[Fix][scala-sttp][circe] Add NaN-tolerant Decoder[Double] for non-finite values (#23611)

* [Fix] Handle NaN and other double serialization types

* Update tests

Author: nikhilsu

modules/openapi-generator/src/main/resources/scala-sttp/additionalTypeSerializers.mustache

@@ -71,5 +71,13 @@ trait AdditionalTypeSerializers {
     case s: String => Json.fromString(s)
     case other => Json.fromString(other.toString)
   }
+
+  implicit final lazy val NanTolerantDoubleDecoder: Decoder[Double] =
+    Decoder.decodeDouble.or(Decoder.decodeString.emap {
+      case "NaN" => Right(Double.NaN)
+      case "Infinity" => Right(Double.PositiveInfinity)
+      case "-Infinity" => Right(Double.NegativeInfinity)
+      case s => Left(s"Cannot decode '$s' as Double")
+  })
 }
 {{/circe}}

modules/openapi-generator/src/test/java/org/openapitools/codegen/scala/ScalaSttpCirceCodegenTest.java

@@ -73,12 +73,16 @@ public void verifyBaseNameFieldMapping() throws IOException {
         assertFileContains(binaryPath, "implicit val encoderBinaryPayload");
         assertFileContains(binaryPath, "implicit val decoderBinaryPayload");
 
-        // AdditionalTypeSerializers: File and Any codecs
+        // AdditionalTypeSerializers: File, Any, and NaN-tolerant Double codecs
         Path serializersPath = Paths.get(outputPath + "/src/main/scala/org/openapitools/client/core/AdditionalTypeSerializers.scala");
         assertFileContains(serializersPath, "FileDecoder");
         assertFileContains(serializersPath, "FileEncoder");
         assertFileContains(serializersPath, "AnyDecoder");
         assertFileContains(serializersPath, "AnyEncoder");
+        assertFileContains(serializersPath, "NanTolerantDoubleDecoder");
+        assertFileContains(serializersPath, "Double.NaN");
+        assertFileContains(serializersPath, "Double.PositiveInfinity");
+        assertFileContains(serializersPath, "Double.NegativeInfinity");
 
         // JsonSupport should NOT use AutoDerivation
         Path jsonSupportPath = Paths.get(outputPath + "/src/main/scala/org/openapitools/client/core/JsonSupport.scala");

samples/client/petstore/scala-sttp-circe/src/main/scala/org/openapitools/client/core/AdditionalTypeSerializers.scala

@@ -48,4 +48,12 @@ trait AdditionalTypeSerializers {
     case s: String => Json.fromString(s)
     case other => Json.fromString(other.toString)
   }
+
+  implicit final lazy val NanTolerantDoubleDecoder: Decoder[Double] =
+    Decoder.decodeDouble.or(Decoder.decodeString.emap {
+      case "NaN" => Right(Double.NaN)
+      case "Infinity" => Right(Double.PositiveInfinity)
+      case "-Infinity" => Right(Double.NegativeInfinity)
+      case s => Left(s"Cannot decode '$s' as Double")
+  })
 }