Don't propagate imports into inlined code

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

@@ -596,6 +596,9 @@ class Inliner(val call: tpd.Tree)(using Context):
           // reference to a private method is kept at runtime.
           cpy.Select(tree)(qual.asInstance(qual.tpe.widen), name)
 
+        case tree: ImportOrExport =>
+          EmptyTree
+
         case tree => tree
       },
       oldOwners = inlinedMethod :: Nil,

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

@@ -8,7 +8,7 @@ import util.SrcPos
 import config.{ScalaVersion, NoScalaVersion, Feature, ScalaRelease}
 import MegaPhase.MiniPhase
 import scala.util.{Failure, Success}
-import ast.tpd
+import ast.{tpd, untpd}
 
 class CrossVersionChecks extends MiniPhase:
   import tpd.*
@@ -21,6 +21,11 @@ class CrossVersionChecks extends MiniPhase:
   override def runsAfterGroupsOf: Set[String] = Set(FirstTransform.name)
     // We assume all type trees except TypeTree have been eliminated
 
+  override def checkPostCondition(tree: Tree)(using Context): Unit = tree match
+    case tree: Import =>
+      assert(untpd.languageImport(tree.expr).nonEmpty, i"illegal tree: $tree")
+    case _ =>
+
   // Note: if a symbol has both @deprecated and @migration annotations and both
   // warnings are enabled, only the first one checked here will be emitted.
   // I assume that's a consequence of some code trying to avoid noise by suppressing
@@ -182,7 +187,8 @@ class CrossVersionChecks extends MiniPhase:
         case t: RefTree => checkUndesiredProperties(t.symbol, t.srcPos)
         case _ =>
       }
-      tree
+      if untpd.languageImport(tree.expr).isEmpty then EmptyTree
+      else tree
     case _ => tree
 
 end CrossVersionChecks

tests/neg/i16156/Defs_1.scala

@@ -0,0 +1,25 @@
+//import quotes.reflect._
+
+trait MyEncoder[T]:
+  def encode: String
+class Context:
+  inline def summonMyEncoder[T]: String =
+    ${ SummonEncoder.impl[T] }
+  implicit val encoderInstance: MyEncoder[String] =
+    new MyEncoder[String] { def encode = "blah" }
+end Context
+
+import scala.quoted._
+
+object SummonEncoder:
+  def impl[T: Type](using Quotes) =
+    import quotes.reflect._
+    Expr.summon[MyEncoder[T]] match
+      case Some(enc) => '{ $enc.encode }
+      case None      => report.throwError("can't do it")
+
+class Repo[T]:
+  val ctx = new Context
+  inline def summonEncoder = { import ctx._ // change to: import ctx.{given, _} for the given example
+    ctx.summonMyEncoder[T]
+  }

tests/neg/i16156/Use_2.scala

@@ -0,0 +1,4 @@
+
+object Use:
+  val repo = new Repo[String]
+  val v = repo.summonEncoder // error happens here!