[REVISIT] Dogfood value discard [ci: last-only]

build.sbt

@@ -170,7 +170,13 @@ lazy val commonSettings = instanceSettings ++ clearSourceAndResourceDirectories
   Compile / scalacOptions += "-Wconf:cat=optimizer:is",
   // We use @nowarn for some methods that are deprecated in Java > 8
   Compile / scalacOptions += "-Wconf:cat=unused-nowarn:s",
-  Compile / scalacOptions ++= Seq("-deprecation", "-feature"),
+  Compile / scalacOptions ++= Seq(
+    "-deprecation",
+    "-feature",
+    //"-Wvalue-discard", // await restarr
+    //"-Wnonunit-statement", // await restarr
+    //"-Wnonunit-if:false", // uncomment to ignore one-legged if or case
+  ),
   Compile / doc / scalacOptions ++= Seq(
     "-doc-footer", "epfl",
     "-diagrams",

src/compiler/scala/reflect/macros/compiler/DefaultMacroCompiler.scala

@@ -13,6 +13,7 @@
 package scala.reflect.macros
 package compiler
 
+import scala.annotation.nowarn
 import scala.tools.nsc.Global
 
 abstract class DefaultMacroCompiler extends Resolvers
@@ -82,7 +83,8 @@ abstract class DefaultMacroCompiler extends Resolvers
       if (vanillaResult.isSuccess && bundleResult.isSuccess) MacroImplAmbiguousError()
     }
 
-    def reportMostAppropriateFailure() = {
+    @nowarn("cat=w-flag-value-discard")
+    def reportMostAppropriateFailure(): Unit = {
       typer.silent(_.typedTypeConstructor(maybeBundleRef)) match {
         case SilentResultValue(result) if looksLikeMacroBundleType(result.tpe) =>
           val bundle = result.tpe.typeSymbol

src/compiler/scala/reflect/reify/Reifier.scala

@@ -138,6 +138,7 @@ abstract class Reifier extends States
         if (reifyDebug) println("=============================")
       } else {
         reifyTrace("reification = ")(untyped)
+        ()
       }
 
       untyped

src/compiler/scala/reflect/reify/codegen/GenTypes.scala

@@ -13,6 +13,8 @@
 package scala.reflect.reify
 package codegen
 
+import scala.annotation.nowarn
+
 trait GenTypes {
   self: Reifier =>
 
@@ -187,13 +189,13 @@ trait GenTypes {
 
     tpe match {
       case tpe @ RefinedType(parents, decls) =>
-        reifySymDef(tpe.typeSymbol)
+        reifySymDef(tpe.typeSymbol): @nowarn("cat=w-flag-value-discard")
         mirrorBuildCall(nme.RefinedType, reify(parents), reifyScope(decls), reify(tpe.typeSymbol))
       case tpe @ ExistentialType(tparams, underlying) =>
         tparams foreach reifySymDef
         reifyBuildCall(nme.ExistentialType, tparams, underlying)
       case tpe @ ClassInfoType(parents, decls, clazz) =>
-        reifySymDef(clazz)
+        reifySymDef(clazz): @nowarn("cat=w-flag-value-discard")
         mirrorBuildCall(nme.ClassInfoType, reify(parents), reifyScope(decls), reify(tpe.typeSymbol))
       case tpe @ MethodType(params, restpe) =>
         params foreach reifySymDef

src/compiler/scala/tools/nsc/ClassPathMemoryConsumptionTester.scala

@@ -12,6 +12,7 @@
 
 package scala.tools.nsc
 
+import scala.annotation.nowarn
 import scala.io.StdIn.readLine
 
 /**
@@ -39,6 +40,7 @@ object ClassPathMemoryConsumptionTester {
     else doTest(args)
   }
 
+  @nowarn("cat=w-flag-value-discard")
   private def doTest(args: Array[String]) = {
     val settings = loadSettings(args.toList)
 
@@ -50,7 +52,7 @@ object ClassPathMemoryConsumptionTester {
     println(s"Loading classpath ${settings.requiredInstances.value} times")
     val startTime = System.currentTimeMillis()
 
-    mains map (_.process(baseArgs))
+    mains.map(_.process(baseArgs))
 
     val elapsed = System.currentTimeMillis() - startTime
     println(s"Operation finished - elapsed $elapsed ms")
@@ -72,7 +74,7 @@ object ClassPathMemoryConsumptionTester {
 
   private def loadSettings(args: List[String]) = {
     val settings = new TestSettings()
-    settings.processArguments(args, processAll = true)
+    settings.processArguments(args, processAll = true): @nowarn("cat=w-flag-value-discard")
     if (settings.classpath.isDefault)
       settings.classpath.value = System.getProperty("java.class.path", ".")
     settings

src/compiler/scala/tools/nsc/Global.scala

@@ -1460,7 +1460,7 @@ class Global(var currentSettings: Settings, reporter0: Reporter)
           case -1   => mkName(str)
           case idx  =>
             val phasePart = str drop (idx + 1)
-            settings.Yshow.tryToSetColon(phasePart.split(',').toList)
+            settings.Yshow.tryToSetColon(phasePart.split(',').toList): @nowarn("cat=w-flag-value-discard")
             mkName(str take idx)
         }
       }

src/compiler/scala/tools/nsc/MainBench.scala

@@ -12,6 +12,8 @@
 
 package scala.tools.nsc
 
+import scala.annotation.nowarn
+
 /** The main class for NSC, a compiler for the programming
  *  language Scala.
  */
@@ -32,7 +34,7 @@ object MainBench extends Driver with EvalLoop {
         theCompiler.settings.Ystatistics.value           = List("all")
         theCompiler.settings.YhotStatisticsEnabled.value = true
       }
-      process(args)
+      process(args): @nowarn("cat=w-flag-value-discard")
       val end = System.nanoTime()
       val duration = (end-start)/1000000
       println(s"${duration}ms")

src/compiler/scala/tools/nsc/PipelineMain.scala

@@ -607,7 +607,7 @@ class PipelineMainClass(argFiles: Seq[Path], pipelineSettings: PipelineMain.Pipe
     def durationMs: Double = {
       val result = (endNanos - startNanos).toDouble / 1000 / 1000
       if (result < 0)
-        getClass
+        getClass: @nowarn("cat=w-flag-value-discard")
       result
     }
     def startMicros: Double = startNanos.toDouble / 1000d

src/compiler/scala/tools/nsc/ScriptRunner.scala

@@ -12,6 +12,7 @@
 
 package scala.tools.nsc
 
+import scala.annotation.nowarn
 import scala.reflect.io.{ AbstractFile, Directory, File, Path }
 import scala.tools.nsc.classpath.ClassPathFactory
 import scala.tools.nsc.io.Jar
@@ -96,7 +97,7 @@ abstract class AbstractScriptRunner(settings: GenericRunnerSettings) extends Scr
         else
           Directory.makeTemp("scalascript").tap { tmp =>
             // delete the directory after the user code has finished
-            Runtime.getRuntime.addShutdownHook(new Thread(() => tmp.deleteRecursively()))
+            Runtime.getRuntime.addShutdownHook(new Thread(() => tmp.deleteRecursively(): @nowarn("cat=w-flag-value-discard")))
             settings.outdir.value = tmp.path
           }
 
@@ -120,7 +121,7 @@ abstract class AbstractScriptRunner(settings: GenericRunnerSettings) extends Scr
       def jarOK = jarFile.canRead && jarFile.isFresher(File(scriptFile))
 
       def recompile(): Option[Throwable] = {
-        jarFile.delete()
+        jarFile.delete(): @nowarn("cat=w-flag-value-discard")
 
         compile match {
           case Some(compiledPath) =>
@@ -131,7 +132,7 @@ abstract class AbstractScriptRunner(settings: GenericRunnerSettings) extends Scr
                   Jar.create(jarFile, compiledPath.toDirectory, mainClass)
                   None
                 } catch {
-                  case NonFatal(e) => jarFile.delete() ; Some(e)
+                  case NonFatal(e) => jarFile.delete(): @nowarn("cat=w-flag-value-discard"); Some(e)
                 }
               } else None
             } else Some(NoScriptError)
@@ -186,7 +187,7 @@ abstract class AbstractScriptRunner(settings: GenericRunnerSettings) extends Scr
     catch {
       case NonFatal(e) => Some(e)
     }
-    finally scriptFile.delete()  // in case there was a compilation error
+    finally scriptFile.delete(): @nowarn("cat=w-flag-value-discard") // in case there was a compilation error
   }
 }
 

src/compiler/scala/tools/nsc/ast/NodePrinters.scala

@@ -14,8 +14,9 @@ package scala.tools.nsc
 package ast
 
 import java.lang.System.{lineSeparator => EOL}
-import symtab.Flags._
+import scala.annotation.nowarn
 import scala.reflect.internal.util.ListOfNil
+import symtab.Flags._
 
 /** The object `nodePrinter` converts the internal tree
  *  representation to a string.
@@ -183,9 +184,7 @@ abstract class NodePrinters {
     }
 
     def treePrefix(tree: Tree) = showPosition(tree) + tree.productPrefix
-    def printMultiline(tree: Tree)(body: => Unit): Unit = {
-      printMultiline(treePrefix(tree), showAttributes(tree))(body)
-    }
+    def printMultiline(tree: Tree)(body: => Unit): Unit = printMultiline(treePrefix(tree), showAttributes(tree))(body)
     def printMultiline(prefix: String, comment: String)(body: => Unit): Unit = {
       printLine(prefix + "(", comment)
       indent(body)
@@ -214,7 +213,7 @@ abstract class NodePrinters {
     }
 
     def traverse(tree: Tree): Unit = {
-      showPosition(tree)
+      showPosition(tree): @nowarn("cat=w-flag-value-discard")
 
       tree match {
         case ApplyDynamic(fun, args)      => applyCommon(tree, fun, args)
@@ -234,7 +233,7 @@ abstract class NodePrinters {
 
         case ld @ LabelDef(name, params, rhs) =>
           printMultiline(tree) {
-            showNameAndPos(ld)
+            showNameAndPos(ld): @nowarn("cat=w-flag-value-discard")
             traverseList("()", "params")(params)
             traverse(rhs)
           }
@@ -311,7 +310,7 @@ abstract class NodePrinters {
         case Super(qual, mix) =>
           printMultiline(tree) {
             traverse(qual)
-            showName(mix)
+            showName(mix): @nowarn("cat=w-flag-value-discard")
           }
         case Template(parents, self, body) =>
           printMultiline(tree) {

src/compiler/scala/tools/nsc/ast/TreeGen.scala

@@ -15,9 +15,9 @@ package ast
 
 import scala.annotation.tailrec
 import scala.collection.mutable.ListBuffer
-import symtab.Flags._
 import scala.reflect.internal.util.FreshNameCreator
 import scala.reflect.internal.util.ListOfNil
+import symtab.Flags._
 
 /** XXX to resolve: TreeGen only assumes global is a SymbolTable, but
  *  TreeDSL at the moment expects a Global.  Can we get by with SymbolTable?
@@ -382,7 +382,8 @@ abstract class TreeGen extends scala.reflect.internal.TreeGen with TreeDSL {
     defineOriginalOwner(anonClass, fun.symbol.originalOwner)
 
     val samDef = mkMethodFromFunction(localTyper)(anonClass, fun)
-    anonClass.info.decls enter samDef.symbol
+    val samDefSym = samDef.symbol
+    anonClass.info.decls.enter(samDefSym)
 
     localTyper.typedPos(fun.pos) {
       Block(

src/compiler/scala/tools/nsc/ast/parser/MarkupParsers.scala

@@ -13,6 +13,7 @@
 package scala.tools.nsc
 package ast.parser
 
+import scala.annotation.nowarn
 import scala.annotation.tailrec
 import scala.collection.mutable
 import scala.collection.BufferedIterator
@@ -318,7 +319,7 @@ trait MarkupParsers {
         debugLastStartElement.push((start, qname))
         val ts = content
         xEndTag(qname)
-        debugLastStartElement.pop()
+        debugLastStartElement.pop(): @nowarn("cat=w-flag-value-discard")
         val pos = r2p(start, start, curOffset)
         qname match {
           case "xml:group" => handle.group(pos, ts)
@@ -382,14 +383,14 @@ trait MarkupParsers {
 
         val ts = new ArrayBuffer[Tree]
         val start = curOffset - 1 // include <
-        content_LT(ts)
+        content_LT(ts): @nowarn("cat=w-flag-value-discard")
 
         // parse more XML?
         if (charComingAfter(xSpaceOpt()) == '<') {
           do {
             xSpaceOpt()
             nextch()
-            content_LT(ts)
+            content_LT(ts): @nowarn("cat=w-flag-value-discard")
           } while (charComingAfter(xSpaceOpt()) == '<')
           handle.makeXMLseq(r2p(start, start, curOffset), ts)
         }
@@ -484,7 +485,7 @@ trait MarkupParsers {
 
         while (doPattern) { }  // call until false
         xEndTag(qname)
-        debugLastStartElement.pop()
+        debugLastStartElement.pop(): @nowarn("cat=w-flag-value-discard")
       }
 
       handle.makeXMLpat(r2p(start, start, curOffset), qname, ts)