implement getMessage in Smithy4sThrowable (#1572)

CHANGELOG.md

@@ -5,6 +5,10 @@ When adding entries, please treat them as if they could end up in a release any
 
 Thank you!
 
+# 0.18.24
+
+* Add `getMessage` implementation in `Smithy4sThrowable` which will be overridden in cases where the error structure contains a message field, but otherwise will be used to prevent a useless `null` result when `getMessage` is called.
+
 # 0.18.23
 
 ## Validated newtypes [#1454](https://github.com/disneystreaming/smithy4s/pull/1454)

modules/bootstrapped/test/src/smithy4s/ErrorMessageTraitSpec.scala

@@ -73,11 +73,20 @@ class ErrorMessageTraitSpec extends FunSuite {
     )
   }
 
-  test("Generated getMessage") {
+  test("Generated - no message") {
     val e = ClientError(400, "oopsy")
 
     val expected = "smithy4s.example.ClientError(400, oopsy)"
-    expect.eql(e.getMessage, null)
+    expect.eql(e.getMessage, expected)
+    expect.eql(e.toString, s"smithy4s.example.ClientError: $expected")
+  }
+
+  test("Generated - has message") {
+    val e =
+      ErrorCustomTypeMessage(Some(CustomErrorMessageType("This is a test.")))
+
+    val expected = "smithy4s.example.ErrorCustomTypeMessage: This is a test."
+    expect.eql(e.getMessage, "This is a test.")
     expect.eql(e.toString, expected)
   }
 

modules/core/src/smithy4s/Smithy4sThrowable.scala

@@ -18,14 +18,8 @@ package smithy4s
 
 trait Smithy4sThrowable extends Throwable { self: Product =>
 
-  /**
-    * implementing toString, because implementing getMessage
-    * lead to `smithy4s.example.ClientError: smithy4s.example.ClientError(400, "oops")`
-    * which felt weird
-    */
-  override def toString(): String = {
+  private def show(message: String): String = {
     val name = getClass().getName()
-    val message = getLocalizedMessage()
     if (message == null) {
       val sb = new StringBuilder()
       sb.append(name)
@@ -41,4 +35,16 @@ trait Smithy4sThrowable extends Throwable { self: Product =>
       s"$name: $message"
     }
   }
+
+  override def getMessage(): String = this.show(message = null)
+
+  /**
+    * implementing toString, because implementing getMessage
+    * lead to `smithy4s.example.ClientError: smithy4s.example.ClientError(400, "oops")`
+    * which felt weird
+    */
+  override def toString(): String = {
+    val message = getLocalizedMessage()
+    this.show(message = message)
+  }
 }