Treat @forceInline specially.

The comment in Namer explains why this is necessary.

Author: odersky

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

@@ -1195,7 +1195,15 @@ class Namer { typer: Typer =>
       instantiateDependent(restpe, typeParams, termParamss)
       ctx.methodType(tparams map symbolOfTree, termParamss, restpe, isJava = ddef.mods is JavaDefined)
     }
-    if (sym.is(Transparent)) sym.setFlag(Erased)
+    if (sym.is(Transparent) &&
+        sym.unforcedAnnotation(defn.ForceInlineAnnot).isEmpty)
+        // Need to keep @forceInline annotated methods 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.
+      sym.setFlag(Erased)
     if (isConstructor) {
       // set result type tree to unit, but take the current class as result type of the symbol
       typedAheadType(ddef.tpt, defn.UnitType)

library/src/dotty/runtime/LazyVals.scala

@@ -25,20 +25,20 @@ object LazyVals {
   final val LAZY_VAL_MASK = 3L
   final val debug = false
 
-  @inline def STATE(cur: Long, ord: Int) = {
+  @forceInline def STATE(cur: Long, ord: Int) = {
     val r = (cur >> (ord * BITS_PER_LAZY_VAL)) & LAZY_VAL_MASK
     if (debug)
       println(s"STATE($cur, $ord) = $r")
     r
   }
-  @inline def CAS(t: Object, offset: Long, e: Long, v: Int, ord: Int) = {
+  @forceInline def CAS(t: Object, offset: Long, e: Long, v: Int, ord: Int) = {
     if (debug)
       println(s"CAS($t, $offset, $e, $v, $ord)")
     val mask = ~(LAZY_VAL_MASK << ord * BITS_PER_LAZY_VAL)
     val n = (e & mask) | (v.toLong << (ord * BITS_PER_LAZY_VAL))
     compareAndSet(t, offset, e, n)
   }
-  @inline def setFlag(t: Object, offset: Long, v: Int, ord: Int) = {
+  @forceInline def setFlag(t: Object, offset: Long, v: Int, ord: Int) = {
     if (debug)
       println(s"setFlag($t, $offset, $v, $ord)")
     var retry = true
@@ -57,7 +57,7 @@ object LazyVals {
       }
     }
   }
-  @inline def wait4Notification(t: Object, offset: Long, cur: Long, ord: Int) = {
+  @forceInline def wait4Notification(t: Object, offset: Long, cur: Long, ord: Int) = {
     if (debug)
       println(s"wait4Notification($t, $offset, $cur, $ord)")
     var retry = true
@@ -75,8 +75,8 @@ object LazyVals {
     }
   }
 
-  @inline def compareAndSet(t: Object, off: Long, e: Long, v: Long) = unsafe.compareAndSwapLong(t, off, e, v)
-  @inline def get(t: Object, off: Long) = {
+  @forceInline def compareAndSet(t: Object, off: Long, e: Long, v: Long) = unsafe.compareAndSwapLong(t, off, e, v)
+  @forceInline def get(t: Object, off: Long) = {
     if (debug)
       println(s"get($t, $off)")
     unsafe.getLongVolatile(t, off)
@@ -88,7 +88,7 @@ object LazyVals {
     x => new Object()
   }.toArray
 
-  @inline def getMonitor(obj: Object, fieldId: Int = 0) = {
+  @forceInline def getMonitor(obj: Object, fieldId: Int = 0) = {
     var id = (
       /*java.lang.System.identityHashCode(obj) + */ // should be here, but #548
       fieldId) % base
@@ -97,7 +97,7 @@ object LazyVals {
     monitors(id)
   }
 
-  @inline def getOffset(clz: Class[_], name: String) = {
+  @forceInline def getOffset(clz: Class[_], name: String) = {
     val r = unsafe.objectFieldOffset(clz.getDeclaredField(name))
     if (debug)
       println(s"getOffset($clz, $name) = $r")