Merge pull request scala#4118 from retronym/ticket/5639

SI-5639 Fix spurious discarding of implicit import

Author: retronym

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

@@ -798,7 +798,7 @@ trait Contexts { self: Analyzer =>
       isAccessible(sym, pre) &&
       !(imported && {
         val e = scope.lookupEntry(name)
-        (e ne null) && (e.owner == scope)
+        (e ne null) && (e.owner == scope) && (!settings.isScala212 || e.sym.exists)
       })
 
     private def collectImplicits(syms: Scope, pre: Type, imported: Boolean = false): List[ImplicitInfo] =

test/files/neg/t2866.check

@@ -0,0 +1,17 @@
+t2866.scala:30: warning: imported `one' is permanently hidden by definition of value one
+    import A.one // warning: imported `one' is permanently hidden by definition of value one.
+             ^
+t2866.scala:42: error: ambiguous implicit values:
+ both value two of type Int
+ and value one in object A of type => Int
+ match expected type Int
+    assert(implicitly[Int] == 2) // !!! Not ambiguous in 2.8.0. Ambigous in 2.7.6
+                     ^
+t2866.scala:50: error: ambiguous implicit values:
+ both value two of type Int
+ and value one in object A of type => Int
+ match expected type Int
+    assert(implicitly[Int] == 2) // !!! Not ambiguous in 2.8.0. Ambiguous in 2.7.6
+                     ^
+one warning found
+two errors found

test/files/neg/t2866.scala

@@ -0,0 +1,59 @@
+// for 2.7.x compatibility
+
+object A {
+  implicit val one = 1
+}
+
+object Test {
+
+  locally {
+    import A._
+    locally {
+      // assert(implicitly[Int] == 1) // error: could not find implicit value for parameter e: Int.
+                                     // !!! Why one A.one?
+      // (I assume you mean: why _not_ A.one? A.one is shadowed by local one.
+      // but the local one cannot be used yet because it does not have an explicit type.
+      implicit val one = 2
+      assert(implicitly[Int] == 2)
+      assert(one == 2)
+    }
+  }
+
+  locally {
+    import A._
+    implicit val one: Int = 2
+    assert(implicitly[Int] == 2)
+    assert(one == 2)
+  }
+
+  locally {
+    import A.one // warning: imported `one' is permanently hidden by definition of value one.
+                 // !!! Really?
+    //assert(implicitly[Int] == 1)
+    implicit val one = 2
+    assert(implicitly[Int] == 2) // !!! why not 2?
+    assert(one == 2)
+  }
+
+  locally {
+    import A.one
+    assert(implicitly[Int] == 1)
+    implicit val two = 2
+    assert(implicitly[Int] == 2) // !!! Not ambiguous in 2.8.0. Ambigous in 2.7.6
+  }
+
+  locally {
+    import A._
+    assert(implicitly[Int] == 1)
+    implicit val two = 2
+    import A.{one => _}
+    assert(implicitly[Int] == 2) // !!! Not ambiguous in 2.8.0. Ambiguous in 2.7.6
+  }
+
+  locally {
+    import A.{one => _, _}
+    implicit val two = 2
+    assert(implicitly[Int] == 2) // not ambiguous in 2.8.0 nor im ambiguous in 2.7.6
+  }
+
+}

test/files/neg/t5639b.check

@@ -0,0 +1,4 @@
+A_2.scala:6: error: could not find implicit value for parameter e: Int
+  implicitly[Int]
+            ^
+one error found

test/files/neg/t5639b/A_1.scala

@@ -0,0 +1,17 @@
+import Implicits._
+
+class Baz
+
+object Test {
+  implicitly[Int]
+}
+
+object Implicits  {
+  implicit val Baz: Int = 0
+  // This implicit was being ignored by `isQualifyingImplicit`
+  // if the classpath contained a class file for `class Baz`.
+  // This is because the package scope contains a speculative
+  // symbol for `object Baz` which is entered by `SymbolLoaders`
+  // before looking inside the class file. (A Java originated
+  // classfile results in the class/module symbol pair.)
+}

test/files/neg/t5639b/A_2.scala

@@ -0,0 +1,11 @@
+import Implicits._
+
+class Baz
+
+object Test {
+  implicitly[Int]
+}
+
+object Implicits  {
+  implicit val Baz: Int = 0
+}

test/files/pos/t5639.flags

@@ -0,0 +1 @@
+-Xsource:2.12

test/files/pos/t5639/A_1.scala

@@ -0,0 +1,17 @@
+import Implicits._
+
+class Baz
+
+object Test {
+  implicitly[Int]
+}
+
+object Implicits  {
+  implicit val Baz: Int = 0
+  // This implicit was being ignored by `isQualifyingImplicit`
+  // if the classpath contained a class file for `class Baz`.
+  // This is because the package scope contains a speculative
+  // symbol for `object Baz` which is entered by `SymbolLoaders`
+  // before looking inside the class file. (A Java originated
+  // classfile results in the class/module symbol pair.)
+}

test/files/pos/t5639/A_2.scala

@@ -0,0 +1,11 @@
+import Implicits._
+
+class Baz
+
+object Test {
+  implicitly[Int]
+}
+
+object Implicits  {
+  implicit val Baz: Int = 0
+}

test/files/pos/t5639/Bar.scala

@@ -0,0 +1,3 @@
+t2866.scala:30: warning: imported `one' is permanently hidden by definition of value one
+    import A.one // warning: imported `one' is permanently hidden by definition of value one.
+             ^

test/files/pos/t5639/Foo.scala

@@ -0,0 +1,44 @@
+// for 2.7.x compatibility
+
+object A {
+  implicit val one = 1
+}
+
+object Test extends App {
+
+  locally {
+    import A._
+    locally {
+      // assert(implicitly[Int] == 1) // error: could not find implicit value for parameter e: Int.
+                                     // !!! Why one A.one?
+      // (I assume you mean: why _not_ A.one? A.one is shadowed by local one.
+      // but the local one cannot be used yet because it does not have an explicit type.
+      implicit val one = 2
+      assert(implicitly[Int] == 2)
+      assert(one == 2)
+    }
+  }
+
+  locally {
+    import A._
+    implicit val one: Int = 2
+    assert(implicitly[Int] == 2)
+    assert(one == 2)
+  }
+
+  locally {
+    import A.one // warning: imported `one' is permanently hidden by definition of value one.
+                 // !!! Really?
+    //assert(implicitly[Int] == 1)
+    implicit val one = 2
+    assert(implicitly[Int] == 2) // !!! why not 2?
+    assert(one == 2)
+  }
+
+  locally {
+    import A.{one => _, _}
+    implicit val two = 2
+    assert(implicitly[Int] == 2) // not ambiguous in 2.8.0 nor im ambiguous in 2.7.6
+  }
+
+}