How to fix ld: library not found for -lzstd installing mysql2
I have a history of problems with installing the mysql2 gem, and this is just another chapter in that tale. If you receive a ld: library not found for -lzstd error when running bundler or otherwise attempt to install the mysql2 gem, this might be the solution.
What I experienced
I am using MacPorts and trying to install the mysql2 gem gave me the following error
$ gem install mysql2 -v 0.5.6
...
ld: library not found for -lzstd
clang: error: linker command failed with exit code 1 (use -v to see invocation)
make: *** [mysql2.bundle] Error 1
make failed, exit code 2
...
TLDR; the solution
What worked for me was telling ld that it can find the libzstd files in the MacPorts lib directory at /opt/local/lib:
$ gem install mysql2 -v 0.5.6 -- --with-ldflags="-L/opt/local/lib"
More details
The relevant part of the error message above is
ld: library not found for -lzstd
This happens when ld wants to include some library, given after -l (in this case libzstd), but can’t. However the library is installed as part of my MacPort installation:
$ ls -1 /opt/local/lib/libzstd*
/opt/local/lib/libzstd.1.5.7.dylib
/opt/local/lib/libzstd.1.dylib
/opt/local/lib/libzstd.a
/opt/local/lib/libzstd.dylib
Seeing that ld can’t an installed library probably means that ld is looking the wrong place - or at the very least, not looking in the right place. So let’s tell it to.
Investigating man ld leads us to the -L/--library-path= command line argument:
-Ldir: Add dir to the list of directories in which to search for libraries. Directories specified with -L are searched in the order they appear on the command line and before the default search path. In Xcode4 and later, there can be a space between the -L and directory.
So maybe telling ld where to find the libraries can help. However, we are not calling ld directly ourselves, but rather RubyGems is calling it for us as part of the installation process.
Luckily, we can forward arguments to the installation process:
$ gem install mysql2 -v 0.5.6 -- --with-ldflags="-L/opt/local/lib"
Building native extensions with: '--with-ldflags=-L/opt/local/lib'
This could take a while...
Successfully installed mysql2-0.5.6
1 gem installed
So basically, we’re telling gem to tell make to tell ld to use /opt/local/lib as the -L argument.
Extra credits
Unfortunately this is a one-time thing. The next time you have to install mysql2, it’ll fail again - there’s no persistence here.
We can, however, take advantage of bundler here. If you do
$ bundle config --local build.mysql2 "--with-ldflags=-L/opt/local/lib"
you tell bundler to tell gem to tell make to tell ld to use /opt/local/lib in all future installations of the mysql2 gem.