irony-install-server with MacPorts

Update: I was only able to get irony to work up to the 2019 version, but irony has been unmaintained since 2023 and has now since suffered significant bit-rot, and I could not get the 2023 version to work. There seems to be other alternatives (e.g. lsp-mode). However, I'm keeping this page for the record.

The irony server provides symbol completion for irony-mode on Emacs. Under the hood, it uses libclang to parse C and C++ source. On Mac OS, the Xcode command line tools comes with clang, but it does not provide the necessary header files. Here are the specific instructions for MacPorts.

$ cd "$(mktemp -d)"  # any empty temporary directory will do.
$ clang -v
Apple clang version 17.0.0 (clang-1700.0.13.3)
Target: x86_64-apple-darwin24.4.0
Thread model: posix
InstalledDir: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin
$ sudo port install cmake clang-17
--->  Computing dependencies for cmake
...
--->  Cleaning cmake
--->  Computing dependencies for clang-17
...
--->  Cleaning clang-17
--->  Scanning binaries for linking errors
--->  No broken files found.                             
--->  No broken ports found.
$ cmake \
  -DLIBCLANG_LIBRARY=/opt/local/libexec/llvm-17/lib/libclang.dylib \
  -DLIBCLANG_INCLUDE_DIR=/opt/local/libexec/llvm-17/include \
  -DCMAKE_MACOSX_RPATH=1 \
  -DCMAKE_INSTALL_RPATH=/opt/local/libexec/llvm-17/lib \
  -DCMAKE_INSTALL_PREFIX=$HOME/.emacs.d/irony/ \
  $HOME/.emacs.d/elpa/irony-20231018.1915/server &&
cmake --build . --use-stderr --config Release --target install

Some notes:

• MacPorts llvm package provides the libclang.dylib, but clang provides the header files for it (see macports #69392).
• LIBCLANG_LIBRARY has to point to the dylib (or the .so on Linux), not the lib/ directory.
• irony-20231018.1915 has a bug where irony.el version string is now ";; Package-Version: 20231018.1915", but the server/src/CMakeLists.txt still uses ";; Version:" to detect the version. Update the string accordingly.
• Requires cl-libify to patch cl to cl-lib. Install it in emacs using M-x package-install cl-libify.