Promote value discard to lint

src/compiler/scala/tools/nsc/settings/Warnings.scala

@@ -112,7 +112,8 @@ trait Warnings {
     )
   ) withAbbreviation "-Ywarn-macros"
   val warnDeadCode         = BooleanSetting("-Wdead-code", "Warn when dead code is identified.") withAbbreviation "-Ywarn-dead-code"
-  val warnValueDiscard     = BooleanSetting("-Wvalue-discard", "Warn when non-Unit expression results are unused.") withAbbreviation "-Ywarn-value-discard"
+  @deprecated("Use lintValueDiscard", since="2.13.3")
+  val warnValueDiscard     = BooleanSetting("-Wvalue-discard", "Warn when non-Unit expression results are unused.") withAbbreviation "-Ywarn-value-discard" withDeprecationMessage "Use -Xlint:value-discard"
   val warnNumericWiden     = BooleanSetting("-Wnumeric-widen", "Warn when numerics are widened.") withAbbreviation "-Ywarn-numeric-widen"
   val warnOctalLiteral     = BooleanSetting("-Woctal-literal", "Warn on obsolete octal syntax.") withAbbreviation "-Ywarn-octal-literal"
 
@@ -149,7 +150,7 @@ trait Warnings {
   val warnExtraImplicit   = BooleanSetting("-Wextra-implicit", "Warn when more than one implicit parameter section is defined.") withAbbreviation "-Ywarn-extra-implicit"
 
   @deprecated("Use lintImplicitRecursion", since="2.13.3")
-  val warnSelfImplicit    = BooleanSetting("-Wself-implicit", "An implicit resolves to an enclosing definition.") withAbbreviation "-Ywarn-self-implicit" withDeprecationMessage "Use -Xlint:implicit-recurses"
+  val warnSelfImplicit    = BooleanSetting("-Wself-implicit", "An implicit resolves to an enclosing definition.") withAbbreviation "-Ywarn-self-implicit" withDeprecationMessage "Use -Xlint:implicit-recursion"
 
   // Experimental lint warnings that are turned off, but which could be turned on programmatically.
   // They are not activated by -Xlint and can't be enabled on the command line because they are not
@@ -194,7 +195,8 @@ trait Warnings {
     val RecurseWithDefault     = LintWarning("recurse-with-default",      "Recursive call used default argument.")
     val UnitSpecialization     = LintWarning("unit-special",              "Warn for specialization of Unit in parameter position.")
     val MultiargInfix          = LintWarning("multiarg-infix",            "Infix operator was defined or used with multiarg operand.")
-    val ImplicitRecurses       = LintWarning("implicit-recurses",         "Implicit resolves to an enclosing definition.")
+    val ImplicitRecursion      = LintWarning("implicit-recursion",        "Implicit resolves to an enclosing definition.")
+    val ValueDiscard           = LintWarning("value-discard",             "A non-Unit value was not used because Unit was required.")
 
     def allLintWarnings = values.toSeq.asInstanceOf[Seq[LintWarning]]
   }
@@ -227,7 +229,8 @@ trait Warnings {
   def warnRecurseWithDefault     = lint contains RecurseWithDefault
   def unitSpecialization         = lint contains UnitSpecialization
   def multiargInfix              = lint contains MultiargInfix
-  def lintImplicitRecursion      = lint.contains(ImplicitRecurses) || warnSelfImplicit
+  def lintImplicitRecursion      = lint.contains(ImplicitRecursion) || warnSelfImplicit
+  def lintValueDiscard           = lint.contains(ValueDiscard) || warnValueDiscard
 
   // The Xlint warning group.
   val lint = MultiChoiceSetting(

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

@@ -1144,7 +1144,7 @@ trait Typers extends Adaptations with Tags with TypersTracking with PatternTyper
           @inline def tpdPos(transformed: Tree) = typedPos(tree.pos, mode, pt)(transformed)
           @inline def tpd(transformed: Tree)    = typed(transformed, mode, pt)
 
-          @inline def warnValueDiscard(): Unit = if (!isPastTyper && settings.warnValueDiscard) {
+          @inline def warnValueDiscard(): Unit = if (!isPastTyper && settings.lintValueDiscard) {
             def isThisTypeResult = (tree, tree.tpe) match {
               case (Apply(Select(receiver, _), _), SingleType(_, sym)) => sym == receiver.symbol
               case _ => false

test/files/neg/implicitly-self.scala

@@ -1,4 +1,4 @@
-// scalac: -Werror -Xlint:implicit-recurses
+// scalac: -Werror -Xlint:implicit-recursion
 //
 
 trait TC[A] { def ix: Int }

test/files/pos/t11813.scala

@@ -1,4 +1,4 @@
-// scalac: -Werror -Xlint:implicit-recurses
+// scalac: -Werror -Xlint:implicit-recursion
 //
 package warner