-Wconf compiler flag for configuring compiler warnings

Warnings are assigned a category.

Warnings can be filtered by category, by message regex, by site where
they are issued, and by source path. Deprecations can additionally be
filtered by origin (deprecated definition) and `since` version.

Filtered warnings can be reported as error, warning, info, summary
(like deprecations) or silent.

Adds a `-rootdir` compiler flag. It is used to relativize file paths
when using source filters (`-Wconf:src=some/source/File.scala:s`).
There might be other uses for it in the future.

Unchecked warnings are now all shown by default (they were summarized
like deprecations before).

The `-deprecation`, `-feature` and `-unchecked` settings are no longer
directly used in the compiler, they are shortcuts for specific `Wconf`
configurations. The compiler only looks at `-Wconf`.

Message filtering is performed in `global.currentRun.reporting`, not
in the `Global.reporter`. The reasons are:
  - Separation of concerns: `Reporter`s worry about how to do reporting,
    removing duplicate messages.
  - Custom `Reporter`s are used by sbt, silencer, REPL, etc. It's too
    hard to do the necessary changes to the `Reporter` interface.
  - The `Wconf` setting could change between compiler runs.
    `currentRun.reporting` respects those changes.

So all warnings in the compiler should go through `global.runReporting`
(which is the same as `global.currentRun.reporting`). This method takes
four parameters: pos, msg, category (new), site (new). The site is
usually `context.owner` (in the frontend) or `currentOwner` (in
transformations).

`Context` has a `warn` method with 3 parameters (pos, msg, category) and
inserts the `owner` as `site`, so this is used in the frontend (context
reporters are also used to support silent mode / trying twice).

The `global.warning` method is deprecated and no longer used.

There are a few calls to `Reporter.warning` left in the codebase where
no `runReporting` is reachable, I think they are all OK not to
categorize / allow filtering. E.g., when running Scaladoc

```
reporter.warning(null, "Plugins are not available when using Scaladoc")
```

build.sbt

@@ -186,6 +186,7 @@ val mimaFilterSettings = Seq {
     ProblemFilters.exclude[DirectMissingMethodProblem]("scala.reflect.io.VirtualFile.unsafeToByteArray"),
     ProblemFilters.exclude[DirectMissingMethodProblem]("scala.reflect.io.ZipArchive#Entry.unsafeToByteArray"),
     ProblemFilters.exclude[DirectMissingMethodProblem]("scala.reflect.io.NoAbstractFile.unsafeToByteArray"),
+    ProblemFilters.exclude[DirectMissingMethodProblem]("scala.reflect.runtime.JavaUniverse#PerRunReporting.deprecationWarning"),
   ),
 }
 

src/compiler/scala/reflect/macros/contexts/FrontEnds.scala

@@ -14,6 +14,7 @@ package scala.reflect.macros
 package contexts
 
 import scala.reflect.macros.runtime.AbortMacroException
+import scala.tools.nsc.Reporting.WarningCategory
 
 trait FrontEnds {
   self: Context =>
@@ -27,7 +28,8 @@ trait FrontEnds {
 
   def hasErrors: Boolean = universe.reporter.hasErrors
 
-  def warning(pos: Position, msg: String): Unit = callsiteTyper.context.warning(pos, msg)
+  // TODO: add WarningCategory parameter in 2.14 (not binary compatible)
+  def warning(pos: Position, msg: String): Unit = callsiteTyper.context.warning(pos, msg, WarningCategory.Other)
 
   def error(pos: Position, msg: String): Unit = callsiteTyper.context.error(pos, msg)
 

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

@@ -24,6 +24,7 @@ import scala.reflect.ClassTag
 import scala.reflect.internal.pickling.PickleBuffer
 import scala.reflect.internal.util.{BatchSourceFile, FreshNameCreator, NoSourceFile, ScriptSourceFile, SourceFile}
 import scala.reflect.internal.{Reporter => InternalReporter}
+import scala.tools.nsc.Reporting.WarningCategory
 import scala.tools.nsc.ast.parser._
 import scala.tools.nsc.ast.{TreeGen => AstTreeGen, _}
 import scala.tools.nsc.backend.jvm.{BackendStats, GenBCode}
@@ -294,7 +295,7 @@ class Global(var currentSettings: Settings, reporter0: Reporter)
   @inline final def devWarning(pos: Position, msg: => String): Unit = {
     def pos_s = if (pos eq NoPosition) "" else s" [@ $pos]"
     if (isDeveloper)
-      warning(pos, "!!! " + msg)
+      runReporting.warning(pos, "!!! " + msg, WarningCategory.OtherDebug, site = "")
     else
       log(s"!!!$pos_s $msg") // such warnings always at least logged
   }
@@ -992,10 +993,11 @@ class Global(var currentSettings: Settings, reporter0: Reporter)
 
   /** The currently active run
    */
-  def currentRun: Run              = curRun
-  def currentUnit: CompilationUnit = if (currentRun eq null) NoCompilationUnit else currentRun.currentUnit
-  def currentSource: SourceFile    = if (currentUnit.exists) currentUnit.source else lastSeenSourceFile
-  def currentFreshNameCreator      = if (curFreshNameCreator == null) currentUnit.fresh else curFreshNameCreator
+  def currentRun: Run               = curRun
+  def currentUnit: CompilationUnit  = if (currentRun eq null) NoCompilationUnit else currentRun.currentUnit
+  def currentSource: SourceFile     = if (currentUnit.exists) currentUnit.source else lastSeenSourceFile
+  def runReporting: PerRunReporting = currentRun.reporting
+  def currentFreshNameCreator       = if (curFreshNameCreator == null) currentUnit.fresh else curFreshNameCreator
   private[this] var curFreshNameCreator: FreshNameCreator = null
   private[scala] def currentFreshNameCreator_=(fresh: FreshNameCreator): Unit = curFreshNameCreator = fresh
 
@@ -1139,9 +1141,9 @@ class Global(var currentSettings: Settings, reporter0: Reporter)
     val isScala300: Boolean = settings.isScala300
 
     // used in sbt
-    def uncheckedWarnings: List[(Position, String)]   = reporting.uncheckedWarnings.map{case (pos, (msg, since)) => (pos, msg)}
+    def uncheckedWarnings: List[(Position, String)]   = reporting.uncheckedWarnings
     // used in sbt
-    def deprecationWarnings: List[(Position, String)] = reporting.deprecationWarnings.map{case (pos, (msg, since)) => (pos, msg)}
+    def deprecationWarnings: List[(Position, String)] = reporting.deprecationWarnings
 
     private class SyncedCompilationBuffer { self =>
       private val underlying = new mutable.ArrayBuffer[CompilationUnit]
@@ -1249,8 +1251,8 @@ class Global(var currentSettings: Settings, reporter0: Reporter)
           val count =
             if (including) first.iterator.count(tester.containsPhase(_))
             else phaseDescriptors.count(pd => tester.contains(pd.phaseName))
-          if (count == 0) warning(s"'$p' specifies no phase")
-          if (count > 1 && !isSpecial(p)) warning(s"'$p' selects $count phases")
+          if (count == 0) runReporting.warning(NoPosition, s"'$p' specifies no phase", WarningCategory.Other, site = "")
+          if (count > 1 && !isSpecial(p)) runReporting.warning(NoPosition, s"'$p' selects $count phases", WarningCategory.Other, site = "")
           if (!including && isSpecial(p)) globalError(s"-Yskip and -Ystop values must name phases: '$p'")
           tester.clear()
         }
@@ -1360,9 +1362,9 @@ class Global(var currentSettings: Settings, reporter0: Reporter)
     private def warnDeprecatedAndConflictingSettings(): Unit = {
       // issue warnings for any usage of deprecated settings
       settings.userSetSettings filter (_.isDeprecated) foreach { s =>
-        currentRun.reporting.deprecationWarning(NoPosition, s.name + " is deprecated: " + s.deprecationMessage.get, "")
+        runReporting.deprecationWarning(NoPosition, s.name + " is deprecated: " + s.deprecationMessage.get, "", "", "")
       }
-      settings.conflictWarning.foreach(reporter.warning(NoPosition, _))
+      settings.conflictWarning.foreach(runReporting.warning(NoPosition, _, WarningCategory.Other, site = ""))
     }
 
     /* An iterator returning all the units being compiled in this run */

src/compiler/scala/tools/nsc/GlobalSymbolLoaders.scala

@@ -14,6 +14,8 @@ package scala
 package tools
 package nsc
 
+import scala.tools.nsc.Reporting.WarningCategory
+
 /**
  * Symbol loaders implementation that wires dependencies using Global.
  */
@@ -34,4 +36,7 @@ abstract class GlobalSymbolLoaders extends symtab.SymbolLoaders {
 
   protected def compileLate(srcfile: io.AbstractFile): Unit =
     currentRun.compileLate(srcfile)
+
+  def warning(pos: Position, msg: String, category: WarningCategory, site: String): Unit =
+    runReporting.warning(pos, msg, category, site)
 }

src/compiler/scala/tools/nsc/PhaseAssembly.scala

@@ -13,6 +13,7 @@
 package scala.tools.nsc
 
 import scala.collection.mutable
+import scala.tools.nsc.Reporting.WarningCategory
 
 /** Converts an unordered morass of components into an order that
  *  satisfies their mutual constraints.
@@ -202,7 +203,7 @@ trait PhaseAssembly {
           edges -= edge
           edge.frm.after -= edge
           if (edge.frm.phaseobj exists (lsc => !lsc.head.internal))
-            warning(msg)
+            runReporting.warning(NoPosition, msg, WarningCategory.Other, site = "")
         }
       }
     }

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

@@ -31,6 +31,7 @@ import scala.math.Ordering.Double.TotalOrdering
 import scala.reflect.internal.util.{BatchSourceFile, FakePos, NoPosition, Position}
 import scala.reflect.io.PlainNioFile
 import scala.tools.nsc.PipelineMain.{OutlineTypePipeline, Pipeline, Traditional}
+import scala.tools.nsc.Reporting.WarningCategory
 import scala.tools.nsc.io.AbstractFile
 import scala.tools.nsc.reporters.{ConsoleReporter, Reporter}
 import scala.tools.nsc.util.ClassPath
@@ -564,7 +565,7 @@ class PipelineMainClass(argFiles: Seq[Path], pipelineSettings: PipelineMain.Pipe
               }
               diagnostic.getKind match {
                 case Kind.ERROR                            => reporter.error(position, msg)
-                case Kind.WARNING | Kind.MANDATORY_WARNING => reporter.warning(position, msg)
+                case Kind.WARNING | Kind.MANDATORY_WARNING => Task.this.compiler.runReporting.warning(position, msg, WarningCategory.JavaSource, site = "")
                 case Kind.NOTE | Kind.OTHER                => reporter.echo(position, msg)
               }
             }