Don't allow mixins in adtMember

Author: kubukoz

modules/protocol-tests/test/src/smithy4s/api/validation/AdtMemberTraitValidatorSpec.scala

@@ -47,6 +47,42 @@ object AdtMemberTraitValidatorSpec extends FunSuite {
     success
   }
 
+  test("return an error when the union is a mixin") {
+
+    val events = eventsWithoutLocations(
+      assembleModel(
+        """$version: "2"
+          |namespace test
+          |
+          |use smithy4s.meta#adtMember
+          |
+          |@adtMember("test#MyUnion")
+          |structure struct {
+          |  testing: String
+          |}
+          |
+          |@mixin
+          |union MyUnion {
+          |  unionMember: struct
+          |}
+          |""".stripMargin
+      )
+    )
+
+    val expected =
+      ValidationEvent
+        .builder()
+        .id("TraitValue")
+        .shapeId(ShapeId.fromParts("test", "struct"))
+        .severity(Severity.ERROR)
+        .message(
+          "Error validating trait `smithy4s.meta#adtMember`: Shape ID `test#MyUnion` does not match selector `union :not([trait|mixin])`"
+        )
+        .build()
+
+    assert(events.contains(expected))
+  }
+
   test("return error when union does not target the structure") {
     val events = eventsWithoutLocations(
       assembleModel(

modules/protocol-tests/test/src/smithy4s/api/validation/AdtTraitValidatorSpec.scala

@@ -52,7 +52,7 @@ object AdtTraitValidatorSpec extends FunSuite {
       .shapeId(ShapeId.fromParts("test", "MyUnion"))
       .severity(Severity.ERROR)
       .message(
-        "Trait `smithy4s.meta#adt` cannot be applied to `test#MyUnion`. This trait may only be applied to shapes that match the following selector: :test(union :not([trait|mixin]))"
+        "Trait `smithy4s.meta#adt` cannot be applied to `test#MyUnion`. This trait may only be applied to shapes that match the following selector: union :not([trait|mixin])"
       )
       .build()
 

modules/protocol/resources/META-INF/smithy/smithy4s.meta.smithy

@@ -24,13 +24,13 @@ structure packedInputs {}
 /// which is the default behavior.
 /// Example usage: @adtMember(MyUnion)
 @trait(selector: "structure :not([trait|error])")
-@idRef(failWhenMissing: true, selector: "union")
+@idRef(failWhenMissing: true, selector: "union :not([trait|mixin])")
 string adtMember
 
 /// Implies that all members of the union are annotated with the `adtMember` trait.
 /// Further signals that the `sealed trait` for this adt will extend the traits
 /// defined by any mixins that are present on all of the adt members.
-@trait(selector: ":test(union :not([trait|mixin]))")
+@trait(selector: "union :not([trait|mixin])")
 structure adt {}
 
 // the indexedSeq trait can be added to list shapes in order for the generated collection