From 3a5767e72de649744ede7f616e61864958ae715f Mon Sep 17 00:00:00 2001
From: Jeremy Lilley <jeremyl@fb.com>
Date: Thu, 20 Sep 2012 15:04:54 -0700
Subject: [PATCH] Fix push_back() to shared fbstring bug.

Summary:
The following asserts:
fbstring str(1337, 'f');
fbstring cp = str;
cp.push_back('f');

This is problematic since ml_.capacity() != capacity() inside fbstring_core
for shared strings, which causes us not to un-share prior to push_back.

Test Plan: Existing tests, add unittest case.

Reviewed By: tudorb@fb.com

FB internal diff: D580267
---
 folly/FBString.h            |  4 ++--
 folly/test/FBStringTest.cpp | 12 ++++++++++++
 2 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/folly/FBString.h b/folly/FBString.h
index 9280bf8b..9ac8918c 100644
--- a/folly/FBString.h
+++ b/folly/FBString.h
@@ -626,7 +626,7 @@ public:
     } else {
       sz = ml_.size_;
       newSz = ml_.size_ + delta;
-      if (newSz > ml_.capacity()) {
+      if (newSz > capacity()) {
         reserve(newSz);
       }
     }
@@ -653,7 +653,7 @@ public:
       reserve(maxSmallSize * 2);
     } else {
       sz = ml_.size_;
-      cp = ml_.capacity();
+      cp = capacity();  // != ml_.capacity() for isShared()
       if (sz == cp) reserve(cp * 3 / 2);
     }
     assert(capacity() >= sz + 1);
diff --git a/folly/test/FBStringTest.cpp b/folly/test/FBStringTest.cpp
index 40dc4359..428bed28 100644
--- a/folly/test/FBStringTest.cpp
+++ b/folly/test/FBStringTest.cpp
@@ -981,6 +981,18 @@ TEST(FBString, testFixedBugs) {
       cp.push_back('?');
     }
   }
+  { // D580267
+    {
+      fbstring str(1337, 'f');
+      fbstring cp = str;
+      cp.push_back('f');
+    }
+    {
+      fbstring str(1337, 'f');
+      fbstring cp = str;
+      cp += "bb";
+    }
+  }
 }
 
 int main(int argc, char** argv) {
-- 
2.34.1