Under -Xsource:3, adjust 2.13.9 change to ignore override type for whitebox macro expansion

src/compiler/scala/tools/nsc/typechecker/Namers.scala

@@ -1120,14 +1120,34 @@ trait Namers extends MethodSynthesis {
 
     /** Computes the type of the body in a ValDef or DefDef, and
      *  assigns the type to the tpt's node.  Returns the type.
+     *
+     *  Under `-Xsource:3`, use `pt`, the type of the overridden member.
+     *  But preserve the precise type of a whitebox macro.
+     *  For `def f = macro g`, here we see `def f = xp(g)` the expansion,
+     *  not the `isMacro` case: `openMacros` will be nonEmpty.
+     *  For `def m = f`, retrieve the typed RHS and check if it is an expansion;
+     *  in that case, check if the expandee `f` is whitebox and preserve
+     *  the precise type if it is. The user must provide an explicit type
+     *  to "opt out" of the inferred narrow type; in Scala 3, they would
+     *  inline the def to "opt in".
      */
     private def assignTypeToTree(tree: ValOrDefDef, defnTyper: Typer, pt: Type): Type = {
       val rhsTpe = tree match {
-        case ddef: DefDef if tree.symbol.isTermMacro => defnTyper.computeMacroDefType(ddef, pt)
+        case ddef: DefDef if tree.symbol.isTermMacro => defnTyper.computeMacroDefType(ddef, pt) // unreached, see methodSig
         case _ => defnTyper.computeType(tree.rhs, pt)
       }
       tree.tpt.defineType {
-        if (currentRun.isScala3 && !pt.isWildcard && pt != NoType && !pt.isErroneous && openMacros.isEmpty) pt
+        val inferOverridden = currentRun.isScala3 &&
+          !pt.isWildcard && pt != NoType && !pt.isErroneous &&
+          openMacros.isEmpty && {
+            context.unit.transformed.get(tree.rhs) match {
+              case Some(t) if t.hasAttachment[MacroExpansionAttachment] =>
+                val xp = macroExpandee(t)
+                xp.symbol == null || isBlackbox(xp.symbol)
+              case _ => true
+            }
+          }
+        if (inferOverridden) pt
         else dropIllegalStarTypes(widenIfNecessary(tree.symbol, rhsTpe, pt))
       }.setPos(tree.pos.focus)
       tree.tpt.tpe

test/files/neg/t12647.check

@@ -0,0 +1,4 @@
+Test_3.scala:6: error: value value is not a member of Result
+  println(resolver.resolve.value)
+                           ^
+1 error

test/files/neg/t12647/Macro_1.scala

@@ -0,0 +1,13 @@
+
+// scalac: -Xsource:3
+
+import scala.reflect.macros.blackbox.Context
+
+trait Result
+
+object Macros {
+  def impl(c: Context) = {
+    import c.universe._
+    q"""new Result { def value = "Was this the answer you sought?" }"""
+  }
+}

test/files/neg/t12647/Resolve_2.scala

@@ -0,0 +1,13 @@
+
+// scalac: -Xsource:3
+
+import language.experimental.macros
+
+trait Resolver {
+  def resolve: Result = ???
+}
+
+class ValueResolver extends Resolver {
+  override def resolve = valueResult
+  def valueResult: Result = macro Macros.impl
+}

test/files/neg/t12647/Test_3.scala

@@ -0,0 +1,7 @@
+
+// scalac: -Xsource:3
+
+object Test extends App {
+  val resolver = new ValueResolver
+  println(resolver.resolve.value)
+}

test/files/pos/t12647/Macro_1.scala

@@ -0,0 +1,13 @@
+
+// scalac: -Xsource:3
+
+import scala.reflect.macros.whitebox.Context
+
+trait Result
+
+object Macros {
+  def impl(c: Context) = {
+    import c.universe._
+    q"""new Result { def value = "Was this the answer you sought?" }"""
+  }
+}

test/files/pos/t12647/Resolve_2.scala

@@ -0,0 +1,13 @@
+
+// scalac: -Xsource:3
+
+import language.experimental.macros
+
+trait Resolver {
+  def resolve: Result = ???
+}
+
+class ValueResolver extends Resolver {
+  override def resolve = valueResult
+  def valueResult: Result = macro Macros.impl
+}

test/files/pos/t12647/Test_3.scala

@@ -0,0 +1,7 @@
+
+// scalac: -Xsource:3
+
+object Test extends App {
+  val resolver = new ValueResolver
+  println(resolver.resolve.value)
+}

test/files/pos/t12647b/Macro_1.scala

@@ -0,0 +1,11 @@
+
+import scala.reflect.macros.whitebox.Context
+
+trait Result
+
+object Macros {
+  def impl(c: Context): c.Tree = {
+    import c.universe._
+    q"""new Result { def value = "Was this the answer you sought?" }"""
+  }
+}

test/files/pos/t12647b/Resolve_2.scala

@@ -0,0 +1,11 @@
+
+import language.experimental.macros
+
+abstract class Resolver {
+  def resolve: Result = ???
+}
+
+class ValueResolver extends Resolver {
+  override def resolve = valueResult
+  def valueResult: Result = macro Macros.impl
+}

test/files/pos/t12647b/Test_3.scala

@@ -0,0 +1,5 @@
+
+object Test extends App {
+  val resolver = new ValueResolver
+  println(resolver.resolve.value)
+}