allow path.add(path) safely

Bug: 882423
Change-Id: Ied2ad2d5dfdf00af8f3ba722b522e9602fea5557
Reviewed-on: https://skia-review.googlesource.com/153260
Commit-Queue: Mike Reed <reed@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>
diff --git a/tests/PathTest.cpp b/tests/PathTest.cpp
index 349a309..cbb2b48 100644
--- a/tests/PathTest.cpp
+++ b/tests/PathTest.cpp
@@ -5069,6 +5069,29 @@
     REPORTER_ASSERT(reporter, rect == compare);
 }
 
+// Be sure we can safely add ourselves
+DEF_TEST(Path_self_add, reporter) {
+    // The possible problem is that during path.add() we may have to grow the dst buffers as
+    // we append the src pts/verbs, but all the while we are iterating over the src. If src == dst
+    // we could realloc the buffer's (on behalf of dst) leaving the src iterator pointing at
+    // garbage.
+    //
+    // The test runs though verious sized src paths, since its not defined publicly what the
+    // reserve allocation strategy is for SkPath, therefore we can't know when an append operation
+    // will trigger a realloc. At the time of this writing, these loops were sufficient to trigger
+    // an ASAN error w/o the fix to SkPath::addPath().
+    //
+    for (int count = 0; count < 10; ++count) {
+        SkPath path;
+        for (int add = 0; add < count; ++add) {
+            // just add some stuff, so we have something to copy/append in addPath()
+            path.moveTo(1, 2).lineTo(3, 4).cubicTo(1,2,3,4,5,6).conicTo(1,2,3,4,5);
+        }
+        path.addPath(path, 1, 2);
+        path.addPath(path, 3, 4);
+    }
+}
+
 #include "SkVertices.h"
 static void draw_triangle(SkCanvas* canvas, const SkPoint pts[]) {
     // draw in different ways, looking for an assert