[backport] SI-6567 Warning for Option(implicitView(foo))

commit 284bd754fa5dfc8bc626b0c5ebe85d872dd044cb
Author: Jason Zaugg <jzaugg@gmail.com>
Date:   Sat Nov 3 16:19:46 2012 +0100

    SI-6567 Warning for Option(implicitView(foo))

    I've seen the reported problem before in the wild. It seems
    worthy of a special warning, so long as we advocate Option.apply
    as an alternative to `if (x == null) Some(x) else None`.

    It is behind -Xlint at the moment, an option that could do with
    some promotion.
    (cherry picked from commit 0bcb9e9169146e3f589c6c9f65cc4a5523b78120)

5 files changed, 35 insertions, 5 deletions

diff --git a/src/compiler/scala/tools/nsc/typechecker/RefChecks.scala b/src/compiler/scala/tools/nsc/typechecker/RefChecks.scala
index 7118375b82..969bb8aceb 100644
--- a/src/compiler/scala/tools/nsc/typechecker/RefChecks.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/RefChecks.scala
@@ -1062,6 +1062,12 @@ abstract class RefChecks extends InfoTransform with scala.reflect.internal.trans
       def apply(tp: Type) = mapOver(tp).normalize
     }
 
+    def checkImplicitViewOptionApply(pos: Position, fn: Tree, args: List[Tree]): Unit = if (settings.lint.value) (fn, args) match {
+      case (tap@TypeApply(fun, targs), List(view: ApplyImplicitView)) if fun.symbol == Option_apply =>
+        unit.warning(pos, s"Suspicious application of an implicit view (${view.fun}) in the argument to Option.apply.") // SI-6567
+      case _ =>
+    }
+
     def checkSensible(pos: Position, fn: Tree, args: List[Tree]) = fn match {
       case Select(qual, name @ (nme.EQ | nme.NE | nme.eq | nme.ne)) if args.length == 1 =>
         def isReferenceOp = name == nme.eq || name == nme.ne
@@ -1563,7 +1569,10 @@ abstract class RefChecks extends InfoTransform with scala.reflect.internal.trans
 
       case Apply(fn, args) =>
         // sensicality should be subsumed by the unreachability/exhaustivity/irrefutability analyses in the pattern matcher
-        if (!inPattern) checkSensible(tree.pos, fn, args)
+        if (!inPattern) {
+          checkImplicitViewOptionApply(tree.pos, fn, args)
+          checkSensible(tree.pos, fn, args)
+        }
         currentApplication = tree
         tree
     }
diff --git a/src/reflect/scala/reflect/internal/Definitions.scala b/src/reflect/scala/reflect/internal/Definitions.scala
index 2a7b55cb5a..4bd0aca9c4 100644
--- a/src/reflect/scala/reflect/internal/Definitions.scala
+++ b/src/reflect/scala/reflect/internal/Definitions.scala
@@ -536,10 +536,12 @@ trait Definitions extends api.StandardDefinitions {
     lazy val ScalaLongSignatureAnnotation = requiredClass[scala.reflect.ScalaLongSignature]
 
     // Option classes
-    lazy val OptionClass: ClassSymbol = requiredClass[Option[_]]
-    lazy val SomeClass: ClassSymbol   = requiredClass[Some[_]]
-    lazy val NoneModule: ModuleSymbol = requiredModule[scala.None.type]
-    lazy val SomeModule: ModuleSymbol = requiredModule[scala.Some.type]
+    lazy val OptionClass: ClassSymbol   = requiredClass[Option[_]]
+    lazy val OptionModule: ModuleSymbol = requiredModule[scala.Option.type]
+      lazy val Option_apply             = getMemberMethod(OptionModule, nme.apply)
+    lazy val SomeClass: ClassSymbol     = requiredClass[Some[_]]
+    lazy val NoneModule: ModuleSymbol   = requiredModule[scala.None.type]
+    lazy val SomeModule: ModuleSymbol   = requiredModule[scala.Some.type]
 
     def compilerTypeFromTag(tt: ApiUniverse # WeakTypeTag[_]): Type = tt.in(rootMirror).tpe
     def compilerSymbolFromTag(tt: ApiUniverse # WeakTypeTag[_]): Symbol = tt.in(rootMirror).tpe.typeSymbol
diff --git a/test/files/neg/t6567.check b/test/files/neg/t6567.check
new file mode 100644
index 0000000000..4c513e64cd
--- /dev/null
+++ b/test/files/neg/t6567.check
@@ -0,0 +1,7 @@
+t6567.scala:8: error: Suspicious application of an implicit view (Test.this.a2b) in the argument to Option.apply.
+  Option[B](a)
+           ^
+t6567.scala:10: error: Suspicious application of an implicit view (Test.this.a2b) in the argument to Option.apply.
+  val b: Option[B] = Option(a)
+                           ^
+two errors found
diff --git a/test/files/neg/t6567.flags b/test/files/neg/t6567.flags
new file mode 100644
index 0000000000..e93641e931
--- /dev/null
+++ b/test/files/neg/t6567.flags
@@ -0,0 +1 @@
+-Xlint -Xfatal-warnings
\ No newline at end of file
diff --git a/test/files/neg/t6567.scala b/test/files/neg/t6567.scala
new file mode 100644
index 0000000000..650e5e39ae
--- /dev/null
+++ b/test/files/neg/t6567.scala
@@ -0,0 +1,11 @@
+class A
+class B
+
+object Test {
+  val a: A = null
+  implicit def a2b(a: A) = new B
+
+  Option[B](a)
+
+  val b: Option[B] = Option(a)
+}