Merge pull request scala#752 from retronym/topic/warn-catch-all-4

SI-2807 Resurrect and refine the promiscuous catch warning.

Author: Adriaan Moors

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

@@ -4863,6 +4863,16 @@ trait Typers extends Modes with Adaptations with Tags {
         case Try(block, catches, finalizer) =>
           var block1 = typed(block, pt)
           var catches1 = typedCases(catches, ThrowableClass.tpe, pt)
+
+          for (cdef <- catches1 if cdef.guard.isEmpty) {
+            def warn(name: Name) = context.warning(cdef.pat.pos, s"This catches all Throwables. If this is really intended, use `case ${name.decoded} : Throwable` to clear this warning.")
+            cdef.pat match {
+              case Bind(name, Ident(_)) => warn(name)
+              case Ident(name)          => warn(name)
+              case _ =>
+            }
+          }
+
           val finalizer1 = if (finalizer.isEmpty) finalizer
                            else typed(finalizer, UnitClass.tpe)
           val (owntype, needAdapt) = ptOrLub(block1.tpe :: (catches1 map (_.tpe)), pt)

test/files/continuations-neg/trycatch2.scala

@@ -12,15 +12,15 @@ object Test {
     fatal[Int]
     cpsIntStringInt
   } catch {
-    case ex =>
+    case ex: Throwable =>
       cpsIntStringInt
   }
 
   def foo2 = try {
     fatal[Int]
     cpsIntStringInt
   } catch {
-    case ex =>
+    case ex: Throwable =>
       cpsIntStringInt
   }
 
@@ -30,4 +30,4 @@ object Test {
     println(reset { foo2; "3" })
   }
 
-}
+}

test/files/neg/catch-all.check

@@ -0,0 +1,10 @@
+catch-all.scala:2: error: This catches all Throwables. If this is really intended, use `case _ : Throwable` to clear this warning.
+	try { "warn" } catch { case _ => }
+                                    ^
+catch-all.scala:4: error: This catches all Throwables. If this is really intended, use `case x : Throwable` to clear this warning.
+	try { "warn" } catch { case x => }
+                                    ^
+catch-all.scala:6: error: This catches all Throwables. If this is really intended, use `case x : Throwable` to clear this warning.
+	try { "warn" } catch { case _: RuntimeException => ; case x => }
+                                                                  ^
+three errors found

test/files/neg/catch-all.flags

@@ -0,0 +1 @@
+-Xfatal-warnings

test/files/neg/catch-all.scala

@@ -0,0 +1,19 @@
+object CatchAll {
+	try { "warn" } catch { case _ => }
+
+	try { "warn" } catch { case x => }
+
+	try { "warn" } catch { case _: RuntimeException => ; case x => }
+
+	try { "okay" } catch { case _: Throwable => }
+
+	try { "okay" } catch { case _: Exception => }
+
+	try { "okay" } catch { case okay: Throwable => }
+
+	try { "okay" } catch { case okay: Exception => }
+
+	try { "okay" } catch { case _ if "".isEmpty => }
+
+	"okay" match { case _ => "" }
+}