Added pkg-config file and .gitignore

[lavoiesl]

This is a redo of #55, which had merge conflicts and seemed abandoned.

I implemented the suggested fix of using the variables provided by GNUInstallDirs

A notable difference is that the snappy.pc is now installed in <prefix>/lib/pkgconfig instead of <prefix>/share/pkgconfig, which seems to be more in line with the other packages installing libraries.

Grabbed the absolute/relative logic from rtrlib/rtrlib#150; when building in Nixos, it overrides GNUInstallDirs to absolute paths, which may not be in the prefix:

Verification using a relative CMAKE_INSTALL_LIBDIR:

$ cat libsnappy.pc
prefix=/usr/local
exec_prefix=/usr/local
libdir=${prefix}/lib
includedir=${prefix}/include

Name: snappy
Description: Fast compressor/decompressor library.
Version: 1.1.7
Libs: -L${prefix}/lib -lsnappy
Cflags: -I${prefix}/include

$ pkg-config libsnappy --libs
-L/usr/local/lib -lsnappy
$ pkg-config libsnappy --cflags
-I/usr/local/include

With an absolute CMAKE_INSTALL_LIBDIR, building with nix:

prefix=/nix/store/hknzbw87dnmz7zq0lf99vjf7bf2l2hps-snappy-1.1.7
exec_prefix=/nix/store/hknzbw87dnmz7zq0lf99vjf7bf2l2hps-snappy-1.1.7
libdir=/nix/store/hknzbw87dnmz7zq0lf99vjf7bf2l2hps-snappy-1.1.7/lib
includedir=/nix/store/z67qhiawswr2jq1p71r4f2987czx3slh-snappy-1.1.7-dev/include

Name: snappy
Description: Fast compressor/decompressor library.
Version: 1.1.7
Libs: -L/nix/store/hknzbw87dnmz7zq0lf99vjf7bf2l2hps-snappy-1.1.7/lib -lsnappy
Cflags: -I/nix/store/z67qhiawswr2jq1p71r4f2987czx3slh-snappy-1.1.7-dev/include

$ pkg-config libsnappy --libs
-L/nix/store/hknzbw87dnmz7zq0lf99vjf7bf2l2hps-snappy-1.1.7/lib -lsnappy
$ pkg-config libsnappy --cflags
-I/nix/store/z67qhiawswr2jq1p71r4f2987czx3slh-snappy-1.1.7-dev/include

Installing the snappy gem (i.e. it properly detected it and didn't recompile snappy):

$ time gem install snappy
Fetching snappy-0.0.17.gem
Building native extensions. This could take a while...
Successfully installed snappy-0.0.17
Parsing documentation for snappy-0.0.17
Installing ri documentation for snappy-0.0.17
Done installing documentation for snappy after 0 seconds
1 gem installed
gem install snappy  1.25s user 0.57s system 80% cpu 2.270 total

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[lavoiesl]

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[lavoiesl]

Is there anything else needed on this PR?

[pwnall]

We will not add pkg-config support for now.

We don't want to get into supporting individual package managers, because the C++ ecosystem hasn't converged into a single solution, and there are quite a few equally reasonable candidates. We can't justify the investment into supporting all the package managers, or into supporting a couple of package managers and trying to rationalize where we drew the line.

[lavoiesl]

I am confused by this decision. pkg-config is fairly standard and the vast majority of libraries I work with that provide headers and dylibs also provide a pkg-confg file.

Without this PR, I am left with the option to add the file via the package managers I would use (homebrew, apt, yum, nix, etc.), which is a ton of repetitive configuration.

It only works currently without a pkg-config because people typically install on a prefix like /usr/local, which most tools look into automatically.

i.e. It only works by accident.

[lavoiesl]

Someone else from my team has also experienced problems compiling the snappy gem on macOS catalina.

They fixed by:

1. export SDKROOT=$(xcrun --show-sdk-path) (this might only be needed on my machine)
2. export CPPFLAGS="-I/usr/local/opt/snappy/include"
3. export LDFLAGS="-L/usr/local/opt/snappy/lib" (not sure if both of these flags are required, only one might be enough)
4. brew remove --force --ignore-dependencies snappy
5. gem pristine snappy -v '0.0.17'

I believe this patch would have fixed his problem.
Please reconsider.

[Soleone]

👍 for reconsidering this patch, thanks!

[bryanparadis]

Thanks for the attempt to get this fixed up @lavoiesl and the workaround instructions.

[mlhamel]

Any chance this be reconsider?? 🙏

It would be super helpful for many different package managers to have snappy supporting pkg-config.

[pwnall]

Sorry, my answer above still stands. We'd only reconsider if there is a Google use case that would justify the ongoing maintenance cost.

I'm going to lock this issue. If googlers want to discuss this, please reach out internally.