From 202b9674aa8041af8ecb59b247ded01ad7bf536b Mon Sep 17 00:00:00 2001
From: Guillaume Martres <smarter@ubuntu.com>
Date: Fri, 6 Apr 2018 01:56:06 +0200
Subject: [PATCH] Fix reporter reuse in TyperState#test

The previous logic was wrong: TyperState#test may be called by the
closure passed to TyperState#test, meaning that the testReporter may
already be in use at that point.
---
 .../dotty/tools/dotc/core/TyperState.scala    | 19 ++++++++++++++++---
 .../tools/dotc/reporting/StoreReporter.scala  |  4 +---
 2 files changed, 17 insertions(+), 6 deletions(-)

diff --git a/compiler/src/dotty/tools/dotc/core/TyperState.scala b/compiler/src/dotty/tools/dotc/core/TyperState.scala
index f54e6af62b4e..10378131be63 100644
--- a/compiler/src/dotty/tools/dotc/core/TyperState.scala
+++ b/compiler/src/dotty/tools/dotc/core/TyperState.scala
@@ -100,7 +100,7 @@ class TyperState(previous: TyperState /* | Null */) {
   def uncommittedAncestor: TyperState =
     if (isCommitted) previous.uncommittedAncestor else this
 
-  private[this] var testReporter: StoreReporter = null
+  private[this] var testReporter: TestReporter = null
 
   /** Test using `op`. If current typerstate is shared, run `op` in a fresh exploration
    *  typerstate. If it is unshared, run `op` in current typerState, restoring typerState
@@ -116,15 +116,17 @@ class TyperState(previous: TyperState /* | Null */) {
       val savedCommitted = isCommitted
       myIsCommittable = false
       myReporter = {
-        if (testReporter == null) {
-          testReporter = new StoreReporter(reporter)
+        if (testReporter == null || testReporter.inUse) {
+          testReporter = new TestReporter(reporter)
         } else {
           testReporter.reset()
         }
+        testReporter.inUse = true
         testReporter
       }
       try op(ctx)
       finally {
+        testReporter.inUse = false
         resetConstraintTo(savedConstraint)
         myReporter = savedReporter
         myIsCommittable = savedCommittable
@@ -189,3 +191,14 @@ class TyperState(previous: TyperState /* | Null */) {
 
   def stateChainStr: String = s"$this${if (previous == null) "" else previous.stateChainStr}"
 }
+
+/** Temporary, reusable reporter used in TyperState#test */
+private class TestReporter(outer: Reporter) extends StoreReporter(outer) {
+  /** Is this reporter currently used in a test? */
+  var inUse = false
+
+  def reset() = {
+    assert(!inUse, s"Cannot reset reporter currently in use: $this")
+    infos = null
+  }
+}
diff --git a/compiler/src/dotty/tools/dotc/reporting/StoreReporter.scala b/compiler/src/dotty/tools/dotc/reporting/StoreReporter.scala
index acb0d573507d..243a4cca0130 100644
--- a/compiler/src/dotty/tools/dotc/reporting/StoreReporter.scala
+++ b/compiler/src/dotty/tools/dotc/reporting/StoreReporter.scala
@@ -20,9 +20,7 @@ import diagnostic.messages._
   */
 class StoreReporter(outer: Reporter) extends Reporter {
 
-  private[this] var infos: mutable.ListBuffer[MessageContainer] = null
-
-  def reset() = infos = null
+  protected[this] var infos: mutable.ListBuffer[MessageContainer] = null
 
   def doReport(m: MessageContainer)(implicit ctx: Context): Unit = {
     typr.println(s">>>> StoredError: ${m.message}") // !!! DEBUG