Add structural classes of dynamicApply before inlining

compiler/src/dotty/tools/dotc/core/Mode.scala

@@ -163,6 +163,6 @@ object Mode {
    */
   val RelaxedOverriding: Mode = newMode(30, "RelaxedOverriding")
 
-  /** We are checking the original call of an Inlined node */
-  val InlinedCall: Mode = newMode(31, "InlinedCall")
+  /** Skip inlining of methods. */
+  val NoInline: Mode = newMode(31, "NoInline")
 }

compiler/src/dotty/tools/dotc/inlines/Inlines.scala

@@ -64,6 +64,7 @@ object Inlines:
       )
       && !ctx.typer.hasInliningErrors
       && !ctx.base.stopInlining
+      && !ctx.mode.is(Mode.NoInline)
   }
 
   private def needsTransparentInlining(tree: Tree)(using Context): Boolean =

compiler/src/dotty/tools/dotc/transform/PostTyper.scala

@@ -366,7 +366,7 @@ class PostTyper extends MacroTransform with InfoTransformer { thisPhase =>
         case tree @ Inlined(call, bindings, expansion) if !tree.inlinedFromOuterScope =>
           val pos = call.sourcePos
           CrossVersionChecks.checkExperimentalRef(call.symbol, pos)
-          withMode(Mode.InlinedCall)(transform(call))
+          withMode(Mode.NoInline)(transform(call))
           val callTrace = ref(call.symbol)(using ctx.withSource(pos.source)).withSpan(pos.span)
           cpy.Inlined(tree)(callTrace, transformSub(bindings), transform(expansion)(using inlineContext(tree)))
         case templ: Template =>
@@ -520,7 +520,7 @@ class PostTyper extends MacroTransform with InfoTransformer { thisPhase =>
       if (sym.isEffectivelyErased) dropInlines.transform(rhs) else rhs
 
     private def registerNeedsInlining(tree: Tree)(using Context): Unit =
-      if tree.symbol.is(Inline) && !Inlines.inInlineMethod && !ctx.mode.is(Mode.InlinedCall) then
+      if tree.symbol.is(Inline) && !Inlines.inInlineMethod && !ctx.mode.is(Mode.NoInline) then
         ctx.compilationUnit.needsInlining = true
 
     /** Check if the definition has macro annotation and sets `compilationUnit.hasMacroAnnotations` if needed. */

compiler/src/dotty/tools/dotc/typer/Dynamic.scala

@@ -7,6 +7,8 @@ import dotty.tools.dotc.ast.tpd
 import dotty.tools.dotc.ast.untpd
 import dotty.tools.dotc.core.Constants.Constant
 import dotty.tools.dotc.core.Contexts.*
+import dotty.tools.dotc.core.Flags.*
+import dotty.tools.dotc.core.Mode
 import dotty.tools.dotc.core.Names.{Name, TermName}
 import dotty.tools.dotc.core.StdNames.*
 import dotty.tools.dotc.core.Types.*
@@ -18,6 +20,7 @@ import ErrorReporting.*
 import dotty.tools.dotc.transform.ValueClasses
 import dotty.tools.dotc.transform.TypeUtils.isPrimitiveValueType
 import reporting.*
+import inlines.Inlines
 
 object Dynamic {
   private def isDynamicMethod(name: Name): Boolean =
@@ -210,7 +213,12 @@ trait Dynamic {
               case _ => tree
             case other => tree
         case _ => tree
-      addClassOfs(typed(scall))
+
+      // We type the application of `applyDynamic` without inlining (arguments are already typed and inlined),
+      // to be able to add the add the Class arguments before we inline the method.
+      val call = addClassOfs(withMode(Mode.NoInline)(typed(scall)))
+      if Inlines.needsInlining(call) then Inlines.inlineCall(call)
+      else call
     }
 
     def fail(reason: String): Tree =

tests/run/i17761.check

@@ -0,0 +1,8 @@
+Normal
+test
+ArraySeq(class java.lang.String, int)
+ArraySeq(test, 42)
+Transparent
+test
+ArraySeq(class java.lang.String, int)
+ArraySeq(test, 42)

tests/run/i17761.scala

@@ -0,0 +1,33 @@
+class MyRecord extends Selectable:
+  def applyDynamic(name: String, paramClasses: Class[_]*)(args: Any*): Any = {
+    println(name)
+    println(paramClasses)
+    println(args)
+    ()
+  }
+
+class MyRecordTransparent extends Selectable:
+  inline transparent def applyDynamic(name: String, paramClasses: Class[_]*)(args: Any*): Any = {
+    println(name)
+    println(paramClasses)
+    println(args)
+    ()
+  }
+
+type Person = MyRecord {
+  def test(a: String, b: Int): Unit
+}
+
+
+type PersonTransparent = MyRecordTransparent {
+  def test(a: String, b: Int): Unit
+}
+
+val person = MyRecord().asInstanceOf[Person]
+val personTransparent = MyRecordTransparent().asInstanceOf[PersonTransparent]
+
+@main def Test: Unit =
+  println("Normal")
+  person.test("test", 42)
+  println("Transparent")
+  personTransparent.test("test", 42)