first commit, demonstrating the following bug

type bound are displayed as:
Refined.Node {type T =   <: Int}

where it should be:
Refined.Node {type T <: Int}

fix the bug, TypeBound now has its own case Formatting subroutine

Author: tribbloid

core/src/main/scala-2.13.7+/latest/splain/SplainFormattersExtension.scala

@@ -58,6 +58,11 @@ trait SplainFormattersExtension extends SplainFormatters {
     }
 
     def formatDecl: Symbol => Formatted = {
+      case sym if sym.hasRawInfo && sym.rawInfo.isInstanceOf[TypeBounds] =>
+        val name = sym.simpleName.toString
+        val bounds = formatType(sym.rawInfo, top = true)
+        val boundsStr = self.showFormatted(bounds)
+        Simple(s"type $name$boundsStr")
       case DeclSymbol(n, t) =>
         Decl(n, t)
       case sym =>

core/src/test/resources/splain/builtin/BasicSpec/__direct/check

@@ -192,6 +192,14 @@ newSource1.scala:21: error: type mismatch;
   }
       f(x)
         ^
+newSource1.scala:9: error: implicit error;
+!I e: Refined.Node {type T <: Int}
+  implicitly[NodeLt[Int]]
+            ^
+newSource1.scala:11: error: type mismatch;
+  Int(1)┃Refined.Node {type T <: Int}
+  val k: NodeLt[Int] = 1
+                       ^
 newSource1.scala:10: error: implicit error;
 !I e: Refined.Node{type T = _$2} forSome { type _$2 <: Int }
   implicitly[NodeLt[Int]]

core/src/test/scala/splain/builtin/BasicSpec.scala

@@ -44,6 +44,8 @@ class BasicSpec extends SpecBase.Direct with BasicFixture {
 
   check(refined2, numberOfErrors = 2)
 
+  check(refined3, numberOfErrors = 2)
+
   check(disambiguateQualified)
 
   check(bynameParam)

core/src/testFixtures/scala/splain/builtin/BasicFixture.scala

@@ -243,6 +243,22 @@ object Refined
     type T
   }
 
+  type NodeLt[T0] = Node {type T <: T0}
+
+  implicitly[NodeLt[Int]]
+
+  val k: NodeLt[Int] = 1
+}
+    """
+
+  final val refined3 =
+    """
+object Refined
+{
+  trait Node {
+    type T
+  }
+
   type NodeAux[T0] = Node { type T = T0 }
   type NodeLt[T0] = NodeAux[_ <: T0]
 

gradle/wrapper/gradle-wrapper.jar

@@ -231,6 +231,10 @@ newSource1.scala:11: error: type mismatch;
   }
   f(x)
     ^
+newSource1.scala:9: error: implicit error;
+!I e: splain.acceptance.builtin.StaticBasicSpec.Refined.Node {type T <: Int}
+  implicitly[NodeLt[Int]]
+            ^
 newSource1.scala:10: error: implicit error;
 !I e: splain.acceptance.builtin.StaticBasicSpec.Refined.Node{type T = _$1} forSome { type _$1 <: Int }
   implicitly[NodeLt[Int]]

gradlew

@@ -54,6 +54,8 @@ class StaticBasicSpec extends Acceptance.SpecBase {
 
   check(refined2, numberOfErrors = 2)
 
+  check(refined3, numberOfErrors = 2)
+
   check(disambiguateQualified)
 
   check(bynameParam)