fixup! [bug#3088][bug#12121] Fix adding/subtracting ListBuffer to/fro…

…m itself quadruple the size of ListBuffer#insertAll
scala · Oct 2, 2020 · 762676c · 762676c
1 parent 433afe7
commit 762676c
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Showing 2 changed files with 60 additions and 6 deletions.
diff --git a/src/library/scala/collection/mutable/ListBuffer.scala b/src/library/scala/collection/mutable/ListBuffer.scala
@@ -127,6 +127,7 @@ class ListBuffer[A]
           val copy = ListBuffer.from(this)
           last0.next = copy.first
           last0 = copy.last0
+          len *= 2
         }
       case xs =>
         val it = xs.iterator
@@ -246,12 +247,29 @@ class ListBuffer[A]
   }
 
   def insertAll(idx: Int, elems: IterableOnce[A]): Unit = {
-    val it = elems.iterator
-    if (it.hasNext) {
-      ensureUnaliased()
-      if (idx < 0 || idx > len) throw new IndexOutOfBoundsException(s"$idx is out of bounds (min 0, max ${len-1})")
-      if (idx == len) ++=(elems)
-      else insertAfter(locate(idx), it)
+    if (idx < 0 || idx > len) throw new IndexOutOfBoundsException(s"$idx is out of bounds (min 0, max ${len-1})")
+    elems match {
+      case elems: AnyRef if elems eq this => // avoid mutating under our own iterator
+        if (len > 0) {
+          val copy = ListBuffer.from(this)
+          if (idx == 0 || idx == len) { // prepend/append
+            last0.next = copy.first
+            last0 = copy.last0
+          } else {
+            val prev = locate(idx) // cannot be `null` because other condition catches that
+            val follow = prev.next
+            prev.next = copy.first
+            copy.last0.next = follow
+          }
+          len *= 2
+        }
+      case elems =>
+        val it = elems.iterator
+        if (it.hasNext) {
+          ensureUnaliased()
+          if (idx == len) ++=(elems)
+          else insertAfter(locate(idx), it)
+        }
     }
   }
 

diff --git a/test/junit/scala/collection/mutable/ListBufferTest.scala b/test/junit/scala/collection/mutable/ListBufferTest.scala
@@ -3,6 +3,8 @@ package scala.collection.mutable
 import org.junit.Assert.{assertEquals, assertTrue}
 import org.junit.Test
 
+import scala.tools.testkit.AssertUtil.assertSameElements
+
 import scala.annotation.nowarn
 
 class ListBufferTest {
@@ -228,4 +230,38 @@ class ListBufferTest {
     b += "b"
     assertEquals(Seq("a1", "b"), b)
   }
+
+  /* tests for scala/bug#12121 */
+
+  @Test
+  def self_addAll(): Unit = {
+    val b = ListBuffer(1, 2, 3)
+    b ++= b
+    assertSameElements(List(1, 2, 3, 1, 2, 3), b)
+  }
+
+  @Test
+  def self_prependAll(): Unit = {
+    val b = ListBuffer(1, 2, 3)
+    b prependAll b
+    assertSameElements(List(1, 2, 3, 1, 2, 3), b)
+  }
+
+  @Test
+  def self_insertAll(): Unit = {
+    val b1 = ListBuffer(1, 2, 3)
+    b1.insertAll(1, b1)
+    assertSameElements(List(1, 1, 2, 3, 2, 3), b1)
+
+    val b2 = ListBuffer(1, 2, 3)
+    b2.insertAll(3, b2)
+    assertSameElements(List(1, 2, 3, 1, 2, 3), b2)
+  }
+
+  @Test
+  def self_subtractAll(): Unit = {
+    val b = ListBuffer(1, 2, 3)
+    b --= b
+    assertSameElements(Nil, b)
+  }
 }