Backport "Map over refs of ImportTypes in TypeMap" to 3.5.1 (#20957)

Backports #20837 to 3.5.1-RC1

compiler/src/dotty/tools/dotc/ast/TreeTypeMap.scala

@@ -69,7 +69,12 @@ class TreeTypeMap(
   }
 
   def mapType(tp: Type): Type =
-    mapOwnerThis(typeMap(tp).substSym(substFrom, substTo))
+    val substMap = new TypeMap():
+      def apply(tp: Type): Type = tp match
+        case tp: TermRef if tp.symbol.isImport => mapOver(tp)
+        case tp => tp.substSym(substFrom, substTo)
+    mapOwnerThis(substMap(typeMap(tp)))
+  end mapType
 
   private def updateDecls(prevStats: List[Tree], newStats: List[Tree]): Unit =
     if (prevStats.isEmpty) assert(newStats.isEmpty)

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

@@ -6295,6 +6295,12 @@ object Types extends TypeUtils {
       val ctx = this.mapCtx // optimization for performance
       given Context = ctx
       tp match {
+        case tp: TermRef if tp.symbol.isImport =>
+          // see tests/pos/i19493.scala for examples requiring mapping over imports
+          val ImportType(e) = tp.info: @unchecked
+          val e1 = singleton(apply(e.tpe))
+          newImportSymbol(tp.symbol.owner, e1).termRef
+
         case tp: NamedType =>
           if stopBecauseStaticOrLocal(tp) then tp
           else

tests/pos-macros/i19436/Macro_1.scala

@@ -0,0 +1,18 @@
+
+import scala.quoted.*
+import scala.compiletime.summonInline
+
+trait SomeImplicits:
+  given int: Int
+
+object Macro:
+
+  transparent inline def testSummon: SomeImplicits => Int = ${ testSummonImpl }
+
+  private def testSummonImpl(using Quotes): Expr[SomeImplicits => Int] =
+    import quotes.reflect.*
+    '{
+      (x: SomeImplicits) =>
+        import x.given
+        summonInline[Int]
+    }

tests/pos-macros/i19436/Test_2.scala

@@ -0,0 +1,2 @@
+
+def fn: Unit = Macro.testSummon

tests/pos/i19493.scala

@@ -0,0 +1,49 @@
+import scala.compiletime.{summonAll, summonInline}
+import deriving.Mirror
+
+type Sc[X] = X
+case class Row[T[_]](name: T[String])
+
+class DialectTypeMappers:
+  given String = ???
+
+inline def metadata(dialect: DialectTypeMappers)(using m: Mirror.Of[Row[Sc]]): m.MirroredElemTypes =
+  import dialect.given
+  summonAll[m.MirroredElemTypes]
+
+def f = metadata(???)
+
+
+object Minimization:
+
+  class GivesString:
+    given aString: String = ???
+
+  inline def foo(x: GivesString): Unit =
+    import x.aString
+    summon[String] // ok
+    summonInline[String] // was error
+
+  foo(???)
+
+
+  trait A:
+    val x: GivesString
+
+    inline def bar: Unit =
+      import this.x.aString
+      summon[String] // ok
+      summonInline[String] // was error
+
+  val a: A = ???
+  a.bar
+
+
+  inline def baz() = (x: GivesString) =>
+    import x.aString
+    summon[String] // ok
+    summonInline[String] // was error
+
+  baz()
+
+end Minimization