Reprioritize UUIDGen.fromSecureRandom to avoid ambiguity on Scala 2.12

core/shared/src/test/scala/cats/effect/ImplicitPriorityPlayground.scala

@@ -0,0 +1,31 @@
+/*
+ * Copyright 2020-2025 Typelevel
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package cats.effect.std
+
+import cats.data._
+import cats.effect._
+
+import java.util.UUID
+
+object ImplicitPriorityPlayground {
+
+  def foo[F[_]: UUIDGen]: F[UUID] = UUIDGen[F].randomUUID
+
+  SecureRandom.javaSecuritySecureRandom[IO].flatMap { implicit random =>
+    foo[Kleisli[IO, String, *]].run("hello world")
+  }
+}

std/js-native/src/main/scala/cats/effect/std/UUIDGenCompanionPlatform.scala

@@ -30,7 +30,7 @@ package cats.effect.std
 
 import cats.effect.kernel.Sync
 
-private[std] trait UUIDGenCompanionPlatform extends UUIDGenCompanionPlatformLowPriority
+private[std] trait UUIDGenCompanionPlatform extends UUIDGenCompanionPlatformMediumPriority
 
 private[std] trait UUIDGenCompanionPlatformLowPriority {
 

std/jvm/src/main/scala/cats/effect/std/UUIDGenCompanionPlatform.scala

@@ -20,7 +20,7 @@ import cats.effect.kernel.Sync
 
 import java.util.UUID
 
-private[std] trait UUIDGenCompanionPlatform extends UUIDGenCompanionPlatformLowPriority
+private[std] trait UUIDGenCompanionPlatform extends UUIDGenCompanionPlatformMediumPriority
 
 private[std] trait UUIDGenCompanionPlatformLowPriority {
 

std/shared/src/main/scala/cats/effect/std/UUIDGen.scala

@@ -26,7 +26,7 @@ import cats.data.{
   OptionT,
   WriterT
 }
-import cats.implicits._
+import cats.syntax.all._
 
 import java.util.UUID
 
@@ -118,6 +118,16 @@ object UUIDGen extends UUIDGenCompanionPlatform {
   ]: UUIDGen[IndexedReaderWriterStateT[F, E, L, S, S, *]] =
     UUIDGen[F].mapK(IndexedReaderWriterStateT.liftK)
 
+  private[std] final class TranslatedUUIDGen[F[_], G[_]](self: UUIDGen[F])(f: F ~> G)
+      extends UUIDGen[G] {
+    override def randomUUID: G[UUID] =
+      f(self.randomUUID)
+
+  }
+}
+
+private[std] trait UUIDGenCompanionPlatformMediumPriority
+    extends UUIDGenCompanionPlatformLowPriority {
   implicit def fromSecureRandom[F[_]: Functor: SecureRandom]: UUIDGen[F] =
     new UUIDGen[F] {
       override final val randomUUID: F[UUID] =
@@ -137,11 +147,4 @@ object UUIDGen extends UUIDGenCompanionPlatform {
         new UUID(msb, lsb)
       }
     }
-
-  private[std] final class TranslatedUUIDGen[F[_], G[_]](self: UUIDGen[F])(f: F ~> G)
-      extends UUIDGen[G] {
-    override def randomUUID: G[UUID] =
-      f(self.randomUUID)
-
-  }
 }