Merge pull request #2905 from retronym/ticket/7801

SI-7801 Fix a nightmarish bug in Symbols#adaptInfos

3 files changed, 33 insertions, 4 deletions

diff --git a/src/reflect/scala/reflect/internal/Symbols.scala b/src/reflect/scala/reflect/internal/Symbols.scala
index d3a0ffb744..d58ea09386 100644
--- a/src/reflect/scala/reflect/internal/Symbols.scala
+++ b/src/reflect/scala/reflect/internal/Symbols.scala
@@ -1435,6 +1435,13 @@ trait Symbols extends api.Symbols { self: SymbolTable =>
       assert(isCompilerUniverse)
       if (infos == null || runId(infos.validFrom) == currentRunId) {
         infos
+      } else if (isPackageClass) {
+        // SI-7801 early phase package scopes are mutated in new runs (Namers#enterPackage), so we have to
+        //         discard transformed infos, rather than just marking them as from this run.
+        val oldest = infos.oldest
+        oldest.validFrom = validTo
+        this.infos = oldest
+        oldest
       } else {
         val prev1 = adaptInfos(infos.prev)
         if (prev1 ne infos.prev) prev1
@@ -1444,10 +1451,7 @@ trait Symbols extends api.Symbols { self: SymbolTable =>
           _validTo = period(currentRunId, pid)
           phase   = phaseWithId(pid)
 
-          val info1 = (
-            if (isPackageClass) infos.info
-            else adaptToNewRunMap(infos.info)
-          )
+          val info1 = adaptToNewRunMap(infos.info)
           if (info1 eq infos.info) {
             infos.validFrom = validTo
             infos
@@ -3473,6 +3477,8 @@ trait Symbols extends api.Symbols { self: SymbolTable =>
       "TypeHistory(" + phaseOf(validFrom)+":"+runId(validFrom) + "," + info + "," + prev + ")"
 
     def toList: List[TypeHistory] = this :: ( if (prev eq null) Nil else prev.toList )
+
+    def oldest: TypeHistory = if (prev == null) this else prev.oldest
   }
 
 // ----- Hoisted closures and convenience methods, for compile time reductions -------
diff --git a/test/files/run/t7801.check b/test/files/run/t7801.check
new file mode 100644
index 0000000000..d72060c684
--- /dev/null
+++ b/test/files/run/t7801.check
@@ -0,0 +1,11 @@
+Type in expressions to have them evaluated.
+Type :help for more information.
+
+scala> val g: scala.reflect.internal.SymbolTable = null; import g.abort
+g: scala.reflect.internal.SymbolTable = null
+import g.abort
+
+scala> class C(val a: Any) extends AnyVal
+defined class C
+
+scala> 
diff --git a/test/files/run/t7801.scala b/test/files/run/t7801.scala
new file mode 100644
index 0000000000..3a3cc97a51
--- /dev/null
+++ b/test/files/run/t7801.scala
@@ -0,0 +1,12 @@
+import scala.tools.partest.ReplTest
+
+// was crashing due to a subtle interaction of the Namer entering packages into
+// enclosing packages by mutating the scope in place without invalidating later
+// entries in the enclosing package class symbols type history.
+//
+// Sadly, I couldn't whittle the test case down further.
+object Test extends ReplTest {
+  override def code = """val g: scala.reflect.internal.SymbolTable = null; import g.abort
+                        |class C(val a: Any) extends AnyVal""".stripMargin
+
+}