From 1a490393d766039332bfccb8b85f264f22c9e9cc Mon Sep 17 00:00:00 2001
From: Nicolas Stucki <nicolas.stucki@gmail.com>
Date: Wed, 1 Mar 2017 09:35:30 +0100
Subject: Make loop in derivesFrom a tailrec loop.

---
 compiler/src/dotty/tools/dotc/core/Types.scala | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

(limited to 'compiler/src/dotty/tools/dotc/core/Types.scala')

diff --git a/compiler/src/dotty/tools/dotc/core/Types.scala b/compiler/src/dotty/tools/dotc/core/Types.scala
index 200e94a1e..3258a1d57 100644
--- a/compiler/src/dotty/tools/dotc/core/Types.scala
+++ b/compiler/src/dotty/tools/dotc/core/Types.scala
@@ -153,16 +153,16 @@ object Types {
 
     /** Is this type an instance of a non-bottom subclass of the given class `cls`? */
     final def derivesFrom(cls: Symbol)(implicit ctx: Context): Boolean = {
-      def loop(tp: Type) = tp match {
+      def loop(tp: Type): Boolean = tp match {
         case tp: TypeRef =>
           val sym = tp.symbol
-          if (sym.isClass) sym.derivesFrom(cls) else tp.superType.derivesFrom(cls)
+          if (sym.isClass) sym.derivesFrom(cls) else loop(tp.superType): @tailrec
         case tp: TypeProxy =>
-          tp.underlying.derivesFrom(cls)
+          loop(tp.underlying): @tailrec
         case tp: AndType =>
-          tp.tp1.derivesFrom(cls) || tp.tp2.derivesFrom(cls)
+          loop(tp.tp1) || loop(tp.tp2): @tailrec
         case tp: OrType =>
-          tp.tp1.derivesFrom(cls) && tp.tp2.derivesFrom(cls)
+          loop(tp.tp1) && loop(tp.tp2): @tailrec
         case tp: JavaArrayType =>
           cls == defn.ObjectClass
         case _ =>
@@ -1011,7 +1011,7 @@ object Types {
           }
           else NoType
         case SkolemType(tp) =>
-          tp.lookupRefined(name)
+          loop(tp)
         case pre: WildcardType =>
           WildcardType
         case pre: TypeRef =>
-- 
cgit v1.2.3


From be5720c18ca6768c7e72d4258677952848db2bb4 Mon Sep 17 00:00:00 2001
From: Nicolas Stucki <nicolas.stucki@gmail.com>
Date: Wed, 1 Mar 2017 10:11:49 +0100
Subject: Add @tailrec to avoid regressions.

---
 compiler/src/dotty/tools/dotc/ast/tpd.scala        |  2 +-
 .../src/dotty/tools/dotc/config/Settings.scala     |  3 +-
 compiler/src/dotty/tools/dotc/core/Signature.scala |  4 +-
 .../src/dotty/tools/dotc/core/SymDenotations.scala |  4 +-
 .../src/dotty/tools/dotc/core/TypeErasure.scala    |  3 +-
 compiler/src/dotty/tools/dotc/core/Types.scala     | 60 +++++++++++-----------
 .../src/dotty/tools/dotc/rewrite/Rewrites.scala    |  3 +-
 .../dotty/tools/dotc/transform/ExplicitOuter.scala |  4 +-
 .../src/dotty/tools/dotc/transform/SymUtils.scala  |  6 ++-
 compiler/src/dotty/tools/io/Jar.scala              |  3 +-
 .../strawman/collections/CollectionStrawMan6.scala |  2 +-
 compiler/test/dotty/tools/dotc/CompilerTest.scala  |  4 +-
 12 files changed, 54 insertions(+), 44 deletions(-)

(limited to 'compiler/src/dotty/tools/dotc/core/Types.scala')

diff --git a/compiler/src/dotty/tools/dotc/ast/tpd.scala b/compiler/src/dotty/tools/dotc/ast/tpd.scala
index e5904156f..458e94b6e 100644
--- a/compiler/src/dotty/tools/dotc/ast/tpd.scala
+++ b/compiler/src/dotty/tools/dotc/ast/tpd.scala
@@ -607,7 +607,7 @@ object tpd extends Trees.Instance[Type] with TypedTreeInfo {
      *  owner to `to`, and continue until a non-weak owner is reached.
      */
     def changeOwner(from: Symbol, to: Symbol)(implicit ctx: Context): ThisTree = {
-      def loop(from: Symbol, froms: List[Symbol], tos: List[Symbol]): ThisTree = {
+      @tailrec def loop(from: Symbol, froms: List[Symbol], tos: List[Symbol]): ThisTree = {
         if (from.isWeakOwner && !from.owner.isClass)
           loop(from.owner, from :: froms, to :: tos)
         else {
diff --git a/compiler/src/dotty/tools/dotc/config/Settings.scala b/compiler/src/dotty/tools/dotc/config/Settings.scala
index 58fa6d366..c2763cdf0 100644
--- a/compiler/src/dotty/tools/dotc/config/Settings.scala
+++ b/compiler/src/dotty/tools/dotc/config/Settings.scala
@@ -6,6 +6,7 @@ import scala.util.{ Try, Success, Failure }
 import scala.reflect.internal.util.StringOps
 import reflect.ClassTag
 import core.Contexts._
+import scala.annotation.tailrec
 // import annotation.unchecked
   // Dotty deviation: Imports take precedence over definitions in enclosing package
   // (Note that @unchecked is in scala, not annotation, so annotation.unchecked gives
@@ -217,7 +218,7 @@ object Settings {
         case "--" :: args =>
           checkDependencies(stateWithArgs(skipped ++ args))
         case x :: _ if x startsWith "-" =>
-          def loop(settings: List[Setting[_]]): ArgsSummary = settings match {
+          @tailrec def loop(settings: List[Setting[_]]): ArgsSummary = settings match {
             case setting :: settings1 =>
               val state1 = setting.tryToSet(state)
               if (state1 ne state) processArguments(state1, processAll, skipped)
diff --git a/compiler/src/dotty/tools/dotc/core/Signature.scala b/compiler/src/dotty/tools/dotc/core/Signature.scala
index b2e627cbe..fcd1e2376 100644
--- a/compiler/src/dotty/tools/dotc/core/Signature.scala
+++ b/compiler/src/dotty/tools/dotc/core/Signature.scala
@@ -4,6 +4,8 @@ package core
 import Names._, Types._, Contexts._, StdNames._
 import TypeErasure.sigName
 
+import scala.annotation.tailrec
+
 /** The signature of a denotation.
  *  Overloaded denotations with the same name are distinguished by
  *  their signatures. A signature of a method (of type PolyType,MethodType, or ExprType) is
@@ -41,7 +43,7 @@ case class Signature(paramsSig: List[TypeName], resSig: TypeName) {
    *  equal or on of them is tpnme.Uninstantiated.
    */
   final def consistentParams(that: Signature): Boolean = {
-    def loop(names1: List[TypeName], names2: List[TypeName]): Boolean =
+    @tailrec def loop(names1: List[TypeName], names2: List[TypeName]): Boolean =
       if (names1.isEmpty) names2.isEmpty
       else names2.nonEmpty && consistent(names1.head, names2.head) && loop(names1.tail, names2.tail)
     loop(this.paramsSig, that.paramsSig)
diff --git a/compiler/src/dotty/tools/dotc/core/SymDenotations.scala b/compiler/src/dotty/tools/dotc/core/SymDenotations.scala
index a3475e14c..8e3b73fc0 100644
--- a/compiler/src/dotty/tools/dotc/core/SymDenotations.scala
+++ b/compiler/src/dotty/tools/dotc/core/SymDenotations.scala
@@ -1040,7 +1040,7 @@ object SymDenotations {
      *  pre: `this.owner` is in the base class sequence of `base`.
      */
     final def superSymbolIn(base: Symbol)(implicit ctx: Context): Symbol = {
-      def loop(bcs: List[ClassSymbol]): Symbol = bcs match {
+      @tailrec def loop(bcs: List[ClassSymbol]): Symbol = bcs match {
         case bc :: bcs1 =>
           val sym = matchingDecl(bcs.head, base.thisType)
             .suchThat(alt => !(alt is Deferred)).symbol
@@ -1056,7 +1056,7 @@ object SymDenotations {
      *  (2) it is abstract override and its super symbol in `base` is
      *      nonexistent or incomplete.
      */
-    final def isIncompleteIn(base: Symbol)(implicit ctx: Context): Boolean =
+    @tailrec final def isIncompleteIn(base: Symbol)(implicit ctx: Context): Boolean =
       (this is Deferred) ||
       (this is AbsOverride) && {
         val supersym = superSymbolIn(base)
diff --git a/compiler/src/dotty/tools/dotc/core/TypeErasure.scala b/compiler/src/dotty/tools/dotc/core/TypeErasure.scala
index ff99008bb..fc18808a3 100644
--- a/compiler/src/dotty/tools/dotc/core/TypeErasure.scala
+++ b/compiler/src/dotty/tools/dotc/core/TypeErasure.scala
@@ -10,6 +10,7 @@ import dotc.transform.ExplicitOuter._
 import dotc.transform.ValueClasses._
 import util.DotClass
 import Definitions.MaxImplementedFunctionArity
+import scala.annotation.tailrec
 
 /** Erased types are:
  *
@@ -244,7 +245,7 @@ object TypeErasure {
         case JavaArrayType(_) => defn.ObjectType
         case _ =>
           val cls2 = tp2.classSymbol
-          def loop(bcs: List[ClassSymbol], bestSoFar: ClassSymbol): ClassSymbol = bcs match {
+          @tailrec def loop(bcs: List[ClassSymbol], bestSoFar: ClassSymbol): ClassSymbol = bcs match {
             case bc :: bcs1 =>
               if (cls2.derivesFrom(bc))
                 if (!bc.is(Trait) && bc != defn.AnyClass) bc
diff --git a/compiler/src/dotty/tools/dotc/core/Types.scala b/compiler/src/dotty/tools/dotc/core/Types.scala
index 3258a1d57..6ff896110 100644
--- a/compiler/src/dotty/tools/dotc/core/Types.scala
+++ b/compiler/src/dotty/tools/dotc/core/Types.scala
@@ -105,7 +105,7 @@ object Types {
     final def isValueTypeOrLambda: Boolean = isValueType || this.isInstanceOf[PolyType]
 
     /** Does this type denote a stable reference (i.e. singleton type)? */
-    final def isStable(implicit ctx: Context): Boolean = stripTypeVar match {
+    @tailrec final def isStable(implicit ctx: Context): Boolean = stripTypeVar match {
       case tp: TermRef => tp.termSymbol.isStable && tp.prefix.isStable
       case _: SingletonType | NoPrefix => true
       case tp: RefinedOrRecType => tp.parent.isStable
@@ -188,7 +188,7 @@ object Types {
     final def isErroneous(implicit ctx: Context): Boolean = existsPart(_.isError, forceLazy = false)
 
     /** Does the type carry an annotation that is an instance of `cls`? */
-    final def hasAnnotation(cls: ClassSymbol)(implicit ctx: Context): Boolean = stripTypeVar match {
+    @tailrec final def hasAnnotation(cls: ClassSymbol)(implicit ctx: Context): Boolean = stripTypeVar match {
       case AnnotatedType(tp, annot) => (annot matches cls) || (tp hasAnnotation cls)
       case _ => false
     }
@@ -277,7 +277,7 @@ object Types {
 // ----- Associated symbols ----------------------------------------------
 
     /** The type symbol associated with the type */
-    final def typeSymbol(implicit ctx: Context): Symbol = this match {
+    @tailrec final def typeSymbol(implicit ctx: Context): Symbol = this match {
       case tp: TypeRef => tp.symbol
       case tp: ClassInfo => tp.cls
 //    case ThisType(cls) => cls // needed?
@@ -292,16 +292,16 @@ object Types {
      */
     final def classSymbol(implicit ctx: Context): Symbol = this match {
       case ConstantType(constant) =>
-        constant.tpe.classSymbol
+        constant.tpe.classSymbol: @tailrec
       case tp: TypeRef =>
         val sym = tp.symbol
-        if (sym.isClass) sym else tp.superType.classSymbol
+        if (sym.isClass) sym else tp.superType.classSymbol: @tailrec
       case tp: ClassInfo =>
         tp.cls
       case tp: SingletonType =>
         NoSymbol
       case tp: TypeProxy =>
-        tp.underlying.classSymbol
+        tp.underlying.classSymbol: @tailrec
       case AndType(l, r) =>
         val lsym = l.classSymbol
         val rsym = r.classSymbol
@@ -325,9 +325,9 @@ object Types {
         tp.cls :: Nil
       case tp: TypeRef =>
         val sym = tp.symbol
-        if (sym.isClass) sym.asClass :: Nil else tp.superType.classSymbols
+        if (sym.isClass) sym.asClass :: Nil else tp.superType.classSymbols: @tailrec
       case tp: TypeProxy =>
-        tp.underlying.classSymbols
+        tp.underlying.classSymbols: @tailrec
       case AndType(l, r) =>
         l.classSymbols union r.classSymbols
       case OrType(l, r) =>
@@ -337,7 +337,7 @@ object Types {
     }
 
     /** The term symbol associated with the type */
-    final def termSymbol(implicit ctx: Context): Symbol = this match {
+    @tailrec final def termSymbol(implicit ctx: Context): Symbol = this match {
       case tp: TermRef => tp.symbol
       case tp: TypeProxy => tp.underlying.termSymbol
       case _ => NoSymbol
@@ -368,11 +368,11 @@ object Types {
      *  Defined by ClassInfo, inherited by type proxies.
      *  Empty scope for all other types.
      */
-    final def decls(implicit ctx: Context): Scope = this match {
+    @tailrec final def decls(implicit ctx: Context): Scope = this match {
       case tp: ClassInfo =>
         tp.decls
       case tp: TypeProxy =>
-        tp.underlying.decls
+        tp.underlying.decls: @tailrec
       case _ =>
         EmptyScope
     }
@@ -394,7 +394,7 @@ object Types {
      *  name, as seen from prefix type `pre`. Declarations that have a flag
      *  in `excluded` are omitted.
      */
-    final def findDecl(name: Name, excluded: FlagSet)(implicit ctx: Context): Denotation = this match {
+    @tailrec final def findDecl(name: Name, excluded: FlagSet)(implicit ctx: Context): Denotation = this match {
       case tp: ClassInfo =>
         tp.decls.denotsNamed(name).filterExcluded(excluded).toDenot(NoPrefix)
       case tp: TypeProxy =>
@@ -620,7 +620,7 @@ object Types {
         val ns = tp.parent.memberNames(keepOnly, pre)
         if (keepOnly(pre, tp.refinedName)) ns + tp.refinedName else ns
       case tp: TypeProxy =>
-        tp.underlying.memberNames(keepOnly, pre)
+        tp.underlying.memberNames(keepOnly, pre): @tailrec
       case tp: AndType =>
         tp.tp1.memberNames(keepOnly, pre) | tp.tp2.memberNames(keepOnly, pre)
       case tp: OrType =>
@@ -827,7 +827,7 @@ object Types {
      *  def o: Outer
      *  <o.x.type>.widen = o.C
      */
-    final def widen(implicit ctx: Context): Type = widenSingleton match {
+    @tailrec final def widen(implicit ctx: Context): Type = widenSingleton match {
       case tp: ExprType => tp.resultType.widen
       case tp => tp
     }
@@ -835,7 +835,7 @@ object Types {
     /** Widen from singleton type to its underlying non-singleton
      *  base type by applying one or more `underlying` dereferences.
      */
-    final def widenSingleton(implicit ctx: Context): Type = stripTypeVar match {
+    @tailrec final def widenSingleton(implicit ctx: Context): Type = stripTypeVar match {
       case tp: SingletonType if !tp.isOverloaded => tp.underlying.widenSingleton
       case _ => this
     }
@@ -843,7 +843,7 @@ object Types {
     /** Widen from TermRef to its underlying non-termref
      *  base type, while also skipping Expr types.
      */
-    final def widenTermRefExpr(implicit ctx: Context): Type = stripTypeVar match {
+    @tailrec final def widenTermRefExpr(implicit ctx: Context): Type = stripTypeVar match {
       case tp: TermRef if !tp.isOverloaded => tp.underlying.widenExpr.widenTermRefExpr
       case _ => this
     }
@@ -857,7 +857,7 @@ object Types {
     }
 
     /** Widen type if it is unstable (i.e. an ExprType, or TermRef to unstable symbol */
-    final def widenIfUnstable(implicit ctx: Context): Type = stripTypeVar match {
+    @tailrec final def widenIfUnstable(implicit ctx: Context): Type = stripTypeVar match {
       case tp: ExprType => tp.resultType.widenIfUnstable
       case tp: TermRef if !tp.symbol.isStable => tp.underlying.widenIfUnstable
       case _ => this
@@ -880,20 +880,20 @@ object Types {
       case tp: TypeRef =>
         if (tp.symbol.isClass) tp
         else tp.info match {
-          case TypeAlias(tp) => tp.dealias(keepAnnots)
+          case TypeAlias(tp) => tp.dealias(keepAnnots): @tailrec
           case _ => tp
         }
       case tp: TypeVar =>
         val tp1 = tp.instanceOpt
-        if (tp1.exists) tp1.dealias(keepAnnots) else tp
+        if (tp1.exists) tp1.dealias(keepAnnots): @tailrec else tp
       case tp: AnnotatedType =>
         val tp1 = tp.tpe.dealias(keepAnnots)
         if (keepAnnots) tp.derivedAnnotatedType(tp1, tp.annot) else tp1
       case tp: LazyRef =>
-        tp.ref.dealias(keepAnnots)
+        tp.ref.dealias(keepAnnots): @tailrec
       case app @ HKApply(tycon, args) =>
         val tycon1 = tycon.dealias(keepAnnots)
-        if (tycon1 ne tycon) app.superType.dealias(keepAnnots)
+        if (tycon1 ne tycon) app.superType.dealias(keepAnnots): @tailrec
         else this
       case _ => this
     }
@@ -913,7 +913,7 @@ object Types {
       dealias(keepAnnots = false)
 
     /** Perform successive widenings and dealiasings until none can be applied anymore */
-    final def widenDealias(implicit ctx: Context): Type = {
+    @tailrec final def widenDealias(implicit ctx: Context): Type = {
       val res = this.widen.dealias
       if (res eq this) res else res.widenDealias
     }
@@ -996,7 +996,7 @@ object Types {
      *  (*) normalizes means: follow instantiated typevars and aliases.
      */
     def lookupRefined(name: Name)(implicit ctx: Context): Type = {
-      def loop(pre: Type): Type = pre.stripTypeVar match {
+      @tailrec def loop(pre: Type): Type = pre.stripTypeVar match {
         case pre: RefinedType =>
           pre.refinedInfo match {
             case TypeAlias(alias) =>
@@ -1004,7 +1004,7 @@ object Types {
             case _ => loop(pre.parent)
           }
         case pre: RecType =>
-          val candidate = loop(pre.parent)
+          val candidate = pre.parent.lookupRefined(name)
           if (candidate.exists && !pre.isReferredToBy(candidate)) {
             //println(s"lookupRefined ${this.toString} . $name, pre: $pre ---> $candidate / ${candidate.toString}")
             candidate
@@ -1051,7 +1051,7 @@ object Types {
      *  Inherited by all other type proxies.
      *  `NoType` for all other types.
      */
-    final def normalizedPrefix(implicit ctx: Context): Type = this match {
+    @tailrec final def normalizedPrefix(implicit ctx: Context): Type = this match {
       case tp: NamedType =>
         if (tp.symbol.info.isAlias) tp.info.normalizedPrefix else tp.prefix
       case tp: ClassInfo =>
@@ -1107,14 +1107,14 @@ object Types {
 
 
     /** The parameter types in the first parameter section of a generic type or MethodType, Empty list for others */
-    final def firstParamTypes(implicit ctx: Context): List[Type] = this match {
+    @tailrec final def firstParamTypes(implicit ctx: Context): List[Type] = this match {
       case mt: MethodType => mt.paramTypes
       case pt: PolyType => pt.resultType.firstParamTypes
       case _ => Nil
     }
 
     /** Is this either not a method at all, or a parameterless method? */
-    final def isParameterless(implicit ctx: Context): Boolean = this match {
+    @tailrec final def isParameterless(implicit ctx: Context): Boolean = this match {
       case mt: MethodType => false
       case pt: PolyType => pt.resultType.isParameterless
       case _ => true
@@ -2101,7 +2101,7 @@ object Types {
   }
 
   object RefinedType {
-    def make(parent: Type, names: List[Name], infos: List[Type])(implicit ctx: Context): Type =
+    @tailrec def make(parent: Type, names: List[Name], infos: List[Type])(implicit ctx: Context): Type =
       if (names.isEmpty) parent
       else make(RefinedType(parent, names.head, infos.head), names.tail, infos.tail)
 
@@ -3676,7 +3676,7 @@ object Types {
         this(x, prefix)
 
       case tp @ HKApply(tycon, args) =>
-        def foldArgs(x: T, tparams: List[TypeParamInfo], args: List[Type]): T =
+        @tailrec def foldArgs(x: T, tparams: List[TypeParamInfo], args: List[Type]): T =
           if (args.isEmpty) {
             assert(tparams.isEmpty)
             x
@@ -3719,7 +3719,7 @@ object Types {
       case _ => x
     }
 
-    final def foldOver(x: T, ts: List[Type]): T = ts match {
+    @tailrec final def foldOver(x: T, ts: List[Type]): T = ts match {
       case t :: ts1 => foldOver(apply(x, t), ts1)
       case nil => x
     }
diff --git a/compiler/src/dotty/tools/dotc/rewrite/Rewrites.scala b/compiler/src/dotty/tools/dotc/rewrite/Rewrites.scala
index c42c808fe..909a145d1 100644
--- a/compiler/src/dotty/tools/dotc/rewrite/Rewrites.scala
+++ b/compiler/src/dotty/tools/dotc/rewrite/Rewrites.scala
@@ -5,6 +5,7 @@ import util.{SourceFile, Positions}
 import Positions.Position
 import core.Contexts.{Context, FreshContext}
 import collection.mutable
+import scala.annotation.tailrec
 
 /** Handles rewriting of Scala2 files to Dotty */
 object Rewrites {
@@ -29,7 +30,7 @@ object Rewrites {
           p2
         }
       val ds = new Array[Char](cs.length + delta)
-      def loop(ps: List[Patch], inIdx: Int, outIdx: Int): Unit = {
+      @tailrec def loop(ps: List[Patch], inIdx: Int, outIdx: Int): Unit = {
         def copy(upTo: Int): Int = {
           val untouched = upTo - inIdx
           Array.copy(cs, inIdx, ds, outIdx, untouched)
diff --git a/compiler/src/dotty/tools/dotc/transform/ExplicitOuter.scala b/compiler/src/dotty/tools/dotc/transform/ExplicitOuter.scala
index d75c32fcc..44308012e 100644
--- a/compiler/src/dotty/tools/dotc/transform/ExplicitOuter.scala
+++ b/compiler/src/dotty/tools/dotc/transform/ExplicitOuter.scala
@@ -16,7 +16,9 @@ import SymUtils._
 import dotty.tools.dotc.ast.tpd
 import dotty.tools.dotc.core.Phases.Phase
 import util.Property
+
 import collection.mutable
+import scala.annotation.tailrec
 
 /** This phase adds outer accessors to classes and traits that need them.
  *  Compared to Scala 2.x, it tries to minimize the set of classes
@@ -367,7 +369,7 @@ object ExplicitOuter {
     def path(start: Tree = This(ctx.owner.lexicallyEnclosingClass.asClass),
              toCls: Symbol = NoSymbol,
              count: Int = -1): Tree = try {
-      def loop(tree: Tree, count: Int): Tree = {
+      @tailrec def loop(tree: Tree, count: Int): Tree = {
         val treeCls = tree.tpe.widen.classSymbol
         val outerAccessorCtx = ctx.withPhaseNoLater(ctx.lambdaLiftPhase) // lambdalift mangles local class names, which means we cannot reliably find outer acessors anymore
         ctx.log(i"outer to $toCls of $tree: ${tree.tpe}, looking for ${outerAccName(treeCls.asClass)(outerAccessorCtx)} in $treeCls")
diff --git a/compiler/src/dotty/tools/dotc/transform/SymUtils.scala b/compiler/src/dotty/tools/dotc/transform/SymUtils.scala
index 05305575e..105f54d3a 100644
--- a/compiler/src/dotty/tools/dotc/transform/SymUtils.scala
+++ b/compiler/src/dotty/tools/dotc/transform/SymUtils.scala
@@ -12,7 +12,9 @@ import StdNames._
 import NameOps._
 import Flags._
 import Annotations._
+
 import language.implicitConversions
+import scala.annotation.tailrec
 
 object SymUtils {
   implicit def decorateSymbol(sym: Symbol): SymUtils = new SymUtils(sym)
@@ -59,14 +61,14 @@ class SymUtils(val self: Symbol) extends AnyVal {
   }
 
   /** The closest enclosing method or class of this symbol */
-  final def enclosingMethodOrClass(implicit ctx: Context): Symbol =
+  @tailrec final def enclosingMethodOrClass(implicit ctx: Context): Symbol =
     if (self.is(Method, butNot = Label) || self.isClass) self
     else if (self.exists) self.owner.enclosingMethodOrClass
     else NoSymbol
 
   /** Apply symbol/symbol substitution to this symbol */
   def subst(from: List[Symbol], to: List[Symbol]): Symbol = {
-    def loop(from: List[Symbol], to: List[Symbol]): Symbol =
+    @tailrec def loop(from: List[Symbol], to: List[Symbol]): Symbol =
       if (from.isEmpty) self
       else if (self eq from.head) to.head
       else loop(from.tail, to.tail)
diff --git a/compiler/src/dotty/tools/io/Jar.scala b/compiler/src/dotty/tools/io/Jar.scala
index 42efc7e06..142226ea5 100644
--- a/compiler/src/dotty/tools/io/Jar.scala
+++ b/compiler/src/dotty/tools/io/Jar.scala
@@ -12,6 +12,7 @@ import java.util.jar._
 import scala.collection.JavaConverters._
 import Attributes.Name
 import scala.language.{postfixOps, implicitConversions}
+import scala.annotation.tailrec
 
 // Attributes.Name instances:
 //
@@ -109,7 +110,7 @@ class JarWriter(val file: File, val manifest: Manifest) {
 
   private def transfer(in: InputStream, out: OutputStream) = {
     val buf = new Array[Byte](10240)
-    def loop(): Unit = in.read(buf, 0, buf.length) match {
+    @tailrec def loop(): Unit = in.read(buf, 0, buf.length) match {
       case -1 => in.close()
       case n  => out.write(buf, 0, n) ; loop
     }
diff --git a/compiler/src/strawman/collections/CollectionStrawMan6.scala b/compiler/src/strawman/collections/CollectionStrawMan6.scala
index 50de63488..c2b87cb0b 100644
--- a/compiler/src/strawman/collections/CollectionStrawMan6.scala
+++ b/compiler/src/strawman/collections/CollectionStrawMan6.scala
@@ -244,7 +244,7 @@ object CollectionStrawMan6 extends LowPriority {
      *  collection type.
      */
     override def drop(n: Int): C[A @uncheckedVariance] = { // sound bcs of VarianceNote
-      def loop(n: Int, s: Iterable[A]): C[A] =
+      @tailrec def loop(n: Int, s: Iterable[A]): C[A] =
         if (n <= 0) s.asInstanceOf[C[A]]
            // implicit contract to guarantee success of asInstanceOf:
            //   (1) coll is of type C[A]
diff --git a/compiler/test/dotty/tools/dotc/CompilerTest.scala b/compiler/test/dotty/tools/dotc/CompilerTest.scala
index 5d16917cc..db12994f4 100644
--- a/compiler/test/dotty/tools/dotc/CompilerTest.scala
+++ b/compiler/test/dotty/tools/dotc/CompilerTest.scala
@@ -500,12 +500,12 @@ abstract class CompilerTest {
     * that aren't in extensionsToCopy. */
   private def recCopyFiles(sourceFile: Path, dest: Path): Unit = {
 
-    def copyfile(file: SFile, bytewise: Boolean): Unit = {
+    @tailrec def copyfile(file: SFile, bytewise: Boolean): Unit = {
       if (bytewise) {
         val in = file.inputStream()
         val out = SFile(dest).outputStream()
         val buffer = new Array[Byte](1024)
-        def loop(available: Int):Unit = {
+        @tailrec def loop(available: Int):Unit = {
           if (available < 0) {()}
           else {
             out.write(buffer, 0, available)
-- 
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