Drop forceInline annotation

It was needed to make Dotty cross-compile to Scala 2
before full bootstrap. Its direct semantics
is about adding the `inline` flag to a symbol
annotated by it. `inline` flag, however, is listed as
one of the flags that are not supposed to be modified
by completion of symbols. Hence, having `forceInline`
annotation is in violation of our own assumptions
about completion. Before full bootstrap, we were not
able to drop this annotation, however, now that we
have the full bootstrap, we can do it.

Author: anatoliykmetyuk

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

@@ -205,7 +205,7 @@ trait ConstraintHandling[AbstractContext] {
     else
       isSubType(tp1, tp2)
 
-  @forceInline final def inFrozenConstraint[T](op: => T): T = {
+  inline final def inFrozenConstraint[T](op: => T): T = {
     val savedFrozen = frozenConstraint
     val savedLambda = caseLambda
     frozenConstraint = true

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

@@ -750,7 +750,6 @@ class Definitions {
   @tu lazy val DeprecatedAnnot: ClassSymbol = ctx.requiredClass("scala.deprecated")
   @tu lazy val ImplicitAmbiguousAnnot: ClassSymbol = ctx.requiredClass("scala.annotation.implicitAmbiguous")
   @tu lazy val ImplicitNotFoundAnnot: ClassSymbol = ctx.requiredClass("scala.annotation.implicitNotFound")
-  @tu lazy val ForceInlineAnnot: ClassSymbol = ctx.requiredClass("scala.forceInline")
   @tu lazy val InlineParamAnnot: ClassSymbol = ctx.requiredClass("scala.annotation.internal.InlineParam")
   @tu lazy val InvariantBetweenAnnot: ClassSymbol = ctx.requiredClass("scala.annotation.internal.InvariantBetween")
   @tu lazy val MainAnnot: ClassSymbol = ctx.requiredClass("scala.main")

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

@@ -918,17 +918,10 @@ object SymDenotations {
     /** Is this a Scala 2 macro */
     final def isScala2Macro(implicit ctx: Context): Boolean = is(Macro) && symbol.owner.is(Scala2x)
 
-    /** An erased value or an inline method, excluding @forceInline annotated methods.
-     *  The latter have to be kept around to get to parity with Scala.
-     *  This is necessary at least until we have full bootstrap. Right now
-     *  dotty-bootstrapped involves running the Dotty compiler compiled with Scala 2 with
-     *  a Dotty runtime library compiled with Dotty. If we erase @forceInline annotated
-     *  methods, this means that the support methods in dotty.runtime.LazyVals vanish.
-     *  But they are needed for running the lazy val implementations in the Scala-2 compiled compiler.
+    /** An erased value or an inline method.
      */
     def isEffectivelyErased(implicit ctx: Context): Boolean =
-      is(Erased) ||
-      isInlineMethod && unforcedAnnotation(defn.ForceInlineAnnot).isEmpty
+      is(Erased) || isInlineMethod
 
     /** ()T and => T types should be treated as equivalent for this symbol.
      *  Note: For the moment, we treat Scala-2 compiled symbols as loose matching,

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

@@ -908,6 +908,6 @@ object Symbols {
     override def toString: String = value.asScala.toString()
   }
 
-  @forceInline def newMutableSymbolMap[T]: MutableSymbolMap[T] =
+  inline def newMutableSymbolMap[T]: MutableSymbolMap[T] =
     new MutableSymbolMap(new java.util.IdentityHashMap[Symbol, T]())
 }

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

@@ -4432,7 +4432,7 @@ object Types {
   abstract class VariantTraversal {
     protected[core] var variance: Int = 1
 
-    @forceInline protected def atVariance[T](v: Int)(op: => T): T = {
+    inline protected def atVariance[T](v: Int)(op: => T): T = {
       val saved = variance
       variance = v
       val res = op

compiler/src/dotty/tools/dotc/parsing/xml/MarkupParsers.scala

@@ -317,7 +317,7 @@ object MarkupParsers {
     }
 
     /** Some try/catch/finally logic used by xLiteral and xLiteralPattern.  */
-    @forceInline private def xLiteralCommon(f: () => Tree, ifTruncated: String => Unit): Tree = {
+    inline private def xLiteralCommon(f: () => Tree, ifTruncated: String => Unit): Tree = {
       assert(parser.in.token == Tokens.XMLSTART)
       val saved = parser.in.newTokenData
       saved.copyFrom(parser.in)

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

@@ -48,7 +48,7 @@ object ConstFold {
       }
     }
 
-  @forceInline private def finish[T <: Tree](tree: T)(compX: => Constant)(implicit ctx: Context): T =
+  inline private def finish[T <: Tree](tree: T)(compX: => Constant)(implicit ctx: Context): T =
     try {
       val x = compX
       if (x ne null) tree.withType(ConstantType(x)).asInstanceOf[T]

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

@@ -33,15 +33,12 @@ import dotty.tools.dotc.transform.{Splicer, TreeMapWithStages}
 object Inliner {
   import tpd._
 
-  /** `sym` is an inline method with a known body to inline (note: definitions coming
-   *  from Scala2x class files might be `@forceInline`, but still lack that body).
+  /** `sym` is an inline method with a known body to inline.
    */
   def hasBodyToInline(sym: SymDenotation)(implicit ctx: Context): Boolean =
     sym.isInlineMethod && sym.hasAnnotation(defn.BodyAnnot)
 
   /** The body to inline for method `sym`, or `EmptyTree` if none exists.
-   *  Note: definitions coming from Scala2x class files might be `@forceInline`,
-   *  but still lack that body.
    *  @pre  hasBodyToInline(sym)
    */
   def bodyToInline(sym: SymDenotation)(implicit ctx: Context): Tree =

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

@@ -830,8 +830,6 @@ class Namer { typer: Typer =>
           else {
             val ann = Annotation.deferred(cls)(typedAnnotation(annotTree))
             sym.addAnnotation(ann)
-            if (cls == defn.ForceInlineAnnot && sym.is(Method, butNot = Accessor))
-              sym.setFlag(Inline)
           }
         }
       case _ =>

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

@@ -165,7 +165,7 @@ trait QuotesAndSplices {
     object splitter extends tpd.TreeMap {
       private var variance: Int = 1
 
-      @forceInline private def atVariance[T](v: Int)(op: => T): T = {
+      inline private def atVariance[T](v: Int)(op: => T): T = {
         val saved = variance
         variance = v
         val res = op