Allow eta expansion during inlining

Fixes #11628

Author: odersky

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

@@ -223,7 +223,7 @@ object EtaExpansion extends LiftImpure {
    */
   def etaExpand(tree: Tree, mt: MethodType, xarity: Int)(using Context): untpd.Tree = {
     import untpd._
-    assert(!ctx.isAfterTyper)
+    assert(!ctx.isAfterTyper || (ctx.phase eq ctx.base.inliningPhase), ctx.phase)
     val defs = new mutable.ListBuffer[tpd.Tree]
     val lifted: Tree = TypedSplice(liftApp(defs, tree))
     val isLastApplication = mt.resultType match {

tests/pos/i11628/macros.scala

@@ -0,0 +1,24 @@
+// assume that this conversion utility is defined in Scala 2
+class Scala2Conversion[T, V](val f: T => V)
+object Scala2Conversion{
+  implicit def create[T, V](implicit f: T => V): Scala2Conversion[T, V] = new Scala2Conversion(f)
+}
+
+// assume this utility in Scala 3, to summon a conversion within a macro
+import quoted._
+def summonConversionImpl(using qctx: Quotes): Expr[Any] = {
+  import qctx.reflect._
+
+  // hardcoded in this example to look for String to Int
+  val conversionTpe = TypeRepr.of[Scala2Conversion[String, Int]]
+
+  Implicits.search(conversionTpe) match {
+    case iss: ImplicitSearchSuccess =>
+      iss.tree.asExpr
+    case isf: ImplicitSearchFailure =>
+      report.error(s"can't find conversion")
+      '{???}
+  }
+}
+
+inline def summonConversion() = ${summonConversionImpl}

tests/pos/i11628/main.scala

@@ -0,0 +1,5 @@
+implicit def s2i(x: String): Int = x.toInt
+
+def main() = {
+  summonConversion()
+}