Merge pull request #10706 from som-snytt/issue/12967-msg

Improve symbol in implicit result check [ci: last-only]

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

@@ -126,14 +126,19 @@ trait Implicits extends splain.SplainData {
     if (settings.areStatisticsEnabled) statistics.stopCounter(findMemberImpl, findMemberStart)
     if (settings.areStatisticsEnabled) statistics.stopCounter(subtypeImpl, subtypeStart)
 
-    val rts = result.tree.symbol
-    if (result.isSuccess && rts != null) {
+    if (result.isSuccess) {
+      val rts = {
+        val infoSym = if (result.implicitInfo != null) result.implicitInfo.sym else NoSymbol
+        infoSym.orElse {
+          val rts0 = result.tree.symbol
+          if (rts0 != null) rts0 else NoSymbol
+        }
+      }
       if (settings.lintImplicitRecursion) {
         val s = if (rts.isAccessor) rts.accessed else if (rts.isModule) rts.moduleClass else rts
         if (s != NoSymbol && context.owner.hasTransOwner(s))
           context.warning(result.tree.pos, s"Implicit resolves to enclosing $rts", WarningCategory.WFlagSelfImplicit)
       }
-
       if (result.inPackagePrefix && currentRun.isScala3) {
         val msg =
           s"""Implicit $rts was found in a package prefix of the required type, which is not part of the implicit scope in Scala 3.

test/files/neg/t12919.check

@@ -4,4 +4,10 @@ Scala 3 migration messages are errors under -Xsource:3. Use -Wconf / @nowarn to
 Applicable -Wconf / @nowarn filters for this fatal warning: msg=<part of the message>, cat=scala3-migration, site=b.V.f
     def f(xs: List[a.A]) = xs.sorted // warn
                               ^
-1 error
+t12919.scala:48: error: Implicit method myClassToSeq was found in a package prefix of the required type, which is not part of the implicit scope in Scala 3.
+For migration, add `import a1.a2.myClassToSeq`.
+Scala 3 migration messages are errors under -Xsource:3. Use -Wconf / @nowarn to filter them or add -Xmigration to demote them to warnings.
+Applicable -Wconf / @nowarn filters for this fatal warning: msg=<part of the message>, cat=scala3-migration, site=a1.Main.f
+    def f[A](x: Seq[a1.a2.MyClass[A]]): Seq[A] = x.flatten
+                                                   ^
+2 errors

test/files/neg/t12919.scala

@@ -1,4 +1,4 @@
-// scalac: -Xsource:3 -Werror
+//> using options -Xsource:3 -Werror
 
 package object a {
   implicit val aOrd: Ordering[A] = null
@@ -34,3 +34,17 @@ package c {
   }
 }
 
+package a1 {
+
+  package object a2 {
+    implicit def myClassToSeq[A](a: MyClass[A]): Seq[A] = a.values
+  }
+
+  package a2 {
+    case class MyClass[A](values: Seq[A])
+  }
+
+  object Main {
+    def f[A](x: Seq[a1.a2.MyClass[A]]): Seq[A] = x.flatten
+  }
+}