Map over ImportTypes in inliner tree type map

The inliner replaces references to parameters by
their corresponding proxys, including in singleton types.
It did not, however, handle the mapping over import types,
the symbols of which way have depended on parameters.

Mapping imports correctly was necessary for i19493
since the `summonInline` resolves post inlining to
a given imported within the inline definition.

Fix #19493

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

@@ -565,6 +565,11 @@ class Inliner(val call: tpd.Tree)(using Context):
           def apply(t: Type) = t match {
             case t: ThisType => thisProxy.getOrElse(t.cls, t)
             case t: TypeRef => paramProxy.getOrElse(t, mapOver(t))
+            case t: TermRef if t.symbol.isImport =>
+              val ImportType(e) = t.widenTermRefExpr: @unchecked
+              paramProxy.get(e.tpe) match
+                case Some(p) => newImportSymbol(ctx.owner, singleton(p)).termRef
+                case None => mapOver(t)
             case t: SingletonType =>
               if t.termSymbol.isAllOf(InlineParam) then apply(t.widenTermRefExpr)
               else paramProxy.getOrElse(t, mapOver(t))

tests/pos/i19493.scala

@@ -0,0 +1,29 @@
+
+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]
+    summonInline[String] // was error
+
+  foo(???)
+end Minimization