Map over refs of ImportTypes in TypeMap (#20837)

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

Both i19493 and i19436 require mapping the type of the expr in an
`ImportType` which is itself the info of a `TermRef`.
In the first issue, for the substitution of an inline def parameter
proxy.
In the second issue, for the parameter of a lambda returned from an
inline def.

Both can be handled in `TypeMap` by mapping over references to
`ImportType`s.
The second case also requires modifying `TreeTypeMap#mapType` such that
the logic mapping over imports is done within a `TypeMap` doing the
symbol substitutions.

Also note these mappings are only necessary for `summonInline`s (which
could have just been made non-inline) resolving
post-inlining to givens imported within the inline definition.

Fix #19493
Fix #19436

Author: odersky

Diff for: 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)

Diff for: 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

Diff for: 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]
+    }

Diff for: tests/pos-macros/i19436/Test_2.scala

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

Diff for: 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