[bionic] Program fails to compile when using flann and LZ4

[Kartik Mohta]

On Ubuntu 18.04, when trying to use the system version of LZ4 with flann in the same C++ code, it causes compile errors.

$ apt-cache policy libflann-dev
libflann-dev:
  Installed: 1.9.1+dfsg-2
  Candidate: 1.9.1+dfsg-2
  Version table:
 *** 1.9.1+dfsg-2 500
        500 http://archive.ubuntu.com/ubuntu bionic/universe amd64 Packages
        100 /var/lib/dpkg/status

$ apt-cache policy liblz4-dev
liblz4-dev:
  Installed: 0.0~r131-2ubuntu3
  Candidate: 0.0~r131-2ubuntu3
  Version table:
 *** 0.0~r131-2ubuntu3 500
        500 http://archive.ubuntu.com/ubuntu bionic/main amd64 Packages
        100 /var/lib/dpkg/status

$ cat test.cpp
#include <lz4.h>
#include <flann/flann.hpp>

int main()
{
  return 0;
}

$ g++ test.cpp
In file included from /usr/include/flann/util/serialization.h:9:0,
                 from /usr/include/flann/util/matrix.h:35,
                 from /usr/include/flann/flann.hpp:41,
                 from test.cpp:2:
/usr/include/flann/ext/lz4.h:196:57: error: conflicting declaration 'typedef struct LZ4_stream_t LZ4_stream_t'
 typedef struct { long long table[LZ4_STREAMSIZE_U64]; } LZ4_stream_t;
                                                         ^~~~~~~~~~~~
In file included from test.cpp:1:0:
/usr/include/lz4.h:196:57: note: previous declaration as 'typedef struct LZ4_stream_t LZ4_stream_t'
 typedef struct { long long table[LZ4_STREAMSIZE_U64]; } LZ4_stream_t;
                                                         ^~~~~~~~~~~~
In file included from /usr/include/flann/util/serialization.h:9:0,
                 from /usr/include/flann/util/matrix.h:35,
                 from /usr/include/flann/flann.hpp:41,
                 from test.cpp:2:
/usr/include/flann/ext/lz4.h:249:72: error: conflicting declaration 'typedef struct LZ4_streamDecode_t LZ4_streamDecode_t'
 typedef struct { unsigned long long table[LZ4_STREAMDECODESIZE_U64]; } LZ4_streamDecode_t;
                                                                        ^~~~~~~~~~~~~~~~~~
In file included from test.cpp:1:0:
/usr/include/lz4.h:249:72: note: previous declaration as 'typedef struct LZ4_streamDecode_t LZ4_streamDecode_t'
 typedef struct { unsigned long long table[LZ4_STREAMDECODESIZE_U64]; } LZ4_streamDecode_t;
                                                                        ^~~~~~~~~~~~~~~~~~

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Andre Phu-Van Nguyen (anguyenara)]

I believe this is affecting compilation of PCL's kdtree flann. So basically flann has it's own copy of lz4.h and it collides with the system package lz4.h?

What's the cleanest workaround? Namespace flann's lz4??

[Jochen Sprickerhof (v-launchpad-jochen-sprickerhof-de)]

I have removed the LZ4 symbols in 1.9.1+dfsg-6 (in Debian unstable). So this should be fixed in the next Ubuntu version.