fixes #8514, TypeApi#baseType exposed into Tasty

compiler/src/dotty/tools/dotc/tastyreflect/ReflectionCompilerInterface.scala

@@ -1205,6 +1205,9 @@ class ReflectionCompilerInterface(val rootContext: core.Contexts.Context) extend
   def Type_baseClasses(self: Type)(using Context): List[Symbol] =
     self.baseClasses
 
+  def Type_baseType(self: Type)(cls: Symbol)(using Context): Type =
+    self.baseType(cls)
+
   def Type_derivesFrom(self: Type)(cls: Symbol)(using Context): Boolean =
     self.derivesFrom(cls)
 

library/src/scala/tasty/Reflection.scala

@@ -1812,6 +1812,17 @@ class Reflection(private[scala] val internal: CompilerInterface) { self =>
       /** The base classes of this type with the class itself as first element. */
       def baseClasses(using ctx: Context): List[Symbol] = internal.Type_baseClasses(self)
 
+
+    /** The least type instance of given class which is a super-type
+     *  of this type.  Example:
+     *  {{{
+     *    class D[T]
+     *    class C extends p.D[Int]
+     *    ThisType(C).baseType(D) = p.D[Int]
+     * }}}
+     */
+      def baseType(cls: Symbol)(using ctx: Context): Type = internal.Type_baseType(self)(cls)
+
       /** Is this type an instance of a non-bottom subclass of the given class `cls`? */
       def derivesFrom(cls: Symbol)(using ctx: Context): Boolean =
         internal.Type_derivesFrom(self)(cls)

library/src/scala/tasty/reflect/CompilerInterface.scala

@@ -876,6 +876,16 @@ trait CompilerInterface {
   /** The base classes of this type with the class itself as first element. */
   def Type_baseClasses(self: Type)(using ctx: Context): List[Symbol]
 
+  /** The least type instance of given class which is a super-type
+    *  of this type.  Example:
+    *  {{{
+    *    class D[T]
+    *    class C extends p.D[Int]
+    *    ThisType(C).baseType(D) = p.D[Int]
+    * }}}
+    */
+  def Type_baseType(self: Type)(cls: Symbol)(using ctx: Context): Type
+
   /** Is this type an instance of a non-bottom subclass of the given class `cls`? */
   def Type_derivesFrom(self: Type)(cls: Symbol)(using ctx: Context): Boolean
 

tests/run-macros/i8514b.check

@@ -0,0 +1,4 @@
+B
+A[[T >: scala.Nothing <: scala.Any] => P[T], scala.Predef.String]
+java.lang.Object
+scala.Any

tests/run-macros/i8514b/Macro_1.scala

@@ -0,0 +1,18 @@
+import scala.quoted._
+
+class A[+X[_], -Y]
+class P[T]
+class B extends A[P, String]
+
+inline def test(): Unit = ${ testExpr }
+
+def testExpr(using QuoteContext): Expr[Unit] = {
+  import qctx.tasty._
+
+  val t = '[B].unseal.tpe
+  val baseTypes = t.baseClasses.map(b => t.baseType(b))
+
+  '{
+    println(${Expr(baseTypes.map(_.show).mkString("\n"))})
+  }
+}

tests/run-macros/i8514b/Test_2.scala

@@ -0,0 +1 @@
+@main def Test = test()