Detect location of libclang library and headers and set include-dirs etc.

[rcook]

This adds setup-time auto-detection of libclang headers and libraries on Linux, Mac OS X and Windows. It also adds a new "development guide" with setup and build instructions.

[chpatrick]

getDirectoryContents also contains . and .., so this recurses forever. Also, this seems like a very expensive way to find libclang... I think it would be better to check the usual suspect locations (/usr/(local/)?lib/llvm-\d+(.\d+)*) and for other cases let the user set the environment variable.

[rcook]

The code at line 60 filters out . and ... It's probably not the most efficient way to locate the libraries but it seems to work pretty well on the different Linux distros I tested against (Centos and Ubuntu) as well as on Windows and OS X without any special cases required. It also only impacts the initial configure step and, so, the overhead doesn't impact every invocation of stack build. It also has the advantage that I've already thoroughly tested it on two Linuxes, Windows and OS X!

[chpatrick]

Hi Richard,

For me it uses up all my memory and freezes my computer (see attached htop). :(

I'm not very comfortable with enumerating every file in /usr. We have a largish non-clang related project at work and the initial stack build already takes way too long. Think about continuous integration - you often have to build from scratch and if it takes minutes longer to get your results because of clang-pure, it's really annoying.

I'm glad to hear that you tested it widely, but could you tell me where Setup.hs found libclang in the tests you performed? If they were all in predictable locations then I would much rather just check those and leave unusual ones up to the user. As far as I know, that's how almost all packages do it (Haskell or otherwise).

[chpatrick]

Ah, I have a solution! The llvm-config command prints out the relevant directories.

chpatrick@obsidian:~$ llvm-config-3.8 --prefix
/usr/lib/llvm-3.8
chpatrick@obsidian:~$ llvm-config-3.8 --includedir
/usr/lib/llvm-3.8/include

Here's how they do it with CMake: https://github.com/Andersbakken/rtags/blob/master/cmake/FindLibClang.cmake

[chpatrick]

This works for me: 17b05bf

What do you think? Does it work on Windows?

[rcook]

Ouch! Sorry about freezing your computer!

Here is a summary of the install locations for the libclang library and primary header Index.h:

Centos 7 (clang-devel package installed via yum)

• /usr/lib64/llvm/libclang.so
• /usr/include/clang-c/Index.h

Ubuntu 14.04 (libclang-dev package installed via apt-get)

• /usr/lib/llvm-3.4/lib/libclang.so
• /usr/lib/llvm-3.4/include/clang-c/Index.h

Windows (LLVM 3.8.1 installed using LLVM .exe installer)

• C:\Program Files\LLVM\bin\libclang.dll
• C:\Program Files\LLVM\include\clang-c\Index.h

Mac OS X (llvm38 package installed via Homebrew)

• /usr/local/Cellar/llvm38/3.8.0/lib/llvm-3.8/lib/libclang.dylib
• /usr/local/Cellar/llvm38/3.8.0/lib/llvm-3.8/include/clang-c/Index.h

I'll test your suggested fix and get back to you with more updates. I like the llvm-config approach with environment variable overrides.

[chpatrick]

Hi Richard,

I've merged the llvm-config version, since it seems to work on OSX and Linux on Travis. If there are any problems let's fix them in another PR.

Thanks for your help!