SI-9847 Nuance pure expr statement warning

Clarify the current warning, which means that an expression
split over multiple lines may not be parsed as naively expected.

When typing a block, attempt minor nuance. For instance, a
single expression is not in need of parens. Try to avoid
duplicate warnings for expressions that were adapted away
from result position.

35 files changed, 207 insertions, 95 deletions

diff --git a/src/compiler/scala/tools/nsc/typechecker/Typers.scala b/src/compiler/scala/tools/nsc/typechecker/Typers.scala
index 9fa3564b2b..6b0bd98f8f 100644
--- a/src/compiler/scala/tools/nsc/typechecker/Typers.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/Typers.scala
@@ -2413,13 +2413,36 @@ trait Typers extends Adaptations with Tags with TypersTracking with PatternTyper
           }
         }
         val stats1 = if (isPastTyper) block.stats else
-          block.stats.flatMap(stat => stat match {
+          block.stats.flatMap {
             case vd@ValDef(_, _, _, _) if vd.symbol.isLazy =>
               namer.addDerivedTrees(Typer.this, vd)
-            case _ => stat::Nil
-            })
-        val stats2 = typedStats(stats1, context.owner)
+            case stat => stat::Nil
+          }
+        val stats2 = typedStats(stats1, context.owner, warnPure = false)
         val expr1 = typed(block.expr, mode &~ (FUNmode | QUALmode), pt)
+
+        // sanity check block for unintended expr placement
+        if (!isPastTyper) {
+          val (count, result0, adapted) =
+            expr1 match {
+              case Block(expr :: Nil, Literal(Constant(()))) => (1, expr, true)
+              case Literal(Constant(()))                     => (0, EmptyTree, false)
+              case _                                         => (1, EmptyTree, false)
+            }
+          def checkPure(t: Tree, supple: Boolean): Unit =
+            if (treeInfo.isPureExprForWarningPurposes(t)) {
+              val msg = "a pure expression does nothing in statement position"
+              val parens = if (stats2.length + count > 1) "multiline expressions might require enclosing parentheses" else ""
+              val discard = if (adapted) "; a value can be silently discarded when Unit is expected" else ""
+              val text =
+                if (supple) s"${parens}${discard}"
+                else if (!parens.isEmpty) s"${msg}; ${parens}" else msg
+              context.warning(t.pos, text)
+            }
+          stats2.foreach(checkPure(_, supple = false))
+          if (result0.nonEmpty) checkPure(result0, supple = true)
+        }
+
         treeCopy.Block(block, stats2, expr1)
           .setType(if (treeInfo.isExprSafeToInline(block)) expr1.tpe else expr1.tpe.deconst)
       } finally {
@@ -2994,7 +3017,7 @@ trait Typers extends Adaptations with Tags with TypersTracking with PatternTyper
       case _                  => log("unhandled import: "+imp+" in "+unit); imp
     }
 
-    def typedStats(stats: List[Tree], exprOwner: Symbol): List[Tree] = {
+    def typedStats(stats: List[Tree], exprOwner: Symbol, warnPure: Boolean = true): List[Tree] = {
       val inBlock = exprOwner == context.owner
       def includesTargetPos(tree: Tree) =
         tree.pos.isRange && context.unit.exists && (tree.pos includes context.unit.targetPos)
@@ -3025,9 +3048,11 @@ trait Typers extends Adaptations with Tags with TypersTracking with PatternTyper
                 ConstructorsOrderError(stat)
             }
           }
-          if (!isPastTyper && treeInfo.isPureExprForWarningPurposes(result)) context.warning(stat.pos,
-            "a pure expression does nothing in statement position; you may be omitting necessary parentheses"
-          )
+          if (warnPure && !isPastTyper && treeInfo.isPureExprForWarningPurposes(result)) {
+            val msg = "a pure expression does nothing in statement position"
+            val clause = if (stats.lengthCompare(1) > 0) "; multiline expressions may require enclosing parentheses" else ""
+            context.warning(stat.pos, s"${msg}${clause}")
+          }
           result
       }
 
diff --git a/test/files/neg/macro-invalidret.check b/test/files/neg/macro-invalidret.check
index ebdc8ec7da..a4d4fc6f34 100644
--- a/test/files/neg/macro-invalidret.check
+++ b/test/files/neg/macro-invalidret.check
@@ -27,7 +27,7 @@ java.lang.NullPointerException
 Macros_Test_2.scala:15: error: macro implementation is missing
   foo4
   ^
-Macros_Test_2.scala:17: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+Macros_Test_2.scala:17: warning: a pure expression does nothing in statement position; multiline expressions may require enclosing parentheses
   foo6
   ^
 two warnings found
diff --git a/test/files/neg/scopes.check b/test/files/neg/scopes.check
index f8e8c3758a..2db9678185 100644
--- a/test/files/neg/scopes.check
+++ b/test/files/neg/scopes.check
@@ -7,7 +7,7 @@ scopes.scala:5: error: x is already defined as value x
 scopes.scala:8: error: y is already defined as value y
     val y: Float = .0f
         ^
-scopes.scala:6: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+scopes.scala:6: warning: a pure expression does nothing in statement position; multiline expressions may require enclosing parentheses
   {
   ^
 scopes.scala:11: error: x is already defined as value x
diff --git a/test/files/neg/stmt-expr-discard.check b/test/files/neg/stmt-expr-discard.check
index 1207e6da50..4a80765365 100644
--- a/test/files/neg/stmt-expr-discard.check
+++ b/test/files/neg/stmt-expr-discard.check
@@ -1,7 +1,7 @@
-stmt-expr-discard.scala:3: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+stmt-expr-discard.scala:3: warning: a pure expression does nothing in statement position; multiline expressions may require enclosing parentheses
     + 2
     ^
-stmt-expr-discard.scala:4: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+stmt-expr-discard.scala:4: warning: a pure expression does nothing in statement position; multiline expressions may require enclosing parentheses
     - 4
       ^
 error: No warnings can be incurred under -Xfatal-warnings.
diff --git a/test/files/neg/t1181.check b/test/files/neg/t1181.check
index 13b73d5381..a9c102853d 100644
--- a/test/files/neg/t1181.check
+++ b/test/files/neg/t1181.check
@@ -1,10 +1,10 @@
-t1181.scala:8: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
-     case (Nil, Nil) => map
-                        ^
 t1181.scala:9: error: type mismatch;
  found   : scala.collection.immutable.Map[Symbol,Symbol]
  required: Symbol
      _ => buildMap(map.updated(keyList.head, valueList.head), keyList.tail, valueList.tail)
                   ^
+t1181.scala:8: warning: a pure expression does nothing in statement position; multiline expressions might require enclosing parentheses
+     case (Nil, Nil) => map
+                        ^
 one warning found
 one error found
diff --git a/test/files/neg/t9847.check b/test/files/neg/t9847.check
new file mode 100644
index 0000000000..e55109b3ef
--- /dev/null
+++ b/test/files/neg/t9847.check
@@ -0,0 +1,45 @@
+t9847.scala:4: warning: discarded non-Unit value
+  def f(): Unit = 42
+                  ^
+t9847.scala:4: warning: a pure expression does nothing in statement position
+  def f(): Unit = 42
+                  ^
+t9847.scala:5: warning: discarded non-Unit value
+  def g = (42: Unit)
+           ^
+t9847.scala:5: warning: a pure expression does nothing in statement position
+  def g = (42: Unit)
+           ^
+t9847.scala:7: warning: a pure expression does nothing in statement position; multiline expressions might require enclosing parentheses
+    1
+    ^
+t9847.scala:12: warning: discarded non-Unit value
+  + 1
+  ^
+t9847.scala:12: warning: a pure expression does nothing in statement position
+  + 1
+  ^
+t9847.scala:11: warning: a pure expression does nothing in statement position; multiline expressions might require enclosing parentheses
+    1
+    ^
+t9847.scala:12: warning: multiline expressions might require enclosing parentheses; a value can be silently discarded when Unit is expected
+  + 1
+  ^
+t9847.scala:16: warning: discarded non-Unit value
+    x + 1
+      ^
+t9847.scala:19: warning: discarded non-Unit value
+  def j(): Unit = x + 1
+                    ^
+t9847.scala:21: warning: a pure expression does nothing in statement position; multiline expressions may require enclosing parentheses
+  class C { 42 }
+            ^
+t9847.scala:22: warning: a pure expression does nothing in statement position; multiline expressions may require enclosing parentheses
+  class D { 42 ; 17 }
+            ^
+t9847.scala:22: warning: a pure expression does nothing in statement position; multiline expressions may require enclosing parentheses
+  class D { 42 ; 17 }
+                 ^
+error: No warnings can be incurred under -Xfatal-warnings.
+14 warnings found
+one error found
diff --git a/test/files/neg/t9847.flags b/test/files/neg/t9847.flags
new file mode 100644
index 0000000000..065e3ca61e
--- /dev/null
+++ b/test/files/neg/t9847.flags
@@ -0,0 +1 @@
+-Xfatal-warnings -Ywarn-value-discard
diff --git a/test/files/neg/t9847.scala b/test/files/neg/t9847.scala
new file mode 100644
index 0000000000..51c16d815f
--- /dev/null
+++ b/test/files/neg/t9847.scala
@@ -0,0 +1,23 @@
+
+trait T {
+
+  def f(): Unit = 42
+  def g = (42: Unit)
+  def h = {
+    1
+  + 1
+  }
+  def hh(): Unit = {
+    1
+  + 1
+  }
+  def i(): Unit = {
+    val x = 1
+    x + 1
+  }
+  def x = 42
+  def j(): Unit = x + 1
+
+  class C { 42 }
+  class D { 42 ; 17 }
+}
diff --git a/test/files/neg/unit-returns-value.check b/test/files/neg/unit-returns-value.check
index f30a506ebe..7ebfbfde29 100644
--- a/test/files/neg/unit-returns-value.check
+++ b/test/files/neg/unit-returns-value.check
@@ -1,13 +1,13 @@
-unit-returns-value.scala:4: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+unit-returns-value.scala:4: warning: a pure expression does nothing in statement position
     if (b) return 5
                   ^
 unit-returns-value.scala:4: warning: enclosing method f has result type Unit: return value discarded
     if (b) return 5
            ^
-unit-returns-value.scala:22: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+unit-returns-value.scala:22: warning: a pure expression does nothing in statement position; multiline expressions might require enclosing parentheses
     i1 // warn
     ^
-unit-returns-value.scala:23: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+unit-returns-value.scala:23: warning: a pure expression does nothing in statement position; multiline expressions might require enclosing parentheses
     i2 // warn
     ^
 error: No warnings can be incurred under -Xfatal-warnings.
diff --git a/test/files/run/contrib674.check b/test/files/run/contrib674.check
index 78325c1810..98c72f34dd 100644
--- a/test/files/run/contrib674.check
+++ b/test/files/run/contrib674.check
@@ -1,3 +1,6 @@
-contrib674.scala:15: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+contrib674.scala:15: warning: a pure expression does nothing in statement position
+    1
+    ^
+contrib674.scala:15: warning: multiline expressions might require enclosing parentheses; a value can be silently discarded when Unit is expected
     1
     ^
diff --git a/test/files/run/contrib674.scala b/test/files/run/contrib674.scala
index 45c9871fc4..bb9dad3686 100644
--- a/test/files/run/contrib674.scala
+++ b/test/files/run/contrib674.scala
@@ -1,7 +1,7 @@
 // causes VerifyError with scala-2.5.1
 
 object Test extends App {
-  def bad() {
+  def bad(): Unit = {
     try {
       1
     } catch {
diff --git a/test/files/run/delay-bad.check b/test/files/run/delay-bad.check
index fcd05c827f..bf41c79a3a 100644
--- a/test/files/run/delay-bad.check
+++ b/test/files/run/delay-bad.check
@@ -1,7 +1,7 @@
-delay-bad.scala:53: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+delay-bad.scala:53: warning: a pure expression does nothing in statement position; multiline expressions may require enclosing parentheses
     f(new C { 5 })
               ^
-delay-bad.scala:73: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+delay-bad.scala:73: warning: a pure expression does nothing in statement position; multiline expressions may require enclosing parentheses
     f(new { val x = 5 } with E() { 5 })
                                    ^
 warning: there was one deprecation warning (since 2.11.0); re-run with -deprecation for details
diff --git a/test/files/run/delay-good.check b/test/files/run/delay-good.check
index b4f6b04af7..ed35b9225f 100644
--- a/test/files/run/delay-good.check
+++ b/test/files/run/delay-good.check
@@ -1,7 +1,7 @@
-delay-good.scala:53: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+delay-good.scala:53: warning: a pure expression does nothing in statement position; multiline expressions may require enclosing parentheses
     f(new C { 5 })
               ^
-delay-good.scala:73: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+delay-good.scala:73: warning: a pure expression does nothing in statement position; multiline expressions may require enclosing parentheses
     f(new { val x = 5 } with E() { 5 })
                                    ^
 
diff --git a/test/files/run/exceptions-2.check b/test/files/run/exceptions-2.check
index 4f8244800a..5cf5e71f41 100644
--- a/test/files/run/exceptions-2.check
+++ b/test/files/run/exceptions-2.check
@@ -1,4 +1,4 @@
-exceptions-2.scala:267: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+exceptions-2.scala:267: warning: a pure expression does nothing in statement position
     try { 1 } catch { case e: java.io.IOException => () }
           ^
 nested1: 
diff --git a/test/files/run/lazy-locals.check b/test/files/run/lazy-locals.check
index 9e88a55d18..4565326bea 100644
--- a/test/files/run/lazy-locals.check
+++ b/test/files/run/lazy-locals.check
@@ -1,7 +1,7 @@
-lazy-locals.scala:153: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+lazy-locals.scala:153: warning: a pure expression does nothing in statement position; multiline expressions may require enclosing parentheses
   {
   ^
-lazy-locals.scala:159: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+lazy-locals.scala:159: warning: a pure expression does nothing in statement position; multiline expressions may require enclosing parentheses
     {
     ^
 forced lazy val q
diff --git a/test/files/run/macro-duplicate.check b/test/files/run/macro-duplicate.check
index 58781b719a..7006b16611 100644
--- a/test/files/run/macro-duplicate.check
+++ b/test/files/run/macro-duplicate.check
@@ -1,3 +1,3 @@
-Test_2.scala:5: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+Test_2.scala:5: warning: a pure expression does nothing in statement position; multiline expressions may require enclosing parentheses
   Macros.foo
          ^
diff --git a/test/files/run/misc.check b/test/files/run/misc.check
index 56116f8104..075dfeff2f 100644
--- a/test/files/run/misc.check
+++ b/test/files/run/misc.check
@@ -1,25 +1,25 @@
-misc.scala:46: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+misc.scala:46: warning: a pure expression does nothing in statement position; multiline expressions might require enclosing parentheses
     42;
     ^
-misc.scala:47: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+misc.scala:47: warning: a pure expression does nothing in statement position; multiline expressions might require enclosing parentheses
     42l;
     ^
-misc.scala:48: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+misc.scala:48: warning: a pure expression does nothing in statement position; multiline expressions might require enclosing parentheses
     23.5f;
     ^
-misc.scala:49: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+misc.scala:49: warning: a pure expression does nothing in statement position; multiline expressions might require enclosing parentheses
     23.5;
     ^
-misc.scala:50: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+misc.scala:50: warning: a pure expression does nothing in statement position; multiline expressions might require enclosing parentheses
     "Hello";
     ^
-misc.scala:51: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+misc.scala:51: warning: a pure expression does nothing in statement position; multiline expressions might require enclosing parentheses
     32 + 45;
        ^
-misc.scala:62: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+misc.scala:62: warning: a pure expression does nothing in statement position; multiline expressions might require enclosing parentheses
     x;
     ^
-misc.scala:74: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+misc.scala:74: warning: a pure expression does nothing in statement position; multiline expressions might require enclosing parentheses
     1 < 2;
       ^
 ### Hello
diff --git a/test/files/run/names-defaults.check b/test/files/run/names-defaults.check
index c358dc5849..722d28dd11 100644
--- a/test/files/run/names-defaults.check
+++ b/test/files/run/names-defaults.check
@@ -1,4 +1,7 @@
-names-defaults.scala:269: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+names-defaults.scala:269: warning: a pure expression does nothing in statement position
+    spawn(b = { val ttt = 1; ttt }, a = 0)
+                             ^
+names-defaults.scala:269: warning: multiline expressions might require enclosing parentheses; a value can be silently discarded when Unit is expected
     spawn(b = { val ttt = 1; ttt }, a = 0)
                              ^
 warning: there were four deprecation warnings; re-run with -deprecation for details
diff --git a/test/files/run/patmatnew.check b/test/files/run/patmatnew.check
index 56b8ac2f4f..117bc28c2d 100644
--- a/test/files/run/patmatnew.check
+++ b/test/files/run/patmatnew.check
@@ -1,10 +1,16 @@
-patmatnew.scala:351: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+patmatnew.scala:351: warning: a pure expression does nothing in statement position
         case 1 => "OK"
                   ^
-patmatnew.scala:352: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+patmatnew.scala:352: warning: a pure expression does nothing in statement position
         case 2 => assert(false); "KO"
                                  ^
-patmatnew.scala:353: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+patmatnew.scala:352: warning: multiline expressions might require enclosing parentheses; a value can be silently discarded when Unit is expected
+        case 2 => assert(false); "KO"
+                                 ^
+patmatnew.scala:353: warning: a pure expression does nothing in statement position
+        case 3 => assert(false); "KO"
+                                 ^
+patmatnew.scala:353: warning: multiline expressions might require enclosing parentheses; a value can be silently discarded when Unit is expected
         case 3 => assert(false); "KO"
                                  ^
 patmatnew.scala:670: warning: This catches all Throwables. If this is really intended, use `case e : Throwable` to clear this warning.
diff --git a/test/files/run/reify_lazyunit.check b/test/files/run/reify_lazyunit.check
index 579ecfe8aa..e6acf5d17b 100644
--- a/test/files/run/reify_lazyunit.check
+++ b/test/files/run/reify_lazyunit.check
@@ -1,4 +1,4 @@
-reify_lazyunit.scala:6: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+reify_lazyunit.scala:6: warning: a pure expression does nothing in statement position; multiline expressions might require enclosing parentheses
     lazy val x = { 0; println("12")}
                    ^
 12
diff --git a/test/files/run/repl-bare-expr.check b/test/files/run/repl-bare-expr.check
index e0a1f4ecd6..bdf8842bb0 100644
--- a/test/files/run/repl-bare-expr.check
+++ b/test/files/run/repl-bare-expr.check
@@ -1,12 +1,12 @@
 
 scala> 2 ; 3
-<console>:11: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+<console>:11: warning: a pure expression does nothing in statement position; multiline expressions may require enclosing parentheses
        2 ;;
        ^
 res0: Int = 3
 
 scala> { 2 ; 3 }
-<console>:12: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+<console>:12: warning: a pure expression does nothing in statement position; multiline expressions might require enclosing parentheses
        { 2 ; 3 }
          ^
 res1: Int = 3
@@ -15,16 +15,16 @@ scala> 5 ; 10 ; case object Cow ; 20 ; class Moo { override def toString = "Mooo
   1 +
   2 +
   3 } ; bippy+88+11
-<console>:11: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+<console>:11: warning: a pure expression does nothing in statement position; multiline expressions may require enclosing parentheses
        5 ; 10 ; case object Cow ; 20 ; class Moo { override def toString = "Moooooo" } ; 30 ; def bippy = {
        ^
-<console>:11: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+<console>:11: warning: a pure expression does nothing in statement position; multiline expressions may require enclosing parentheses
        5 ; 10 ; case object Cow ; 20 ; class Moo { override def toString = "Moooooo" } ; 30 ; def bippy = {
            ^
-<console>:11: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+<console>:11: warning: a pure expression does nothing in statement position; multiline expressions may require enclosing parentheses
        5 ; 10 ; case object Cow ; 20 ; class Moo { override def toString = "Moooooo" } ; 30 ; def bippy = {
                                   ^
-<console>:11: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+<console>:11: warning: a pure expression does nothing in statement position; multiline expressions may require enclosing parentheses
        5 ; 10 ; case object Cow ; 20 ; class Moo { override def toString = "Moooooo" } ; 30 ; def bippy = {
                                                                                          ^
 defined object Cow
diff --git a/test/files/run/repl-no-imports-no-predef.check b/test/files/run/repl-no-imports-no-predef.check
index c2c8d21c0a..7c4ee82c78 100644
--- a/test/files/run/repl-no-imports-no-predef.check
+++ b/test/files/run/repl-no-imports-no-predef.check
@@ -76,13 +76,13 @@ y: Int = 13
 scala> 
 
 scala> 2 ; 3
-<console>:11: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+<console>:11: warning: a pure expression does nothing in statement position; multiline expressions may require enclosing parentheses
        2 ;;
        ^
 res14: Int = 3
 
 scala> { 2 ; 3 }
-<console>:12: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+<console>:12: warning: a pure expression does nothing in statement position; multiline expressions might require enclosing parentheses
        { 2 ; 3 }
          ^
 res15: Int = 3
@@ -92,16 +92,16 @@ bippy = {
   1 +
   2 +
   3 } ; bippy+88+11
-<console>:11: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+<console>:11: warning: a pure expression does nothing in statement position; multiline expressions may require enclosing parentheses
        5 ; 10 ; case object Cow ; 20 ; class Moo { override def toString = "Moooooo" } ; 30 ; def
        ^
-<console>:11: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+<console>:11: warning: a pure expression does nothing in statement position; multiline expressions may require enclosing parentheses
        5 ; 10 ; case object Cow ; 20 ; class Moo { override def toString = "Moooooo" } ; 30 ; def
            ^
-<console>:11: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+<console>:11: warning: a pure expression does nothing in statement position; multiline expressions may require enclosing parentheses
        5 ; 10 ; case object Cow ; 20 ; class Moo { override def toString = "Moooooo" } ; 30 ; def
                                   ^
-<console>:11: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+<console>:11: warning: a pure expression does nothing in statement position; multiline expressions may require enclosing parentheses
        5 ; 10 ; case object Cow ; 20 ; class Moo { override def toString = "Moooooo" } ; 30 ; def
                                                                                          ^
 defined object Cow
@@ -143,10 +143,10 @@ scala>   (  (2 + 2 )  )
 res24: Int = 4
 
 scala> 5 ;   (  (2 + 2 )  ) ; ((5))
-<console>:11: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+<console>:11: warning: a pure expression does nothing in statement position; multiline expressions may require enclosing parentheses
        5 ;   (  (2 + 2 )  ) ;;
        ^
-<console>:11: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+<console>:11: warning: a pure expression does nothing in statement position; multiline expressions may require enclosing parentheses
        5 ;   (  (2 + 2 )  ) ;;
                    ^
 res25: Int = 5
@@ -163,16 +163,16 @@ res28: String = 4423
 scala> 
 
 scala> 55 ; ((2 + 2)) ; (1, 2, 3)
-<console>:11: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+<console>:11: warning: a pure expression does nothing in statement position; multiline expressions may require enclosing parentheses
        55 ; ((2 + 2)) ;;
        ^
-<console>:11: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+<console>:11: warning: a pure expression does nothing in statement position; multiline expressions may require enclosing parentheses
        55 ; ((2 + 2)) ;;
                 ^
 res29: (Int, Int, Int) = (1,2,3)
 
 scala> 55 ; (x: scala.Int) => x + 1 ; () => ((5))
-<console>:12: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+<console>:12: warning: a pure expression does nothing in statement position; multiline expressions may require enclosing parentheses
        55 ; (x: scala.Int) => x + 1 ;;
        ^
 res30: () => Int = <function0>
@@ -183,7 +183,7 @@ scala> () => 5
 res31: () => Int = <function0>
 
 scala> 55 ; () => 5
-<console>:11: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+<console>:11: warning: a pure expression does nothing in statement position; multiline expressions may require enclosing parentheses
        55 ;;
        ^
 res32: () => Int = <function0>
diff --git a/test/files/run/repl-parens.check b/test/files/run/repl-parens.check
index 6516f4ea90..477d4d462f 100644
--- a/test/files/run/repl-parens.check
+++ b/test/files/run/repl-parens.check
@@ -18,10 +18,10 @@ scala>   (  (2 + 2 )  )
 res5: Int = 4
 
 scala> 5 ;   (  (2 + 2 )  ) ; ((5))
-<console>:11: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+<console>:11: warning: a pure expression does nothing in statement position; multiline expressions may require enclosing parentheses
        5 ;   (  (2 + 2 )  ) ;;
        ^
-<console>:11: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+<console>:11: warning: a pure expression does nothing in statement position; multiline expressions may require enclosing parentheses
        5 ;   (  (2 + 2 )  ) ;;
                    ^
 res6: Int = 5
@@ -38,16 +38,16 @@ res9: String = 4423
 scala> 
 
 scala> 55 ; ((2 + 2)) ; (1, 2, 3)
-<console>:11: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+<console>:11: warning: a pure expression does nothing in statement position; multiline expressions may require enclosing parentheses
        55 ; ((2 + 2)) ;;
        ^
-<console>:11: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+<console>:11: warning: a pure expression does nothing in statement position; multiline expressions may require enclosing parentheses
        55 ; ((2 + 2)) ;;
                 ^
 res10: (Int, Int, Int) = (1,2,3)
 
 scala> 55 ; (x: Int) => x + 1 ; () => ((5))
-<console>:11: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+<console>:11: warning: a pure expression does nothing in statement position; multiline expressions may require enclosing parentheses
        55 ; (x: Int) => x + 1 ;;
        ^
 res11: () => Int = <function0>
@@ -58,7 +58,7 @@ scala> () => 5
 res12: () => Int = <function0>
 
 scala> 55 ; () => 5
-<console>:11: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+<console>:11: warning: a pure expression does nothing in statement position; multiline expressions may require enclosing parentheses
        55 ;;
        ^
 res13: () => Int = <function0>
diff --git a/test/files/run/t3488.check b/test/files/run/t3488.check
index 314dfc7838..75b2c3b07f 100644
--- a/test/files/run/t3488.check
+++ b/test/files/run/t3488.check
@@ -1,7 +1,13 @@
-t3488.scala:4: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+t3488.scala:4: warning: a pure expression does nothing in statement position
   println(foo { val List(_*)=List(0); 1 } ())
                                       ^
-t3488.scala:5: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+t3488.scala:4: warning: multiline expressions might require enclosing parentheses; a value can be silently discarded when Unit is expected
+  println(foo { val List(_*)=List(0); 1 } ())
+                                      ^
+t3488.scala:5: warning: a pure expression does nothing in statement position
+  println(foo { val List(_*)=List(0); 1 } (1))
+                                      ^
+t3488.scala:5: warning: multiline expressions might require enclosing parentheses; a value can be silently discarded when Unit is expected
   println(foo { val List(_*)=List(0); 1 } (1))
                                       ^
 0
diff --git a/test/files/run/t4047.check b/test/files/run/t4047.check
index 3c41e6e244..c31f2f0858 100644
--- a/test/files/run/t4047.check
+++ b/test/files/run/t4047.check
@@ -1,13 +1,13 @@
-t4047.scala:23: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+t4047.scala:23: warning: a pure expression does nothing in statement position; multiline expressions may require enclosing parentheses
   a.foo
     ^
-t4047.scala:24: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+t4047.scala:24: warning: a pure expression does nothing in statement position; multiline expressions may require enclosing parentheses
   a.foo
     ^
-t4047.scala:26: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+t4047.scala:26: warning: a pure expression does nothing in statement position; multiline expressions may require enclosing parentheses
   b.foo
     ^
-t4047.scala:27: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+t4047.scala:27: warning: a pure expression does nothing in statement position; multiline expressions may require enclosing parentheses
   b.foo
     ^
 Unit: called A.foo
diff --git a/test/files/run/t4680.check b/test/files/run/t4680.check
index 21c5f9e567..749ce4c627 100644
--- a/test/files/run/t4680.check
+++ b/test/files/run/t4680.check
@@ -1,7 +1,7 @@
-t4680.scala:51: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+t4680.scala:51: warning: a pure expression does nothing in statement position; multiline expressions may require enclosing parentheses
     new C { 5 }
             ^
-t4680.scala:69: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+t4680.scala:69: warning: a pure expression does nothing in statement position; multiline expressions may require enclosing parentheses
     new { val x = 5 } with E() { 5 }
                                  ^
 warning: there was one deprecation warning (since 2.11.0); re-run with -deprecation for details
diff --git a/test/files/run/t5380.check b/test/files/run/t5380.check
index 731a798301..19471ac2d2 100644
--- a/test/files/run/t5380.check
+++ b/test/files/run/t5380.check
@@ -1,7 +1,7 @@
-t5380.scala:3: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+t5380.scala:3: warning: a pure expression does nothing in statement position
     val f = () => return try { 1 } catch { case _: Throwable => 0 }
                                ^
-t5380.scala:3: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+t5380.scala:3: warning: a pure expression does nothing in statement position
     val f = () => return try { 1 } catch { case _: Throwable => 0 }
                                                                 ^
 t5380.scala:3: warning: enclosing method main has result type Unit: return value discarded
diff --git a/test/files/run/t7047.check b/test/files/run/t7047.check
index 32bd581094..129ce3eeca 100644
--- a/test/files/run/t7047.check
+++ b/test/files/run/t7047.check
@@ -1,3 +1,3 @@
-Test_2.scala:2: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+Test_2.scala:2: warning: a pure expression does nothing in statement position; multiline expressions may require enclosing parentheses
   Macros.foo
          ^
diff --git a/test/files/run/t7747-repl.check b/test/files/run/t7747-repl.check
index c5e92e9d79..621a70205e 100644
--- a/test/files/run/t7747-repl.check
+++ b/test/files/run/t7747-repl.check
@@ -15,13 +15,13 @@ scala> val z = x * y
 z: Int = 156
 
 scala> 2 ; 3
-<console>:11: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+<console>:11: warning: a pure expression does nothing in statement position; multiline expressions may require enclosing parentheses
        2 ;;
        ^
 res0: Int = 3
 
 scala> { 2 ; 3 }
-<console>:12: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+<console>:12: warning: a pure expression does nothing in statement position; multiline expressions might require enclosing parentheses
        { 2 ; 3 }
          ^
 res1: Int = 3
@@ -30,16 +30,16 @@ scala> 5 ; 10 ; case object Cow ; 20 ; class Moo { override def toString = "Mooo
   1 +
   2 +
   3 } ; bippy+88+11
-<console>:11: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+<console>:11: warning: a pure expression does nothing in statement position; multiline expressions may require enclosing parentheses
        5 ; 10 ; case object Cow ; 20 ; class Moo { override def toString = "Moooooo" } ; 30 ; def bippy = {
        ^
-<console>:11: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+<console>:11: warning: a pure expression does nothing in statement position; multiline expressions may require enclosing parentheses
        5 ; 10 ; case object Cow ; 20 ; class Moo { override def toString = "Moooooo" } ; 30 ; def bippy = {
            ^
-<console>:11: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+<console>:11: warning: a pure expression does nothing in statement position; multiline expressions may require enclosing parentheses
        5 ; 10 ; case object Cow ; 20 ; class Moo { override def toString = "Moooooo" } ; 30 ; def bippy = {
                                   ^
-<console>:11: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+<console>:11: warning: a pure expression does nothing in statement position; multiline expressions may require enclosing parentheses
        5 ; 10 ; case object Cow ; 20 ; class Moo { override def toString = "Moooooo" } ; 30 ; def bippy = {
                                                                                          ^
 defined object Cow
@@ -81,10 +81,10 @@ scala>   (  (2 + 2 )  )
 res10: Int = 4
 
 scala> 5 ;   (  (2 + 2 )  ) ; ((5))
-<console>:11: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+<console>:11: warning: a pure expression does nothing in statement position; multiline expressions may require enclosing parentheses
        5 ;   (  (2 + 2 )  ) ;;
        ^
-<console>:11: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+<console>:11: warning: a pure expression does nothing in statement position; multiline expressions may require enclosing parentheses
        5 ;   (  (2 + 2 )  ) ;;
                    ^
 res11: Int = 5
@@ -101,16 +101,16 @@ res14: String = 4423
 scala> 
 
 scala> 55 ; ((2 + 2)) ; (1, 2, 3)
-<console>:11: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+<console>:11: warning: a pure expression does nothing in statement position; multiline expressions may require enclosing parentheses
        55 ; ((2 + 2)) ;;
        ^
-<console>:11: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+<console>:11: warning: a pure expression does nothing in statement position; multiline expressions may require enclosing parentheses
        55 ; ((2 + 2)) ;;
                 ^
 res15: (Int, Int, Int) = (1,2,3)
 
 scala> 55 ; (x: Int) => x + 1 ; () => ((5))
-<console>:13: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+<console>:13: warning: a pure expression does nothing in statement position; multiline expressions may require enclosing parentheses
        55 ; (x: Int) => x + 1 ;;
        ^
 res16: () => Int = <function0>
@@ -121,7 +121,7 @@ scala> () => 5
 res17: () => Int = <function0>
 
 scala> 55 ; () => 5
-<console>:11: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+<console>:11: warning: a pure expression does nothing in statement position; multiline expressions may require enclosing parentheses
        55 ;;
        ^
 res18: () => Int = <function0>
diff --git a/test/files/run/t8196.check b/test/files/run/t8196.check
index d11dc27e68..8a07ebb6d7 100644
--- a/test/files/run/t8196.check
+++ b/test/files/run/t8196.check
@@ -1,4 +1,4 @@
-t8196.scala:26: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+t8196.scala:26: warning: a pure expression does nothing in statement position; multiline expressions might require enclosing parentheses
     form2.g1 // comment this line in order to make the test pass
           ^
 warning: there were two feature warnings; re-run with -feature for details
diff --git a/test/files/run/try-2.check b/test/files/run/try-2.check
index 987d3462df..7fd45414da 100644
--- a/test/files/run/try-2.check
+++ b/test/files/run/try-2.check
@@ -1,4 +1,4 @@
-try-2.scala:41: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+try-2.scala:41: warning: a pure expression does nothing in statement position
       10;
       ^
 exception happened
diff --git a/test/files/run/try.check b/test/files/run/try.check
index f742ccb0df..d9521c2362 100644
--- a/test/files/run/try.check
+++ b/test/files/run/try.check
@@ -1,4 +1,4 @@
-try.scala:65: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+try.scala:65: warning: a pure expression does nothing in statement position; multiline expressions might require enclosing parentheses
       1+1;
        ^
 1 + 1 = 2
diff --git a/test/files/specialized/tb3651.check b/test/files/specialized/tb3651.check
index 8a3f686ef5..8e104f13ff 100644
--- a/test/files/specialized/tb3651.check
+++ b/test/files/specialized/tb3651.check
@@ -1,4 +1,4 @@
-tb3651.scala:8: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+tb3651.scala:8: warning: a pure expression does nothing in statement position; multiline expressions might require enclosing parentheses
     lk.a
        ^
 0
diff --git a/test/files/specialized/tc3651.check b/test/files/specialized/tc3651.check
index e2dbadf22c..1e56d196fd 100644
--- a/test/files/specialized/tc3651.check
+++ b/test/files/specialized/tc3651.check
@@ -1,4 +1,4 @@
-tc3651.scala:12: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+tc3651.scala:12: warning: a pure expression does nothing in statement position; multiline expressions might require enclosing parentheses
     lk.a
        ^
 0
diff --git a/test/files/specialized/td3651.check b/test/files/specialized/td3651.check
index 1a709fd0a7..697443ffe9 100644
--- a/test/files/specialized/td3651.check
+++ b/test/files/specialized/td3651.check
@@ -1,7 +1,7 @@
-td3651.scala:12: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+td3651.scala:12: warning: a pure expression does nothing in statement position; multiline expressions might require enclosing parentheses
     b.a
       ^
-td3651.scala:16: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
+td3651.scala:16: warning: a pure expression does nothing in statement position; multiline expressions might require enclosing parentheses
     der.a
         ^
 0