SI-6616 Check that unsafe operations are only called on the presentation compiler thread.

The method that checks the actual constraint is @elidable, expecting it to be used
for nightly builds but stripped-off in release builds. This way we don't lose any
performance, but 'fail-fast' in IDE nightlies.

This assumes that release builds will have at least `-Xelide-below ASSERTION`, but
this pull request does not do that.

3 files changed, 9 insertions, 0 deletions

diff --git a/src/reflect/scala/reflect/internal/SymbolTable.scala b/src/reflect/scala/reflect/internal/SymbolTable.scala
index 2424e75949..881a5ee5d6 100644
--- a/src/reflect/scala/reflect/internal/SymbolTable.scala
+++ b/src/reflect/scala/reflect/internal/SymbolTable.scala
@@ -6,6 +6,7 @@
 package scala.reflect
 package internal
 
+import scala.annotation.elidable
 import scala.collection.{ mutable, immutable }
 import util._
 
@@ -107,6 +108,11 @@ abstract class SymbolTable extends macros.Universe
     val global: SymbolTable.this.type = SymbolTable.this
   } with util.TraceSymbolActivity
 
+  /** Check that the executing thread is the compiler thread. No-op here,
+   *  overridden in interactive.Global. */
+  @elidable(elidable.WARNING)
+  def assertCorrectThread() {}
+
   /** Are we compiling for Java SE? */
   // def forJVM: Boolean
 
diff --git a/src/reflect/scala/reflect/internal/Symbols.scala b/src/reflect/scala/reflect/internal/Symbols.scala
index a6f156f947..449102dc00 100644
--- a/src/reflect/scala/reflect/internal/Symbols.scala
+++ b/src/reflect/scala/reflect/internal/Symbols.scala
@@ -1213,6 +1213,7 @@ trait Symbols extends api.Symbols { self: SymbolTable =>
         }
         val current = phase
         try {
+          assertCorrectThread()
           phase = phaseOf(infos.validFrom)
           tp.complete(this)
         } finally {
@@ -1283,6 +1284,7 @@ trait Symbols extends api.Symbols { self: SymbolTable =>
           infos = infos.prev
 
         if (validTo < curPeriod) {
+          assertCorrectThread()
           // adapt any infos that come from previous runs
           val current = phase
           try {
diff --git a/src/reflect/scala/reflect/internal/Types.scala b/src/reflect/scala/reflect/internal/Types.scala
index 403bf7d492..cdfff12855 100644
--- a/src/reflect/scala/reflect/internal/Types.scala
+++ b/src/reflect/scala/reflect/internal/Types.scala
@@ -146,6 +146,7 @@ trait Types extends api.Types { self: SymbolTable =>
     /** Undo all changes to constraints to type variables upto `limit`. */
     //OPT this method is public so we can do `manual inlining`
     def undoTo(limit: UndoPairs) {
+      assertCorrectThread()
       while ((log ne limit) && log.nonEmpty) {
         val (tv, constr) = log.head
         tv.constr = constr