknown-debug.md

@@ -0,0 +1,18 @@
+---
+applies_to: ["client"]
+authors: ["landonxjames"]
+references: ["smithy-rs#4137"]
+breaking: false
+new_feature: false
+bug_fix: true
+---
+
+Fix bug with enum codegen
+
+When the first enum generated has the `@sensitive` trait the opaque type
+underlying the `UnknownVariant` inherits that sensitivity. This means that
+it does not derive `Debug`. Since the module is only generated once this
+causes a problem for non-sensitive enums that rely on the type deriving
+`Debug` so that they can also derive `Debug`. We manually add `Debug` to
+the module so it will always be there since the `UnknownVariant` is not
+modeled and cannot be `@sensitive`.

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

@@ -194,7 +194,12 @@ data class InfallibleEnumType(
                 This is not intended to be used directly.
                 """.trimIndent(),
             )
-            context.enumMeta.render(this)
+
+            // The UnknownVariant's underlying opaque type should always derive `Debug`. If this isn't explicitly
+            // added and the first enum to render this module has the `@sensitive` trait then the UnknownVariant
+            // inherits that sensitivity and does not derive `Debug`. This leads to issues deriving `Debug` for
+            // all enum variants that are not marked `@sensitive`.
+            context.enumMeta.withDerives(RuntimeType.Debug).render(this)
             rustTemplate("struct $UNKNOWN_VARIANT_VALUE(pub(crate) #{String});", *preludeScope)
             rustBlock("impl $UNKNOWN_VARIANT_VALUE") {
                 // The generated as_str is not pub as we need to prevent users from calling it on this opaque struct.

codegen-client/src/test/kotlin/software/amazon/smithy/rust/codegen/client/smithy/generators/ClientEnumGeneratorTest.kt

@@ -106,6 +106,55 @@ class ClientEnumGeneratorTest {
         project.compileAndTest()
     }
 
+    // The idempotency of RustModules paired with Smithy's alphabetic order shape iteration meant that
+    // if an @sensitive enum was the first enum generated that the opaque type underlying the Unknown
+    // variant would not derive Debug, breaking all non-@sensitive enums
+    @Test
+    fun `sensitive enum in earlier alphabetic order does not break non-sensitive enums`() {
+        val model =
+            """
+            namespace test
+
+            @sensitive
+            @enum([
+                { name: "Foo", value: "Foo" },
+                { name: "Bar", value: "Bar" },
+            ])
+            string FooA
+
+            @enum([
+                { name: "Baz", value: "Baz" },
+                { name: "Ahh", value: "Ahh" },
+            ])
+            string FooB
+            """.asSmithyModel()
+
+        val shapeA = model.lookup<StringShape>("test#FooA")
+        val shapeB = model.lookup<StringShape>("test#FooB")
+        val context = testClientCodegenContext(model)
+        val project = TestWorkspace.testProject(context.symbolProvider)
+        project.moduleFor(shapeA) {
+            ClientEnumGenerator(context, shapeA).render(this)
+        }
+        project.moduleFor(shapeB) {
+            ClientEnumGenerator(context, shapeB).render(this)
+            unitTest(
+                "impl_debug_for_non_sensitive_enum_should_implement_the_derived_debug_trait",
+                """
+                assert_eq!(format!("{:?}", FooB::Baz), "Baz");
+                assert_eq!(format!("{:?}", FooB::Ahh), "Ahh");
+                assert_eq!(format!("{}", FooB::Baz), "Baz");
+                assert_eq!(FooB::Ahh.to_string(), "Ahh");
+                assert_eq!(
+                    format!("{:?}", FooB::from("Bar")),
+                    "Unknown(UnknownVariantValue(\"Bar\"))"
+                );
+                """,
+            )
+        }
+        project.compileAndTest()
+    }
+
     @Test
     fun `it escapes the Unknown variant if the enum has an unknown value in the model`() {
         val model =