Fix #9928: Don't treat import contexts as properly nested

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

@@ -247,7 +247,7 @@ object Contexts {
             else
               outer.implicits
           if (implicitRefs.isEmpty) outerImplicits
-          else new ContextualImplicits(implicitRefs, outerImplicits)(this)
+          else new ContextualImplicits(implicitRefs, outerImplicits, isImportContext)(this)
         }
       implicitsCache
     }
@@ -777,7 +777,7 @@ object Contexts {
 
   @sharable object NoContext extends Context(null) {
     source = NoSource
-    override val implicits: ContextualImplicits = new ContextualImplicits(Nil, null)(this)
+    override val implicits: ContextualImplicits = new ContextualImplicits(Nil, null, false)(this)
   }
 
   /** A context base defines state and associated methods that exist once per

compiler/src/dotty/tools/dotc/typer/Implicits.scala

@@ -295,7 +295,10 @@ object Implicits:
    *                   name, b, whereas the name of the symbol is the original name, a.
    *  @param outerCtx  the next outer context that makes visible further implicits
    */
-  class ContextualImplicits(val refs: List[ImplicitRef], val outerImplicits: ContextualImplicits)(initctx: Context) extends ImplicitRefs(initctx) {
+  class ContextualImplicits(
+      val refs: List[ImplicitRef],
+      val outerImplicits: ContextualImplicits,
+      isImport: Boolean)(initctx: Context) extends ImplicitRefs(initctx) {
     private val eligibleCache = EqHashMap[Type, List[Candidate]]()
 
     /** The level increases if current context has a different owner or scope than
@@ -304,7 +307,8 @@ object Implicits:
      */
     override val level: Int =
       if outerImplicits == null then 1
-      else if migrateTo3(using irefCtx)
+      else if isImport && (irefCtx.owner eq outerImplicits.irefCtx.owner)
+              || migrateTo3(using irefCtx)
               || (irefCtx.owner eq outerImplicits.irefCtx.owner)
                  && (irefCtx.scope eq outerImplicits.irefCtx.scope)
                  && !refs.head.implicitName.is(LazyImplicitName)
@@ -370,7 +374,7 @@ object Implicits:
         val outerExcluded = outerImplicits exclude root
         if (irefCtx.importInfo.site.termSymbol == root) outerExcluded
         else if (outerExcluded eq outerImplicits) this
-        else new ContextualImplicits(refs, outerExcluded)(irefCtx)
+        else new ContextualImplicits(refs, outerExcluded, isImport)(irefCtx)
       }
   }
 

compiler/src/dotty/tools/dotc/typer/ImportSuggestions.scala

@@ -13,6 +13,7 @@ import ast.{untpd, tpd}
 import Implicits.{hasExtMethod, Candidate}
 import java.util.{Timer, TimerTask}
 import collection.mutable
+import scala.util.control.NonFatal
 
 /** This trait defines the method `importSuggestionAddendum` that adds an addendum
  *  to error messages suggesting additional imports.
@@ -58,10 +59,12 @@ trait ImportSuggestions:
     val seen = mutable.Set[TermRef]()
 
     def lookInside(root: Symbol)(using Context): Boolean =
-      if root.is(Package) then root.isTerm && root.isCompleted
-      else !root.name.is(FlatName)
-        && !root.name.lastPart.contains('$')
-        && root.is(ModuleVal, butNot = JavaDefined)
+      explore {
+        if root.is(Package) then root.isTerm && root.isCompleted
+        else !root.name.is(FlatName)
+          && !root.name.lastPart.contains('$')
+          && root.is(ModuleVal, butNot = JavaDefined)
+      }
 
     def nestedRoots(site: Type)(using Context): List[Symbol] =
       val seenNames = mutable.Set[Name]()
@@ -245,12 +248,11 @@ trait ImportSuggestions:
         match
           case (Nil, partials) => (extensionImports, partials)
           case givenImports => givenImports
-    catch
-      case ex: Throwable =>
-        if ctx.settings.Ydebug.value then
-          println("caught exception when searching for suggestions")
-          ex.printStackTrace()
-        (Nil, Nil)
+    catch case NonFatal(ex) =>
+      if ctx.settings.Ydebug.value then
+        println("caught exception when searching for suggestions")
+        ex.printStackTrace()
+      (Nil, Nil)
     finally
       timer.cancel()
       reduceTimeBudget(((System.currentTimeMillis() - start) min Int.MaxValue).toInt)

tests/neg/i9928.scala

@@ -0,0 +1,26 @@
+trait Magic[F]:
+  extension (x: Int) def read: F
+
+object Magic:
+  given Magic[String]:
+    extension(x: Int) def read: String =
+      println("In string")
+      s"$x"
+
+opaque type Foo = String
+object Foo:
+  import Magic.{given _}
+  def apply(s: String): Foo = s
+
+  given Magic[Foo]:
+    extension (x: Int) def read: Foo =
+      println("In foo")
+      Foo(s"$x")
+
+  def test: Unit =
+    (3.read: Foo)  // error: ambiguous
+
+
+@main def Test = {
+  Foo.test
+}

tests/run/i9928.check

@@ -0,0 +1,2 @@
+In foo
+In foo

tests/run/i9928.scala

@@ -0,0 +1,44 @@
+trait Magic[F]:
+  extension (x: Int) def read: F
+
+trait LowPrio:
+  given Magic[String]:
+    extension(x: Int) def read: String =
+      println("In string")
+      s"$x"
+
+object test1:
+  object Magic extends LowPrio
+
+  opaque type Foo = String
+  object Foo extends LowPrio:
+    import Magic.{given _}
+    def apply(s: String): Foo = s
+
+    given Magic[Foo]:
+      extension (x: Int) def read: Foo =
+        println("In foo")
+        Foo(s"$x")
+
+    def test: Unit =
+      (3.read: Foo)
+
+object test2:
+  object Magic extends LowPrio:
+    given Magic[Foo]:
+      extension (x: Int) def read: Foo =
+        println("In foo")
+        Foo(s"$x")
+
+  opaque type Foo = String
+  object Foo extends LowPrio:
+    import Magic.{given _}
+    def apply(s: String): Foo = s
+
+    def test: Unit =
+      (3.read: Foo)
+
+
+@main def Test =
+  test1.Foo.test
+  test2.Foo.test