Handle binding of beta reduced inlined lambdas

Fixes scala#16374

Author: nicolasstucki

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

@@ -161,14 +161,14 @@ class InlineReducer(inliner: Inliner)(using Context):
     */
   def betaReduce(tree: Tree)(using Context): Tree = tree match {
     case Apply(Select(cl @ closureDef(ddef), nme.apply), args) if defn.isFunctionType(cl.tpe) =>
-      // closureDef also returns a result for closures wrapped in Inlined nodes.
-      // These need to be preserved.
+      val bindingsBuf = new DefBuffer
       def recur(cl: Tree): Tree = cl match
+        // closureDef also returns a result for closures wrapped in Inlined nodes.
+        // These need to be preserved.
         case Inlined(call, bindings, expr) =>
           cpy.Inlined(cl)(call, bindings, recur(expr))
         case _ => ddef.tpe.widen match
           case mt: MethodType if ddef.paramss.head.length == args.length =>
-            val bindingsBuf = new DefBuffer
             val argSyms = mt.paramNames.lazyZip(mt.paramInfos).lazyZip(args).map { (name, paramtp, arg) =>
               arg.tpe.dealias match {
                 case ref @ TermRef(NoPrefix, _) => ref.symbol
@@ -183,9 +183,10 @@ class InlineReducer(inliner: Inliner)(using Context):
               newOwners = ctx.owner :: Nil,
               substFrom = ddef.paramss.head.map(_.symbol),
               substTo = argSyms)
-            Block(bindingsBuf.toList, expander.transform(ddef.rhs)).withSpan(tree.span)
+            expander.transform(ddef.rhs)
           case _ => tree
-      recur(cl)
+      val reduced = recur(cl)
+      Block(bindingsBuf.toList, reduced).withSpan(tree.span)
     case _ => tree
   }
 
@@ -281,7 +282,7 @@ class InlineReducer(inliner: Inliner)(using Context):
         // Test case is pos-macros/i15971
         val tptBinds = getBinds(Set.empty[TypeSymbol], tpt)
         val binds: Set[TypeSymbol] = pat match {
-          case UnApply(TypeApply(_, tpts), _, _) => 
+          case UnApply(TypeApply(_, tpts), _, _) =>
             getBinds(Set.empty[TypeSymbol], tpts) ++ tptBinds
           case _ => tptBinds
         }

tests/pos/i16374a.scala

@@ -0,0 +1,7 @@
+def method(using String): String = ???
+
+inline def inlineMethod(inline op: String => Unit)(using String): Unit =
+  println(op(method))
+
+def test(using String) =
+  inlineMethod(c => print(c))

tests/pos/i16374b.scala

@@ -0,0 +1,9 @@
+def method(using String): String = ???
+
+inline def identity[T](inline x: T): T = x
+
+inline def inlineMethod(inline op: String => Unit)(using String): Unit =
+  println(identity(op)(method))
+
+def test(using String) =
+  inlineMethod(c => print(c))