Add support for @deprecatedInheritance

compiler/src/dotty/tools/dotc/core/Definitions.scala

@@ -1006,6 +1006,7 @@ class Definitions {
   @tu lazy val ProvisionalSuperClassAnnot: ClassSymbol = requiredClass("scala.annotation.internal.ProvisionalSuperClass")
   @tu lazy val DeprecatedAnnot: ClassSymbol = requiredClass("scala.deprecated")
   @tu lazy val DeprecatedOverridingAnnot: ClassSymbol = requiredClass("scala.deprecatedOverriding")
+  @tu lazy val DeprecatedInheritanceAnnot: ClassSymbol = requiredClass("scala.deprecatedInheritance")
   @tu lazy val ImplicitAmbiguousAnnot: ClassSymbol = requiredClass("scala.annotation.implicitAmbiguous")
   @tu lazy val ImplicitNotFoundAnnot: ClassSymbol = requiredClass("scala.annotation.implicitNotFound")
   @tu lazy val InlineParamAnnot: ClassSymbol = requiredClass("scala.annotation.internal.InlineParam")

compiler/src/dotty/tools/dotc/interactive/InteractiveDriver.scala

@@ -47,14 +47,10 @@ class InteractiveDriver(val settings: List[String]) extends Driver {
 
   private val compiler: Compiler = new InteractiveCompiler
 
-  private val myOpenedFiles = new mutable.LinkedHashMap[URI, SourceFile] {
-    override def default(key: URI) = NoSource
-  }
+  private val myOpenedFiles = new mutable.LinkedHashMap[URI, SourceFile].withDefaultValue(NoSource)
   def openedFiles: Map[URI, SourceFile] = myOpenedFiles
 
-  private val myOpenedTrees = new mutable.LinkedHashMap[URI, List[SourceTree]] {
-    override def default(key: URI) = Nil
-  }
+  private val myOpenedTrees = new mutable.LinkedHashMap[URI, List[SourceTree]].withDefaultValue(Nil)
   def openedTrees: Map[URI, List[SourceTree]] = myOpenedTrees
 
   private val myCompilationUnits = new mutable.LinkedHashMap[URI, CompilationUnit]

compiler/src/dotty/tools/dotc/reporting/Message.scala

@@ -57,8 +57,7 @@ object Message:
     def openLambda(tp: LambdaType): Unit =
       openedLambdas += tp
 
-    val seen = new collection.mutable.HashMap[SeenKey, List[Recorded]]:
-      override def default(key: SeenKey) = Nil
+    val seen = new collection.mutable.HashMap[SeenKey, List[Recorded]].withDefaultValue(Nil)
 
     var nonSensical = false
 

compiler/src/dotty/tools/dotc/rewrites/Rewrites.scala

@@ -15,7 +15,7 @@ import dotty.tools.dotc.reporting.CodeAction
 
 /** Handles rewriting of Scala2 files to Dotty */
 object Rewrites {
-  private class PatchedFiles extends mutable.HashMap[SourceFile, Patches]
+  private type PatchedFiles = mutable.HashMap[SourceFile, Patches]
 
   private case class Patch(span: Span, replacement: String) {
     def delta = replacement.length - (span.end - span.start)

compiler/src/dotty/tools/dotc/semanticdb/SemanticSymbolBuilder.scala

@@ -20,8 +20,7 @@ class SemanticSymbolBuilder:
   private val locals = mutable.HashMap[Symbol, Int]()
 
   /** The local symbol(s) starting at given offset */
-  private val symsAtOffset = new mutable.HashMap[Int, Set[Symbol]]():
-    override def default(key: Int) = Set[Symbol]()
+  private val symsAtOffset = new mutable.HashMap[Int, Set[Symbol]]().withDefault(_ => Set[Symbol]())
 
 
   def symbolName(sym: Symbol)(using Context): String =

compiler/src/dotty/tools/dotc/transform/CountOuterAccesses.scala

@@ -43,9 +43,7 @@ class CountOuterAccesses extends MiniPhase:
     // LambdaLift can create outer paths. These need to be known in this phase.
 
   /** The number of times an outer accessor that might be dropped is accessed */
-  val outerAccessCount = new mutable.HashMap[Symbol, Int] {
-    override def default(s: Symbol): Int = 0
-  }
+  val outerAccessCount = new mutable.HashMap[Symbol, Int].withDefaultValue(0)
 
   private def markAccessed(tree: RefTree)(using Context): Tree =
     val sym = tree.symbol

compiler/src/dotty/tools/dotc/transform/PatternMatcher.scala

@@ -504,9 +504,7 @@ object PatternMatcher {
     }
 
     private class RefCounter extends PlanTransform {
-      val count = new mutable.HashMap[Symbol, Int] {
-        override def default(key: Symbol) = 0
-      }
+      val count = new mutable.HashMap[Symbol, Int].withDefaultValue(0)
     }
 
     /** Reference counts for all labels */

compiler/src/dotty/tools/dotc/typer/Checking.scala

@@ -1150,9 +1150,7 @@ trait Checking {
 
   /** Check that class does not declare same symbol twice */
   def checkNoDoubleDeclaration(cls: Symbol)(using Context): Unit = {
-    val seen = new mutable.HashMap[Name, List[Symbol]] {
-      override def default(key: Name) = Nil
-    }
+    val seen = new mutable.HashMap[Name, List[Symbol]].withDefaultValue(Nil)
     typr.println(i"check no double declarations $cls")
 
     def checkDecl(decl: Symbol): Unit = {

compiler/src/dotty/tools/dotc/typer/RefChecks.scala

@@ -114,6 +114,16 @@ object RefChecks {
     }
   end checkSelfAgainstParents
 
+  /** warn if `@deprecatedInheritance` is present */
+  def warnDeprecatedInheritance(cls: ClassSymbol, parentTrees: List[Tree])(using Context): Unit =
+    val psyms = cls.parentSyms
+    for (psym, pos) <- psyms.zip(parentTrees.map(_.srcPos))
+        annot <- psym.getAnnotation(defn.DeprecatedInheritanceAnnot)
+    do
+      val msg = annot.argumentConstantString(0).getOrElse("")
+      val since = annot.argumentConstantString(1).getOrElse("")
+      report.deprecationWarning(em"inheritance from $psym is deprecated (since: $since): $msg", pos)
+
   /** Check that self type of this class conforms to self types of parents
    *  and required classes. Also check that only `enum` constructs extend
    *  `java.lang.Enum` and no user-written class extends ContextFunctionN.
@@ -123,6 +133,8 @@ object RefChecks {
       val psyms = cls.asClass.parentSyms
       checkSelfAgainstParents(cls.asClass, psyms)
 
+      warnDeprecatedInheritance(cls.asClass, parentTrees)
+
       def isClassExtendingJavaEnum =
         !cls.isOneOf(Enum | Trait) && psyms.contains(defn.JavaEnumClass)
 

compiler/src/dotty/tools/dotc/util/Stats.scala

@@ -19,9 +19,7 @@ import collection.mutable
 
   @volatile private var stack: List[String] = Nil
 
-  val hits: mutable.HashMap[String, Int] = new mutable.HashMap[String, Int] {
-    override def default(key: String): Int = 0
-  }
+  val hits: mutable.Map[String, Int] = new mutable.HashMap[String, Int].withDefaultValue(0)
 
   inline def record(inline fn: String, inline n: Int = 1, inline skip: Boolean = timerOnly): Unit =
     if (enabled && !skip) doRecord(fn, n)

tests/init/pos/patternMatcher.scala

@@ -1,8 +1,6 @@
 import scala.collection.mutable
 
 class Translater:
-  val count = new mutable.HashMap[Int, Int] {
-    override def default(key: Int) = 0
-  }
+  val count = new mutable.HashMap[Int, Int].withDefaultValue(0)
   count.get(10)
   val n = 10

tests/warn/i19002.check

@@ -0,0 +1,36 @@
+-- Deprecation Warning: tests/warn/i19002.scala:5:20 -------------------------------------------------------------------
+5 |class TBar1 extends TFoo // warn
+  |                    ^^^^
+  |                    inheritance from trait TFoo is deprecated (since: FooLib 12.0): this class will be made final
+-- Deprecation Warning: tests/warn/i19002.scala:6:20 -------------------------------------------------------------------
+6 |trait TBar2 extends TFoo // warn
+  |                    ^^^^
+  |                    inheritance from trait TFoo is deprecated (since: FooLib 12.0): this class will be made final
+-- Deprecation Warning: tests/warn/i19002.scala:11:20 ------------------------------------------------------------------
+11 |class CBar1 extends CFoo // warn
+   |                    ^^^^
+   |                   inheritance from class CFoo is deprecated (since: FooLib 11.0): this class will be made final
+-- Deprecation Warning: tests/warn/i19002.scala:12:20 ------------------------------------------------------------------
+12 |trait CBar2 extends CFoo // warn
+   |                    ^^^^
+   |                   inheritance from class CFoo is deprecated (since: FooLib 11.0): this class will be made final
+-- Deprecation Warning: tests/warn/i19002.scala:17:20 ------------------------------------------------------------------
+17 |class ABar1 extends AFoo // warn
+   |                    ^^^^
+   |                   inheritance from class AFoo is deprecated (since: FooLib 10.0): this class will be made final
+-- Deprecation Warning: tests/warn/i19002.scala:18:20 ------------------------------------------------------------------
+18 |trait ABar2 extends AFoo // warn
+   |                    ^^^^
+   |                   inheritance from class AFoo is deprecated (since: FooLib 10.0): this class will be made final
+-- Deprecation Warning: tests/warn/i19002.scala:7:16 -------------------------------------------------------------------
+7 |def TBar3 = new TFoo {}  // warn
+  |                ^^^^
+  |                inheritance from trait TFoo is deprecated (since: FooLib 12.0): this class will be made final
+-- Deprecation Warning: tests/warn/i19002.scala:13:16 ------------------------------------------------------------------
+13 |def CBar3 = new CFoo {}  // warn
+   |                ^^^^
+   |                inheritance from class CFoo is deprecated (since: FooLib 11.0): this class will be made final
+-- Deprecation Warning: tests/warn/i19002.scala:19:16 ------------------------------------------------------------------
+19 |def ABar3 = new AFoo {}  // warn
+   |                ^^^^
+   |                inheritance from class AFoo is deprecated (since: FooLib 10.0): this class will be made final

tests/warn/i19002.scala

@@ -0,0 +1,19 @@
+//> using options -deprecation
+
+@deprecatedInheritance("this class will be made final", "FooLib 12.0")
+trait TFoo
+class TBar1 extends TFoo // warn
+trait TBar2 extends TFoo // warn
+def TBar3 = new TFoo {}  // warn
+
+@deprecatedInheritance("this class will be made final", "FooLib 11.0")
+class CFoo
+class CBar1 extends CFoo // warn
+trait CBar2 extends CFoo // warn
+def CBar3 = new CFoo {}  // warn
+
+@deprecatedInheritance("this class will be made final", "FooLib 10.0")
+abstract class AFoo
+class ABar1 extends AFoo // warn
+trait ABar2 extends AFoo // warn
+def ABar3 = new AFoo {}  // warn