MemoryWriter allocation issue

[meox]

I wrote this test case, but it fails:

TEST(OStreamTest, MemoryWriterAllocation) {
  fmt::MemoryWriter w;
  size_t final_len{};
  const size_t l = 10000;

  for (size_t i = 0; i < l; i++) {
    const std::string token = std::to_string(i);
    final_len += token.size();
    w << token;
  }

  const std::string rs = w.str();
  EXPECT_EQ(w.size(), final_len);
}

I'm getting this stack trace:

ostream-test: malloc.c:2372: sysmalloc: Assertion `(old_top == (((mbinptr) (((char *) &((av)->bins[((1) - 1) * 2])) - __builtin_offsetof (struct malloc_chunk, fd)))) && old_size == 0) || ((unsigned long) (old_size) >= (unsigned long)((((__builtin_offsetof (struct malloc_chunk, fd_nextsize))+((2 *(sizeof(size_t))) - 1)) & ~((2 *(sizeof(size_t))) - 1))) && ((old_top)->size & 0x1) && ((unsigned long) old_end & pagemask) == 0)' failed.

Program received signal SIGABRT, Aborted.
0x00007ffff7027067 in __GI_raise (sig=sig@entry=6) at ../nptl/sysdeps/unix/sysv/linux/raise.c:56
56      ../nptl/sysdeps/unix/sysv/linux/raise.c: File o directory non esistente.
(gdb) bt
#0  0x00007ffff7027067 in __GI_raise (sig=sig@entry=6) at ../nptl/sysdeps/unix/sysv/linux/raise.c:56
#1  0x00007ffff7028448 in __GI_abort () at abort.c:89
#2  0x00007ffff706a0ad in __malloc_assert (
    assertion=assertion@entry=0x7ffff715a748 "(old_top == (((mbinptr) (((char *) &((av)->bins[((1) - 1) * 2])) - __builtin_offsetof (struct malloc_chunk, fd)))) && old_size == 0) || ((unsigned long) (old_size) >= (unsigned long)((((__builtin_offs"..., file=file@entry=0x7ffff715628d "malloc.c", line=line@entry=2372, 
    function=function@entry=0x7ffff715660b <__func__.11291> "sysmalloc") at malloc.c:293
#3  0x00007ffff706cd90 in sysmalloc (av=0x7ffff7397620 <main_arena>, nb=19232) at malloc.c:2369
#4  _int_malloc (av=0x7ffff7397620 <main_arena>, bytes=19210) at malloc.c:3800
#5  0x00007ffff706e020 in __GI___libc_malloc (bytes=19210) at malloc.c:2891
#6  0x00007ffff79132e8 in operator new(unsigned long) () from /usr/lib/x86_64-linux-gnu/libstdc++.so.6
#7  0x000000000049c5c0 in __gnu_cxx::new_allocator<char>::allocate (this=0x7fffffffd950, __n=19210) at /usr/include/c++/4.9/ext/new_allocator.h:104
#8  0x00000000004a3298 in fmt::internal::MemoryBuffer<char, 500ul, std::allocator<char> >::grow (this=0x7fffffffd950, size=12810) at /home/meox/git/fmt/fmt/format.h:807
#9  0x000000000048e4f8 in fmt::Buffer<char>::resize (this=0x7fffffffd950, new_size=12810) at /home/meox/git/fmt/fmt/format.h:702
#10 0x000000000048c23d in fmt::operator<< <std::string, char> (writer=..., value="3479") at /home/meox/git/fmt/fmt/ostream.h:138
#11 0x000000000048711c in OStreamTest_MemoryWriterAllocation_Test::TestBody (this=0x71e240) at /home/meox/git/fmt/test/ostream-test.cc:203
#12 0x00000000004cf88e in testing::internal::HandleSehExceptionsInMethodIfSupported<testing::Test, void> (object=0x71e240, method=&virtual testing::Test::TestBody(), 
    location=0x4e9263 "the test body") at /home/meox/git/fmt/test/gmock-gtest-all.cc:3562
#13 0x00000000004c9c24 in testing::internal::HandleExceptionsInMethodIfSupported<testing::Test, void> (object=0x71e240, method=&virtual testing::Test::TestBody(), 
    location=0x4e9263 "the test body") at /home/meox/git/fmt/test/gmock-gtest-all.cc:3598
#14 0x00000000004aacff in testing::Test::Run (this=0x71e240) at /home/meox/git/fmt/test/gmock-gtest-all.cc:3635
#15 0x00000000004ab46f in testing::TestInfo::Run (this=0x71e150) at /home/meox/git/fmt/test/gmock-gtest-all.cc:3810
#16 0x00000000004aba78 in testing::TestCase::Run (this=0x71d490) at /home/meox/git/fmt/test/gmock-gtest-all.cc:3928
#17 0x00000000004b2119 in testing::internal::UnitTestImpl::RunAllTests (this=0x71d150) at /home/meox/git/fmt/test/gmock-gtest-all.cc:5799
#18 0x00000000004d06cd in testing::internal::HandleSehExceptionsInMethodIfSupported<testing::internal::UnitTestImpl, bool> (object=0x71d150, 
    method=(bool (testing::internal::UnitTestImpl::*)(testing::internal::UnitTestImpl * const)) 0x4b1e96 <testing::internal::UnitTestImpl::RunAllTests()>, 
    location=0x4e9b40 "auxiliary test code (environments or event listeners)") at /home/meox/git/fmt/test/gmock-gtest-all.cc:3562
#19 0x00000000004ca9be in testing::internal::HandleExceptionsInMethodIfSupported<testing::internal::UnitTestImpl, bool> (object=0x71d150, 
    method=(bool (testing::internal::UnitTestImpl::*)(testing::internal::UnitTestImpl * const)) 0x4b1e96 <testing::internal::UnitTestImpl::RunAllTests()>, 
    location=0x4e9b40 "auxiliary test code (environments or event listeners)") at /home/meox/git/fmt/test/gmock-gtest-all.cc:3598
#20 0x00000000004b0eab in testing::UnitTest::Run (this=0x71cc00 <testing::UnitTest::GetInstance()::instance>) at /home/meox/git/fmt/test/gmock-gtest-all.cc:5413
#21 0x00000000004a570d in RUN_ALL_TESTS () at /home/meox/git/fmt/test/./gtest/gtest.h:20062
#22 0x00000000004a5694 in main (argc=1, argv=0x7fffffffe058) at /home/meox/git/fmt/test/test-main.cc:57

[effzeh]

Same here with MinGW 6.3 on Windows.

This seems to be a bug in the FormatBuf implementation in ostream.h. operator<< defined here in ostream.h is quite greedy and gets picked up for a (const) std::string.

I'm quite sure that this is incorrect: it sets the end pointer past the buffer when invoked here with size() > 0. But I don't have the time right now to investigate that further.